Spring rate...?? ( and other suspension issues...)

[CorseChris]

Does anyone happen to know...the spring rate for a standard Beta Coupe front strut, or maybe the rate used on an HF2000 rear? (Probably the same thing).

I'm currently using some of these struts on my car (can't afford Ledas just yet) and I'm finding them a bit under-damped with the 280lb springs I have fitted. I modified them to take 2 1/4" coil-over springs so new springs are cheap and easy to get.

I'm thinking about 220lb would do for now until I can get something better and adjustable by way of dampers.

Thoughts anyone?

Ta

[catswhiskers]

Dont know about the standard rates Chris but my Corse is being built using 2.25 dia. springs rated at 350lb fronts and 400lb rears. Together with AVO adjustable coilover shocks. Thats with the V6 installation.
Dont know how it rides yet ( but hopefully I will soon ) ;)

Mick

[CorseChris]

Hi Mick,

I'm using 350lb at the front on mine with AVO Pro-Race dampers, which feels good. What wheel-rate does that 400lb come out to? Probably won't help me though as my strut dampers aren't adjustable, hence my problem. :(

[catswhiskers]

Sorry Chris, cant answer that one. The spec came from Napier when I bought the kit.

Mick

[Stratos]

Chris, you have to remember that Mick has a Corse I, so has wishbones at the rear rather than struts, so his rear settings won't be too much use to you.


On the Corse S, I am using 500lb Front and 350lb Rear. That is what I was running at Abingdon.

On the Allora, which had been modified to have a suspension setup similar to the Corse at the front, I was using 450lb Front and 350lb Rear.

Both cars were fitted with V6.

On rougher events, eg Keevil, over bumpy tarmac, the rear was too hard, and I think that 325lb, or even 300lb, would have been better. With 350lb it skipped over the rough tarmac, and I think with a lower rate, it would have have absorbed the bumps and ripples better.

I think that for a Corse S on the road, I would tend to go for 400lb Front and 300lb Rear. However, If you are happy with the 350lb at the front, I would stick with it.

Have you fitted anti-roll bars?

Hope this is some help.

[CorseChris]

Thanks David.

I was hoping to persude Mick to get his tape measure out and tell me lower wishbone pivot to shock mount & pivot to wheel centre dimensions so I could work out the wheel rate. Unsprung weight will be quite different of course so the resonant frequency will be off, but it's somewhere to start I suppose.

My real problem at the moment is that I can't do anything about the damping at the rear so have to adjust the spring rate to suit. It'll probably be a bit too soft really, but as long as it's better matched to the damper it should be a better compromise for now. In terms of how it feels under compression, it's pretty well balanced with the 350 front/280 rear, but the back kicks up on rebound if I hit a big dip and it feels quite underdamped.

Your figures will certainly come in handy once I have some decent rear struts and can adjust damping to accomodate different spring rates. Neil Simons used to run 500lb front springs as well....I'll drop him a line and see what he used to run at the back of his car as well.

Did you go for Gaz struts at the back by the way? ISTR you mentioned you might.

No anti-roll bars as yet...early days!!

[Stratos]

I'm running AVO struts at the rear, and AVO coil-overs at the front.

[CorseChris]

Ah, thanks David. I'll go check them out and see how much I need to save up. Just proves I didn't get to look at your car doesn't it :(

I like the AVO Pro-Race dampers I put on the front of mine. I opted for the 1.9" units to give a wee bit more clearance.

[Stratos]

£300 each plus VAT for the AVO struts.

I'm using 2.25 springs on both ends.

I was going to just use my Leda Struts from the Allora, but Leda quoted me execessively long timescales for refurbishment, and they wouldn't have been ready in time for Abingdon.

[CorseChris]

£300 each...they will most definately have to wait! They do look nice though.

[colin artus]

I think the original Beta spring rate was 135 lb/in. Uprated inserts used to be available for the struts.

Colin

[CorseChris]

Thanks Colin. The inserts are new KYB ones (I think..). No wonder they feel a bit underdamped though. Even a bit of uprating would leave them struggling with a 280lb spring I should imagine. I'll try maybe 200lb or 220lb and see how that works out for now.

[Stratos]

Empty out the oil, and replace it with gear oil.

I used to do this with Mk1 Escorts in the late 70s/early 80s because I couldn't afford Bilsteins. Worked quite well with Ford struts, but haven't tried with a Lancia strut.

[CorseChris]

I once did this trick with the struts on my MonteCarlo (used ATF IIRC)...but I don't think I can do it with the inserts I've got unfortunately. I'll have a look at the weekend assuming I have some time left after pulling & stripping the motor. Might be a good way forward for now, but in the end, there isn't any way to do it properly without spending some cash I suppose.

Thanks for all the input guys.

[Martin K]

After my big accident I did a great deal of research into, and testing of, spring rates. As a result, if you can let me have the the corner weights of your car, or at least front and rear weights, plus some dimensions from the front lower wishbone and coilover, I can suggest some spring rates for off road/fast road/track use that will give you a balanced car which you can tune with the anti-roll bars (if you have them fitted).

A word of warning (from experience!): if the dampers are too stiff, as were the early Ledas supplied by Hawk, you will have a car that is a nightmare to drive and setup. So make sure your dampers are correctly rated to match your spring rates.

Martin

[CorseChris]

Hi Martin,

Thanks for that- I'll measure the wishbone & front damper at the weekend and report back. Inner pivot to shock mount, inner pivot to lower balljoint, shock lengths & inclination?? I don't have corner weights yet but it was weighed at SVA as 450kg front 500kg rear.

My main problem at present is that I can't afford to get decent rear dampers so I'm stuck with basically standard items, I reckon my springs are way too strong (280lb). Longer term I'll probably opt for the AVO struts David has used. Front's are AVO Pro-Race with 350lb springs so should be pretty close for what I want (fast road, I suppose you'd call it).

[Martin K]

My car came with 300lb "competition" springs for the rear, using the normal rear Chapman struts and the normal Hawk front suspension, with I think 450 lb fronts.

It was way to hard at the rear so I tried 250 lb springs for my second event. Still too hard. My third event I got 4th overall at Goodwood - a fast rally stage you'll agree - and I was trying 100 lb springs at the rear!!! Loads of traction, but a bit too soft. So I went back to the 250's and changed the fronts (harder) to try and get some balance for the next tarmac event. Over did it a little and suffered too much understeer - particularly in slow corners, and some pattering under braking. So bought some more front springs, and went midway in stiffness between the 450's and the second set of fronts I had tried. This worked pretty well on Tarmac but I still wasn't happy. Wish I'd done some reading first and worked out what I really needed as I ended up with a garage full of springs!

For the first loose event I used the 100 lb rear springs, remembering the great result at Goodwood - again great traction but too much suspension travel (and no decent, progressive, bump stops). For the rear, I reckon 150 lb springs would be perfect on the loose, along with some decent foam bump rubbers, and 220lb max for the black stuff, but more likely 200 lb rears.

As I can't remember the lever arm ratio of the front suspension, or the damper inclination, I can't give you the spring rates, but I would use a front wheel rate of about 160 lb to balance with 200 lb rear springs.


I am pretty sure, from memory, that standard Beta fronts are a mere 90 lbs.

However, the dampers, if in reasonable nick with no leaks, should be good enough to control stiffer springs, as stiffer springs need less bump and rebound damping than softer springs, not more. This is because the energy in the spring increases with the square of the compression displacement. A 180 lb spring will compress half the amount of a 90 lb spring for the same input, so the energy it absorbs going over a bump that needs to be contained by the damper is less.

Say there is 400 lbs corner weight and 100 lbs springs. The static spring compression (i.e. at ride height) will be 4".

The energy in the spring (Ve) is given by:

Ve = 1/2 Kx^2 where K is the spring constant and x is the displacement.

So in the first instance:

Ve = 1/2 * 100 * 16 which equals 800

If we change that for a 200 lb spring it will be compressed by only 2"
so in this second case:

Ve = 1/2 * 200 * 4 which equals 400

So, a stronger spring needs less damping than a softer spring.

And not a lot of people know that...........

Martin

[CorseChris]

Martin,

As ever, thanks for the info. I suspect 180 or 200 would be a good figure for me to try next. I'll add a couple of inches to the free length of the spring though!

Interesting little equation for the energy, but it does raise a question that I can't answer though - why does a 280 lb spring feel so badly under-damped if the original spec was so low? I can see that the stored engergy will be less with a higher spring constant for the same applied force but from what little I remember of my physics lessons many years ago, a stronger spring needs a stronger damping force for the same time of decay of oscillation. Displacement doesn't enter into it. The initial amplitude would be halved with double the spring strength, say, but the resonant frequency would be up. Maybe it's this increase in frequency that is taking care of increasing the damping force given the same actual damper unit?? The trouble with most of the simplistic views of these systems is they are just that - simplistic. Sadly, my maths isn't up to the challenge these days (if it ever was) so I just have to use the empirical approach.

I once tried the Colin Chapman method - soft springs/hard dampers, but I overdid it and ended up with a car that jacked itself down to the ground as you drove along!

The dampers are new KYB gas pressurised inserts, so should basically be standard specification. I noticed the problem when at speed and hitting a big dip - the back end felt very unhappy in the sense that it took a good few yards to settle back down again. No sense of loss of directional stability, just very 'bouncy' at the rear. Front was fine. There is no bump-steer at the rear of the Corse S as you may know. Front bump steer is fully adjusted out as well so I don't think I was confusing symptoms in this case. It just felt like the tail end of the dip launched the back of the car upward and it couldn't control it.


Edit to add....just got your PM Martin - thanks! Understanding is slowly forming (I think...) :)

180lb spings it is! (but I'll check the front wheel rate before ordering anything)

[Martin K]

Just something to bear in mind Chris

The gas pressurisation of the strut or damper forces it into the open position when not fitted. This force is still applied when fitted to the car. Although it should not be taken into account when calculating wheel frequencies, it does have an impact on ride height.

Some racing Koni's I use have a gas pressure equating to 70lbs/in of spring when at ride height. If doing spring length calculations without allowing for the 'gas spring' effect the car will end up with a higher ride height, and the spring less compressed at ride height, than you might otherwise expect!

In our case, 240 lb rear springs + 70 lb 'gas spring effect' meant that the static deflection was 0.77 of what would have been expected without the gas spring effect. With 180 lb springs that would have been 0.72 of the expected static deflection.

Just thought I'd mention it....

Back to the dampers. A damper will not change the frequency of the spring or the wheel frquency - it can't. All it can do is dissipate some of the energy in the spring (as heat) so that the spring doesn't shoot past it's natural free length in rebound (critical damping) or goes slightly over length before returning to it's free length (under-damping), this return motion being controlled by the bump damping. Yes, with a harder spring that has a higher frequency, it is dissipating this energy over a shorter period, but it is dissipating less energy. Almost all dampers are naturally 'piston speed' sensitive anyway. Trying to force oil through a small hole at one speed will be easier than at a higher speed. Without looking, the resistance probably squares with speed. So a higher spring rate will see a 'stiffer' damper at it's higher natural frequency i.e. higher rate of changing length and higher piston speed.

In practice, if the damping is too tight, the spring won't reach it's free length within it's natural cycle - that is over damping and leads to 'jacking down'. Jacking down causes suspension travel problems, particularly after successive bumps combine to increase the effect. The lowering effect this has on the the car can cause undesirable geometry changes which can lead to cornering problems and braking problems among others. Overdamping also reduces the ability of the tyre patch to stay in touch with the surface, reducing grip. The damper needs to allow the spring to do it's job of keeping the tyre on the road. To do this the spring needs to be at it's working length ready for the next surface irregularity as soon as possible after it has dealt with the last one. Overdamping prevents this.

Most road cars are underdamped - for comfort. Most competition cars are also under damped, but to a lesser degree. The spring SHOULD be allowed to
extend past it's natural length before returning to it's free length, but in under one cycle rather than in two cycles as in a 'comfortable' road car. (3 cycles and you'll fail the MOT!)

A damper also needs to MOVE to work! In cars with very high wheel rates (ground effect cars, for example) the suspension linkages are designed so that the wheel movement is multiplied so that the damper is made to move more than the wheel movement. A Formula 1 car with an effective weight of 1000 lbs on each front wheel at speed may, because of lever arm ratios etc, need 6000 lb springs to produce a wheel rate of 1500 lb/inch. It can be seen that a vertical movement of 12 mm in the wheel will give only 3 mm movement at the damper if it was mounted co-axially with the coilspring. Frequently the dampers are therefore mounted separately from the coilsprings with a linkage to magnify this movement, just so that the damper can be made to do some useful work! However, with this leverage the STIFFNESS of the damper also has to increase in the same ratio as the leverage applied.

When damper movements are small, the problem of sticktion arises. Sticktion is a combination of the forces which combine to resist the damper to move from one postion to another, and is largely composed of friction between pistons and seal, but also by resistance in the valves changing from closed to open and other energy absorbing losses. In struts, cornering hard puts loads on the piston rod which causes increased friction in the top seal, and as the piston is forced against the side of the damper tube, more friction there also.

In some dampers with high sticktion, either static, or dynamic as in the case of hard conering with a strut, the amount of force needed to overcome the sticktion might be enough sticktion to prevent the wheel moving up after hitting some irregularity in the road. This is more likely to occur with harder springs than soft. It is also more likely to happen with poorly designed and manufactured dampers than with good ones.

Be happy!

Martin

[CorseChris]

Martin,

I think you've given me enough here to make a pretty good stab at sorting it - thank you. I'll be measuring up this weekend and I'll get some parts next week. Engine should be back in & sorted by next weekend and I should have my springs on by then, so I can go play. Somehow I don't think I'll have to look far for a big surface defect in our roads......

[CorseChris]

Right, just measured the front setup. These figures are reasonably accurate I hope...

Lever arm ratio is 22:31 (roughly 0.71). This is inner pivot to shock mount:inner pivot to lower balljoint. Hope I have it right.
Shock inclination is 16.5 degrees (so actual rate is multiplied by 0.96)
Spring currently fitted is 325lbf/in

So I reckon I've got a wheel-rate of about 220lbf/in

I'll try and work out the sprung weight this weekend....

I reckon I can fit the springs off the rear onto the front with no bother (fronts are 8" long but a bit short, rears are 10.5" long at present, lots of room on the damper for adjustment), so that would give me a wheel rate of about 190lbf/in. Possibly still a bit on the high side (if I understand Martin correctly now!) but at least it will be a big enough change (about -14%) I'll stand a chance of feeling it. Just hope it's not so close to the new rear rate I end up with a porpoise....might pay me to buy a set of 240lbf/in springs as well.

These figures are certainly starting to look a lot softer than those you are using Dave, but then I want a comfy road car version.

More anon...


...and I just remembered my front dampers are 1.9" so I can't use the rear springs on them.

[Martin K]

Chris

You need to square the lever arm ratio. That makes your wheel rate of about 157 lbs with the 325 lb springs fitted.

Martin

[CorseChris]

Ah, thanks Martin. I really must buy a copy of that book I think....

..so my front wheel rate is pretty much smack on where you suggested I put it with a 180 rear. Probably why it feels OK to my uneducated behind then!!

[CorseChris]

Speaking of which...which book should I buy??

[Martin K]

There are two or three that I would suggest.

Engineer to Win - Carroll Smith - Motorbooks International
The Race and Rally Car Source Book - Allan Staniforth - Haynes Publishing
Competition Car Suspension Design, construction and tuning - Allan Staniforth - Haynes Publishing

Tune to Win is also a good book to have on your shelves - Carroll Smith - Aero Publishers Inc

[Steve Strain]

Hi Guys

Greatings from downunder.
Great thread thanks I will need to print it and re-read it.
I am currently finishing a HF2000 to HF3000 conversion and am thinking of using 280lb race coils. (For anyone interested I have posted a few photos in my gallery but I am having some difficulty loading any more!!)

For what it is worth I raced my Guy Croft 2.0l Beta powered HF2000 in the local Targa NZ, intermarque and other club events with 200lb rear race coils. I fabricated my own rear struts from tubing and had Bilstein inserts fitted. The inserts were valved and dyno'd to match the spring rate by a local suspension shop. For the beta motor they were a great combination giving an excellent ride on the road though maybe a bit soft for the track.

Again for what its worth, the 200lb same springs under the weight of the V6 now look a bit sad. Uncompressed the spring length is 250mm but sag to 190mm.

I think I will try what ever there is around 280lb and revalve the insert to match.

Steve

[Martin K]

Hi Steve

A static deflection of 60mm with a 200 lb spring rate gives an unsprung weight at the rear of 209 kilos per corner. You don't say what the deflection was with the Beta, but with the V6 the wheel frequency is now about 124 cpm. That is pretty firm already. 280 lb springs will put that up to nearly 147 cpm - static deflection about 42 mm. It's my firm belief that you would get a better result by increasing the rears to only 230 lbs, giving a wheel frequency of 133 cpm and a static deflection of 50 mm. I reckon you should try those first, particularly if springs are as cheap in Oz as they are here. You may find that the Bilsteins you have will work ok with the new springs as piston speed will only change by about 5% with 230 lb springs - test and see! What rate are they? If they are around 270/75 I think you'll be ok. With 280 lbs springs the change in piston speed will be nearly 16% so different valving may be necessary.

You will probably find some of the extra weight from the V6 will be on the front wheels - have you checked that? It is likely that if you increase the rear spring rates a rise at the front will need to be considered. Probably to around 440 lbs if the lever arm ratio is the same as Chris's Corse and you go with the 230 rears. The damper is also more inclined on the Hawk compared to the Corse, so a little more stiffness may be required beyond that to compensate.

Do let us know how you get on!

Martin

[Martin K]

Hi

Just read what I wrote and I forgot that the Bilsteins have a 'gas spring' effect, so what I wrote about rear wheel frequencies is complete b*&&^%ks! They must in fact be lower that I have calculated. That also makes the front figures I gave wrong of course!

Without knowing either the actual unsprung corner weight, or the value in lbs of the 'gas spring' effect of the Bilstein I can't give correct figures.

Martin

[CorseChris]

Morning folks,

Had a chance to measure the front unsprung weight yesterday - came to about 70lb give or take a pound or two. I think that for my purposes, this will be accurate enough. Wheel/tyre was 35lb. Upright is Fiat 132, disc is Thema turbo, brakes are Wilwood Dynalite, dampers are AVO Pro Race 1.9". (Spring & damper only came to 5lb total).

Putting this number into my wonderful spreadsheet (based on Martin's formula and assuming I got it right) it gives a wheel frequency of 114cpm. (Sprung weight is about 425lb).

I opted for 190lbf/in rear springs, using the scientific method of that being what the supplier had in stock!

Thanks for the book recommendations Martin - I'll get busy on Amazon.

Steve, any time I can expose my ignorance to millions for the benefit if all, I'll be happy to oblige ;)

I didn't get around to weighing the rear - I'll do that Friday.

[CorseChris]

Measured the rear corner yesterday and fitted the new springs. Came out to about 75lb, so with the 190lb springs, that gives me a wheel frequency of 119cpm. Feels pretty good so far.

Thanks Martin!

[Martin K]

You are definitely in the ball park for a good handling car with good grip (if all you wheel angles are right of course!) - even if the ride might be a touch harsh.

Please report back on how it drives.

By the way, I know it's not a Stratos but it is kind-of son of. What do you think of the new race car? http://www.phoenixcarcompany.co.uk/

Martin

[CorseChris]

Hi Martin,

It feels pretty good so far. A firm ride but not harsh. Handles surface defects pretty well. Feels good on corners. Took a run out to Broadway hill last night. Despite not having a lot of power to hand, the Audi that was following me 'enthusiastically' seemed to lose interest as soon as the first bend approached. Didn't see it again by the time I was halfway round the second bend.


....and I can't properly describe how good that Monte of yours looks without expletives :) I used to have an S1 Monte and often wish I kept it. The Gp5 car was the ultimate version of it I think. I still have a Tamiya kit of one! Nice. Where will you be running the car?

[chris.richard]

By the way, I know it's not a Stratos but it is kind-of son of. What do you think of the new race car?

Wow! :) :)
Mutt's nuts I'd say. I presume it'll go as well as it looks! ;)

[Sando]

absolutely MINT ! :)
Look forward to seeing that out Martin.
Rob

[Martin K]

Cheers guys!

How does it go? Well, we will see. The original produce 440 bhp from 1429 cc at around 1.4 - 1.5 bar. I was talking to a guy with an RS200 at the weekend. The BDT is 1800 cc and produces about 550 bhp from 2 bar.

We have 2043 cc - and can use upto 2 bar with the turbo fitted. Engine management is Pectel T6 with 8 injectors. Big, big intercooler. So what do you reckon - enough grunt?

Chassis wise, well the suspension is a close Dallara's design as we can get, plus we have adjustable Koni race dampers and a driver adjustable front anti-roll bar. Also we have current Pirelli rubber, which must be better than 1980 rubber. In the weight department we are currently UNDER the 750 Kg of the factory cars. However we are likely to have to add considerable ballast for some race series. In Britsports, for instance we would need to weigh in at 1100 Kg - ouch! Brakes should be up to it though, with 330 mm x 28 mm AP vented discs all round and we are trying Bremsport 4 pot calipers, although I have a set of APs should they not work out. We will are using EBC pads.

Aerodynamically the cd from Pininfarina's wind tunnel was .32 (I suspect without the rear wing, actually!) 400 bhp would make it a 170 mph car. 500 bhp would make it a 200 mph car.

I will keep the website up to date on progress, and put up a calendar showing track days, static shows, tests and races that we will be attending - so bookmark that page now!

Bye for now

Martin

p.s. initial wheel frequencies will be 128 cpm rear and 122 cpm front - but that's a secret so don't shout about it as the driver wants 600 lb springs all round because he believes racing cars should be stiff!

[Steve Strain]

Okay I am excited, I have been doodling with numbers for ages (and havent done any work) and now need to share my new found wisdom.

At the risk of getting this totally wrong (I am just a mere kiwi CA) I thought I would volunteer my logic that hopefully might get corrected.

For now I am going to stick with my current 200lb rear springs and the front (whatever they are - as supplied with the kit in 1989). They felt good with the beta and all I have done is add some more weight with the V6 conversion.

The rear springs have a static deflection of approx 75mm for a cpm of approx 109 but what about the front? I have since read that they should not be the same but be within 10% and the front to be a lower figure (hence my need to know what I have got).

I started following an earlier post and attempted to calculate the front leverage ratio on my transformer chassis (different angles to the corse) but got stuck not knowing the weight or spring rate in Nm.
- Top shock pivot down to bottom arm is approx 260mm
- Bottom pivot to lower shock pivot is approx 260mm
- Bottom pivot to balljoint is approx 360mm

Give or take I guess this to be 2:1 ratio. Raising and lowering the front suspension gives 45mm spring travel and Static Travel of 90mm.

Since my maths is crap I thought there must be an easier way of arriving at the approx static suspension travel on the front and cpm without a calculation involving unknowns.

To confirm the static travel I put a jack under the front chassis and lifted the car until the front suspension was at full droop (but with the wheel still touching the floor). I then measured the distance from the floor to a static point on the car (starting height) and the distance across the spring.
I then lowered the car and (bounced it a few times to settle the shock) then re measured the distance from the floor to the same point on the car and across the spring.
The spring shortened by approx 45mm and the height of the car changed by aprox 90mm. Static wheel travel theory confirmed at approx 2:1

To calculate the cpm I looked at the formula (*&$@!@%).
Although I know the mass of the V6 conversion to be 590lb or 267kgs (200lb x 2.95 inch deflection on the rear - note that the beta engine was 560lb), I dont know the front spring rates, how to convert lb's to Nm (is it 270Nm being 200x1.35?) or the mass. Anyway the doodle results I got always seemed to be a decimal out (typical accountant?).
Anyway I thinks there must be an easier way.

With a bit of research I found a graph (typical accountant?). It shows an apparent linear relationship between Static Suspension Travel and cpm (although they fiddle the scale on the static axis to make it a straight line).
Some of the measures are as follows.

50mm = approx 137cpm
75mm = approx 109cpm
90mm = approx 97cpm
100mm = approc 90cpm
125mm = approx 84cpm
175mm = approx 70cpm

My questions now are
1. Is 109 and 97 (rear to front) reasonable for a road going Stratos?
2. Does anyone know what the front spring rate is in lb and Nm or what the weight is so I can calculate the cpm more accurately? (With the beta installed I believed the weight to be 380lb each corner).

I have learned that on a track a stiffly sprung car with a high cpm will get tossed about on bumps but a soft cpm will follow the surface better but wallow more on corners so a compromise is required.
I gather that there are no magic numbers but I believe racing cars of the 60's had cpms of 70-80, 1970's wingless cars had 90-100 and up to 100-125 for a modern wingless race car.
So is perhaps 109 and 97 a good compromise for a road car?

Comments?

Steve

[Martin K]

Well done, is all I can say!

Arthur Mallock used to use static deflection only as his way of setting up/understanding the setup of a car, so your method is fine. Working back static deflection to cpm is also fine. The ratio between static dflection and cpm is linear, so the straight line graph is a satisfactory method. The only thing that I think makes this system less accurate is that it is very difficult sometimes to measure changes in spring length of a 1 mm or less, but the changes in cpm can be quite large, particularly with hig lever arm ratios and stiff springs, as at the front of the Hawk. Approximating these readings is not a good idea either as the errors can be large.

On that subject, your front lever arm ratio would appear to be:

360/260 = 1.385 so I would expect the spring to move 0.722 the distance that the wheel moved. So for 90 mm movement at the wheel I would expect 65 mm at the spring. Of course the damper is not vertical, so it's angle away from the vertical probably explains the difference. If you give me the dimensions of the top shock mounting relative to the lower shock mounting (vertical and horizontal) I can work it out for you. The overall motion ratio you have observed suggests that this angle is 15% dregrees from the vertical.

This in turn would give an overall leverage squared ratio of 2:1. If the weight on the front is the same as with the old engine this would indicate a spring rate of 220 lbs/in, a wheel rate of 110 lb/in and a cpm of 99.5.

I have not heard of the 10% stiiffness differential front to rear before, but 10 cpm is what Staniforth uggest. So 99.5:109 is good, but in the case of the Hawk and it's falling rate characteristic in the front suspension, maybe this is a little soft.

I'd say that you were deffinitely in the ball park with your rates though. You land firmly on the border between the soft end of a track car and the top end of a road car - the border according to Staniforth being 100 cpm.

Unfortunately, although you know the front cpm, without knowing either the spring rate or the sprung cornerweight of the car, it is impossible to work out what rate spring you have from knowing the cpm without knowing the weight of the car - above I simply made a guess based on the car's previous weight. Similarly it is impossible to work out the weight of the car without knowing the spring rate. To go any further (e.g. select a slightly stiffer front spring to close the front/rear cpm gap) you need to find out the weight of the car or the spring rate - can't Hawk give you the latter?

But I reckon as you are in the ballpark it is now a case of test driving the car under the conditions you want it to perform best (e.g. road going comfort or track handling) and make a judgement. I hope that you have a front anti-roll bar - with that you can dial out the front end 'wallow' and balance the car on the track by increasing front roll stiffness without damaging grip.

Good luck

Martin

[colin artus]

The front springs supplied by Transformer were 325 lb/in if my memory serves.

Colin

[Sando]

Interesting stuff guys.
Colin I agree. That is what was written on the end of my Standard Hawk Springs 325Lb/in.

You have to take them off to find it though Steve!!

Sounds like my car is way too stiff!

Cheers
rob

[Martin K]

The front springs supplied by Transformer were 325 lb/in if my memory serves.

Colin

Colin, do you know the dimensions that would give the angle of the front coilover when mounted? That would help too.

Thanks

Martin

[Martin K]

Working on the basis that your front springs are in fact 325 lb/in items, the sprung weight on the front must be 500 lbs per corner to give the deflections you have observed. This gives a wheel rate of approximately 163 lb/in and a front wheel frequency of 107 cpm. This is a bit too close to the rear frequency. So you have a choice - stiffen the rear or soften the front. 280 lb front springs would give a front wheel frequency of 99 cpm which will match well with the 200 lb/109 cpm rears. 230 lb rear springs would give a rear wheel frequency of 117 cpm and will go well with the 325 lb/107 cpm fronts. Either combo should work, but obviously the softer the front option will give a nicer ride on the road.

To confirm my front weight figure, the gross weight of the car should be 1123 Kg with 604.5 Kg on the rear and 518.2 Kg on the front.

Steve, did we meet once in Farringdon, London back in 1990 or 1991 when you bought some X19 headlamp mounting shells from me?

Good luck

Martin

[Stratos]

Martin,

When you are considering these spring rates, how do you factor in weight transfer under braking?

Is it an issue that needs considering?

[Martin K]

No - weight transfer under braking is not part of the equation. If you design the wheel frequencies for braking then you will end up with a car that is way to hard and will understeer like hell in corners. Also, with a very hard front you will lose grip under braking from 'pattering'.

[Stratos]

But, I don't think that you can take spring rates in isolation.

Ride height might be used to lower the centre of gravity of the car, and affect roll in cornering.

Softer spring rates will provide more roll in cornering, and produce weight transfer to the outside cornering wheel, which should provide higher grip levels.

Softer spring rates would allow the nose to dip further changing the centre of gravity, altering the weight distribution between front and back wheels, and thus the level of grip on the front and back wheels.

Softer springs will probably produce greater changes in camber, slip angles, etc which might have an effect on corning ability and levels of grip.

(PS Not trying to say I know any answers, or that these factors actually have a significant bearing. Just trying to be argumentative to provoke discussion.)

How do you feel these factors impact on decisions on spring rates?

[Martin K]

Well I think you should try and isolate in your mind what the different suspension components are for.

The main job, above all others, of the springs and dampers is to maintain the tyre contact patch with the road as the car negotiates the irregularities of the surface - hence the difference between 'race tarmac' settings, rally tarmac settings, road tarmac settings and settings for the various grades of loose surface. The amount of weight transfered to the outside wheels is not determined by the rate of the springs. Although the amount which goes to the front outside wheel and the rear outside wheel is, the total will remain the same. A 1 G corner will transfer the same weight to the outside wheels whatever springs you use.

Anti-roll bars are used to increase roll stiffness and to give control over weight transfer, giving the ability to tune front/rear bias to match the grip levels available from the tyres.

The front doesn't have to dive under braking, if the geometry is designed to prevent it, so geometry should be used to control dive under braking. The height of the centre of gravity can therefore be controlled. Of course the centre of gravity will still move forward, even if it doesn't move down, but harder or softer front springs won't change the amount of weight transfered forwards.

A mid/rear engined vehicle is at a huge advantage here as the centre of gravity will always be nearer the center of the car than with a front engined car. The extra weight - and therefore grip - available on the front wheels can be taken advantage of if you have a bias pedal box, which enables you to increase the braking effort on the front. If the suspension designer decided to build in dive at the front or squat at the rear, rather than it being there by accident, then it will be there for the purpose that he had in mind and is not necessarily a bad thing.

The changes in wheel angle, such as camber and caster, should be defined and controlled by the suspension geometry and initial settings. Suspensions are normally designed to add negative camber as the wheel moves up, this giving correct control of the tyre camber (i.e. adding negative camber to compensate for the positive camber induced in roll by relative movement of the suspension pickuip points) in roll. If the suspension is NOT allowed to compress in a corner, the roll will still be present, so the susension mounting points will move giving positive camber, but the negative camber will not be added by the suspension as it is not allowed to travel sufficiently. In Formula 1 they use huge static negative camber on the front wheels for that very reason.

Slip angles are generated by the tyre, and the springs will only affect the distribution of the slip angles between the front outside tyre and the rear outside tyre.

Of course, all suspension settings are a compromise, and it is necessary to consider the whole package. However, by concentrating on the prime function of components you can make subtle changes to the RIGHT component to get the change in handling you are looking for.

An example.
Take a car with 140 lb front springs and 230 lb rear springs - and accept from me that the wheel frequencies are 121 and 128 respectively.

To limit the amount of roll, without changing pickup points etc, you could add antil roll bars. In doing so the front roll bar is set harder than the rear roll bar, so that in a 1G turn almost all the weight of the car is transfered onto the outside wheels but completely in proportion - mainatining the balance of the car. So if the tyres are gripping then apart from going on two wheels the car is at it's conering limit.

But you don't want to go to all the trouble and expense of adding anti roll bars and then finding settings for them - you want 4 cheap and easy to fit stiff springs to get the same roll resistance. So you you do the maths and buy a set of 405 lb fronts and 435 lb rears to get exactly the same roll stifness result. The resulting wheel frquencies are 177 rear and 206 front. Oh, and you need a new set of dampers to match the new springs too, or your existing ones re-valved - at extra cost. As you have had to increase the front spring rate more than the rear, what was a nicely balanced car in slow, medium and fast corners now understeers in anything but fast, 1G corners. And when you hit the brakes you feel the front tyres skip and slide and - you get scared - and end up braking earlier for the same corner next lap.

Now, both optins are valid, but in overall performance and handling of the car, which method do you think it would be best to adopt?

Bye for now!

Martin

[Stratos]

:) Now look at what an excellent post I coaxed out of you. I'm sure that between you and Chris, you could extract the important elements out of this thread and create a series of newsletter articles on suspension setup ..... over to the newsletter editor... Chris, are you there???



I'm sure some others can now continue the discussion, but I'll ask another couple of questions to get things moving .....

How would you calculate the anti-roll bar settings?

How would you design anti-dive into the suspension?

[Martin K]

My god! The man wants my blood!

[Stratos]

Well, Martin, it's your own fault for giving such high-quality informative answers to difficult questions.

We've come to expect high standards from you now.

[Steve Strain]

Hi Martin

You might be the first virtual blood donor!

Just reading your post again,

I agree that measuring the spring deflection to the mm is difficult and it can be different from side to side and even from one attempt to the next, hence I believe cpm can only be an approx guide. To get around this and spring angles I thought about measuring the movement from a static point on the body work however even this might be a few mm's out due to the tyres compressing a bit.

The distance from the inner lower arm pivot is approx 260mm to the top and bottom shock pivots. This gives a shock angle of 45 degrees (also confirmed with a protractor with the car on its wheels). The distance from the same inner lower arm pivot to the ball joint is 360 mm.
My initial thought was that the lever ratio could thus be greater than 2:1 hence my 45:90mm results. See attached image

The 10% difference was mentioned by one of our local LTSA certifiers who said that if they are too close the car might "PONGO" (no doubt a techy term).

I took one of the springs off but cant find any lb markings. Colins and Chris's comments certainly ring bells at 325lb (I had thought 350lb). I would suggest for the track that yes they are too soft but are perfectly okay on the road.

I did have roll bars front and rear fitted with both set to their softer (1 inch from each end) settings for the beta engine. But for the V6 I have only the front bar fitted since the rear one will not fit around the V6 lump.

What a great memory - yes I am sure we did meet though it would be more like late 1990 than 1991 as I had returned to NZ from my OE by the end of 1990. I am not great on names or places but I recall we met at a pub (had a drink together with our partners). Were you building the Honda powered car at the time? I recall I was selling the headlight mounts but probably spent more at the bar.

regards

Steve

[Martin K]

Unfortunately anti-roll bars are not so straight forward. The problem is that first you have to be able to calculate the vertical position of the roll centres - both at the front and the rear of the car. The reason for this is that the roll centre is the pivot point about which the car rolls. It is very difficult for me to describe in just words what a few pictures would show so clearly. But one of the best 'descriptors' of this is by Staniforth and may help you visualize the problem.

Take an old shoe box and a knitting needle long enough to pass through the box from one end to the other. The showbox is your car (Paint it if you want it to be more realistic :D )

At one end of the box, mark a position half way across the box horizontally and halfway up the box vertically. Make a hole with the knitting needle. At the other end of the box, marke a position half way across the box horizontally and ONE QUARTER of the way up the box vertically. Make a hole with the needle again. Now, from the ouside of the box, pass the needle throgh one hole, diagonally through the box and out of the other hole. The two holes represent the roll centres front and rear and the needle represents the roll axis of your car. Take one end of the needle in each hand - or have a friend hold it for you, so that the bottom of the box is 50 mm above a table top. If you now roll the needle between your fingers you will see that the box twists down on one side, but if you observe the top corners of the box the lateral (horizontal) movement is different front and rear. If you have the friend mentioned above doing the holding, push one top corner of the box horizontally and you will see that the resulting movement in the box is a rotation about the roll centre axis.

Hopefully this demonstrates to you that the horizontal force involved produces a torque (which we call roll) which acts around the roll centre, front and rear.

In a corner the force which induces roll is the centifugal force acting on the mass of the car. The force is essentially applied horizontally and this transfers weight towards the outside of the car, by causing the centre of gravity to shift towards the outside too.

If the roll centre is relatively low i.e. somewhere between a few centimetres above the ground and a few centimetres above the ground, then the leverage that the forces have in a corner which produce roll are higher than if the roll centre is relatively high e.g. closer to the height of the car's centre of gravity. This should be seen clearly from the shoebox car. It should also be clear that the shoebox car need a stiffer anti roll bar than the rear, because for a given force the amount of roll is greater, or indeed it might be clear that one anti roll bar would control the roll of the whole car - front and back. Which indeed it would, up to a point.

The calculations needed to find the roll centre are different depending on the type of suspension, and on the position of the suspension pivot points. So even on the same car at different ride heights, for example, the roll centre is different. If on the Hawk you use the lower rather than the upper inner mount for the front track control arm then the roll centre moves. Having located the roll centre it is a matter of calculating the torque which induces roll, how much you want to limit roll, how much roll is already resisted by the springs, and how much roll you wish to resist with the anti roll bar. Then the length of the bar that can be fitted and where it will be located, where it will connect on the suspension to apply it's force and the length of any lever arm ratios involved, and of course the lever arms and their affect on the anti-roll bar itself.

All of the above is possible, but I feel beyond me to describe in this forum for every type of suspension and every car setup. So, my appologies, but I can't really go any further on the subject here.

Martin

ps.s anyway - this thread was spring rates, wasn't it? heh heh heh!

[Stratos]

ps.s anyway - this thread was spring rates, wasn't it? heh heh heh!

That was soon fixed - you don't get out of it that easily. :rolleyes:

[Martin K]

Dave, you bugger!

(oops - Can I say that???)

[Martin K]

What a great memory - yes I am sure we did meet though it would be more like late 1990 than 1991 as I had returned to NZ from my OE by the end of 1990. I am not great on names or places but I recall we met at a pub (had a drink together with our partners). Were you building the Honda powered car at the time? I recall I was selling the headlight mounts but probably spent more at the bar.

It was a Shepherd Neame pub called The Betsy - hows that for a memory?

[Martin K]

The distance from the inner lower arm pivot is approx 260mm to the top and bottom shock pivots. This gives a shock angle of 45 degrees (also confirmed with a protractor with the car on its wheels). The distance from the same inner lower arm pivot to the ball joint is 360 mm.
My initial thought was that the lever ratio could thus be greater than 2:1 hence my 45:90mm results. See attached image

Thanks for the new dimensions.

Inclining the coil and damper at 45 degrees reduces it's stiffness to 0.71 of it's original - i.e. approx 230 lbs. Being inclined therefore means that 1 cm of vertical movement at the lower pickup will only compress the coil 0.71 cm.

The lever arm ratio is 1.384615:1, so the coil will move 0.7222 of the wheel movement. 0.71 x 0.72222 will give the coil compression compared to the wheel movement. So the coil should compress 45.9 mm if the wheel moves 90 mm up.

This gives the front total weight as being 535 kilos with 588.5 lbs of sprung weight appearing on each wheel, giving a wheel rate of 166 lb/in and a front cpm of 106. This bit is wrong! Corrected in a later posrt.

The rear 200 lb springs are compressing 2.95 inches, I think you said. This means a sprung weight of about 519 lbs per rear corner. The wheel rate is 200 lb/in (being a Chapman strut) so the rear wheel frequency is 116.5 cpm.

I reckon that is fairly hard, and if the front feels soft maybe it is because of a) dive under braking or b) the fact that as the suspension travels up, the spring will become progressively softer due to the inclination of the damper increasing.

If you increase the load on the car so that the wheel deflects the wheel a further 90 mm up, caused either by cornering loads, a bump or dive under braking, the wheel rate will have fallen to only 140 lb/in - a 12.5% fall.

My new estimate for the weight of the car is therefore 1075 Kg, with 540 Kg on the rear wheels and 535 Kg on the front. This bit is also wrong, correted in a later post.

[SUSIT]

Hi Martin,
I am suprised the weight on the front wheels almost matches the rear, I may be getting confused (Iam a nurse not an engineer) but I always thought most Stratos including replicas had a 70/30 weight distribution or there abouts

Stephen

[Martin K]

I can't tell you whether the weights are 'real world' figures - but for the spring rates given and the deflections measured by Steve that is the weight distribution. Unless I've cocked up on the lever arm ratio - I'll check when I get home and update if necessary.

[CorseChris]

My car was weighed at SVA as 450kg front 500kg rear. Corse S, Beta engine, lots of 'surplus' kit on board. Couldn't say if that is typical or not though.

[Martin K]

My car was weighed at SVA as 450kg front 500kg rear. Corse S, Beta engine, lots of 'surplus' kit on board. Couldn't say if that is typical or not though.

Of course for setting up the suspension the driver (or crew) should be on board, plus all fluids and 1/2 tank of fuel. What would that make the weight of your car do you think Chris? Steve has obviously got a lot of something extra in his car - maybe sound deadening? Spare wheel and lead lined carpets?

Maybe we could have a thread where owners volunteer their vehicle weights from the SVA test for comparison? That would be interesting.....

[Sando]

Sounds like I've made a bit of a Horlics of my spring rates then Martin.
My Car (Hawk) weighed 880kg at SVA with full tanks but no driver (I think I'm about 80Kg) or Carpet etc I've probably added a few Kg since too.. (me and the car! :D ) Door bars and a little bit of carpet in the boot, extinguisher etc. Say 900Kg for the car now plus the 80Kg for me.

I Assumed an approx 60/40 Rear - front weight distribution as I'd seen this in tests on Dave's and John's cars in CCC. My Fag packet computer made that just over 2000lb Giving Approx 800lb across the front and 1200lb across the rear.

I then through absolutely no scientific calculations took an average of what other people said they were using and went for 500lb front springs (which I thought was 250 at the wheel) but I guess I missed the bit of leverage from the wheel to the bottom of the coilover, so is a bit lower)
This is without the Front Anti Roll Bar though...

I then went for 350lb at the rear which I knew would be stiff, and I also have a rear ARB. It does skip about on a bumpy road though but I knew it would do so I suppose you know what to expect.
I must say it did handle remarkably well when fully loaded and two up when we drove round the Alps. It has it's understeery moments as much as its oversteery moments but on the whole I've driven worse :D
- AND touch wood I've not spun it yet :rolleyes: .. in 6000 miles of hooliganism and trying (which I'm quite proud of cos it's been well on the edge and past it, many times!)

All your theory has made me think I should have approached it from the softer end first though, so I'm thinking of putting the old 325 fronts on with the ARB and giving 250 rears a go just to see if it does make things more controlable. Mind you I didn't want to own a strat to be civilised, I wanted to be living on the edge anyway!!
:D
Thanks for your very informative posts
Rob

[Martin K]

Rob

Let me run your numbers through my gas powered calculator and see what I find out before you do anything quite so dramatic!

Interesting to note that it felt better 'loaded' - in other words with lower wheel frequencies than unloaded.

[Martin K]

The motion ratio that I gave as 1.958141856:1 is correct.

So for a deflection of 90 mm the weight on the wheel must be about 426 lbs. This gives a total weight of about 924 kilos with 58% on the rear and 42% at the front.

Sorry to all concerned - but thanks for making me look at it again.

Martin

[Martin K]

I then through absolutely no scientific calculations took an average of what other people said they were using and went for 500lb front springs (which I thought was 250 at the wheel) but I guess I missed the bit of leverage from the wheel to the bottom of the coilover, so is a bit lower)
This is without the Front Anti Roll Bar though...

I then went for 350lb at the rear which I knew would be stiff, and I also have a rear ARB. It does skip about on a bumpy road though but I knew it would do so I suppose you know what to expect.
I must say it did handle remarkably well when fully loaded and two up when we drove round the Alps. It has it's understeery moments as much as its oversteery moments but on the whole I've driven worse :D

Hey, Sando. Have you got any fillings left?

You would appear to have a front wheel frequency of 141 cpm and a rear frequency of 154 cpm based on your weight distribution guess work. Static deflection of the springs would confirm this. Do you have about 38 mm at the rear and 45 mm (wheel) 28 mm (spring) at the front?

I'd say that it was just too hard for the road - and for the track!

As your car is quite light, 325 front springs would give a cpm of 113 and 220 lb/in rears would give 122 cpm at that end. Wheel static deflections will be 60 mm rear and 70 mm front. I'd say you would enjoy that more.

But if you want something a little harder, try the 250 lb rears and 375 fronts - giving 130 cpm and 122 cpm respectively.

[Sando]

Hi Martin, thanks.
Somehow I thought you might say that ! :)

I did think it was on the stiff side but not mega stiff, I still have my teeth, look :D and it seems fairly well balanced.
I'm not sure about the static deflection, I'll try measuring that at the weekend, its definitly in the order you suggest though.

250R / 375F should get me back towards reality and keep the balance. I'm also going to go down the V6 route soon which I expect will put around 20-30kg on the overall weight. Would that make the 250R and 375F closer to your ideal cpm? I may not be to get the rear ARB back on then either so it may wag it's tail a bit?
Thanks again, your computer is way better than mine ;)
Rob

[Martin K]

Hey Sando!

I would agree - or the cpm figures would - that your car is pretty well balanced on the basis that the front and rear cpm's are 'in sync'.

However, I think you will find greater levels of grip giving even better handling, and a superior ride quality (as you enjoyed with a loaded car) if you go a little softer.

I also think you were extremely fortunate in your guess work to arrive at front and rear spring rates that gave a reasonable - if hard - balance.

Adding a V6 and 30 kilos will likely change the balance. Given a front/rear weight after the installation I could advise you better. But with, at a guess, 60% going on the rear and 40% on the front you would have 127 cpm rear with the 250 lb springs and 120 cpm front with 375 lb springs.

Not bad, probably a bit on the 'girly soft' side for you! ;) heh heh heh

Martin

Is anyone doing any forest rallying in a Strat?

I saw the Munari car going through the woods on the Goodwood Festival of Speed rally stage. The suspension was soaking up the bumps wonderfully. I reckon that the rear cpm was less than 100 and the front less than 90. Much harder and the car would have been tossed around all over the place. I am sure, from memory and looking at the picture of Steve's front coilover, that there is not much bump travel on the Hawk (I don't know about the Cores or others), which could give problems on big bumps, I think.

I did some chassis work on the Peugeot Super 1600 106 Kit Car after the works had given up trying to sort it out. We managed to improve the car - and the results - on tarmac (Jim Clarke and Manx) and on the loose (Kielder and the Welsh forest) by 'applying the science'. As there was not much travel on the front struts to cope well with rough stages (about 120 mm of bump travel and 100 mm of rebound travel) I had some progressive springs made to use on the loose. Unloaded the coil rate was 125 lbs. They then increased at a rate of 5% per 25 cm so at ride height they were 160 lb/in with a cpm of 87 and at full travel (before the progressive 30mm bump stops came into operation) they were 190 lb/in with a cpm of 95. On all but the biggest bumps on the roughest stages the car never used it's bump stops and the driver found the car much easier to keep in a straight line, better under braking and more stable in the corners. The rear cpm was set at 94 which, although marginally softer than the front when the front was at full travel, the rear was stiffer than the front most of the time. Anyway, it worked out well.

[Stratos]

I did some chassis work on the Peugeot Super 1600 106 Kit Car Anyway, it worked out well.

Samson's ??

[Martin K]

Yep! Good friends of mine... but spelt Sansom!

[SUSIT]

I am planning some forrest stages in my Stratos but its an Allora and the front suspension could do with a redesign. Watching this thread with great interest.
keep it going please.

Stephen Struthers

[Sando]

I also think you were extremely fortunate in your guess work to arrive at front and rear spring rates that gave a reasonable - if hard - balance.

....other peoples hard work with a bit of Sando educated guesswork on the fag packet computer !

Another quickie for everyone
What is the best way to alter the rear Camber on a Hawk?
(with fixed length bushed wishbone) I've found that I have 1deg Neg on one side and 1deg pos on the other. I want to even them up. Should I go for 1deg neg both sides? should I slot the lower strut-hub mounting or slot the strut top mounting? this may mean a longer slot?

Rob

[Steve Strain]

Hi Rob

Use cam bolts. As per the name they are a bolt with a small "cam shaft" lobe. When you rotate the bolt they give approx +/- 0.75 degrees movement.
On the struts I made (see picture) I used two washers that have a hex head instead of the normal top bolt. Through the centre is a drilled offset hole. I got these 15 years ago from Leda.
To fit them I simply enlarged the bolt holes on the strut flanges. The adjustment is a little fiddly since you have to rotate both washers the same amount. With this arrangement I can get +/- 2 degrees of adjustment. I have marked 0.0 and 0.5 degrees with a centre punch for easy reference.
I run close to 0.00 with the big tyres.

If I was doing it again I would use the cam bolt arrangement it is simpler.

regards

Steve

[SUSIT]

My Subaru Legacy use's a cam bolt on the front strut but no idea how much adjustment available

[Chris J]

Rob

When I got my first HF 2000, it had positive camper on one rear wheel and no camber on the other, using standard Beta struts.

I was advised to enlarge the top hub/upright mounting hole on the strut (not the upright itself) and weld a washer in the right place once the correct camber was found. In the end I never bothered to do that because the replacement Ledas I fitted seemed to sort the problem out.

The car I have now has fabricated tube stuts with Bilstein inserts and the same type of cam bolts that Steve S. has already mentioned (see photo attached). I think these cam bolts are robbed from some Ledas, but that's a guess.

[Chris J]

Sorry, here's the photo:

[SUSIT]

Chris, Iam going down the bilstein route, do you know what rate the bilstein's are and what spring rates you are using

Stephen

[Chris J]

Stephen

My brother has similar struts made up for him with Bilstein inserts for Corsas/Novas. I can find out exactly what those are and the price of them.

The ones on my car, came fitted to the car when I bought it. I have'nt really studied them too much. I've been too busy at the other end! I do know that the 2 1/2" diameter springs are 300lb and they're quite long, but I've yet to measure the free length. The struts were fabricated by Gartrac.

[SUSIT]

Thanks Chris I have already spoken to Bilstein and they quote £600 a set. Cant remember if thats plus VAT. What I am trying to avoid is the cost of revalving several times when I get the rates wrong. One of the disadvantages of a non ajustable set up.At present I dont think any of the others available are up to serious forrest use, although I did use Leda struts on the front of my SD1 in the stages with a rebuild every 4 events or so.
Stephen

[Sando]

Thanks for the camber answers chaps. I'll look out for some Cam bolts then and mod the bottom of the strut to even things up. Even with no camber on either wheel this should make a difference once they are the same !

cheers
Rob

[Stratos]

I have already spoken to Bilstein and they quote £600 a set. Cant remember if thats plus VAT.

Same price as AVO.

[Martin K]

Of course this must make for a difficult decision. AVO which you can adjust or Bilstein with proven track record in forest rallying and known to have great fade resistance - but you have to get the rate correct when you buy them as they are not adjustable other than having them re-valved. I was going to put Bilsteins on my 1967 historic Porsche 912 rally car, but decided to go for Koni adjustables for this very reason.

The Montecarlo Turbo used Bilstein dampers/struts originally, but because I could not be certain of our finished weight and therefore spring rates I decided that we would have to use adjustable dampers which can also be re-valved - at least initially - if we were to have a hope of finding the right settings. Of course this also allows for different 'tuning' at different tracks.

I had also experienced supplier problems with Bilsteins for the Phoenix 037 (6 per car!) - but I believe they have been resolved now.

On the subject of camber adjustment, we use the 'cam' nuts too, both front and rear.

Martin

[CorseChris]

Of course for setting up the suspension the driver (or crew) should be on board, plus all fluids and 1/2 tank of fuel. What would that make the weight of your car do you think Chris? Steve has obviously got a lot of something extra in his car - maybe sound deadening? Spare wheel and lead lined carpets?

Maybe we could have a thread where owners volunteer their vehicle weights from the SVA test for comparison? That would be interesting.....


Sorry, been away......as Rob's, my car as weighed at SVA was full fluids & fuel, no driver/passenger/luggage. Reckon I'd add about 85kg for me, then remove about 16kg for half a tank of gas, so total about 1019kg. Balance probably not very far from the SVA figures.

Just back from a few miles in north Wales and 2-up, boot full of junk, very nice indeed! Just need another 100bhp or so is all.

[chris.richard]

Static Suspension Travel

Bit of an oxymoron, surely?

And my brain hurts after reading all this!

[Martin K]

Just back from a few miles in north Wales and 2-up, boot
full of junk, very nice indeed! Just need another 100bhp or so is all.

So, I take it you mean that the numbers seem to work for you?? If so, that's great :)

[Martin K]

Bit of an oxymoron, surely?

And my brain hurts after reading all this!

I take it you are not serious and really do understand the concept.

However, to be clear: Imagine the car on jacks with the wheels just off the ground. As the jacks are lowered and the weight of the car is put onto it's wheels, the suspension will move from full droop to a position where the weight of the car and the force of the springs are in equllibrium. This movement gives us the static deflection of the springs and suspension arms - i.e. there are no dynamic loads only static ones.

Then dynamic loads are added - acceleration or deceleration, lateral as when cornering or fore/aft when braking or accelerating, or vertical as when bumps and dips in the road cause the wheels to move up and down. These dynamic forces cause the suspension components to move from their static positions and the loads carried by the suspension are obviously no longer just the static loads.

But I am sure you knew that.....

Martin

p.s. it's good to exercise your grey matter accasionally!

[CorseChris]

So, I take it you mean that the numbers seem to work for you?? If so, that's great :)


Certainly am Martin - thank you for your help & patience. It's at the hard end of the range for a road car but still feels nice.

Just need to sort out the total lack of performance and it'll be done.

[Martin K]

No worries! Pleased to help.

[SUSIT]

Thanks for the camber answers chaps. I'll look out for some Cam bolts then and mod the bottom of the strut to even things up. Even with no camber on either wheel this should make a difference once they are the same !

cheers
Rob


These might be of use to you
http://cgi.ebay.co.uk/14MM-CAMBER-CRASH-BOLTS-ALIGNMENT-ADJUSTERS_W0QQitemZ8009499925QQcategoryZ40192QQrdZ 1QQcmdZViewItem

[CorseChris]

Well spotted! Time for a punt.....

[CorseChris]

Mm $16.95 from Summit racing....starting price already at £12.00. And they are too big. Perhaps not!

[Sando]

...never mind, It's the thought that counts.... ;)
Thanks Stevie.
Rab :cool:

[CorseChris]

Absolutely! Thanks anyway Steve.

Beta strut bolts are 12mm aren't they? The same firm do make 12mm bolts...and Leda do as well of course. Wonder what they cost....

[rutthenut]

A google search found the following message, indicating that BMWs may use this style of part - bet it costs more from there than anywhere else though!
http://member.rivernet.com.au/btaylor/BMWText/technical/E36CamberCorrectionBolt.html


And this forum describes why they are alternatively known as 'crash bolts' (to realign geometry after a crash!)
http://forums.probetalk.com/archive/index.php/t-8634.html

Also factory part numbers for (US) Neons in this faw (MOPAR Chrysler parts, possibly available over here too, as the car is sold in the UK?)
http://faq.neons.org/faq/FAQ_S.html

Similar info for Toyota Celica parts
http://users.ameritech.net/trdcelica/suspension.htm

[CorseChris]

I remember discussing this method of adjusting camber on a strut about 20 years ago. It struck me as a bit of a bodge at the time, but if it's good enough for BMW (even though they won't admit it) I guess it'll be good enough for me. The Toyota idea looks slightly better using an accurately 'necked' bolt. At least its repeatable. Lexus seem to use cam bolts with no apology at all and even mark a scale on the large static washer!

Perhaps I'll just slot the top holes and be done with it.

I'm running about -1.75 degrees at the back which I feel is probably a bit much for what I do with the car. Can't adjust it at present.

[CorseChris]

Found these which should fit as long as I was right about it being a 12mm bolt (they do a 14mm as well).

http://www.camskill.co.uk/products.php?plid=m3b0s10p511

£33 a pair inc everything. I looked closer at the ones from Summit, but they charge about $24 'handling' for foreign orders, plus shipping which will probably be another $50 based on recent enquiries I've made from US suppliers.

Might try a pair of these some time. Cheaper than replacing tyres that have worn out on one edge.....

[rutthenut]

There's a good description of these parts from H+R, and various sizes listed, at
http://www.hrsprings.com/site/products/triplec.html

Now who's going to confirm the bolt size for the Beta McPherson strut mount?

By the way, Camskill also do the Toyo R888 tyres, which seem a good alternative to Yoko and other road legal track-type tyres. (I've got some, just hope for dry tarmac)

[chris.richard]

Now who's going to confirm the bolt size for the Beta McPherson strut mount?


Exactly which bolt is it you need the size of? I've a pair of struts lying about.

[rutthenut]

Exactly which bolt is it you need the size of?

The diameter (and required length) of the pair of bolts that go through the legs of the strut, where it connects to the hub carrier.

I think mine have a 19mm nut/head size, but I'm not taking them off to measure them...

[CorseChris]

I measured the hole size on the struts at the weekend - 12mm as suspected. Didn't measure length though.

I bought those 14mm 'crash bolts' anyway. Never know....

[BAS]

Just got a set of cam bolts from Camskill, very fast delivery ordered them 3pm Friday got them this morning.

The Part Number is 35410, M12 X 62mm length. (My strut bracket width is about 47mm outside face to outside face)

With one fitted in the top bolt hole of each side you can adjust the camber up to 1.5deg + or 1.5deg-.
You can fit two to each side and get up to 3deg + or -.

If your tyre clears the strut body by more than 15mm using these to dial in more negative camber is easy but with 345 tyres fitted clearance on the strut body could be a problem, I had to add in a wheel spacer to get enough clearance.

So I now have 0deg of camber on each side instead of 0.5+ one side and 1.5+ the other, looks much better. :D

Road test yet to come!!! :)

[chris.richard]

Presumably you only need cam bolts to adjust rear camber if you don't have rose joints at the inner end of the wishbone?

[SUSIT]

Presumably you only need cam bolts to adjust rear camber if you don't have rose joints at the inner end of the wishbone?

I would agree with that Chris but its hell of an expense to get two new wishbones and then buy some rose joints (ask me how I know that :rolleyes: )
What spring rates did you go for & why out of interest?

[BAS]

Yes Chris, but over the length of the strut 1 deg = about 10mm of added length to the lower wishbone and that could have implications on the cv joint end float on full drop.

[chris.richard]

Yes Chris, but over the length of the strut 1 deg = about 10mm of added length to the lower wishbone and that could have implications on the cv joint end float on full drop.

I thought that there was more likely to be a problem on rebound if it bottomed out? Or are you worried about the joint separating?

[chris.richard]

What spring rates did you go for & why out of interest?
I've got the wrong ones I'm sure! The wheel froquencies calculate out at 148 cpm rear and 125 cpm front. I think I'll need to soften them significantly.

[Mark Cowling]

Hi Chris out of interest what spring poundages give those CPM, Regards Mark.

[chris.richard]

525 front, 400 rear. calculated with two 90kg occupants, and no ballast weight.

[Mark Cowling]

Hi Chris thanks for that Regards Mark.

[Mark Cowling]

Hi all when working out the CPM for the car I have been adding the two rear corner weights together & dividing by two because of the large difference with the engine being at one side and only the gearbox at the other this must give a average CPM, is it possible to put different poundage springs on the two back corners to acheive the same CPM? or am I missing something,Regards Mark.

[Martin K]

Hi all when working out the CPM for the car I have been adding the two rear corner weights together & dividing by two because of the large difference with the engine being at one side and only the gearbox at the other this must give a average CPM, is it possible to put different poundage springs on the two back corners to acheive the same CPM? or am I missing something,Regards Mark.

Yes, it's possible, but the way you have been calculating the CPM and spring rates, by taking the average weight, is the 'normal' method.

[Mark Cowling]

Thanks for that Martin Regards Mark.

[Sptwoman]

Back on the subject of cambolts. Are these (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=130217152589&ssPageName=ADME:X:RTQ:GB:1123) any good? They are M12 and 63MM long.

[CorseChris]

Look identical to the ones on my car.

[Sptwoman]

Cheers Chris, It's only down the road from me so will pop down with some readies...

[Sando]

Do you get 2 or is that per bolt?

[Sptwoman]

Well Bob, I popped round and got a pair for £20!! Seems good value!!

[Sando]

cool :cool: