Corner Weights

[Steve Strain]

Hi Guys

Help needed please – What do I do next – are 200lb springs too light for an Alfa conversion?

During the Beta to Alfa conversion the car suspension has been apart and all prior setting have been lost. I now need to restore the ride height and set corner weights before attempting a wheel alignment but have a problem, the RR suspension feels a lot harder than the LR!.

As a starting point I simply adjusted the spring platforms to achieve a 150mm ground clearance at all 4 corners of the car. (This seems to be about the lowest height achievable at the front of the car). Then last weekend I put my car on to a set of electronic scales.

My Stratos (spec –1989 HF2000 with Alfa 3.0S, full fuel tanks, ABS, 4x4pot Wilwood vented discs, heater plus approx 5kgs of tool kit (in boot), no spare wheel or carpets yet, 200lb rear springs on Bilstein struts and 350lb front over Spax), weighed 950kgs split as follows

LF 180.5kgs
LR 305.0kgs
RF 171.0kgs
RR 293.0kgs

The scales also indicated (with rounding)
• 63%R and 37%F weight split
• 50% weight split diagonally across the car (LR to RF) and
• 50% weight split to the Left and Right sides of the car.

I am sure that a half-turn down on the high readings plus a half turn up on the low readings may have evened out the paired axel weights. So with nothing more than a ruler I thought these static results were quite good.

However I am also interested in what happens when sitting in and driving the car and how the springs react to my added weight. Since I weight 74kgs the results changed to 1,024kgs split as follows

LF 201.0kgs
LR 330.0kgs
RF 197.5kgs
RR 295.5kgs

This gave a similar overall result
• 61%R and 39%F split and
• 50% diagonally and
• 50% L side vs R side.

Note the small change (293.0-295.5) or the relative inability of the RR to absorb my weight. This result may confirm my thought that the RR suspension is harder (or less compliant) than the LR.

This is what I think the issue might be.
1. To achieve the even ride height the RR spring is under more tension than the LR due to the engine position and weight bias to the rear RHS.

2. Given the higher static LF weight (180kg compared to the LF 171kg) the RR may in-fact be also pushing against the opposite LF, meaning the RR spring platform may be set too high!

Since I can’t move the engine around to address point 1 I thought it worth checking point 2.
I have yet to re-weight the car again but tried the following (which in hindsight I should have probably done first)

1. I measured and marked the mid point of the chassis front and rear.
2. Jacked the car up at the mid point so the rear wheels were clear of the ground.
3. I adjusted the front spring platforms so that the rear corners of the car were the same distance from the ground. (A spirit level also confirmed the car was level).
4. Repeated the process by jacking up the front at the mid point and adjusted the back spring platforms.

As thought I was able to lower the RR spring platform by 5 to 6mm yet keep the unifrom ride height.

I am hoping that on retesting the corner weights that
1. They will still be even from side to side, diagonally etc
2. Also when I add my weight it will be taken up by the springs more evenly i.e. in theory - 18kgs each side.

I have since driven the car and conclude that yes there is a slight improvement but the RR is still noticeably (uncomfortably) harder.

My question is –
1. Would increased rear spring rates make the suspension more compliant?
If so what rate should I go to, say 250lb?

2. If I increase the rear spring rates will more of my added weight be added to the front of the car and change the 60/40 split?
Since the front springs will be relatively more compliant this could be possible.

3. Will the rear ride be harder with increased rear spring rates or will they just handle the load better?

I eagerly await your pearls of infinite wisdom

Steve :o

[Martin K]

Without changing the weight distribution of the engine/gearbox and the driving position, corner weight perfection cannot be achieved. However, to balance the car as best as possible with you sitting in it, the corner weights should be:

LF 206.6
LR 324.4
RF 191.9
RR 301.1

To achieve this, either the left front or right rear spring pan needs to be adjusted UP so that more load is carried on that diagonal pair.

Adjusted this way the same front/rear split will be acheived (as that cannot be changed simply by adjusting spring pans) but the left/right distribution will become 51.9%/48.1% (both front and rear) and diagonal weights will be in balance as best you can get them, with the front left/rear right pair carrying 49.6% of the weight and the front right/rear left pair carrying 50.4% of the weight.

These target corner weights are independent of the spring rates you finally settle on.

Martin

To answer your questions, though, harder rear springs won't make the suspension more compliant - the opposite in fact. Making both rear springs harder will not 'move' your weight either forwards or backwards. Harder rear springs will make the ride - harder!

Also, sorry to disappoint you, but as you are sitting on the left hand side of the car there is no magic to make you weight appear in the middle of the car, thus distributing your weight more evenly around the car!

[Steve Strain]

Hi Martin

Thanks for your comments, I have learnt alot over the last few weeks and realise that although perfection is unachievable it is great to have the theory to work to.
In NZ we sit on the same side of the car as you - does that make a difference to the target weights you mention?


Thanks

BTW here is a neat site for calculating Weight and Percentage

http://www.stockcarproducts.com/pstech5.htm

[rutthenut]

Personally, I think I would find 200lb springs a bit weak for the rear of a V6 kit. They probably work well in general ride and wheel control during bump etc (depending on your dampers) but they will most likely allow for quite a bit of body roll during cornering.

Certainly not how I would want it on a track, but keeping a fair amount of compliance will make for a more driveable car the rest of the time. Plenty of discussions in the forum, and elsewhere, about spring rates and the like. Much - like my comments - being pure opinion and not absolute fact. Your experience may vary.

As for adjusting spring platform position to set a desired ride height, that is likely to go against the requirements for getting an even corner-weight figure. If aiming for more balanced corner weights (side-to-side) then think of changes to the platform height as 'pushing' a wheel harder onto the ground at that corner, which wil change the weight carried by that unit. Martin has had some of the better comments around corner weights, if you can get the concepts correct in your mind.

Certainly info on the web around this subject. I still like the 'Race and Rally Car Source Book' to explain suspension geometry, but other books cover the topic too.

Regards,

[Martin K]

I forgot you drove on the left! But the numbers I gave are still applicable.

It's funny, but all the other corner weights I have looked at for this engine in this car show that more weight is on the right hand side of the car. Seeing your left weight bias made me jump to conclusions - a very bad thing to do!

John is absolutely right. If you (can) set the ride heights spot on the corner weights will be wrong.

When it comes to handling in corners, corner weight balance is much more important than ride height, particularly if you want the car to behave in the same way in left hand corners and right hand corners. If you left the corner weights as they are, and all other things being equal, because of uneven weight transfer the car would tend to overteer more on right hand bends and understeer more on left hand bends.

[Sando]

Interesting stuff as always.

Guys can you just clarify from where you are looking for your Lefts and rights on your cornerweights..... :)
Steve I was confused in your post about a couple of them
Probably me being a bit simple, but I wanted to be absolutely sure what was being measured where.

Thanks
Rob :cool:

[Martin K]

Interesting stuff as always.

Guys can you just clarify from where you are looking for your Lefts and rights on your cornerweights..... :)
Steve I was confused in your post about a couple of them
Probably me being a bit simple, but I wanted to be absolutely sure what was being measured where.

Thanks
Rob :cool:

Good point, Rob

I was working from a plan view - i.e. the driving seat looking forward - that is the usual way of looing at it. Perhaps Steve is looking from the front! That would explain the 'Left' being heavier than the 'Right'

[Steve Strain]

Thanks for the comments guys, greatly appreciated

I hope the following helps.

The weights I reported are from the back of the car looking forward RR= Right Rear, LR = Left Rear etc. Driver sits on the right side.

In the earlier "Spring Rate" thread we decided that for road use 200lb rear springs were okay as they gave approx 115cpm.
Yes I agree these would be no good on the track but then I hardly ever drive on the track, this is a road car.

Most guides I have read say to set the car first at the desired ride height then adjust the platforms. Unfortunately I only had time to measure the initial weights and not adjust them but in another week or so I hope to get another go.
Given the odd initial result - the RR didnt change when I sat in the car and it feels hard on the road I thought I would ask for advice as to why this might be or where to start looking?

I have checked the suspension moves freely so wonder if could it be faulty springs?
Although they are new I am thinking that (although the labels say so) they may not be a pair.
Maybe the LR is just a few turns too high.

Steve

[Martin K]

Thanks for the comments guys, greatly appreciated

I hope the following helps.

The weights I reported are from the back of the car looking forward RR= Right Rear, LR = Left Rear etc. Driver sits on the right side.

In the earlier "Spring Rate" thread we decided that for road use 200lb rear springs were okay as they gave approx 115cpm.
Yes I agree these would be no good on the track but then I hardly ever drive on the track, this is a road car.

Most guides I have read say to set the car first at the desired ride height then adjust the platforms. Unfortunately I only had time to measure the initial weights and not adjust them but in another week or so I hope to get another go.
Given the odd initial result - the RR didnt change when I sat in the car and it feels hard on the road I thought I would ask for advice as to why this might be or where to start looking?

I have checked the suspension moves freely so wonder if could it be faulty springs?
Although they are new I am thinking that (although the labels say so) they may not be a pair.
Maybe the LR is just a few turns too high.

Steve


The LR needs to go UP to take more load - then it should deflect more too.

What dampers do you have fitted? I had some Ledas supplied by Hawk which were way too stiff. Stiff dampers can give a very hard ride.

[Steve Strain]

Yes I too had Leda's (non adjustable) - they were originally purchased with the kit to match the cut down Beta springs. Unfortunately both were rubbish.
I swapped the Leda's for Bilstein inserts which have supposedly been valved to match the 200lb springs.

Perhaps I should get these checked out again?

[Steve Strain]

Hi Guys

I have found the problem with the rear suspension giving odd weights (when adding my weight).
The Bilstein struts are binding under load. This is due to the lack of movement in the top strut mounting bush causing a side load. Not much movement is required as the suspension moves up and down but the nolathane bush I have made is either too wide across the top spring mount and/or too stiff under load.

I have long since disposed of the original Beta mounting system (since the rubber had perished and are unobtainable new over here) but wonder what the orginal stratos used?
Ideally a mount like a rose joint (on its side) would give perfect movement under load.

Does anyone have any suggestions or detailed pictures of the original or something I can adapt?

thanks

[strat6v]

Demon Thieves do some rose jointed top mounts. Same things from Trans Auto Sport (TAS) in the uk.

[Stratos]

Steve,

I use the rose-jointed top mounts from TAS too.

[Steve Strain]

Got one. Down here they are called a "pillow ball" (only God knows why)?

Now I Just have to find a mate for it.

I have a little machining to do to the top spring platform and a couple of spacers to make so it will pivot nicely. Then I will check the struts move freely.

It should look a treat!

Cheers

Steve

[pimms]

Don't know if you have a Hawk but i got these from Gerry's, at a price!

Cheers

[chris.richard]

Don't know if you have a Hawk but i got these from Gerry's, at a price!

Cheers

They look nice! Bet the price isn't! :rolleyes: