spring rates for competition use

[roger001]

I am in the process of converting my HF 3000 (originaly a transformer HF2000 of 1985 vintage) for track racing with aview to using it in the Auto italia series in class C, for production specification cars, which allows for a change in spring rates and damper internals but not for any changes in suspension layout, has any one any experience of which spring rates are appropriate as the original road springs will be too soft, the car currently has an Alfa 12V V6 installed. Currently I am in the "learning "part of the curve, racing a 1500 Alfa 33, in The Alfa Romeo Owners club series and a few Auto italia races when they come my end of the country.

[rutthenut]

Hi there Roger.

For information, the spring rates on my car are 550lbs/in at the front and 360lbs/in at the rear - and they could definitely be stiffer than that for track use. Not so much so at the front.

If you want to mess around with numbers, there are plenty of calculations that you can perform to try and work out an 'optimal' rate. I went through this process once, using a spreadsheet, which can be quite interesting. The result can be to get a figure for the harmonic frequency of the suspension units at each corner of the car. You can adjust this figure according to your requirements.

Information on this is in the 'Race and Rally Car Source Book' by Allan Staniforth, and probably in 'Race Car Suspension' too. Other books have more or less on the topic.

Of course, this is all theory and you need to compare this with the perceived results found in practice.

The main point to consider with springing is that there is the 'spring rate' and the 'wheel rate'. The former number is what you quote when buying the stuff, but the latter rate is the one you should use when considering the effect on the car.

As the rear suspension uses a strut, there is little difference between the two, as there is little leverage between the wheel and the actual spring. Actually, at least one of the books states that the ratio between the two is 1:1 but - being awkward - I would disagree on that. It really depends on the contact patch of the wheel and the angle of the strut. If the centre of the hub/wheel/tyre is outboard of the strut centre line, then there will be some leverage in the suspension. But it would be fair to say that the ratio should be quite small.

A further thought on this, if you have wide group 4 rear wheels and tyres, you can find that the actual rate can vary tremendously if the tyre loading varies between the inner and outer edges. This happens on an uneven surface, at least, and may arise due to weight transfer and dynamics during cornering. Just consider that with a wheel that is twelve inches wide, if the tyre tracks over a bump close to its outer edge, the leverage against the spring would be near double to that when load may be on the inner edge.

The front suspension design is more important in calculating spring rates, as there is a definite difference between the length of the lower wishbone and the lower shock/spring mounting point. I haven't got any of these numbers around at the moment, but you can imagine that the spring may be about 3/4 of the way from the inner wishbone mount to the hub centre (or even the distance measured from the wishbone inner point to the centre of the tyre contact patch, there are plenty of alternatives).

The two lengths measured against the wishbone provide one amount of leverage of wheel over spring rate. For instance, a spring rate of 400lbs/in may result in a simple wheel rate of 300lbs/in (ratio of 3:4 between the lengths).

But there is yet another consideration at the front, as the spring is mounted in an inclined position. On the Hawk (and the original Stratos) the top mount is coincidental with the upper wishbone pivot, whereas the Corse has a separate upper mount for the spring/damper unit. I don't know about the Allora suspension here. Depending on the angle of inclination (should the be 'the angle of the dangle', or should I avoid that phrase?), the effective rate of the spring is reduced further. The inclination on the standard suspension is somewhat close to 45 degrees (depending on spring height).

I remember that when I did all the maths for the front suspension angles and lengths, the result was that the wheel rate was near as dammit half of the spring rate (on the Hawk setup). Hence my 550lbs/in springs provide a wheel rate of 275lbs/in.

Yet a further complication is that as the suspension travels through its arc, the angle of inclination increases - which has the effect of reducing the wheel rate of the suspension. The farther that the angle gets past 45 degrees, the worse this will get.

Rising-rate suspension can be quite good, but reducing-rate suspension is far from ideal. My view on this is that if there is not a great deal of suspension travel overall, the change in rate is going to be less noticeable, so perhaps not such a big deal after all when looking at a tarmac/race car.

This is one point where theory indicates that the Corse front suspension is an improvem ent on the Lancia/Hawk design (and I would agree with that point). Again, my view is that this makes more difference in the theory than it might do in real world effects.

But I have had additional front damper/spring mounts added to the chassis of my 'lightweight' racer, which positions the top of the unit a bit further outboard, hence nearer to vertical. Actually, the thought of a better geometry design here was less important to me (but no harm at all) than the benefit of being able to much more easily change the front springs without having to dismantle the upper wishbones to do so. So, two benefits from this mod.

So, that's plenty of theory (and woffle) - hope it isn't a case of teaching you to 'suck eggs', but more like 'food for thought'.

I also realise that you probably couldn't change the front spring mounts if you wanted to as you are aiming to keep to the production class rules.

I find the whole area of suspension theory quite interesting, don't know about the rest of you. I've thought about putting together some software based on the Stratos settings so that the different numbers could be generated by tweaking any of the individual parameters. The results would really only be for comparative purposes, but could lead to insight into the setup of the car.

Any thoughts on suspension software out there?

[Stratos]

Originally posted by rutthenut
Hi there Roger.

But there is yet another consideration at the front, as the spring is mounted in an inclined position. On the Hawk (and the original Stratos) the top mount is coincidental with the upper wishbone pivot, whereas the Corse has a separate upper mount for the spring/damper unit. I don't know about the Allora suspension here. Depending on the angle of inclination (should the be 'the angle of the dangle', or should I avoid that phrase?), the effective rate of the spring is reduced further. The inclination on the standard suspension is somewhat close to 45 degrees (depending on spring height).

This is one point where theory indicates that the Corse front suspension is an improvem ent on the Lancia/Hawk design (and I would agree with that point). Again, my view is that this makes more difference in the theory than it might do in real world effects.



John,

The Allora design is similar to the Hawk in that the top mount of the shock is on a bolt which runs through the top wishbone mounting points.

I found that, on the bumpy rallies I was doing, I was managing to bend this bolt because all the bump was being passed to the centre of this bolt when I ran out of suspension travel.

My Allora has now been changed to have the top mount of the shock separate to the wishbone mounting points. I also moved it upwards and slightly outwards, so it is now similar to the Corse design. All of this has given me more suspension travel, less stress on the wishbone pickup points and top shock absorber mounting point, and a more vertical shock absorber, which will reduce the change in spring rate under suspension movement.

Several other things were changed at about the same time, so I'm not absolutely certain what helped most, but when I made this change the car certainly seemed to handle better.

I am doing rallying, rather than racing, so I probably don't need to be quite as stiff as you guys, plus my front suspension design is now different to yours, so maybe my setup is of no use to you, but in case it helps, I'm running 450lb at the front and 350lb at the rear.

[rutthenut]

David, sounds like we've both made similar modifications to the front suspension, away from the standard Lancia design.

I have considered getting an adapter made to allow for this alternate type of shock mounting so that it can be retro-fitted to the existing chassis, as I wouldn't mind changing my old car to have a separate shock mount. But I've done nowt on that so far.

You did at least experience a problem with the standard design, where you describe the pivot bolt bending. Obviously this likelihood would be reduced if the shocks do not bottom out and/or have extra bump stops to decrease the loading, but there will always be a limit to the travel and rallying is most likely to find it. Using a separate mount makes a lot of sense in this regard.

An alternative modification could have been to add an additional mounting point/plate for the pivot bolt, adjacent to the shock bushing, so that it is held in a stronger form of twin-shear mount, but that would only help in taking the load and would not provide any of the benefits of improved geometry and easier servicing access.

Still, enough of my woffle on that particular point, methinks!

Cheers all

[Stratos]

Originally posted by rutthenut
David, sounds like we've both made similar modifications to the front suspension, away from the standard Lancia design.



Do you reckon this means that we're better than Mike Parkes and the other Lancia Stratos designers? <grin>

[rutthenut]

Re - better than Mike Parkes etc... ;-)

Hmmm, can't exactly agree with that one!

That would also mean agreeing that the Corse chassis is better than the Hawk - I don't know if that is really true or not, and I honestly don't want to get into that potential argument. There are certainly differences, and none of the chassis' are likely to be the deciding factor in performance at the level we all drive at.

I'd prefer to just see what people have achieved with the cars, in terms of results. Trouble is, there have been more Corse variants in motorsport than Hawks - so far - so I could be onto a loser there! I would like to see more of all the models out there competing at some level of competition, then it can come down to the driving abilities of the owners, which is what should matter most.

Perhaps the argument for which is the better front suspension design is more easily answered. The separate shock mounting as on our cars and Corse chassis is certainly best from a theoretical point of view, but you have to look at the results achieved by Lancia themselves to indicate that the suspension design is not exactly bad, after all... So what use is all that theory?

Cheers

[Stratos]

Originally posted by rutthenut
Re - better than Mike Parkes etc... ;-)

Hmmm, can't exactly agree with that one!



John, My comment was only meant in jest.



Originally posted by rutthenut
That would also mean agreeing that the Corse chassis is better than the Hawk - I don't know if that is really true or not, and I honestly don't want to get into that potential argument. There are certainly differences, and none of the chassis' are likely to be the deciding factor in performance at the level we all drive at.


John,

I never meant to imply that.

I think arguments about which is better are pointless. We all should just get out there and enjoy driving (competetive or not) whichever variant (Transformer, Hawk, Allora, Litton, CAE, or LANCIA) of the Stratos we have the pleasure to own.

Personally, I just love seeing Stratos in whatever format.

[rutthenut]

John, My comment was only meant in jest.

I never meant to imply that.


Sorry - I did realise that and should have included a smiley too!!!


Also agree with your statement about just seeing the cars in action, whichever form they may take.

I may be biased, but I do appreciate the merits of all the cars out there regardless of my own opinions.

[David May]

I'm not so sure that there is not some truth in that 'better than Mike Parkes' joke...

I've met a few guys from the period who generally agree that they did a great job with what they had, but that they only got it right the next time, when they started from scratch (037).

I think it's no coincidence that only the best drivers got good results from the original Stratos (despite many years of intensive development.)

Dave M

[JohnB_SPY8808053]

Why do you feel that the 037 (which was based on the Scorpion/Montecarlo) was more of a 'from scratch' design than the Stratos (whic was not based on any existing production car)?

If the 037 was a better car (and it probably was), I would think that it was better because they were able to use all the things they had learned from the Stratos. Also, the 037 was a Group B car where the Stratos was in Group 4, so the engineers had a lot more freedom to try new ideas, use exotic materials and otherwise go crazy with the design.

Just thinking out loud...

John B.

[David May]

I'm not trying to say anything about good or bad cars (I personally prefer the Stratos in all aspects) and I do agree that the 037 probably started out with a cleaner sheet of paper and easier rules.

Probably the nastiest aspect of the Stratos was the strut rear suspension, which as I understand it was more-or-less forced on them to allow enough room to change drop-gears quickly on rallies despite the wide overall power unit package.
The 037 with its longitudinal layout had no such limits and particularly the rear suspension is much more elegant (twin spring dampers, fully adjustable, geometrically correct..)

There is surprisingly hardly any more use of exotic materials on the 037 despite the 10 years between the designs, although probably due to not having had to homologate so many road cars, there is more use of welded tubing and less formed sheet-metal than the Stratos. The use of some of the Montecarlo centre tub was probably for marketing reasons, as that seem to be about the only part which ever had anything to do with a Lancia (not that the Stratos was any more Lancia in that sense.)

Dave M

[JohnB_SPY8808053]

Thanks for the discussion. I like both cars too and someday hope to have a reproduction 037 to park beside the reproduction Stratos in the garage.

I tend to think that the Stratos had the cleaner sheet to start with since it was not based in any way on an already existing car. Because it used the Montecarlo/Scorpion center section, the 037 was in some ways restricted to what could be built around it. You are right in that the suspension of the 037 was not too affected by this though. The Group B regulations also allowed for just about any set-up imaginable.

Even though the Stratos chassis was incredibly stiff, I would think that the space frames used in the 037 were stronger and lighter. It seems like I read somewhere that they were made from a chromoly steel alloy (or was that the Delta S4). The 037 also used kevlar and carbon fiber instead of fiberglass. While these materials are not particularly high-tech these days, they were quite advanced when compared to the Stratos.

I had always thought that had Fiat not killed it, the Stratos would have evolved into an engine and rear suspension configuration similar to the 037 but I read something interesting the other day that changed my mind. Apparently Maglioli was asked by Fiat to stop developing a Ferrari 308 powered version of the Stratos after they had cancelled the project. It seems he was hoping that this would show the Fiat management that there was still a lot of development potential left in the car.

John B.

[rutthenut]

Re. rear suspension design of the original Stratos - didn't the factory try out a wishbone system in the early days, with some failures in rough surface rallies? Or was that just some early problems with the strut configuration?

Hadn't realised that the strut design was chosen with some regard the ease of access when changing drop gears, although I know that this was an area of design consideration for the rally car.

Even so, it doesn't look like using a strut-type suspension causes the factory teams any real problems in getting designs that work in rallying - look at all the Group A cars (and WRC?) that use[d] struts.

[Stratos]

John,

You are right about the factory trying double wishbones at the rear, and then discarding them in favour of struts after failure during rough road testing.

But, one thing that must be considered, is the quality of roads in the early 70s, especially those used for rallying. Todays versions of classic 70s rallies, such as Monte Carlo, San Remo, Corsica, Catalunya are all running on pure asphalt. back in the 70s these same rallies were a mixture of asphalt and gravel, because many of the roads were unmade, and so they were much rougher than conditions met by current rally cars - and certainly much rougher than roads any of us would consider driving our cars on!!!

John is also correct in stating that modern WRCs (World Rally Cars) run with struts all round. In fact, Mitsubishi only recently changed from wishbones to struts when they designed the Lancer WRC to replace the Group A Lancer - although their lack of success with the new design might actually indicate that the wishbone design was in fact better.

[JohnB_SPY8808053]

I thought that they had to abandon the double wishbone setup to accomodate the transversly mounted V6. As far as I know, there were no V6 powered cars with double wishbones but they might have tried them on the beta powered prototype.

The initial suspension failures (Tour de Corse & Costa del Sol 1972) were caused by the lower rear wishbone failing because at first these had been made from stamped metal sheet. These early wishbones were just not strong enough to survive a rally and they were also prone to changing shape under racing conditions, which created very unpredictable handling characteristics. It took them a while to figure out the cause but as soon as they did, the problem was solved by simply changing the construction of the wishbones.

John B.

[Stratos]

The second prototype had twin wishbones - the one which is pictured as either white or flourescent orange/red.

I might have some pictures from the World Stratos Meeting 2000 in Austria which show it. If I haven't, I know I have it on the video footage I took of the event, so maybe I can pull a still from there.

It'll be after Abingdon before I get time to do that though.