Help Stop The Roll!

[jonah 1]

Yeah it would, the wider rear essentailly lowers the centre of gravity, and the weld in cage stops the chassis twist, so that benefit is passed to the front of the car.

I'm not sure if that's right. Widening won't lower the CoG but it will increase the amount of roll resistance for a given suspension setting. But if the inner wheel is already off the ground, maximum lateral weight transfer has alreay been reached and roll resistance is zero. So anything you change in the rear suspension can't reduce the amount of roll. (I think this is right anyway! )

 

Stiffer cage would reduce the difference in roll angle between the front and rear of the car... but wouldn't reduce the total or average amount. In fact I think it's the opposite... because the amount of roll is being controlled solely by the front wheels, the tilt at the front end can't be reduced by stiffening the cage, all it will help do is reduce the amount of chassis droop on the unloaded rear corner.

[Jonmurgie 2]

Nice ideas coming out of you lot now!!

 

The cage is already welded in, not bolted (well the rear points are bolted as it goes to the rear beam mounts) so it's quite stiff, even the 2 mounts above the windscreen are welded, unlike most OMP cage installs!

 

I was thinking of spacers actually, need small ones on the front to get the height down any more and was looking at having some rear camber plates made up so could add some width that way I guess?! Will see when I get the beam off in June...

[nick 3]

Nice tits......

 

Nick

 

Sorry, went a bit off topic there...

[Rob Thomson 6]

Jon, you obviously need a 309 rear beam with 23mm TBs and a 25mm ARB...

[smckeown 1]

Jon, you obviously need a 309 rear beam with 23mm TBs and a 25mm ARB...

 

Are you sure he needs a wider and effectively softer ARB/TBs ?

[Jonmurgie 2]

Rob's only saying that as he hsa that lot for sale...

[smckeown 1]

I wonder if this is because the 205 has a short wheel base, and the 309 being longer would eliminate ?

[jonah 1]

Wheelbase doesn't affect lateral weight transfer so won't change the amount of body roll.

[DaveK 0]

Wheelbase doesn't affect lateral weight transfer so won't change the amount of body roll.

 

But surely a wider track would stop the other wheel lifting off the ground as much.

effectively putting stabilisers on, all be it a small set (nice one ripp)

[max0 5]

Rear strut brace?

Lower the car to reduce center of gravity?

Stiffer Springs?

wider track - spacers / 309 beam / wider wheels?

 

How much petrol was in the tank as that could cause quite a lot weight transfer if full?

 

is the rear window glass or perspex as i know of a AX GT with 300 bhp ( with a perspex rear window which flexes more than rolf harris wobble board

[hengti 2]

i think you're going to have to look at seriously stiffening the springs (and whatever the equivalent is at the back) to seriously reduce roll

 

petrol tank is flat and already at the lowest point in the chassis; don't think that drastic top end weight reduction is going to help much - there's not really much weight up top in a stripped car (poly windows might help though)

 

best get the cheque book out again!

[veloce200 3]

bet your front wishbones are pointing up at the outboard end - they should point down. raise the front til they are parallel or just below at the outboard end. You are getting massive weight transfer on the front end which is lifting the rear, also I would say arb is a tad too big so you have virtually no droop on the rear.

Edited April 11, 2006 by veloce200

[jonah 1]

But surely a wider track would stop the other wheel lifting off the ground as much.

effectively putting stabilisers on, all be it a small set (nice one ripp)

Yes, widening the track (at the front) would help, that's not the same as wheelbase.

 

wider track - spacers / 309 beam / wider wheels?

i think you're going to have to look at seriously stiffening the springs (and whatever the equivalent is at the back) to seriously reduce roll

 

People keep saying to stiffen / widen the rear end... it WON'T help when one rear wheel is already off the ground!

 

Rear strut brace?

No comment

[hengti 2]

looking at Jon's piccie, it would seem that the problem of the o/s rear lifting is due to weight transfer - the n/s front is compressing

 

hence the suggestion of (much) stiffer springs (on reflection, probably only for the front). as with any tinkering though, there are pros and cons - the ride would likely be unbearable and you'd run the risk of tipping it over if you hit a big kerb at speed on very sticky tyres

 

 

i'd personally leave it be - you could spend a fortune on a fancy set up and be cornering as flat as a race car, but then everything becomes very unforgiving and not quite as much fun in my opinion

[veloce200 3]

looking at Jon's piccie, it would seem that the problem of the o/s rear lifting is due to weight transfer - the n/s front is compressing hence the suggestion of (much) stiffer springs (on reflection, probably only for the front).

 

if you add more front spring and not rear it will understeer more. if the wishbone is going above parallel at the outboard end under load no sensible amount of spring rate will stop it rolling.

[Sam 4]

I think you need 25mm rear bars

[Guest smokinslim]

Going against the grain a little here but why not try softening the rear end a bit. By the sounds of it you probably have one of the stiffest beams around (N.b. TBs and ARB).

When i got my car it still had its original beam as far as i know, 17ish years old and not mentioned in the service history. The arms moved freely but were v stiff so i'd guess it was heading for a seizure... and i could get a wheel off the ground round my local asda roundabout no problem lol

 

Or better still just soften the rear ARB, keep the TBs as they are. The stiffer the ARB, the more the trailing arms will imitate each others movements if that makes sense.

 

If you have access to other springs, TBs, ARBs, etc why not try swapping things around a bit and see what works best. Surely it down to personal preference to some degree anyway.

 

I know i'd sooner come out of a corner on three wheels than the roof though

[veloce200 3]

Going against the grain a little here but why not try softening the rear end a bit.

 

your're not going against the grain - i suggested a softer arb a few posts b4 Having now looked at some pics of Johns car though I think I can confidently say it is too low at the front. raise the front - end of problem - also ZERO COST !

Edited April 12, 2006 by veloce200

[Jonmurgie 2]

I know i'd sooner come out of a corner on three wheels than the roof though

Quality

 

Too low on the front, I don't think I'm that low at all to be fair... have seen much lower 205's out on track, the FCS stickered up 205 also at Llandow was SLAMMED and seemed to be cornering flatter (maybe slower though?!)

 

I guess I'm only really going on about the roll from pictures after the event as driving the car I can feel the roll but it doesn't feel like it effects much to be fair, I have MUCH more issues with locking the rear brakes up all the time and it sometimes makes the car unstable just before turning in! Always so many little things left to improve...

[smckeown 1]

as well as the need for a bias valve (I assume you have one), that would indicate too much weight transfer jon, and stiffer springs would help that surely ?

[jonah 1]

your're not going against the grain - i suggested a softer arb a few posts b4

Yep so did I!

Having now looked at some pics of Johns car though I think I can confidently say it is too low at the front. raise the front - end of problem - also ZERO COST !

I'm not convinced by that though. Front roll stiffness is dependent on spring rate and anti-roll bar stiffness only, it doesn't depend on ride height or the angle of the wishbones. Raising the front end (without changing spring rates) would only put the CoG higher, increasing lateral weight transfer and therefore increasing the amount of roll.

 

 

I'm going to retract my comments about rear track width though. Having thought about it again, I think a wider rear track would help. I maintain that stiffer rear TB's / ARB will not though!

 

Out of interest Jon, how does it handle when it's starting to lift that rear wheel?

Edited April 12, 2006 by jonah

[Jonmurgie 2]

As I say I don't really notice that it cocks a leg in a corner as it doesn't seem to through the car off balance or anything?!

 

I might look at getting some 15mm spacers all round though as I need a bit more clearance on the front end...

[veloce200 3]

Yep so did I!

 

I'm not convinced by that though. Front roll stiffness is dependent on spring rate and anti-roll bar stiffness only, it doesn't depend on ride height or the angle of the wishbones. Raising the front end (without changing spring rates) would only put the CoG higher, increasing lateral weight transfer and therefore increasing the amount of roll.

 

lowering the car so the wishbones are below parallel drops the front roll centre way below ground from it's initial location above ground (this is an inherent problem with MacStrut) whilst this lowers static CofG in a corner the roll centre moves dramatically and there is more leverage (the distance between so even stiff springs cannot prevent greater body roll. I'm not going to write an essay explaining it. I have given customers this advise before and they all agreed it worked. I would suggest John tries it. It's not just about CG height it's front and rear roll couples. You will NEVER see a production car with Mac Strut wishbones pointing up. With double wishbone it s a different story altogether. Why do you think people move pick up points for racing?

[Wurzel 16]

My avatar picture is me running a standard 309 rear beam with Bilstein Sprintline suspension kit on Goodyear F1 tyres. The rear lifted considerably on that particular corner.

 

My thoughts on this are, with the weld in cage, the shell is going to be as stiff as it can be. If money were no object and a stack of different ARB/TB thicknesses were at hand, the maximum effective bar could be found for a given front suspension set up. As said, as soon as the rear wheel lifts, there is no point in stiffening the rear further. Reucing the rear ARB thickness will certainly allow the inside rear wheel to droop but as there is no weight on it to give grip, what's the point?

 

Imagine the car static and you push down on the front corner. Given enough force the car will pivot on the opposite front and diagonally rear wheel. The corner opposite the one with the downward force on will lift. The only thing that will delay this is to use stiffer springs on the front. The stiffness that can be used is down to the amount of grip the tyres can give before understeer occurs.

 

I think rear wheel lift is inevitable on this type of car really, and maybe not such a bad thing. When my rear was lifting, I wasn't even aware of it until I saw he pics. The car certainly didn't feel that different.

 

As has been said in many threads before, suspension settings for one given instance, will most certainly be a compromise for another

[smckeown 1]

come to think about it, i have seen plenty of race 205s that were higher at the front than the rear