Ride height/tyres/understeer question

[L7 FST]

I want to reduce the mid corner/exit understeer I experience on track in my very standard roadgoing Roadsport. I want to do this as cheaply as possible.

 

I'm planning to fit a rear ARB as a first step. And, since I need new tyres (I currently run R888s on 14" rims) I was planning to get some 205-width Yokos for the rear, and 185-width for the fronts, which would raise the ride height at the rear by about 15mm, which I believe is a good way to counteract understeer (I don't have adjustable platforms).

 

Does that seem a good idea - or are there any catches I might not have thought of?

 

Another possibility would be to choose the softer compound Yokos for the fronts.

 

Any comments appreciated, or other economical suggestions?

 

Thanks

 

Stephen

[siran]

a softer front bar is a good step,also check your toe front & rear

[Paul Deslandes]

Its preferable to fix a problem at one end by adjusting that end, rather than compensating at the other, at least at first. By fitting a rear arb you're going to make the back end worse when in fact, by the sound of it, you want to make the front end better! What arb do you have on the front? Have you tried taking it off? What camber and toe do you have on the front? Have you played with tyre pressures?

 

As for tyres, I would have thought that SG compound 888s are better than 048s (32s not available in small sizes anymore ☹️) but if you must, go for soft front and medium rear. 2G 888s are too soft for track and road and will overheat very quickly.

 

Others will give you better ideas but I'd start with what I'd got before laying out dosh, other than on tyres if you need them of course.

 

Paul

 

 

[L7 FST]

Thanks. I already have the softest (orange) ARB on the front. Also, they don't do soft compound R888s in my 14" size - hence considering the switch to Yokos. Any views on the ride height question?

 

Stephen

[FlymoFraser]

What is the rake at the moment? You can tune understeer/ oversteer by changing the rake and I believe 15 mm difference is the recomended amount.

 

If you have adjustable platforms, it's probably worth getting the car properly set up for corner heights, rake, toe in, camber etc, you shouldn't "need" a rear ARB or different tyres to dial out understeer.

 

Worth a look at this thread here

 

Edited by - Neil1202 on 29 Nov 2008 16:05:27

[Stationary M25 Traveller]

... unfortunately ...... see first post ..... "I don't have adjustable platforms"

 

 

[BYKer Will]

On the r888 toyo's if memory serves 2G or GG as on the tyre is medium and SG (super gooey} are the softer ones.

 

GG certainly don't overheat on road or track on a blackbird at least. My fronts have done about 6000 miles inc 14 trackdays and are still only half worn. In the same time I have gone thru 1 and a half rears in GG.

 

I will be going for SG next time at least on the front. Sorry if you can't get them in 14 inch

 

 

Will

[FlymoFraser]

SM25T- doh!

 

First step then is to get adjustable platforms 😬

[Grubbster]

I have a similar sounding car to yours - Roadsport on narrow track with 14" wheels, R888's no adjustable platforms or rear ARB, standard front ARB. IMO it has a surprisingly good balance and a few 'much better than me' drivers who have tried it on track have also said that there is nothing wrong with the handling. Obviously all a bit subjective as 2 cars are never the same and neither are the drivers. Adjustable platforms would enable a better setup of course but maybe some small adjustments to camber and toe at the front would help - Redline made a couple of changes to mine when they serviced it and it made a real difference, I think the main thing they did was give it a very small amount of toe-in.

[Willie.]

Cheap fix:

Dab of brakes and sharp turn in

Power on, opposite lock

Adjust angle of car with throttle

Exit corner feeling like a hero.

 

Willie

 

 

[L7 FST]

Thanks for your suggestions.

 

Grubster may be right that I should look at camber and toe in/out before doing anything else. And Opposite Lock's technique tip is fine, but I'd prefer not to have to work so hard to get the car turned in! I'd just prefer a much 'pointier' feel than I have.

 

I guess I'll probably try my various proposed steps one by one over the course of my season of trackdays and see what works....

 

Any further wisdom gratefully received!

 

Stephen

[Neil_K]

Do you have an LSD? A LSD with too high a preload for a Seven can give understeer as described.

 

Where am I?

[Peter Carmichael]

So you don't want me to tell you to get a stiffer front bar to cure understeer and stop it driving like a blancmange

[L7 FST]

Blancmange it is, but would a stiffer front bar really reduce understeer??

[Grubbster]

I'd be interested to hear your thoughts Peter - I don't have an understeer problem but I am planning to fit a rear ARB and stiffer front ARB to reduce roll. Please tell all

 

Please support Roger in his Indian Ocean rowing race! 4350 miles in about 100 days

[Richard Price]

L7 FST,

If you have completely standard roadsport suspension with the 10mm orange bushed front ARB, then replacing the front ARB with the red bushed 5/8" bar, works well.

 

Whilst convention says that a stiffer front bar will make the car tend towards understeer, this does not always hold true! As the car rolls more, the tyres make a less favourable angle with the road, and loose grip. However, with a stiffer front ARB, the angle the tyres make with the road is improved, and understeer is reduced.

 

I use standard springs and dampers, with a red front ARB, and no rear ARB. It seems to work OK in the clubs speed championship .

 

 

[L7 FST]

Peter. Well, that's certainly an affordable place to start, so I'll try it... Thank you!

[CageyH]

If there is nothing wrong withthe tyres, put the money towards adjustable platforms as well.

 

Only dead fish go with the flow....!

[L7 FST]

Fair point but - going back to my original question - will raising the rake by using a slightly bigger diameter rear tyre have the same effect on handling of a car as would raising the rake by the same amount through adjustable platforms? I assume the answer must be yes...?

[CageyH]

Yes. It is the rake that is important.

Platforms are the long term answer for adjusting the corner weights etc.

 

Only dead fish go with the flow....!

[Willie.]

Yes...but you're also increasing rear end grip.

 

Raising the rear is so that the front takes more weight and the rear is lighter. Its a balance thing, and you feel it most on turn in (eg, If you've a high rake and you turn in on the brakes you can feel the back squim, with a low rake it feels secure).

 

So you raise rake to make the rear lighter...then stick on wider/grippier tyres and you're probably back to where you left off. Its a balance thing.

 

I reckon those who suggested the red front bar are probably correct. What camber do you run? You could try another 1/4 or even 1/2 degree, may be better in the corners, but you'll scrub the inside edges of the tyres on straights. If it works, you'll know you need a stiffer bar.

 

Willie

[Peter Carmichael]

I'm not going to dwell on the semantics of attempting the impossible of "reducing weight" by raising ride height when the rest of the advice is reasonably appropriate and the subjective observations are good.

 

The significant things that happen with ride height changes are twofold:

1. you change the geometry of rear roll steer

2. you change the roll axis and the position of the CoG WRT to the roll axis

 

If your CoG is a long way above the roll axis, the car will roll, giving you lots of feedback at the limit of adhesion. If your CoG is close to coincident with the roll axis, the car will break away with little warning.

 

The rear suspension rolls about the a-frame mounting point on the de-dion tube/axle.

 

The front suspension rolls about a virtual centre which is tricky to calculate. If you have the lower wishbones horizontal, it can be said with certainty that the roll centre height is between ground level and the lower wishbone. This is not a bad place for it.

 

Fitting bigger tyres... does not change the roll axis or the rear steer characteristics that I have described. Fitting bigger tyres on the front changes the trail of the steering geometry, affecting self-centreing and feedback.

[Peter Carmichael]

Part 2:

 

If you adjust front ride height, you affect the position of the roll centre very markedly.

 

If you adjust rear ride height, you affect the position of the CoG above the roll axis.

 

Rake is a measurement. The handling characteristics are achieved by geometry that is imperfectly described by the rake measurement in itself.

[L7 FST]

Damn! And just when I thought I'd begun to understand it.......

[Willie.]

PC - you know what I meant. Rear "feels" lighter.

 

L7 FST, keep in your mind that Peter is thinking about adjustable platforms, thus increasing "ride height" means screwing platforms up. If the car rolls about the A-Frame mount, and the Centre of Gravity is an inch above this, you'll get little roll and snappy break away. If the CoG is a foot above the roll axis (A Frame mount), then you'll get stacks of roll and a more progressive break away (Think of Double Decker bus vs 7).

 

What he's saying is simply that by fitting bigger tyres you will not change the distance between the roll axis and the centre of gravity...you're simply moving the whole thing up.

 

However, I still think a larger diameter tyre of equal width will make the rear feel lighter and prone to oversteer, but I don't want to start a war on your thread.

 

Willie