Setup Question - looking for a little more oversteer

[davedlr]

Hello,

 

I might be looking for the Holy Grail here. Basically, on track I find the car quite throttle adjustable in terms of line, but inherently it understeers. I know this is largely because of the VX engine up front, but given the following spec, are there any suggestions (including driving style) to shift the balance towards oversteer? (I've tried trail braking but it still seems I can't provoke oversteer.)

 

Our car is the following spec:

- track focussed, VX 2.0 powered

- English live axle with Quaife ATB LSD

- Freestyle AVO adjustable suspension - equally set front and rear to +8 clicks

- Rear tyres 205/60/13 Toyo R888s - Medium compound

- Front tyres 185/60/13 Toyo R88s - Soft compound

 

cheers!

 

 

 

[Mick Day]

To 'cure' understeer there are a number of routes you can take:

1) Soften front end...damper or a/r bar or springs.

2) Stiffen rear end...damper or a/r bar or springs.

3) Raise the rear ride height.

4) Increase front tyre pressures.

5) Decrease rear tyre pressures.

6) Increase negative camber on front wheels.

7) Decrease rear negative camber.

 

Only change one thing at a time.

 

[Z3MCJez]

A few comments and a few more options:

 

3a) Lower the front ride height

4) / 5) I'm not sure this is the right way round. It depends where pressures are to start with. If the fronts are already too hard, then making them harder will make it worse. I'd try and aim for equal tyre pressures all round when in use (I.e. tyres are warm, brakes are hot).

8) Use narrower rear tyres. I don't know how may hp you're putting out but the rear might be overtyred.

9) Increase toe-out.

 

Jez

[charlie_pank]

More power, power earlier? - can often be a lot to do with driving style. LSD?

 

 

back here because I want to be.

 

Edited by - charlie_pank on 18 Oct 2010 13:32:06

[davedlr]

Thanks guys - lots of things to try there.

 

As for tyre pressures, I find they are quite even @ 21 psi all round after a spirited track session.

 

Whilst experimenting I have been quite brutal in applying extra power, earlier. All it succeeds in doing is pushing the nose wider into understeer.

 

The engine puts out around 180bhp (2.0 on twin 45 Webers), so I think using the wider (205) rear tyres is probably a large part of why the rear will not come unstuck.

It's very friendly and safe, but for track days where its not about ultimate pace, it would be nice to be more go-kart like opposite lock moments.

[Mick Day]

Tyre pressure changes can be a bit of a moveable feast as sometimes it has the opposite effect.

 

With 180 BHP maybe 185 section rear tyres would be better.

 

But before you change this experiment with ride heights: front down, rear up & damper settings as this will be the cheapest/easiest option.

 

Don't drop the front end too much as a smashed sump..........................

[davedlr]

Thanks Mick.

 

Looks like I had better get another track day in before the end of the year to try all these things out. Sounds like a good excuse anyway!

[The Village Idiot]

I think your answer will be more in the setup of the car than the tyres. I run 205's on the rear with 130hp and don't have understeer, in fact it is the rears that let go first if the car is going to slide.

 

Dicks

[Z3MCJez]

At 180bhp you're in R300 territory, and they run 205s (at least the race cars do). I suspect rake is the best place to start - I.e. raise the rear. 150mm difference - front lower than back (measured at the back of the front wishbone, where it joins and under the front of the rear cycle wing) as a start point.

 

Jez

[CageyH]

150mm 😳 😳

 

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

[Paul Deslandes]

I think he means 15mm.

 

I have a 250bhp Vx and ran 205 888 soft all round with little or no under-steer. I suspect the heavy Vx front end might benefit from a bit more rubber on the front.

 

I now run 215 Kumhos all round with the same satisfactory result.

 

 

 

Edited by - Paul Deslandes on 18 Oct 2010 17:08:16

[Pendennis]

A heavier engine bay would normally cause oversteer

 

Personally I don't like talking about rake, however I am well aware how it fixes issues such as these, but it may hide inherent suspension problems.

 

There could be many reasons why it understeers when it shouldn't.

Check front and rear camber. Maybe try a bit of toe out at the front. Presuming your front is narrower than the rear, it should have some toe in at the rear.

Spring rates maybe too stiif front or too soft at the rear.

Front ARB maybe too stiff in relation to front springs.

Check front castor, you may have too little.

Do you use a rear ARB?

 

PS, I love these threads, always read a wide variety of ideas based on experience

 

Want to rent an 18th century Farmhouse in Rural Somerset?

[Richard Price]

Dave,

You don't tell us what sort of spring rates or ARB's you run.

 

How much does it roll? If its rolling, then another factor may be roll induced camber change.

How do your front tyres wear?

 

 

Pendennis said

it should have some toe in at the rear.

That's a bit tricky on a live axle car. However, I have measured a live axle car that had some -ve camber (but the owner did not know the history of the car, other than it had been hillclimbed a few years ago with some success) I don't know if it had a bent axle by accident or design.

 

In my K series car (with about 140bhp) I've been running 215 Kumhos all around in sprints and hillclimbs, and have had good balance and even (front to back) tyre wear.

 

 

 

 

[EFA]

Fit Freestyle super wide track but retain your outboard dampers. This will 100% eliminate understeer which means the back will let go first.

 

Alternatively sell your car and buy one intended to have a VX in the front. 😬 This will however still understeer like a pig.

 

 

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[Z3MCJez]

Yes - 15mm rake 😳 Sorry.

 

In the class I race in there's mandated spring rates, so that is something that I know nothing about. However, what is clear is that there are many ways to skin the cat!

 

Jez

[Red SLR]

Defo raise the R-RH - thats your best tool for getting more power oversteer. Use caution when testing settings too - as I have found out a couple of times! Collected about 4 large cones at Elvington once doing about 100mph because I was running silly r-rh. HTH!

 

 

[davedlr]

Thanks all - I will report back once I have done some experimenting.

 

I'm guessing I need C-spanners to change the ride height on the AVOs?

[Allen Payne]

If the threads are clean, and without any weight on them, you should be able to adjust them by hand

[Mick Day]

Another trick is to put a blob of yellow paint on the lower spring perches so that you know when you've wound on 1 turn. Remember that you'll need more turns to change the ride height on the front than the rear.