Fixing Understeer

[jamie077366]

Hi all.

I have a limited knowledge of suspension so help me out. I have a rover v8 manta hatch used for track days, 400lb front springs, 130/180 progresive rear springs, Koni adjustable shocks front, spax at back, set quite stiff, gte ride hight.. for some reason It sits slightly higher at the back.

Problem is it roll's into corners with understeer and seams to "pitch" onto out side front wheel, while spinning inside rear. Under my understanding if i stiffen front to stop picthing (if thats the right word) stifening front will promote understeer. Would be interested in any ones thoughts?

Thanks, Jamie.

[Retro Power]

You're understanding is quite right, certainly stiffening the front on its own will tend to create understeer.

My first thoughts are:

What camber are you running on the front? I'd be inclined to run as much as you can get from the standard setup, also by increasing the caster (swap caster shims for thinner washers and move the top arm back a bit) to get more camber on lock.

Next, have you got a rear anti-roll bar on it? If so, give it a try with it disconnected (easy to do reversibly, just take the droplink bolt out of one end, and keep it with you so it can go back easily at the track) this "should" help limit the amount of rear wheel lift you get for a given amount of body angle.

Following that, the only other way you can prop the car up more is by uprating front springs and/or anti roll bar, but as you say, both will cause knock on effects with understeer on less than smooth corners.

I have struggled to get on with Spax adjustable dampers on mantas. I found that when I had a bump rate that was anything like acceptable, the rebound rate was way off (and led to lack of grip on the unloaded wheel). Might just have been me, but on my old 16v exclusive i binned them and fitted bilsteins which transformed the car. I'm always wary of makign this statement as I am biased as we are Bilstein stockists, but then the reason that we are is because they work well!!! If it were my car I'd only use Blstein dampers.

You can also play with suspension mounting points to move the roll centre, but that's getting tricky and unnecesary really.

[lamchop77]

Jaime

If i were you i would get hold of a copy of Allan Staniforths book Comprtition car setup, it is a goldmine of info.

I used to run a class 3 grasser and had similar understeer problems. Do as Retro Power has said concerning the front camber, (turn the top ball joint to give you more). Running the springs you have will be a pretty hard setup, you can try disconnecting the front anti roll bar which will soften the front end. This will help to stop the understeer but could make the roll too much. A fix for the chevettes was to machine down the middle of the anti roll bar to soften it, the cars were built with understeer to make them feel safe!!!

To cure the understeer you basically have to either soften the front or stiffen the rear or a mixture of both!!! But if you go too far one way you can go past the point of the cure and make the situation worse!!! This is where Mr Staniforths book comes in handy as it explains things a whole lot better than i can.

To me the rear springs are too soft, usually they would be around the 200+ mark, also because the car is pitched forward the c of g will move that way which will promote understeer, so i would look at getting the car at least sitting level, preferably an inch lower at the rear before i did anything else. I did have a similar prob on my GTE and i cut a few coils from the rears to get it to sit right (took them from the end where the coils are closest). I would also soften the dampers to a middle setting and start adjusting from there. Make sure that the front suspension isn't bottoming on the bump stop during cornering as that will cause understeer the moment it touches, (instantly overloads the front tyres).

Now i've mentioned tyres, have you checked them? Are the fronts harder than the rears? How old are they? If they are harder on the front you will get understeer, try swopping them and see if that makes a difference. Are all your bushes ok?

Last thing, keep a notebook of what you have done so you can always reset if thing go pear shaped, and only do one adjustment at a time.

HTH

Chris

[jamie077366]

Thanks Retro pwer and Cris, thats given me loads to try and get stuck in with, will cut coil out back first and then look at camber. Camber is standard berlinetta at mo.

Thanks again, Jamie.

[lamchop77]

Jaime

A lot of people do say not to cut coils so be aware that if you do this it is at your own risk.

The coils i cut were the ones that compress totally when the car is sat, i did it one at a time until the ride height looked ok. Be aware that if you cut too much the spring can become too short and could become loose when the suspension gets to full extension.

The ideal solution is get the car to the right ride height and get a set of springs made to correct poundage and length later on. Retro Power may be able to advise the best sets to buy, i know that a few people have had problems with spring lengths on certain kits. Which springs are yours?

Chris

[jamie077366]

Ya, used to do it years ago when funds wouldn't allow proper lowering springs! Car only used for track days, wife won't let kids in it so don't worry!

Spring were bought of ebay, 'on line' i think company was called, there still listed, described as fast road/rally.

Jamie

[Ems]

On my Manta I've got spax dampers with uprated springs that are standard ride height. The understeer on my car has gone since I turned the upper ball joint round and fitted the LSD

[mantadoc]

Stiffening is a balance. Being too hard will make it understeer, so will running out of suspension travel if it's too soft.

Additionally no point exceeding the effective spring rate of your tyres, because then the tyres become your suspension

Stiffening doesn't necesserily give more understeer. Basically it depends on the starting point and what you have to start. If it's soggy to start with you can go quite a way where everything is improvement before you get to a point where you reach trade offs where to make one thing better you make another worse.

Turning the ball joints around gets a couple more degrees of camber unless already done and many are.

Some reinforce the top wishbones then slot the mounting holes for more camber but you have to know what you are doing.

Don't forget to use your ears, on dry tarmac if the car slides and tyres quiet suspension is too soft (if pressures right) if the tyres sound like tearing paper suspnsion is better than tyres.

I swear by these