Hi all........after spent the last 2 years installing a new engine meagsquirt ect......and a rolling road set up I when out for a run, now the general driving is fantastic goes round corners like its on rails, straight line speed is ok its when you lift off the throttle the front gets very un stable, ok so the things that have changed are the weight of the engine/gearbox and the the front and rear spring rates. The rear's where 200 and are now 300 and the front where 150 and now 200.....any thoughts......Gordon

sounds like to much springing at the rear, have you tried running the springs the opposite way round, for info a locost race car will be around 300ish at the front and 150ish at the back.

Lewis

What engine did you have and what do you have now what is the difference in weight. May be worth putting the 200s on the back and the 300s on the front

Doh beat me by seconds lol

Could indeed be spring rates, but then I found my car much improved by going from 350 lb/in to 425 at the front (still experimenting with the back but expecting 300 to be in the ballpark). The weight of your car and of course the angle and mounting position of the shocks (which changes their leverage and hence 'effective' spring rate) makes a difference so don't necessarily assume that your spring rates have to be the problem.

Worth checking rear toe - if you have not got a small amount of toe in then the car will be less stable in a straight line and under braking.

Have you played with adjusting the shocks? they may need to be tweaked to suit the new springs rates?

The description "unstable at the front" makes me think a bumpsteer/roll steer or toe-in problem. It could also be a damper problem -- over damped.

Start by checking the toe-in front and rear with the car loaded as is normally driven.

The rear wheels should always have some toe-in any toe-out on the rear will give truly evil handling.

The front wheels can be parallel to a very small amount of toe-in, on the front toe in stabilises the steering especially in a straight line but too much will stop car turning in.


[Edited on 30/11/12 by britishtrident]

Another vote for rear toe out being the culprit. Have you altered the rear suspension?

Cheers!

Hi people.....many thanks for the reply's....the original engine/gearbox was an Austin maxi unit (weight un-known) and now it has an toyota MR2 unit.......the 1st set up had no problems, I've been running 24 front and 26 rear tyre pressures, shocks are AVO coil overs with damping set to 5 rear and 2 front, there have been no suspension changes at all apart from springs, I was thinking of setting the damping rate to its lowest setting back and front and lower the tyre pressures..........not too sure what the rear tracking has been set at but its been said that between 2-4 mm in would be good...............

Does it get unstable in a straight line when you lift off or is it when cornering? Cant really tell from your opening post.

If its when cornering then basically you have more grip at the front than the rear which probably means the rear is too stiff.

[Edited on 30/11/12 by MRLuke]

Hi it gets unstable when you lift off...........