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mark warren
19-08-02, 02:42 PM
Since getting my SRV8 on the road it seems to suffer from terrible bump steer, and is hard work to keep in a straight line when it hits a dip in the road! It has spax suspension all round and an anti roll bar on the front. I am wondering if the spings on the front are the wrong ones as I have a rover V8 fitted and I understand the springs are stiffer for the chevy engines. Is there any way of solving this and checking which springs I have actually got on the car. Can anyone help?

kdavies3
19-08-02, 03:50 PM
You've probably already done this but you should check your camber and castor settings, if they're out you will have the symptoms you describe.
I can't tell you what they should be on your car mines a Dax.

Kev Davies

graham
19-08-02, 04:07 PM
Hi, speak to me I have an SR V8. I had to change my springs as mine was a Rover V8 version with the appropriate springs. But I have a Chevy in mine. Basically remove your spring/damper units, remove spring from damper carefully with the proper compressor tools and written on the seat on one of the ends is a number like this "10 S 300". meaning 10" length by 300lbs strength.

I have a complete set of 6 x Rover V8 springs from a RV8 based car available to you if required.

Regards

Graham

And yes you would need to get all the suspension aligned for geometry perhaps when you have the springs and ride heights correct first.

mark warren
19-08-02, 05:02 PM
Thanks for that I will try to take one off this weekend and have a look. Are you saying that the if they have the numbers on the bottom that you have quoted then they are the correct ones or the wrong ones?

Let me know, thanks.

maxGD059
19-08-02, 05:43 PM
Mark
If you have true 'bump steer' it implies that your steering rack is not set at the correct height. Has it been off at all or infact are you sure that it absolutely spot on when you fitted it?

Cheers

Richard
(It'll only be a 5 minute job)

russell_ram
19-08-02, 07:23 PM
Mark,

True 'bump steer' has nothing to do with spring rates.

Bump steer is the change in toe angle (either pos or neg) as the suspension goes into compression (and also rebound). This is due to the difference in pivot position of the steering arm inner knuckle compared to the wishbone inner pivots. Because the track control arms are not infinately long their change in angle as the suspension moves up or down (because they effectively get shorter or longer as the angle changes from normal ride height) pulls or pushes the steering arm independant of what you do at the steering wheel. This is exacerbated by poor suspension geometry.

Of course you can minimise this by having the springs very stiff so that the suspension doesn't move much, but is better fixed by fixing the poor geometry that causes it.

The other often miss-named 'bump steer' is due to the centre of the tyre contact patch not being on the steering/hub pivot axis. The effect this gives is that, due to the offset of the force at the tyre contact patch being away from the steer axis, going over a bump tends to twitch the steering to one side. This is normally caused in our case by the 'wider than standard' wheels not having the same offset ratio compared to the original wheels ie all the extra width added on the inside or outside and not equally both sides, hence causing this offset of contact patch that wasn't there on the donor car.

You need to decide which effect you have before you can consider what the appropriate action is to remedy it.

Russ

The geometry thing is much easier to demonstrate on a 3D computer model than to describe!!

mark warren
20-08-02, 10:30 AM
Thanks for that. One thing I know I have to do is to get the geometry set up properly aswell. I will check the springs rating this weekend but after what you have just stated I think the sooner I get it booked in somewhere to be set up the better!

maxGD059
20-08-02, 11:31 AM
Mark
One quick way to check your rack height when you've got the front spring/damper units off, is to move the hub from the position of full droop to full compression & have someone watch the steering wheel. If it moves then this proves that the centres of the arc of suspension movement & that of the steering arm are not in line. ie your rack is at the wrong height. These things are better to understand in the flesh so to speak, but from this simple test you can see if the rack is too high or low. A simple adjustment may mean you dont have to go to the expense of a full professional check up as you suggest

Cheers

Richard
(It may be only be a 5 minute job)- but mine wasnt

dave
20-08-02, 10:14 PM
The SR chassis does suffer from bumb steer due to the steering rack being located in the wrong place, but it is not just a case of moving the rack up and down as the steering arm ends are also in the wrong place to work with this rack.
There is a solution but it involves fitting a modified Sierra rack at the correct height, the sierra rack is the ideal length ( between inner pivots) and if the existing threads are cut off the ends and new threads cut then the rack will work and the bumpsteer will disapear. The only problem then is that the input from the column comes in in just the wrong place ie. straight through your front chassis upright.
To cure this with less hassel you may be best talking to Cheng Lim at Thunder road cars, if there is an easier solution he will know it.;-)

maxGD059
21-08-02, 08:33 AM
>The SR chassis does suffer from bumb steer

I'm glad Andy Burrows convinced me years ago then

Cheers

Richard
(It'll only be a 5 minute job)