Bump steer / steering rack heights

[Alastair]

Hi

 

First of all - I'll come clean and mention that I am a Westfield owner. Boo, hiss boo I hear you say

1991 Narrow body with Fiat 2L Twin Cam.

 

But - i'm not getting a straight answer from the Westfield owners site - so I thought i'd contact you fine lot.

 

The situation is that I have just had my suspension geometry all set up by a laser kit (castor, KPi, toe etc etc) - all is good now and the engineer commented that the car had been well finished by the previous owner.

 

However he was slightly concerned by the downward droop of the steering rod arms from the steering rack to the outboard balljoint at the wheel. On exiting the rack the rods drop by up to 2" at the outboard end. This he thought was perhaps a recepie for bump steer amongst other problems. He advised I spoke to fellow westfield owners to see if this good or bad.

 

Certainly from what I have read in Des Hamills book (Suspension geometry and tuning) he clearly states that a kit cars steering rack and steering rods should be level from wheel to wheel. - Makes sense to me but those Westfield boys couldn't give me a definative answer *mad*

 

What do you guys think?

 

cheers

Al

[Normans_Ghost]

He's correct, but do you suffer from bump steer and if so can you get the rack lowered to straighten the t/rod? If answer to either is NO then, as you can't do anything about it don't worry.

 

Norman Verona, 1989 BDR 220bhp, Mem No 2166, the full story here

[Alastair]

Norman

 

cheers. Certainly I do get quite bad 'light spots' when driving down a country road etc. The steering is not as controlled or as stiff as i'd like it to be. I probably could drop the rack but it would be a garage job.

 

but you agree that the rods and rack should be level yes?

[Paul Richards]

Steering rack and steering arms don't have to be level.

I think first you need to establish whether you actually have bump steer or not.

Bump steer is movement of the wheel in or out during movement of suspension and produces a car which is unstable over bumps.

I'm surprised that he didn't check for you. An easy way is to simply remove the coil spring from the damper and refit the damper. With car jacked up and wheel removed, use a G clamp or similar to attach a long piece of metal or a brush handle to the disc. With wheels in a straight ahead mode, lift the suspension through its normal travel and watch the end of the length of metal. The length will exaggerate any movement. It is difficult sometimes to get no movement, but it can be reduced and or confined to part of the travel least used, by moving steering rack. Do this both sides (They can be different).

As an aside, excessive slope of the steering arm may not be good as it may cause binding of the track rod end and potentially cause damage. Whilst you have the spring off move the suspension through its normal travel and at regular intervals move the wheels from lock to lock and check for any stiffness or binding.

 

Paul Richards

Joint AO - L.A.D.S. (Lancashire and District Sevens)

Growing old is compulsory - Growing up is optional

[tjm]

can't help thinking the advice you are starting to get here is..

1) Check whether you actually have bump steer (and that doesn't mean looking at the angle of the arms!) and there isn't something else wrong.

2) decide whether this is a good or bad thing

3) Decide if it is actually fixable (or worth fixing)

4) give up worrying and enjoy driving like thousands of others with standard suspension setups...

 

which (strangely enough) is pretty much the advice you were given on the westfield board

 

The reason you didn't get a straight answer there is there isn't one or there would be very simple instructions in the build manual!

I have to admit I find it amusing that you want to listen to a guy at a tyre shop (or what you read in a book which sounds grossly oversimplified!) over the accumulated knowledge of owners, some of whom are pretty experienced engineers and race drivers. You might not have got the advice you wanted but it was good advice! (and no, none of it came from me!)

[Blatman]

😬 😬 😬

 

[Shaun_E]

There have been discussions about bumpsteer on this forum specifically about measuring it and possible corrections for it (on a Caterham). I have had this measured on my car and there was very little bump steer present although some other owners have found a significant amount. It will affect the ride and handling and it can be virtually eliminated by (in my case) raising the steering rack a little. Oliver, who did this for me with the aid of a home made rig, has a spreadsheet that calculates the bump steer and also the required alterations to eliminate it. I think it is impossible to completely eliminate it but a significant improvement can be made on some cars.

 

My specific problem and it's solution

A thread started by Oliver

 

Yellow SL #32