Is this Bump Steer??

[Tom86]

Hi,
Does anyone know what could be causing this? is it Bump Steer? when I drive along and have to make a gradual left or right turn where I have to hold the steering wheel at a constant angle and I hit a bump. I get a jolt through the steering wheel causing the steering wheel to wiggle in my hand this give a floating unstable kinda feeling in the front end making it hard to to maintain a smooth line while turning.

This doesn't happen when I drive along in a straight line and hit a bump. It only happen when I turn at a constant angle the severity of the jolt increase with speed and size of bump. Is this an alignment issue or something else?

[RobertoX]

It's difficult to say for sure, it could be bump steer (geometry related) or it could be due to some compliance somewhere. Do you have standard suspension? Are you using standard wheel allignment? Are you using different wheels? (width &offset combination can effect it). What is the condition of your components? (worn bushes/ball joints etc)

[Julz01]

by the user name and what his talking about it would be a good guess that he has a ae86 with S13 front suspension in it

[RobertoX]

What makes you say s13 suspension?

[Julz01]

alot of people that have put the s13 setup in the ae86 talk about having alot of bumpsteer, from memeory its beacuase some of the s13 coilover setups are too short and give alot of bump steer, Ive just got the normal setup havnt driven one with it as of yet.

[SeptemberSquall]

make a bump steer guage
it's easy to do
refer fred phun 'how to make your car handle' for a description of what bump steer is and how to measure it

in basic terms

bump steer is the tendency of the wheel to 'steer' with suspension travel
ie. when the suspension goes through a bump or rebound motion it will either toe out or toe in the attached wheel

toe in on bump is not so bad, promotes greater stability than toe out on bump
toe out on bump creates the same effect of static toe out, meaning the car is more prone to 'dart', but becuase it's only when subjected to bump loads it makes an unpredictable situation worse.

if your suspension geometry is factory then your bump steer should not be more or less than factory geometry, generally not a problem you'd notice on a road car. if you've changed something it may have increased bump steer.

for the OP: if this problem has developed without changes being made to the suspension geometry it's unlikely to be caused by bump steer - your problem is probably somewhere else. if you've changed something and it's suddenly doing this, it could be but may not necessarily be bump steer.

hth

[o_man_ra23]

Compliance in a tie rod end will often make your car veer when trying to travel straight, or make it so that you start steering with minimal effect, then suddenly the car turns sharply. If this is not happening, it is unlikely to be compliance in a tierod end. Compliance in a balljoint seems to make the car move around on the highway regardless of turning angle.

[pato]

atm i have around 4degrees toe out on the front, ( not intentionally )
and i have similar problems,
alignment issues could be a cause

[Tom86]

I'm running a Greddy Coilover setup for ae86 with normal normal alignment except for -2 degrees negative camber. Everything in the car is car bushes/ball joints/ tie rod etc has all been replaced. I think Julz01 might be onto something here with his S13 comment. Because to lower the car I adjust the overall length of the strut maybe I've actually shorten it too much causing it to be too short like the S13 setup Julz01 is talking about.

How can I correct this? without going back to the original ride height? I can't fit RCA because the lower control arm will touch the disc rotor (I'm running a non-standard brake setup). Is there another way to correct this

[RobertoX]

Fair enough commet about the s13 suspension, I just thought that there was something in the original post that I missed.

Making a bump steer guage is a good idea, I'm not sure how puhn suggests it but I've done this before by attaching a flat surface to a wheel and then used 2 dial guages to measure the toe change as I moved the suspension through it's range of travel. This worked fairly well but you need a reliable way of preventing the steering rack from moving.

If you can't adjust the bump steer by putting a RCA in, an alternative is to change the mounting points inboard. Bump steer is effected by a huge amount the positions of the LCA/castor rod (which essentially form an A-arm) and steering
rack ball joint. You may be able to play around with the positions of these things but it may turn out to be very complicated/difficult (eg having to move the rack around
or something).
This all starts to become quite complicated because you have to actually understand how the geometry is effected rather than just resetting it to it's factory position as you do with RCAs.

By the way, you aren't running 'lock spacers' are you?

[Tom86]

By the way, you aren't running 'lock spacers' are you?

No I'm not running a 'lock spacers' but I am running a Quaife quick rack, but they are not much different to standard rack except for the quicker ratio. So I don't think that is the problem.

[RobertoX]

I was just wondering because they push the inner steering ball joints out. I thing the quaife rack would be the same length (from end to end, where the rack ends are screwed in).

[allencr]

Is the 'quick rack' an entire rack or new parts?

Any play between the rack gear & housing and/or the rack to pinion adjustment?
Can you look out the window and see if it's possibly the inside, unloaded tire doing the shaking?

[Hurricane]

ive got a similar problem in my ke20 since it its got a different front end in it, i think ive ttraced it to one of my steering arm bushes being worn, but with mine the steering doesnt jump around it more just want so steer the car heavyer into the corner for a second.

what about running more caster to help with the AE86?

cheers,dan

[Smokey228]

Compliance in a balljoint seems to make the car move around on the highway regardless of turning angle.

Hrmmm... This sounds like what i might have... I thought it was the blame of the steering rack...

I'll have to look into these ball joints etc...

Cheers,
Jase