heavy85 Posted April 22, 2009 Share Posted April 22, 2009 Over the winter I did the following: - Converted front LCA from offset bushings to heim. This also had the negative effect of shortening the front track by a 1/2"-3/4" since the offset bushings were all the way out and I did not move the pivot point out. - Changed from 225 to 300 lb front springs - Converted from conventional tie-rods to rod-end to adjust bumpsteer. - Shaved the 1" 'bumpsteer' spacers down to approx 3/4" for wheel clearance to the new bumpsteer adjustable rod-ends - ironic isn't it - Converted to big brakes (Outlaw, two-piece rotors up front). I had a track school last weekend and noticed the car wanted to pull hard when I hit rumble strip or curbing. I was taking it easy and feeling the edges so never before much used them except when I pushed really hard. I never noticed it to this extent before but added adjustable bumpsteer due to the occasional feedback into the wheel on the road and a particular bump at a different track. I dialed in the bumpsteer to very close to zero with spacers and just re-verified that it's still there. What could I be missing here to explain this pulling / steering wheel movement when I hit the rumble strips? Seems like bumpsteer but I'm just not measuring any? It's very unsettling and feels like it wants to jerk the car off the road. Thanks Cameron Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 22, 2009 Share Posted April 22, 2009 What you're describing sounds like bumpsteer to me. Mine was most apparent going up a short rise at Buttonwillow. Hit that rise and the suspension would compress and the car would do a sharp jerk to the right, almost emergency lane change like. I adjusted out the bumpsteer and it didn't twitch at all afterwards. I checked mine with a stand and dial indicators on the front and rear of the rotor. Then I jacked the chassis up and down and watched the dial indicators for differences front and rear, and moved the LCA pivot up (slotted crossmember) to fix. Did you use a bumpsteer gauge to check yours? If not, how did you adjust it? You should be in BETTER shape for having removed the camber bushings, because that should make your tie rods and control arms the same length. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted April 22, 2009 Author Share Posted April 22, 2009 I made a plate that bolts to the hub, leveled it and marked 1" increments, removed springs, and measured toe change through suspension travel using two dial indicators against the plate. I'm not convinced it's actually bumpsteer but not sure. Thinking it's more of a mechanical thing where the input from the curbs are pushing the tires around. Maybe since the stiffer springs are less compliant so instead of soaking up the bump the front end has to climb up the curb which pushes back into the wheel? I'm stretching but measuring it I just dont get toe change with bump. Cameron Quote Link to comment Share on other sites More sharing options...
jt1 Posted April 22, 2009 Share Posted April 22, 2009 One possibility is that you are changing from toe in to toe out, or vice versa. Say if your running 1/32 toe in, and you jump a curb with the right front, and in bump you go to toe out, the car can react abruptly. Lots of scrub radius can do the same thing, but unless you changed wheels it's unlikely you've changed that. jt Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 22, 2009 Share Posted April 22, 2009 There is camber thrust, but I don't think that is your problem, and stiffer springs should reduce camber thrust, so it should be better now than it was before. It really just sounds like bumpsteer to me. I'd suggest you try measuring it again. Maybe jack the chassis up and down with a jackstand under the control arm like I did. It lets the dial indicators stay stationary in terms of up and down movement and just measure the horizontal and toe changes. Also measure in the area of the suspension that you will be driving in; don't measure it at full droop. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 22, 2009 Share Posted April 22, 2009 One possibility is that you are changing from toe in to toe out, or vice versa. Say if your running 1/32 toe in, and you jump a curb with the right front, and in bump you go to toe out, the car can react abruptly. That's a good description of bumpsteer. Lots of scrub radius can do the same thing, but unless you changed wheels it's unlikely you've changed that. Lots of scrub radius makes a car hard to steer and gives steering wheel kickback, but it doesn't change the direction the car is traveling unless the wheel moves. Quote Link to comment Share on other sites More sharing options...
260DET Posted April 23, 2009 Share Posted April 23, 2009 What wheel alignment figures does it have? And it sounds like the ride height and front roll center may have changed although that may not be relevant to your problem. But alignment eg toe, can be. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted April 23, 2009 Author Share Posted April 23, 2009 What wheel alignment figures does it have? And it sounds like the ride height and front roll center may have changed although that may not be relevant to your problem. But alignment eg toe, can be. 1/8" out, 2.5 camber, a little more than stock caster. Dont know how alignment could be affecting it? Cameron Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted April 23, 2009 Share Posted April 23, 2009 Cam, Which way does it pull? If you hit the strips on the right does it push right or left? Not that thats gunna help my meager brain come up with much, but it might help someone else. Dave Quote Link to comment Share on other sites More sharing options...
260DET Posted April 23, 2009 Share Posted April 23, 2009 1/8" toe out should be OK , keeping in mind that any toe out tends to create instability. Which may be countered by increasing caster. So I would increase caster as much as possible which usually is not much on a S30 because of front side wheel clearance problems and leave that. Then if the problem still exists try reducing the toe out. On the bump steer question, if its present then it will show up by driving straight along some bumpy road. If you hit some decent size bumps and they do not affect the steering wheel then you don't have bump steer. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted May 3, 2009 Author Share Posted May 3, 2009 Update. I remeasured on the rotor instead of the toe plate I made and found the drivers side was off. Maybe the toe plate was bent - but if so not sure why the passengers side was still measured OK? Anyway, I took about 1/8" of spacers out of the drivers side and it's much better. Still moves the steering wheel around a bit on big bumps but I'm wondering if the bumpsteer is still off a little and my measurements are in error or if it's something else. Hold the steering wheel and it stays put but if you let go of the wheel and hit a bump it will move. Cameron Quote Link to comment Share on other sites More sharing options...
JMortensen Posted May 3, 2009 Share Posted May 3, 2009 If one wheel hits a bump and you can feel that feedback through the steering wheel, that is totally normal. What is not normal or wanted is for you to be sawing at the wheel and the car to be tracking in a steady arc, or for you to hit a bump and have the car jerk suddenly to one side or the other. Sounds to me like you've got it fixed. Congratulations. Quote Link to comment Share on other sites More sharing options...
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