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YOUR RESEARCHfor those who've adjusted front bumpsteer...
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Adjust flat spacers
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Leading evidence: 'Adjust flat spacers' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Adjust flat spacers' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion
You're unlikely going to get to zero bumpsteer with these suspensions, especially without a facility to adjust your ride heights, ie.
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Suggestion
Smith�s works should be mandatory before anyone touches a factory suspension , but don�t read him too closely or you�ll be replacing every but and bolt with AN rated fasteners.
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Suggestion
The geometry will change through out the suspension range.
Replace throughout the range of suspension travel can be kept
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Suggestion · Original poster
the geometry of toe changes throughout the range of suspension travel can be kept to a minimum.
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Suggestion
Smith�s works should be mandatory before anyone touches a factory suspension , but don�t read him too closely or you�ll be replacing every but and bolt with AN rated fasteners.
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Suggestion
The idea is that toe still changes with suspension travel, but because it starts from the parallel to the ground position, the change in length of the tie rods are minimized.
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....on a lowered car with standard (non-GT3) wheel carriers, and adjustable bump steer kit.
did you space the tie rod end CLOSER or FARTHER away from the steering knuckle?
I have the Rennline adjustable bump steer kit with H&R sport springs (GT3 lower control arms also) on my Boxster, and trying to achieve essentially zero bumpsteer. But no matter if I'm using NO spacers or ALL spacers, I'm getting what appears to be toe out on full suspensions compression. What am I doing wrong?
I dont understand why the appearance of toe out at full compression is an issue. Your alignment should be set up at weighted ride height. The geometry will change through out the suspension range. Not sure u can have an alignment in spec at ride height and dial out the toe at full bump.
maybe it's not, but my understanding is that is the purpose of a bump steer kit, to dial out bump steer on compression (or droop). the geometry of toe changes throughout the range of suspension travel can be kept to a minimum.
IE static toe measurements at ride height do not necessarily reflect dynamic toe measurements with compression/droop
I am far from an expert on these things, but my basic understanding is that the bump steer adjustment is intended to put the tie rod in a neutral or parallel with the ground, static position. The idea is that toe still changes with suspension travel, but because it starts from the parallel to the ground position, the change in length of the tie rods are minimized. If they start from a steep angle, the effective length varies more with the arc of the tie rod.
^^^ This... As an aside - I asked my local Porsche dealer to install a bump steer kit on my lowered 996 (Torque Solutions bs adjustable tie rod ends with Bilstein B8's and H&R sport springs). They refused, and said "they didn't fit". Later I took the car to a local indy shop. They installed them, but had to do some modification to the links (clearly why the dealer wouldn't do it - and yes it works, as there's little to no bump steer)... I'm not sure which kit you have, but it's possible it needs to be modified a bit.
thanks guys for the responses. In my reading I believe the tie rod end needs to be essentially parallel with the control arm throughout the arc of travel.
dporto - sounds like I have the same shocks/springs as you. Rennline tie rods/bump steer kit. No modification necessary; how many spacers do you have between the steering knuckle and the tie rod end?
Hey Joe,
It's funny you should ask, as I'm in the process of changing out my stuts/shocks for a KW v3 system. I literally just got done popping the passenger side tie rod end about 40 minutes ago. Unfortunately I can't be sure how many spacers were on it (below where the tie rod attaches to the hub) but if my memory serves me, I think it was 1 - 1/4" straight spacer and 1 - conical spacer about 1" long... I won't get back to the garage until tomorrow . If it's different I'll let you know.
You're unlikely going to get to zero bumpsteer with these suspensions, especially without a facility to adjust your ride heights, ie. coilovers with adjustable perches. Your goal is to
minimize
toe change at a given ride height throughout the range of kinematic movement of the suspension in both bump and droop. What you're really trying to avoid is toe out in bump. Bumpsteer generally gets more exacerbated the lower you go. In general, over-lowering a car is one of the quickest ways to end up with an ill-handling car not only because of bumpsteer but also because of it where it locates your roll centers. Get it too low (or too high) and it will lead to excessive load transfer resulting in a decrease in overall grip at that axle.
To answer your questions, minimum bump steer correction (comparable to a stock tie rod) is achieved by placing all of the spacers above the steering knuckle. Maximum correction is achieved by placing them below it. Intermediate correction would be some combination of above and below.
Assuming you're using a bump steer gauge:
Basic procedure
1 - measure the toe position at static ride height
2 - compress suspension 1 inch, measure change in toe position
3 - droop suspension 1 inch, measure change in toe position
4 - adjust flat spacers
5 - repeat 1-4 until toe change is minimized
6 - Do this again up to a limit of 2 inches droop and 2 inches of compression
Don't obsess about the measurements at the extremes because the majority of time your suspension will be moving within that -2" to + 2" range (which is of course a 4" range in total from static ride height).
My philosophy and experience on vehicle dynamics and kinematics has been that there's very little to gain but a lot to lose if you get it wrong. You can make the car undriveable if you induce a lot of toe change with your adjustments. Unless this is a race car much of this is going to be lost on you anyway and could be avoided by....not overlowering the car.
Great post, thanks cogito_ergo_zoom!
you confirmed what I was suspecting. And I agree it�s probably a minimal issue at this point - I�m just overthinking it. I�ve thought about buying a real bumpsteer gauge but with my simple street suspension right now, there�s more important issues to refine my car�s handling than bump steer
Tune to Win by Carroll Smith is essential reading. In fact all of his books are.
If you want to learn more about bump steer specifically this is a very good paper by Longacre Racing.
http://www.longacreracing.com/techni...aspx?item=8162
[QUOTE=Cogito_Ergo_Zoom;16506215]Tune to Win by Carroll Smith is essential reading. In fact all of his books are.
If you want to learn more about bump steer specifically this is a very good paper by Longacre Racing.
http://www.longacreracing.com/techni...aspx?item=8162
[/QUOTE
Smith�s works should be mandatory before anyone touches a factory suspension , but don�t read him too closely or you�ll be replacing every but and bolt with AN rated fasteners.
