bump steer kit. What adjustments to toe? [Archive]

JstnRyan

04-17-2009, 08:52 AM

[Holy crap this is going to be a long post. I wish I could include pictures with this post, to make things a LOT easier to understand, unfortunately I just sold my previous BSK, as I feel I can accomplish the suspension geometry I require without it being installed.]

Since every car is slightly different (especially ride hight, suspension component angles, etc..), and bump steer kits are sort of built "universally," adjusting a bump steer kit is a trial and error process. As with all things suspension geometry (AKA "alignment"), adjusting one measurement can (and almost always does) affect one or more other measurements, so properly adjusting your BSK is going to take a good bit of time on the alignment rack. Here's the adjustment process as I understand it from research, and experimenting with them on my car:

When you install a rear BSK on your car you are replacing the non-adjustable OEM toe-arm with a rod which has essentially two new adjustable qualities. The first is rod-length, and the other is rod-leveling. First, you might want to go and find a few pictures of common BSKs to familiarize yourself with what they look like, and the individual parts so my non-technical explanation may be a bit clearer. Observe the fact that one or both ends of the BSK will have threaded rod-ends with locking nuts which have a range that they can be screwed-in or unscrewed to affect the overall length of the arm. Then observe how the end which is toward the outside of the car (the wheel) has a "bolt" with threads on both sides, has a series of spacers on it, and is capped on both sides with a locking nut or castle nut and cotter pin. The "top" of that bolt connects to the wheel hub assembly, and the bottom connects to the BSK rod itself. This bolt assembly and spacers affect the rod's arc (I previously referred to this as "rod-leveling").

The first thing you'll want (or your alignment tech will want) to do is screw the rod ends as far into the body of the BSK as you can (keeping in mind the thread direction and locking nuts). The next step can be performed before or after you but the arm on the car, but it involves adjusting the rod ends out (unscrewing them) so that the BSK's total length approximates that of the OEM rod. It is important to adjust (unscrew) both rod ends equally, thread for thread. You want to avoid having one rod end being all the way in, and the other out a ways, as this creates a weak point for failure. If necessary, count the number of exposed threads on each, and try to keep them as close as possible. If you're performing this adjustment after you mount the rod on the car, note that one end of the rod is "clock-wise threaded" and the other is "anti-clock-wise threaded" meaning that you can twist the rod itself to screw/unscrew both ends at the same time.

During installation, you'll also want to rearrange the spacers on the outboard end of the BSK so that the arm is in the "middle" of the spacers. For instance: most S2000 BSKs include 4 spacers (or 3 spacers and 1 end cap). You'll want to start with 2 spacers above, (toward the hub) then the rod end, then 2 spacers (or 1 spacer and 1 end cap) below. You can now install this end of the BSK on the hub, with the locking nuts or castle nuts.

After installing your BSK and setting your ride height, you're ready for alignment adjustments. Somewhere in this process the alignment tech (or you) will set the rear toe. Adjusting the toe is, among other things, going to involve carefully adjusting the rod length (as described above, by turning the body of the BSK), and then tightening down the rod-end nuts.

---- At this point we're assuming you've successfully adjusted your car's geometry at normal ride height. ---- Now the fun part...

In order to actually adjust the anti-bump-steer qualities of your new suspension set up, you need to move the suspension through its range of travel and measure the CHANGE IN TOE throughout that range. You have a few options for this; remove springs, have a bunch of friends sit on your trunk, winch the frame down from underneath, etc.. However you accomplish it, you need to push the car down, or move the wheel up a MEASURABLE distance, and that distance needs to be repeatable.

First you need to move the suspension through that measurable distance, measure the distance so it can accurately be repeated, and then observe (measure) the change in toe. Or to say it another way: record the toe when the suspension is compressed to that measurable distance.

Now remove the lower nut on the bolt that connects the rod to the hub assembly, remove the spacers, and remove the BSK rod end by sliding it down over the bolt. It's up to you what you try next, but you need to either move a spacer from the bottom of the arm to the top of the arm, or move a spacer from above to below, then reinstall the entire assembly. So now you have either:
Nut - spacer - rod end - spacer - spacer - spacer - hub assy - nut
OR:
Nut - spacer - spacer - spacer - rod end - spacer - hub assy - nut

Now you repeat the procedure. Compress suspension to measured distance, record toe. Repeat this for as many configurations of spacers that you desire (the more the better). What you're doing is essentially changing the angles of the triangle formed by the three mounting points that comprise the BSK (chassis, outer rod end, hub). It is this angle change that affects the amount of increased toe you see when your suspension moves, "flexing" this imaginary triangle.

The end result is that you want to find the configuration of spacers and rod ends that results in the LEAST amount of TOE CHANGE from the amount of toe you have at normal ride height. This is the configuration that you'll do your final install with. Once you hit this point, you need to recheck your final geometry (alignment) settings, torque everything down, and you're good to drive.

Now that I've fully confused everyone :crazy: I hope this helps the process a little. If there's enough interest, I might be convinced to get my hands on another BSK to do a full installation/adjustment DIY with pictures. PM me with questions, comments.