Bumpsteer

[brsvo]

I have been working on my suspension and checked bumpsteer. Then ordered the MM bumpsteer kit and installed it. Went through the process of checking and adjusting and here is what I ended up with. I am very pleased with the Drivers side (in black) but the passenger side stinks (in Red). The area in ride height isn't too bad but the droop is excessive. I have .090" spacers in the DS and no spacers in the PS. (Thus no more adjustment) What is your opinion?

[MikeFleming]

Neither one looks particularly good. You should be able to do MUCH better.

Try raising (first) then lowering the rack using offset bushings o change the steering arm angle. Then measure again.

Herd's a plot of the Red Baron after adjusting BS. Note over the 5" of measured travel, there's a total toe change of 0.011". Details are in the Red Baron Modifications thread.

9442

[brsvo]

I am measuring 8 inchs of travel versus your 5.You were working with all new parts including relocated pickup points on the K frame. MM says to shoot for .020" per inch or less. They also state this may not be possible in the entire range of travel and ride height and bump are most critical.I accomplish that for the most part in the DS and ride height of the PS. I can't take any more shims out of the PS and that was the direction it was getting better. I do have a set of offset bushings. Raising the rack up did not seem right. I was raising the pick up point on the outside tie rod so lowering the rack would make sense in my mind? Thanks for your input.

[Jack Hidley]

BRSVO,

In the bump travel direction, your graph for the left and right side curve in the opposite directions. This means that the steering rack is not centered. Your rack is moved too much towards the passenger's side of the car. To get the rack centered follow steps 1, 15, 17-22 in the installation instructions linked below.

http://www.maximummotorsports.com/assets/install/pdf/steering/MMST-13r1.pdf

Once this is done, don't turn the steering wheel. You will now need to adjust the outer tie rods to get them both set to the same toe setting.

Once this is done, you can return to bumpsteering each side of the car.

The drawing below is a sketch of the optimal geometry for minimum bumpsteer. When the rack is not centered, the left and right tie rods have different lengths. This changes the curvature of the bumpsteer curves.


9452

[brsvo]

Thanks for the heads up. I assume the center is not the housing but the steering wheel relative to the rack. I will re index the flex coupling so the rack is on center. Looks like its off only one spline will that make that much difference?

[Jack Hidley]

The rotational angle of the steering wheel has no affect on anything, other than how it looks. The inner tie rod pivots need to be equal distance from the centerline of the car. Assuming that the steering rack hosing is bolted to the k-member in the correct location and that the k-member is bolted to the chassis in the correct location, then the inner tie rod pivots will end up equal distances from the car centerline, when the procedure I linked above is followed.

The rack needs to be moved towards the driver's side slightly, then the driver's side tie rod will need to be turned toe in and the passenger's side tie rod will need to be turned toe out, to get the wheels pointing in the correction directions again.

Controlling both of the above assumptions is not easy. There are some aftermarket k-members for instance that move the steering rack mount points over 3/8" on the k-member. The only way to fix this is to move the rack 3/8" the other way. This puts the inner tie rods in the correct location, but seriously limits the steering angle when turning one direction. The only easy way to detect this is through the shape of the left and right bumpsteer curves.

[brsvo]

Well my car has the stock rack on a stock K frame. I re centered the rack and re did the tie rod ends. Now I just have to take the springs back out and redo the bump tests. Just when I got it back on the road too.