Bump Steer

[ausracer05]

Hi there Guys

I have a issue with my 1996 single seat jimco a-arm buggy. when going down the straights it is very unsettled in the rear and am fighting it the whole time. I was told that its my Bumpsteer ??? So if it is how do i fix it as i have never done it before. Would a anti roll bar work??

Any help would be great

Thanks

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[racer56]

I would check the toe in the rear first. A small amount of toe-in in the rear = more stability.

[ausracer05]

how do you adjust it to get toe in??

[redmist]

Definitions first. Bump steer is the ability for the front end to alter toe during bump, in essence the front end steers by itself under bump. It sometimes feels like the back end is to fault as when the front end steers the back end will step out.

My Jimco is of a similar age to yours and probably of similar design. The biggest problem I had was with the power steering solution. It ran a Charlynn PS remote servo/ram. Which requires a small amount of slop to work correctly. As such it tended to wander at speed. In addition the rack was poorly placed which in itself created bump steer. We cut the mounts from the rack and integrated a new Fortin rack. We played with it for 10 hours placing it then calculating the bump through every inch of travel. We got it very very close to perfect. As I can now do 140mph without a hint of bump steer I think you can get a very high top speed with a stable ride.

[ausracer05]

Hi there

Thanks i already run a fortin 2" rack in it so how do i do all the calculations?? i have not done this before

[gawdodirt]

Hi there

Thanks i already run a fortin 2" rack in it so how do i do all the calculations?? i have not done this before

I have never heard of any calculations for the actual placement of the rack. It is more of a tack it in place, on a mount , and measure the result of toe change on one tire. As they're both the same, you only really need to test on one side. It's a trial and error kind of thing. But, you said your issue is with the rear. Racer 56 was right. Check the toe in on the rear first.

GD

[Scott_F]

It doesn't have to be trial and error. There is a good thread here on RDC describing how to locate the inner TRE using CAD.

[gawdodirt]

It doesn't have to be trial and error. There is a good thread here on RDC describing how to locate the inner TRE using CAD.

I understand that it is available using a CAD program. I have a copy of Susprog 3D and get the location through that.
But it appears that this guy does not. So I was describing a method available to most anyone.

GD

[kmc54]

Any updates man?

Bump steer occurs when your steering geometry doest match your suspension geometry... your inner steering pivot should equal your lower arm pivot, and your outter steering pivot should fall inline with your reardiff and your kingpin line...

Maybe something could've tweaked or shifted?