Bump steer

[citiracer]

We discovered that our RF has 1/4" of toe out at 3" of compression from ride height. How bad is that? I'm going to fix it but I'm wondering what to expect. Are we gonna set the world on fire our next time out?

[CHUMBA]

Whats your toe out at ride height? is this 1/4 in addition to your reg toe out? To answere your last question NO.

[citiracer]

The last question was just sort of being silly but yes this an ADDITIONAL 1/4" of toe out. We start out at 1/4" out. So the net is 1/2" out at 3" of compression on RF. That seems like a lot to me but that's why I'm asking because I don't know how bad it really is. I played with it a little more this afternoon and by moving the outer tie rod end up about 1/2" (it had a spacer in it), I got about half of it out. I'm going back out now to lower the inner tie rod end about 1/2" (spacer there too) to see if I can get it closer to 0.

[CHUMBA]

We run about 1/2 out, our chassis builder told me .040 out per inch of compression was ok, that would mean .120 out at 3 inches of compress. I posted a question on here about bump steer a couple of weeks a go, you can look back and read it. ( I dont know to put a link to go to it ) but from what I was told you are real close and should be good to go. But I think there is more to it than people are willing to say.

[BIGFREAK101]

Well I have to ask what chassis you using. You mayhave the wrong spindle. On car you may want to go to a inch longer right tie rod tube and a inch shorter left. The front end of the car makes it turn. Now would u put a half inch of toe or more on your car and try to drive it it drags the frontend THIS IS BAD!!!

I bet you have hard time keeping this car down on the bottom of the race track coming off the corners it always floats up and that is a symptoms of having the bump off.

Now the new chassis we went to this year is set up to bump at full compression on Rt ft is about. .075ths toe out and about. .030ths change in the left drop so here we have no more than a .105ths. Total. Yes in my beleaf you have way to much so a spindle change may be needed. I know TWM has a nice rt spindle. Its what's on ours .

Ways to reduce the bump Indy fry
#1. Longer upper a arm this reduces camber gain
#2. Longer tie rod length
#3. Lower the inner tie rod mount
#4. Raise the outer spindle mount up and closer to the back of the rotor. IE WHY I SAID TO JUST CHANGE SPINDLE.
Hope this helps

[CHUMBA]

Why change the spindle? Its a GRT

[BIGFREAK101]

I guess I should say try everything else first and if it won t come in under .100ths then you need to change the sp indle mounting point for the steering arm. To get bump under that .100ths. Need to look at a frt end program u can learn a lot.

[citiracer]

Our car is a 2005 MasterSbilt that was just updated over this past winter with all new S7front end from MasterSbilt so I'm 99.9% sure the spindle is correct.
I have managed to get most of the bump out of it by raising the outer tie rod end and lowering the inner tie rod end. But now I am getting a little bit of toe out on compression and rebound which tells me that the tie rod is too long. I'll be playing more with that. All this rain hasn't allowed us to race much but we sure out getting our homework in.

[Ltemodel]

One thing you really need to keep in mind along with the bump is the ackerman in the front end. I've measured some cars that actually have reverse ackerman under counter steer. Having a 1/4" of bump under compression might not be so bad if the ackerman isn't right.
I would get some toe plates and find out were your front end is when the tires are turned then determine where your bump needs to be. Bump steer is important, but the tire side walls are so flexible, the difference between an 1/8" and a 1/4" won't be noticeable if everything else doesn't jive.

Good Luck,
Kevin