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Old 12-06-2004, 06:56 PM   #1
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Default What is Bump Steer?

I hear a lot about bump steer. Is it really an issue? I've heard that's designed into the chassis. I'm running a Sportwerks Mayhem and don't know if I should be concerned about it or not.
Anyone?
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Old 12-06-2004, 09:47 PM   #2
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bump steer is when your front tires toe in or toe out when the suspension goes thru its travel....its best not to have any, most cars and trucks have a little bit...but some have way to much....it can usually be corrected some by raising or lowering the tie rod pivit points
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Old 12-06-2004, 09:51 PM   #3
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It can be used as a tuning option, wouldn't really call it an issue. Bump out is when the tires toe-out when car is compressed, bump in is when tires turn in when compressed. If steering link is parallel to the lower arm should be zero bump steer, when the bellcrank stud is raised(or spindle stud lowered) it puts doanward angle into the tie rod as it moves from center of car to the outside of car, when link is angled that way it will give bump in, when link is angled the other way it will give bump out. To get more or less you can just raise/lower one or the other stud on your car depending if there's any clearance issues or not.
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Old 12-28-2004, 11:22 AM   #4
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I dont think there is any car on the market with zero bumpsteer as its almost impossible to do with the amount of travel off road cars have.

The first discription sums it up pretty well, the second isnt very accurate though. The length of the tie rod and lower arm being equal has just about zero influence on the bump steer
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Old 12-28-2004, 07:59 PM   #5
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I think what slobbatech wrote is correct the angle of the steering
tie rod does change the bump steer he is not talking about the
lenght of the tie rod just the angle of it compaired to the angle of
the lower arm

BY the way Slobbatech is Jesse Robbers the current 2wd mod
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Old 12-28-2004, 09:31 PM   #6
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Or, when you're racing and you hit something, you bounce off of that tube/wall/block (hope not) and your rc goes in a different direction, you can say, "Wow, lots of bump steer going on out there today." (And then some people will start agreeing with you, or not.)

As long as the upper tie-rod/upper arm is equal in angle to the lower arm, you won't see any change in the toe during suspension travel. Best way would be to measure the middle of the arm to the middle of the rod at both ends, to see if they're equal distance, if not, see if you can move the tie-rod/upper arm on different shock tower holes to get the angle as close to the lower arm as possible.

Gramps.
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Old 12-28-2004, 09:44 PM   #7
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Quote:
Originally posted by madweazl
I dont think there is any car on the market with zero bumpsteer as its almost impossible to do with the amount of travel off road cars have.

The first discription sums it up pretty well, the second isnt very accurate though. The length of the tie rod and lower arm being equal has just about zero influence on the bump steer
Have you pushed the Revo's frontend up and down?? It has almost zero bumpsteer in it entire suspension travel!!!! I couldn't believe it at first until I stood there moving it through it's travel for about 10 minutes. LOL
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Old 12-28-2004, 11:38 PM   #8
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The Losi XXX series of cars has very little bump steer; as Slobbatech said, we will sometimes add washers to either the bellcrank or spindle ballstuds to add bump-steer as a tuning option.

madweazl - He didn't say anything about the length of the arm and steering link..
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Old 12-29-2004, 02:26 AM   #9
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I think "Absolute Zero" bump steer is going to be the next big thig in car design in the future.....a car that keeps perfect toe angle through all bumps, jumps and what not. I run one spacer under each of the spindles, for bump-in....tried bump-out, it was nooo good!
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Old 12-29-2004, 07:59 AM   #10
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Quote:
Originally posted by brad996
I think what slobbatech wrote is correct the angle of the steering
tie rod does change the bump steer he is not talking about the
lenght of the tie rod just the angle of it compaired to the angle of
the lower arm

BY the way Slobbatech is Jesse Robbers the current 2wd mod
national champ
Absolutely, changing the length of the tie rob (whats being done when raising and lowering the pivot point of the inner tie rob) will influence bump steer and it can be used as a tuning option.

I reread his post and noticed I made a comment about the arm and tie rod being equal length, not sure what I had on my mind but he didnt state that lol. What was stated is that if the links were parallel with one another there would be no (or little) bump steer. This isnt correct however. I'm just here to promote learning, as I have plenty of learning to do

This website had a pretty good definition for bump steer (the first paragraph isnt very good but oh well), incorrect statements about bump steer are posted all the time.

By the way, madweazl is a 7 time R/C Geek National Champion And I have a good bit of experience with full scale off road buggies Our buggy has 24 inches of travel, weighs just over 1900lbs and is powered by a 3.2 liter Acura VTEC (soon to be turboed). Oh, and while close to no bump steer its still present
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Old 12-29-2004, 10:36 AM   #11
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Bump steer is probably the most complex issue that comes up on our cars.It's not a simple matter of the arms and tie rods being the same length or angle but that they travel in the same arc,which is usually near impossible to obtain.Everything else in the front end affects it-such as changing the toe or the ackerman.To make it worse,you can sometimes acheive zero bump with the wheels straight ahead but still have some when the wheels are turned due to the difference in angle between the steering arms and the front kickup.Oval racers will use it to their advantage by inducing some on the left to manipulate the ackerman or adding some bump-in on the right to keep the car on line as it takes bumps in the corner.This of course doesn't work when you turn both ways.Fortunatly most modern R/C cars have been engineered with it in mind and it isn't usually a big problem.Generally speaking for our purposes bump-out is going to be bad and you just need to check for it and shim the tie rod ball studs to minimize it.If you really want to drive yourself crazy you can experiment with different combinations of ackerman and bump steer.(picture mad scientist pulling his hair out)
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