what is bumpsteer?

[kenny7231]

what is bump steer how do u tell if u have bump steer??

[87 pathy]

true newbie question.. its just as it sounds, if you hit a bump or the front end flexes at all, the wheels turn. this is generally due to inproper stearing geometry.

[piratebuggy]

The attitude on this forum sucks to say the least-ooh I know something you don't . Ok-look-bumpsteer is (as stated) when you hit a bump-the vehicle wants to turn (as not stated) without the steering wheel turning.This is usually caused by the steering linkage not moving with the suspension properly. Such as the lifted Jeep without the drop pitman arm,the steering linkage doesn't operate on the same plane as the axle,which results in the wheels being steered when the suspension moves. Stated another way-you're driving along with out moving the steering wheel,hit a bump, and the vehicle steers itself one way or the other,when the suspension returns to normal,steers itself back. I think that's a better explanation than what was given before. If you have bumpsteer-you will know what I'm talking about,sometimes it's not that severe depending on the amount of suspension travel(how hard the bump was). Offroad at slow speeds it's not much of an issue,but when the speeds get up,it can be downright dangerous.

[HsOffRoad]

Unless you are using fully hydraulic steering, there is a mechanical linkage that connects your tires and your steering wheel. There is no way that the tires can turn without the steering wheel moving unless one of the pieces of the mechanical linkage is boken, loose, or flexing. When you experience bump steer, the steering wheel moves, contrary to what was stated in the last post.

As for why bump steer happens, it's quite simple. The arc that the draglink travels in has to match the arc of the suspension as it cycles. Otherwise, when the suspension moves, the draglink moves on a different arc, causing the tires to steer left or right to accomodate the different paths they are taking during the cyle of the supension - that much of the above post is correct. The ideal situation is to maintain the proper geometry to keep the suspension & the draglink cyling on the same arc. Since thats not always feasible, a common solution is to lengthen the draglink - by doing so the changes in angle (and therefore steering effective length & steering input) are lessened for a given amount of vertical movement of the suspension. Another method is to lessen the initial angle that the draglink has (relative to flat) to lessen the rate of change in it's effective length for a given amount of travel. This is the purpose of drop pitman arms, raised steerign arms, & 95% of the other steering correction products offered by off-the-shelf lift kit companies.

Bump steer can also be caused by insufficient caster or lose, worn, or improperly installed parts. But in most discussions you will find people are relating it to draglink arc in regards to suspension arc, as stated above in the first paragraph.

Hope this helps.

Hans

[piratebuggy]

Oh boy-here we go again. Look-study alignment as I have and you will get this also. Bump steer is the vehicles direction being changing without the steering wheel moving. Yes -it is not only possible ,I've driven vehicles where this is occuring at a very alarming rate. Lack of directional stability is the reason for the steering wheel trying to move in relation to changes in the surface the vehicle is travelling on. Directional stability issues can occur due to alignment angles being incorrect for example.Look this stuff up HsOffRoad-look under alignment and handling or something-but stop spreading unsubstatiated Bull shit.

[87 pathy]

i was trying to over simplify it so the guy would understand.. i'm an engineer and the way you guys explained it.. even had me confused. Not that i don't agree. The sum of it is GENERALLY, bump steer is caused by your axle moving laterally during articulation. the steering wheel doesn't move but the tires turn.. as in steering.

as for the attitude of this forum sucking... ya well its pirate.. and everybody here has an attitude. I was making a fucking joke about it being a newbie question.. this is a newbie forum.. I did try to give a simple expanation and most people all over pirate would have just said.. SEARCH you fucking idiot.. so.. i thought i was being nice.

[jetboy]

[QUOTE=87 pathy]i was trying to over simplify it so the guy would understand.. i'm an engineer and the way you guys explained it.. even had me confused. Not that i don't agree. The sum of it is GENERALLY, bump steer is caused by your axle moving laterally during articulation. the steering wheel doesn't move but the tires turn.. as in steering.QUOTE]

It generally has nothing to do with the axle moving laterally, unless you have an extremely loose suspension. it is essentially as Hs explained earlier in the radius of the arc traveled but the axle as it flexes, or as it moves vertically measured where the steering link is connected (which depends on the design of your steering), and the arc of the that steering link. the differing distances traveled leads to EITHER the steering wheel moving, or the tires changing direction. You notice on the street by hitting a bump and having the vehicle dart in one direction, or on the trail when you flex and the steering wheel spins.

a cross over steering setup will eliminate most of the bump steer as long as the cross over link is not too steep.

[87 pathy]

[QUOTE=jetboy]

Originally Posted by 87 pathy

i was trying to over simplify it so the guy would understand.. i'm an engineer and the way you guys explained it.. even had me confused. Not that i don't agree. The sum of it is GENERALLY, bump steer is caused by your axle moving laterally during articulation. the steering wheel doesn't move but the tires turn.. as in steering.QUOTE]

It generally has nothing to do with the axle moving laterally, unless you have an extremely loose suspension. it is essentially as Hs explained earlier in the radius of the arc traveled but the axle as it flexes, or as it moves vertically measured where the steering link is connected (which depends on the design of your steering), and the arc of the that steering link. the differing distances traveled leads to EITHER the steering wheel moving, or the tires changing direction. You notice on the street by hitting a bump and having the vehicle dart in one direction, or on the trail when you flex and the steering wheel spins.

a cross over steering setup will eliminate most of the bump steer as long as the cross over link is not too steep.

The pan hard sags, and pulls the axle to the left by force on the pitman through the drag link(typically) which in turn pushes the tires to turn right (laterally, when the vehicle is longitudinal). when it compresses exact oposite. Yes it does happen because of the difference in arc between the drag link and the Pan hard, or track bar (same thing).

[piratebuggy]

OK ok -here's the point I'm trying to make here-and I think it's important(at least to an alignment tech). Bump steer is where the vehicle turns in relation to a bump in the road without the steering wheel moving. Hit a bump and the steering wheel moves-this is directional instability,usually caused by not enough caster angle for example. The reason this is important, and very different between the two,is so someone can figure out why their vehicle is behaving like it is. It's really two very different things. Without writing a book here because I've been proven to be unable to clearly explain things in other threads- if the vehicle darts to one side without the steering wheel moving when hitting a bump,that's bumpsteer.And yes it does happen because the steering linkage is set up incorrectly. It is not moving with the axle properly,the thing with the panhard bar can be a slight bumpsteer problem also. If you are driving along,and the steering wheel wants to move(usually have to let go of the wheel to check this) when you hit a bump-that's directional instability-and can be caused by a low caster angle. Usually a little of this is ok,where it gets to be a problem is on the highway and the vehicle wants to wander excessively. A stock vehicle with proper alignment will never have a bumpsteer problem unless somethings been changed from stock setup suspension wise. A stock vehicle with low caster angles can experience directional stability problems and want to wander in relation to the bumps in the road. There are of course exceptions to this but I'm hoping this basics of the bumpsteer will help someone to figure this out. I'm certified in alignment and other areas and I believe this is important to the many modified vehicle owners out there to diagnose any problems. I can try to explain further if any one is interested,there is more to this.

[jetboy]

[QUOTE=87 pathy]

Originally Posted by jetboy

The pan hard sags, and pulls the axle to the left by force on the pitman through the drag link(typically) which in turn pushes the tires to turn right (laterally, when the vehicle is longitudinal). when it compresses exact oposite. Yes it does happen because of the difference in arc between the drag link and the Pan hard, or track bar (same thing).

Your right. I was thinking 4 link.

[87 pathy]

its harder to get rid of bump steer with a 4 link, because there is typically no arc of travel. You must have your drag link as flat as can be in relation to your axle. or run hydrualic.

yes i agree there is heaps more to it. but i think its covered and explained weill enough.. hope this guy can figure it out now.

[kwrangln]

Jesus Christ, you overeducated fawksticks can confuse the issue.

Its real simple, your drag link is at an angle when the suspension is at rest. When the suspension compresses, this angle flattens out effectivly making the drag link longer. This change in effective length pushes the wheels to the passenger side, which is called bump steer.

[87 pathy]

Originally Posted by kwrangln

Jesus Christ, you overeducated fawksticks can confuse the issue.

thats what we were trying to do

[piratebuggy]

Agreed- I was trying to explain every aspect of it so someone with another type of suspension could also understand it. But that's exactly what I was trying to convey-thanks!