Bump steer

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scott67fj40

scott67fj40

10 Year 15 Year
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Mar 6, 2007
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Spring Tx
Could someone define bump steer and what causes it. I dont think I have grasped the full concept of it. thank you.:confused:
 
Bump Steer

When your suspension flexes - your tires steer without the steering wheel moving..

minimize this by keeping your drag link parallel with the axle, (Drop pitman, ect)

ill let someone with more experience on Linked suspensions explain further..

with a 3 link, im pretty sure the goal is to have the panhard, or track bar parallel with the drag link, and mount in a similar fashion, IE (LHD axle mount on the passenger side, Frame mount Drivers side)
 
Isotel said:
Bump Steer

When your suspension flexes - your tires steer without the steering wheel moving..

minimize this by keeping your drag link parallel with the axle, (Drop pitman, ect)

ill let someone with more experience on Linked suspensions explain further..

with a 3 link, im pretty sure the goal is to have the panhard, or track bar parallel with the drag link, and mount in a similar fashion, IE (LHD axle mount on the passenger side, Frame mount Drivers side)
Click to expand...
Howdy! You've got it pretty good. Rigs with lots of lift tend to have the steering box much higher than the axle/steering arm, so the drag link sits at a very steep angle, compared to the stock arrangement, which is almost flat/level/ parallel to the axle. As the front suspension on a lifted rig compresses, without moving the steering wheel, the drag link moves and pushes the steering arm to the right( on a LHD rig). More bump = more steer. Big bump at speed makes the rig veer to the right. Can be a bit of a problem/surprise. Typical solution is lower steering box and /or pitman arm. Raise steering arm and /or install a high steer kit.

I have done both and now my drag link is only 10 degrees off of level. Not enough to notice even when I am flying thru the open desert, doing my imitation of Ivan Stewart! Of course, having the tires aired down to 10 ro 15 psi makes the ride and steering kind of loose anyway. Sort of like a roller coaster without the track!! John
 
this is bumpsteer.

bumpsteer.JPG


PS that is a drag link
 
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I pretty much knew that the drag link and track bar needed to be parallel and about the same length but I also was told that the rear links could give you some funny steering problems too. Like when the suspension flexes in the rear it can make your rig kinda steer one way or the other with you front weels staying straight. Kind of like rear steering when it flexes in the rear. Make any sense?
 
I have already built my suspension and noticed the rear steer issue. thats why I was wondering if that was part of bump steer.
 
Rear steer is not a component of bump steer.
 
Ok, so what causes rear steer? My upper and lower links are not the same length, is that where it comes from?
 
The lower link travels in an arc instead of straight up and down.

There are lots of variables to what causes rear steer;
short links
high angles to your links

Actually, it all depends on suspension design..
 
scott67fj40 said:
I have already built my suspension and noticed the rear steer issue. thats why I was wondering if that was part of bump steer.
Click to expand...

With a 4 lint double triangulated adding a panhard can cause rear steeer . ?

In the 80 factory rear suspension setup .. ( lower links paralell ) the panhard can cause rear steeer ?
 
4 link doubly triangulated would most likely bind like a madman with a panhard bar..

panhards do not cause rear steer.



There is some confuction here.

Bump steer is a steering axle (not just front because you could have a rear steering problem as well) that, during articulation, forces the wheels to move back and forth with the steering wheel straight.

Rear steer is when a tire tries to force itself under the truck during droop.

I'll try to find pics..
 
The reason of my question Mace ( and sorry for much question bothering you .. :frown: ) it's I " feel " in mate 80 series something close to bump steer .. but in the rear ..

It's lifted with OME J and stock bump stop and arms ( control and panhards ) in factory attachments .. when you hit a " bump " in the road at WH speed .. you " feel " like the rear of the Cruiser " turn " to one side .. and the front for the other side ..

I thought this coul be solved droping the factory attachment point for panhards front and rear .. ( but itś less hard in front .. )
 
Potentially if the rear PH is at a nasty angle it can move the axle sideways when you go over bumps.

Stranger things have happened..
 
I noticed on my rig that when I go over a small hole, like driving down a dirt road or something, that when the front wheel goes over the hole I feel nothing but a hole or bump, but when the rear goes through it, it seems that the truck moves to one side or another slightly, depending on which side the hole is on dictates the direction it goes. I was thinking that the upper links being shorter than the lower links is what may be causing it to do so. My lowers are slightly angled out from the frame to the axle and the uppers are angled much more to the center from the frame. But the length is quite a bit different because of where I had to put them.
 
different length uppers and lowers vary the rotation of the third during articulation, not lateral movement (simplified)
 
I may need to post a pic..........
 
It almost has a " loose feel " as I drive over holes or bumps at a moderate or faster speed coming from the rear. Maybe a sway bar or "anti sway bar" would help. I am curently not running one front or rear.
 
Please :)
 
I will try and get a pic on here tonight.
 
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