Bump Steer

[YZ Otis]

Thought I'd post a simple definition here for bump steer. Some peeps think it's from bumping into things and some think it's the bump your hands feel when ya bump into things. Bump steer is a result of your suspension geometry and the change in toe as the suspension travels through it's arc when hitting a bump. Like the bike changing direction when ya haven't turned the handlebars. Like unexpectedly changing your line through a corner when hitting a bump. A steering stabilizer does not change bump steer but any change to your suspension geometry can affect bump steer.

C/P - I stole and modified this ... burp

Bump steer-- is the introduction of steering input caused by a bump in the road surface. When a wheel travels up and down over a bump, it actually swings in an arc. If the steering tie-rod does not swing in the same arc as the suspension, the wheel will have an increase or decrease in toe and will result in a slight steering effect. Virtually all suspension geometries on atv's have some degree of bump steer, though it will be very slight. However, modifying a atv's suspension by using widening kits can increase the amount of bump steer. Bump steer causes tire scrub, and loss of traction if experienced during cornering. If you're altering you atv's suspension, measures should be taken to minimize or eliminate bump steer.

Not postin this to pick on anyone, just as info. Been doin a lot of work on my blaster to minimize bump steer so it's kinda on my mind. Blaster bump steer isn't all that bad ... just when I get after something I sometimes get carried away. Any corrections, additions or fixes are welcome.

 

[Blaaster]

Good info!

Bump steer is extremly noticable when landing big jumps, where the suspension is pushed to the limit.

If a +6 widening kit is used the toe can be affected by up to 1/2", which is one hell of a lot.

If you land clean, bump steer is not so noticable, but land first on one front wheel and it will raise its ugly head.

As the second wheel lands, after steering correction, it is pointing in a awkward direction and tends to drag the other wheel to itself, making it want to duck under the bike, resulting in lack of control.

Bump steer can be lessened when using lowering kits by using more than the prescribed toe out.

Speaking from experience bump steer is cruel on tie rods, one needs aftermarket ones, and strong ones at that.

My lads bike set up for flat track. Suffers a lot of bump steer!

 

[kf7lcw]

Good post! I didn't even know such a thing existed, news to me lol

 

[Prime]

Good info!

Bump steer is extremly noticable when landing big jumps, where the suspension is pushed to the limit.

If a +6 widening kit is used the toe can be affected by up to 1/2", which is one hell of a lot.

If you land clean, bump steer is not so noticable, but land first on one front wheel and it will raise its ugly head.

As the second wheel lands, after steering correction, it is pointing in a awkward direction and tends to drag the other wheel to itself, making it want to duck under the bike, resulting in lack of control.

Bump steer can be lessened when using lowering kits by using more than the prescribed toe out.

Speaking from experience bump steer is cruel on tie rods, one needs aftermarket ones, and strong ones at that.

My lads bike set up for flat track. Suffers a lot of bump steer!

You say this blaster suffers from a lot of bump steer...is this because it is using lowering blocks or simply just because of the width? And racing flat track there shouldn't be too many 'bumps' as it is hard-packed clay.

 

[brandoz28]

it's because the a arm mounts have moved, and the tie rod mounts have not (all on the frame side of course)


this changes the arcs that they swing in. if you take the shocks out, and cycle the suspension, you will see the changes in the toe.

 

[Blaaster]

good info!

Bump steer is extremly noticable when landing big jumps, where the suspension is pushed to the limit.

If a +6 widening kit is used the toe can be affected by up to 1/2", which is one hell of a lot.

If you land clean, bump steer is not so noticable, but land first on one front wheel and it will raise its ugly head.

As the second wheel lands, after steering correction, it is pointing in a awkward direction and tends to drag the other wheel to itself, making it want to duck under the bike, resulting in lack of control.

Bump steer can be lessened when using lowering kits by using more than the prescribed toe out.

Speaking from experience bump steer is cruel on tie rods, one needs aftermarket ones, and strong ones at that.

My lads bike set up for flat track. Suffers a lot of bump steer!

edited this bit

suffers a lot of bump steer, when he raises it and rides MX.!

I must have been having one of those out of brain experiences, and not completed the sentence.:-[

Its not the height that causes the problem, its the arc the spindles travel in that causes major changes to the toe in/out.

Adjustment can be made to the toe to suit each application, if you lower the bike, adjust for more toe out, and vice versa!

Widening kits are definatly not the best way to go if you are intending to jump a lot. .

 

[Prime]

Ok, I didn't see the widening kit before, but now that I take a closer look I see it. So, with extended arms and tie rods, lowered for flat track, it should not suffer bump steer, correct? (at least not enough to be noticeable)

 

[Triple_B]

Here is an excellent slow motion video of "Bump Steer". Although it is not an ATV, it is relatively the same thing. Watch the entire thing (only 40 seconds long)

 

[yzrider]

i have noticed a increase in the bumpsteer on my dads warrior after installing 5" spacers, but it is not enough to worry me....

 

[Blaner]

wow TripleB thats a cool vid! ja dont believe you can ever get rid of bump steer entirely on a quad, you do after all have 2 wheels and not one, if the left hits a bump and the right doesnt, it will bump.

With that said, it can be minimized, i must be honest and admit I do have some bump steer on my 450 setup. Only noticeable at top speed on a gravel road. Id like to at some stage adjust a weld or two to eliminate it but time is a factor. Oddly, despite that, my turn in ability (sharpness) improved dramatically from stock as well as overall steering lightness

 

[YZ Otis]

Polaris made an effort to eliminate bump steer with the Predator Pro Steer in 03. It had links from the steering stem flag to idler arms located in what a computer deemed the ideal position in relation to the a-arms. Good marketing trick but not a better steering setup (IMHO). Added more weight, 6 more moving joints to wear & get sloppy and the bike won't turn as sharp as their 4x4 Scrambler. They've gone back to a standard quad type steering.

Here's a pic of the stem/idler arm mount with the links that go to the stem flag.

A Cousin brought his Predator by a few years ago and it couldn't get around our trail without being pushed backwards in a few places.

i have noticed a increase in the bumpsteer on my dads warrior after installing 5" spacers, but it is not enough to worry me....

Spacers & flipped wheels are another deal altogether. Best setup is where the wheel rotates on an axis near the center of your wheel/tire down through the spindle ball joints. The more you offset the wheel, the more leverage it has on your suspension parts ... it may amplify bump steer but it doesn't change the angle of toe in/out at the spindle. Depending on your castor more offset will lift the front of the bike by pushing down on the inside wheel and try to lift the out side wheel. Oooops, sorry, I can't explain this in words, you'll have to look it up.

 

[Blaner]

thats interesting...but yes, too many moving parts.

 

[Blaaster]

Ok, I didn't see the widening kit before, but now that I take a closer look I see it. So, with extended arms and tie rods, lowered for flat track, it should not suffer bump steer, correct? (at least not enough to be noticeable)

With extended A arms there is still the problem of bump steer, but the Widening kits seem to make it much worse.

Long travel shocks can also aggravate as well, as the spindles can travel up and down further, therefore varying the distance between them and the steering stem.