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Old 01-18-2009, 05:35 PM   #1
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Default What is bump steer?

I did some research and found this meaning "occurs when the steering angle of the front wheels changes as the suspension moves up and down through its range of travel. Generally speaking, Bump Steer is undesirable.
"

However, how do you know if you have it? What will your car/truck do. How do you know if its another issue?

Thanks.
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Old 01-18-2009, 05:46 PM   #2
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Originally Posted by portyansky View Post
I did some research and found this meaning "occurs when the steering angle of the front wheels changes as the suspension moves up and down through its range of travel. Generally speaking, Bump Steer is undesirable.
"

However, how do you know if you have it? What will your car/truck do. How do you know if its another issue?

Thanks.
If you put your car on a car stand, you can allow the front suspension to hang over the front of your table to check it. Using your thumb under the suspension arm and fingers over the shock tower, compress the suspension and look at the wheel. You will notice that it moves when the suspension goes up and down.

All you can do is limit it, or control when it happens. Generally, it is considered desirable to have the wheels toe out at the bottom, and stay fairly neutral through the rest of the range of travel. That is for off road cars. For on road cars I believe they eliminate it completely.

Anyhow, you can adjust it by changing the shims on the ackerman plate, although the factory setting is probably good...
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Old 01-18-2009, 05:50 PM   #3
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better answer posted before mine hehe.
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Old 01-18-2009, 05:51 PM   #4
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Originally Posted by pitpop View Post
If you put your car on a car stand, you can allow the front suspension to hang over the front of your table to check it. Using your thumb under the suspension arm and fingers over the shock tower, compress the suspension and look at the wheel. You will notice that it moves when the suspension goes up and down.

All you can do is limit it, or control when it happens. Generally, it is considered desirable to have the wheels toe out at the bottom, and stay fairly neutral through the rest of the range of travel. That is for off road cars. For on road cars I believe they eliminate it completely.

Anyhow, you can adjust it by changing the shims on the ackerman plate, although the factory setting is probably good...
So when I compress the arms, I do not want the toe to change much, or any at all, right?
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Old 01-18-2009, 05:54 PM   #5
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Bump steer comes into play in a few areas, normally when the suspension is fully compressed, you want to go full right, but it will not turn, the ends of your steering come into contact with somthing undesirable,

Or, when you hit ruts, your steering has a mind of it's own, IE, you are hauling down the straight, hit a rut, oops 180 deg?

Another Bump steer happpens if you have your EPA's Set wrong, You turn right...An the Buggy wants to turn left? What happens is your servo moves to the max spot, finds resistance, and tries to center, (thats its Job)

There are some other cases that will create bump steer, I just had one this week...I came off a triple, an hit on one front wheel, my servosaver actually over camed, I was on the front staight doing doughnuts!!!!

Having your servo saver a bit weak can also cause bumpsteer!
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Old 01-18-2009, 07:44 PM   #6
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You can change bump steer by adding or subtracting shims at akerman plate or knuckle.Most cars can be modded enough to make it toe out at full compression or full extention. Most people find it best when max bumpsteer(toe out) is at full extention.That will help coming out of corners & not cause problems at other times. Some MFG build max bump steer(toe out) at max compression & that will make the car violently twitchy at the absolute worst times like jump landings,ruts,or simply a gentle way on the straight that compresses the susp. Nobody has designed a buggy without bumpsteer,thats almost impossable but like mentioned above it can be changes & moved around. Look at the front of your car from head on & note the difference between angles of the steering link & axles.If you could keep those 2 lined up perfectly through the entire susp throw you would have close to zero bumpsteer. I usually split the difference between the 2 like if theres a 4 deg difference at full extention then I shim to get 4 deg at full compression but on the opposite angle. It should work out like this,instead of 2 deg of toe out at the top or bottom you get 1 deg at top & bottom or what ever combination you want. With my last car it had enough bumpsteer to be considered a problem by most drivers & I put alot of effort into removing as much as possable.The car I drive now has about 0.5deg of bump & thats so little I have never bothered working with it. Its up to you & what you like & if your really bored you can also change the width of your akerman plate & do radicle changes with that. With all that said you know of corse that as soon as you turn the wheels from center all the work you did goes out the window.
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Old 03-26-2017, 06:06 PM   #7
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Default Changing bumpsteer when shortening camber link?

Does camber link positioning change bump steer? Ex: my buggy is an rb6 and at 25 degrees caster it was noted zero bumpsteer shims on the hub/knuckle were needed to achieve zero bumpsteer. However, I have shortened my front camber link to the outer hole on the tower (kit is middle), as well as took the 1mm shim off the ballstud. Will this change my bumpsteer since I am increasing cambergain with a very short front link? Thx all

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Originally Posted by butch man View Post
You can change bump steer by adding or subtracting shims at akerman plate or knuckle.Most cars can be modded enough to make it toe out at full compression or full extention. Most people find it best when max bumpsteer(toe out) is at full extention.That will help coming out of corners & not cause problems at other times. Some MFG build max bump steer(toe out) at max compression & that will make the car violently twitchy at the absolute worst times like jump landings,ruts,or simply a gentle way on the straight that compresses the susp. Nobody has designed a buggy without bumpsteer,thats almost impossable but like mentioned above it can be changes & moved around. Look at the front of your car from head on & note the difference between angles of the steering link & axles.If you could keep those 2 lined up perfectly through the entire susp throw you would have close to zero bumpsteer. I usually split the difference between the 2 like if theres a 4 deg difference at full extention then I shim to get 4 deg at full compression but on the opposite angle. It should work out like this,instead of 2 deg of toe out at the top or bottom you get 1 deg at top & bottom or what ever combination you want. With my last car it had enough bumpsteer to be considered a problem by most drivers & I put alot of effort into removing as much as possable.The car I drive now has about 0.5deg of bump & thats so little I have never bothered working with it. Its up to you & what you like & if your really bored you can also change the width of your akerman plate & do radicle changes with that. With all that said you know of corse that as soon as you turn the wheels from center all the work you did goes out the window.
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Old 03-27-2017, 06:38 AM   #8
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Quote:
Originally Posted by JAE View Post
Does camber link positioning change bump steer? Ex: my buggy is an rb6 and at 25 degrees caster it was noted zero bumpsteer shims on the hub/knuckle were needed to achieve zero bumpsteer. However, I have shortened my front camber link to the outer hole on the tower (kit is middle), as well as took the 1mm shim off the ballstud. Will this change my bumpsteer since I am increasing cambergain with a very short front link? Thx all
No, the only thing that affects bump steer is the angle of the steering rod throughout suspension travel.

If at full extension the steering rods point downward (from the center of the car outward), then as the suspension compresses the tyres will point inward (bump-in) as the distance between the bellcrank and the steering knuckle is reduced.
Similarly, if at full extension the steering rods are about level; when the suspension is compressed, the tyres will point outward (bump-out) as the distance between the bellcrank and the steering knuckle is increased.
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Old 03-28-2017, 01:06 AM   #9
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Quote:
Originally Posted by JAE View Post
Does camber link positioning change bump steer? Ex: my buggy is an rb6 and at 25 degrees caster it was noted zero bumpsteer shims on the hub/knuckle were needed to achieve zero bumpsteer. However, I have shortened my front camber link to the outer hole on the tower (kit is middle), as well as took the 1mm shim off the ballstud. Will this change my bumpsteer since I am increasing cambergain with a very short front link? Thx all
No, the only thing that affects bump steer is the angle of the steering rods and how it changes throughout suspension travel.

For example, if at full extension (full droop - car on a stand) the steering rods point downwards (i.e. the inside of the rod is higher than the outside of the rod), as the suspension compresses, the steering rod will level out, as well as the distance between the steering knuckle and the bellcrank (or inner mounting point of the steering rod) will shorten, and thus the wheels will toe-in slightly (giving bump-in).

Similarly, if at full extension the steering rods are relatively level, then as the suspension compresses, the steering rod will point upwards (i.e. the outside of the rod is higher), as well as the distance between the steering knuckle and bellcrank will lengthen, making the wheels toe-out slightly (giving bump-out).
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Old 03-28-2017, 05:56 AM   #10
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Wow. This thread is over 8 years old. I really feel old now. Lol.
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