Measuring Bump Steer at home???

atomicjoe23

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What's the best/most practical way to measure bump steer on a vehicle if you don't have any fancy equipment???

Thanks!
 

WannaB-class5

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I did this a few weekends ago. I simply made sure there was no toe in or out at "ride height" then dooped out and checked toe, bumped it, checked toe. To check toe in or out just measure to the inside front of each tire, then the inside back of each tire. Done and done. Takes forever!
 

atomicjoe23

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Thanks guys!!! That should get us started on making improvements for next years race buggy. . .

. . .now how do I reduce bump steer, i.e. what part of my design do I need to change to affect bump steer. . .talking about unequal length A-arms?
 

punchdrunk monkey

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Couldn't you clamp a straight edge to your hub or rotor (something flat/straight), set the hub at ride height and meassure from your straight edge to fixed reference point. Then cycle your suspension and meassure to the same reference point?
 

Tech Tim

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Thanks guys!!! That should get us started on making improvements for next years race buggy. . .

. . .now how do I reduce bump steer, i.e. what part of my design do I need to change to affect bump steer. . .talking about unequal length A-arms?

Here is a start:

thedirtforum said:
In order to accomplish zero bump the tie rod must fall between an imaginary line that runs from the upper ball joint through the lower ball joint and an imaginary line that runs through the upper a-arm pivot and the lower control arm pivot. In addition, the centerline of the tie rod must intersect with the instant center created by the upper a-arm and the lower control arm.



The tie rod must travel on the same arc as the suspension when the car goes through travel. Simply matching lengths and arcs to prevent any unwanted steering of the front tires.

The drawing is for a roundy round car, so the tierod placement may look a little wierd, but as long as you keep it in the same arc as the upper and lower joints you can move it higher or lower to suit. There is still more to do the keep the bumpsteer to a minimum through it's travel, but not being in the same arc is most common cause of bumpsteer that I've seen.
 

atomicjoe23

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Thanks for the pic and explanation. . .that's what we wanted to accomplish and I'm pretty sure that we did. . .I will double check maybe we were off just a little. . .but I think we were as close as we could get using a stock Yamaha YFZ450 steering knuckle. . .

. . .I may have to design some knuckle of our own though. . .
 

Triaged

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Measure the toe at a bunch of different points (5 at least but every inch of travel would be nice) and plot them on a graph. The shape of the curve will tell you what direction you need to go.
 

Giant Geoff

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Couldn't you clamp a straight edge to your hub or rotor (something flat/straight), set the hub at ride height and meassure from your straight edge to fixed reference point. Then cycle your suspension and meassure to the same reference point?

x2, That’s how I still to it today, if you do something physical, you get a physical answer out of it. If you use some kind of calculation, the answer you get has to be translated to reality and that’s were the flaw accusers if you don’t get it right.

If the type of car you’re working on has wheel scrub, plum bob down on both ends of your strap to be able to know the bump steer amount.

For a front buggies style beam you weld a piece off the back of the spindle and clamp a straight edge off the rotor and you’ll know the bump steer is gone when the 2 pieces stop moving from each other.
 
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