Does lowering a Miata change the bump steer curve?
06-26-2017, 02:27 AM
#1
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Does lowering a Miata change the bump steer curve?
I would think lowering the car would make your problem worse. At factory ride height, the tire rods are roughly parallel with the rack. When you lower your ride height, the rack sits lower than the tire rod ends, forcing the tire rods to point up and effectively reaching out a shorter distance. I have my car lowered a bit on coilovers, and I recently added rack spacers to eliminate bump steer. I had to dial out a fair amount of toe after adding the shims to pull the wheels back to neutral toe. 1/2" rack spacers created ~4mm toe out at each wheel on my setup.
I supposed you could try shimming your rack up, but it sounds like you're coming up really short.
I supposed you could try shimming your rack up, but it sounds like you're coming up really short.
If you lower the static ride height…The ball joint plane remain would remain the same, and whilst the instant center (of the tie rod, upper arm, lower arm) at static ride height would move, with the mounting points and relative lengths of the tie rod, upper and lower arms still being the same…the bump steer curve should also be the same, albeit with the car at its new static ride height sitting at a different point on it.
What I am missing?
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06-26-2017, 06:58 AM
#2
Correct the curve itself will not change, your position on that curve does change. Keep in mind it is a curve not a linear line, you may be moving into a more aggressive area of the curve. No reason to guess at this, pull the springs or back off the adjusting sleeves until the car sits on the bump stops. Measure toe, then Jack up the car .5 or 1" at a time and measure toe at each ride height to see what the curve is. Now you can make an informed decision if you are in an undesirable part of the curve.
I did this on a Duramax 3/4 ton truck and found over 2"of toe change...... No wonder it ate tires.
I did this on a Duramax 3/4 ton truck and found over 2"of toe change...... No wonder it ate tires.
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06-26-2017, 05:37 PM
#3
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Correct the curve itself will not change, your position on that curve does change. Keep in mind it is a curve not a linear line, you may be moving into a more aggressive area of the curve. No reason to guess at this, pull the springs or back off the adjusting sleeves until the car sits on the bump stops. Measure toe, then Jack up the car .5 or 1" at a time and measure toe at each ride height to see what the curve is. Now you can make an informed decision if you are in an undesirable part of the curve.
I did this on a Duramax 3/4 ton truck and found over 2"of toe change...... No wonder it ate tires.
I did this on a Duramax 3/4 ton truck and found over 2"of toe change...... No wonder it ate tires.
& yes, best get the spring out and plot it. Won't happen in the short term but will happen...
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