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Hot!Bump Steer

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nut.161
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2020/06/25 09:35:48 (permalink)
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Bump Steer

After just registering the mr2 and a good amount of driving kms on it i have noticed an alarming amount of bump steer, mostly front but some rear. I have read through various threads across the internet but there doesn't seem to be much of a consensus on sorting the issue.
My car is a 92 Aus model, with what appear to be lower king springs on stock struts. (nothing to compare to), the rest of the suspension all looks/feels in serviceable condition.  Car tracks nice and straight but i would like to get a wheel alignment.
#1


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    Falcon
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    Re: Bump Steer 2020/06/25 14:56:29 (permalink)
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    These little cars respond to a wheel alignment. Poor alignment they can respond with poor behavior.
    Can be tricky to diagnose problems as they only have 500 - 600 kgs. on front axle.
    Tyres can make a huge effect on handling too along with wheel offset etc.
    Are you sure it's bump steer you're experiencing ?
    That's a shadowy looking bloke in the photo.
    #2
    nut.161
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    Re: Bump Steer 2020/06/25 15:46:02 (permalink)
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    Smooth roads and bends I dont experience it, but catch a bump with only one wheel and it will yank the steering wheel or get stuck in a wheel track and it pulls around. Rear seems only super minor as I have only noticed it a few times.
    Has non staggered wheels atm but I am planning to get that back to factory offset soon. Tyres are re003, bit camber worn on front inners.

    Yeah that shadowy guy doesnt like the cold.
    #3

    Falcon
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    Re: Bump Steer 2020/06/26 07:33:06 (permalink)
    +1 (1)
    I've heard good reports on the RE003 so I doubt they are at fault. You describe classic symptoms of tramlining when you say "stuck in a wheel track and it pulls around".  RE003 are not inclined to do this. Some other tyres are fair buggers for this behavior. I personally avoid any tyre with anything resembling a sharp / square shoulder.
    I will probably get mud chucked at me but I would suggest that front wheel off set and/or toe setting is more likely to be the culprit. (Wheel off set has nothing to do with wheel stagger). These cars originally came with +45mm offset.
    McPherson strut design has bump steer in it but it rarely exhibits itself under normal driving conditions.
    Those lowered King springs could be contributing to these symptoms too. There is very little bump travel available so on a one wheel bump it could very well be hitting right into the bump stop where loads immediately shoot to infinity.
    What is commonly described as camber wear often has little to do with camber but is more likely to be as a result of incorrect toe setting for the camber being used.
    All these opinions are purely my own observations and experiences over many years and are offered as a guide that I would hope is helpful. Soooo only reasonably clean mud please.
    #4
    Reddtarga
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    Re: Bump Steer 2020/06/26 10:57:17 (permalink)
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    No mud Doug.
    Bumpstops are not a very good spring subsitute. 
    I recently replaced King springs from a freind's early model SW20 because there was zero bump travel with them.
    Refitted stock springs to it along with a stock alignment, and a lot of bad things dissappeared.
     
    I also use Bridgestone re 003's on the front and they do not tramline even on badly grooved roads.
     

    1990 ADM NA
    Any advice you get from me may only be worth what you paid for it.
     
     
     
     
     
    #5
    TwoDogs
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    Re: Bump Steer 2020/06/26 15:48:25 (permalink)
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    I'm with Falcon on wheel offset, magnified by wider tyres.
    I get a different response in the steering wheel going over a parking lot speed hump at an angle.
    First the outside edge of one front tyre strikes the bump first, then soon the inside edge of the other tyre - different amount of steering wheel torque. Would indicate offset as not ideal (given L&R caster, camber and toe are the same).
    Are your wheels stock ? What are the tyre dimensions? I looked long and hard to find cheap aftermarkets that had offsets similar to stock. Settled for 17x7 on the front and 18x8 on the back, yes driving downhill.
     
    Also what targa says is true, returning the car to original height will help also. 
    If you lower a car, then all the geometry changes. There are compensating blocks that can return the control arm angles to original, similar for steering (tie rod) angles, but the factory dialed in the macpherson struts and wheels pretty well, perhaps a little soft. I've got Eibach springs and they are firm, gotta slow down over bumps or it is unpleasant, but with standard sway bars I have very little roll. It hooks around bends nicely.
    The compensating blocks I mention help reduce body roll. 
     
    #6
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