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WYZEUP

Bump steer correction

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Hey guys,

 

Currently working my way through the certification process on my car and as i have changed steering racks a bumpsteer test needed to be done.

Only changed to e36 rack and have spaced in the middle of the subframe and test has come back with 40mm of bumpsteer....would hate to know what some uncertified vehicles have after this change.

Has anyone here got any knowledge on correcting bump steer or any solutions, i did consider raising the steering rack which also means i need to lift the motor which will cause some driveline issues?

 

any help would be great so i can get it sorted :)

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You should first identify what the cause of your bump steer is  and equally importantly what it was before the change.

Ideally the rack ends and the lower control arms should scribe the same arcs through suspension compression and rebound so their respective lengths (end to end across the car) remain  aligned  

The common problem with lowered cars is that the tie rod arms and the lower control are track through different arcs  so the lower control arm will often scribe a more acute arc in compression meaning it gets shorter quicker when compared to the steering and as a result the vehicle "toes out".

This may be your problem or it may be something else like the rack height or position 

 

BTW the LVV  test is a load of rubbish as it mixes up suspension articulation and  ride height  with geometric testing and it uses very rudimentary tools so it  is unlikely to produce clear / reliable data. A bump alignment test on a  wheel alignment machine would be far more informative, you can do it like this: 

1) Set the car up on the alignment machine, properly loaded  and confirm alignment is correct,

2) Cinch the car down onto the bump stops and monitor the toe setting - record the final value,

3) Lift the car up either with the jack on the machine or jacks under jacking points and monitor toe setting - record the final value 

If you really want to get picky do this again at 20 and 30 Degrees steering angle  

The monitoring as you compress and extend the suspension will show up any fatal flaws  - what you are looking for is a small progressive change in one direction only as you move away from the "static" position.  

 

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