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Stiction in suspension

Suspension Tuning & Optimization

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I am optimizing an IRS in a Cobra replica. The upper and lower control arms use Heim joints for the pivot points. The arms move freely however they will not move under their own weight. There is some amount of 'stiction' in the system, probably due to tolerances in the joint spacing when the joints are tightened and the heim balls receive a slight bind.

My question is how much is too much? How free should the arms be? The main arm weighs approx. 12 lbs. As I commented, I can move it freely thru its full range of motion however it will not droop if released.

The system has been put on the road and has about 500 miles on it so some break-in has been accomplished yet this 'stiffness' exists.

Am I chasing the last .0001% or is it something that should be addressed?

? ? ?


Hi Paul,

Race or Road usage? On the road, I wouldn't be too concerned about it, as long as they do not have any points through the travel where the load is inconsistent. They most likely will be freer moving than the equivalent "Poly" bushes would be.

For Race use, i would like into the angles a bit further, just to confirm that there isn't a bent mount or similar that is causing the stiction. If all of the mounts are correct and not putting inappropriate loading into the arms (and the joints are torqued to spec) then it may be that the joints being used have a natural stiction that requires more than the 12lb to move them. Some of the larger hiem joints that I have used in racecar suspensions have retained a fair amount of stiction intheir actions, even after a few years of use.

We usually reply within 12hrs (often sooner)

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