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Sway Bar Pre-load

Suspension Tuning & Optimization

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Discussion and questions related to the course Suspension Tuning & Optimization

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I have read a lot about "pre-load" on sway bars during installation, where the goal is for there to be zero pre-load on the sway bar while the car is resting on its wheels vs. installing while the car is suspended with the wheels at full droop. How important is this to complete in this way, and what are the implications if you do not install the end links in this way?

There should be no "preload"in either case, but the main focus is usually with the vehicle's weicht supported by the wheels.

Any pre-load across the bar will affect the weight jacking/effective spring pre-loads and so effective spring forces on the wheel assemblies. This can affect the under/over steer balance left to right.

You're not thinking of the recommendation of tightening bushings with the vehicle's weight on them, to prevent torsional loadings in them?

I have seen roll bars that have no preload on them when the vehicles weight is being supported by its wheels and suspension gaining cross load on the bars at full droop as the ride height adjustments have made it so that the full droop positions across the axle are different. Setting the links in this condition will lead to the bars having preload when they are back under the load of the vehicle. This is also why you disconnect the links when you are doing ride height adjustments.

That would definitely be something that would need checking and remedying then,Stephen, as it means the net spring rates on all four corners will be altering across the axles as the suspension moves.

There are applications where it may give a benefit, especially beam live axles under acc'n out of corners, but unless one knows what one's doing, better to be fixed before experimentation.

Sorry for the delay in response, its been a busy couple of weeks.

Thanks guys for the responses.

@Gord - You're not thinking of the recommendation of tightening bushings with the vehicle's weight on them, to prevent torsional loadings in them?

I think what I referring to is load on the bar itself vs. the bushings. To be more specific, I installed coilovers on my car and did so with the car elevated on a QuickJack, tightening all bolts while in this position. I did not however adjust ride height when doing this, as my car had already been moderately lowered with lowering springs on stock dampers by a performance tuner prior to the coilover install.

OK, as it seems you haven't finished the tightening of the components'fixing points at the normal ride height, I'd start with backing them all off and re-torquing them.

The second thing is "coilovers" normally have adjustable spring seats, what did you do to check they were correctly set - an approximation can be achieved by the position of the seats relative to each other, but an actual check on wheel plates should really be done, as there is a tolerance on the spring rates and lengths.

Okay this is good to know, I am not sure how I will do this in a home garage setting, but I suppose I could use a combo of ramps and blocks.

In regards to the springs, I arbitrarily set each of them to the middle point, expecting to have to adjust once installed. However, after I installed them the ride height was exactly where I wanted it and it was even across the wheels, so I havent touched them since. I now only adjust damper settings prior to on-track use and it has made a world of difference.

Thanks for the help an advice, I appreciate it!

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