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Discussion and questions related to the course Motorsport Wheel Alignment Fundamentals
When torqueing the suspension bolts down to factory spec after performing necessary alignment change- should I torque them while the car's in the air or should I tighten them first then torque while the suspension is loaded (on the ground). Is there any difference between the two?
I would say the answer is... it depends. I would say in general, if you are tightening something after making an adjustment you should ideally torque it before putting the car back on the ground. Part of this is to stop things moving once it goes on the ground, the other is it stops you from leaving things loose my mistake! One exception I can think of to this is for any component that has a polymer bush with a crush tube, let's say what would be typical on a front inner pivot of a lower control arm. I've added some pictures below as an example.
For a case like this, when the suspension moves up and down this bushing I've highlighted rotates. If you were to tighten the through-bolt that clamps this bushing to the subframe while the suspension was hanging in full droop, the neutral (un-twisted) state of the bush is with the suspension in full droop.
That means when the car is sitting at ride height this bushing will be pre-stressed. When the suspension is compressed (when the chassis rolls or you go over a bump) this bushing will be more stressed by twisting even more.
The point being, for any component with a bushing like this, you ideally only want to tighten it once the car is sitting in a neutral position (ride height). Otherwise, you're overstressing the bushing and it will wear out quicker than it otherwise would.
Also worth noting that not all bushings like these have the inner crush-tube bonded to the rubber. Some aftermarket ones (like many polyurethane ones) are designed to rotate once tight, so they don't suffer as badly from this.
It also depends on what is accessible to you with the car on the ground, some things will be tough to get to without having a 4-post hoist!