ngng

Per the procedure, you torque the wheels off the ground, break the nut loose, then retorque one last time. What purpose does this achieve versus a single torquing?

mdrums

You are seating the wheels to the surface....this is the way it was explained to me...this way you get a true 444ft lbs of torque

Fred R. C4S

It's not actually about bolt torque per se. It's actually about joint preload. Bolt torque is a simple way of "estimating" how much load is preloaded to the bolt to clamp the joint properly. In a perfect world, we'd measure bolt stretch or strain. The purpose of the initial tightening is to overcome the thread friction and seat the joint. When we back off slightly, the subsequent re-torquing gives us a better chance that we have achieved the targeted preload in the bolt. More of our torque goes into turning the nut, not overcoming thread friction. Thusly we further stretch the bolt to the desired amount that results in our targeted preload.

Let's not even get into the discussion of spring rates of the bolts vs that of the clamped joint. Bolted joints can seem simple. They've been around since Archimedes invented the screw. But in fact, they can be complicated if you really analyze them.

My God.I haven't had to think about the science of bolted joints since the '70s. I'm having flashbacks and they're getting kinda scary.

ngng

Thank you, that makes sense!

mdrums

Thanks Fred....great explaination!