=0 wheel fell off
01-02-2011, 05:10 PM
#1
Senior Member
Thread Starter
=0 wheel fell off
so i was just driving down the road and pop, all 6 bolts just stapped. clean brakes i have no idea what happen. any else ever have this happen? my father said it was from the torque. what do you think?
01-02-2011, 07:34 PM
#6
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01-02-2011, 10:00 PM
#9
Resident Engineer here:
So a few things can happen to cause it. First, those lug nuts/bolts are responsible for the force transfer from your vehicle to the ground, if its accelerating or stopping. Bolts are horrible in shear, but excellent in tension. So the bolts are providing the clamping force between your wheel surface and the axle surface.
Under Torque: When you torque the bolts(via the nuts), you are setting up the clamping force. The bolt is now in tension, this is how they properly work. If they are not torqued properly, the stopping and acceleration forces are sufficient to make the wheel surface move relative to the axle surface, now the bolts are in shear, which is bad. (The threads of the bolt are stress risers, this is why shear pins are round with no geometry on their surface).
Over Torque: On the other side, if you over torque the bolts (via the nuts), you can yield the bolts. When you torque a bolt, it actually stretches and gets longer, but it will return to its original length when you take the nuts off (as long as you don't reach the Yield point). If you torque it beyond its yield point, it won't return to its original length, sort of like stretching taffy. So bad things start to happen beyond this point, which can allow relative motion between wheel surface and axle surface, bolts in shear again and failure can occur.
This is why its important to use a Torque wrench, on one of the most important connections on a vehicle, it keeps you from going too low and too high...
So a few things can happen to cause it. First, those lug nuts/bolts are responsible for the force transfer from your vehicle to the ground, if its accelerating or stopping. Bolts are horrible in shear, but excellent in tension. So the bolts are providing the clamping force between your wheel surface and the axle surface.
Under Torque: When you torque the bolts(via the nuts), you are setting up the clamping force. The bolt is now in tension, this is how they properly work. If they are not torqued properly, the stopping and acceleration forces are sufficient to make the wheel surface move relative to the axle surface, now the bolts are in shear, which is bad. (The threads of the bolt are stress risers, this is why shear pins are round with no geometry on their surface).
Over Torque: On the other side, if you over torque the bolts (via the nuts), you can yield the bolts. When you torque a bolt, it actually stretches and gets longer, but it will return to its original length when you take the nuts off (as long as you don't reach the Yield point). If you torque it beyond its yield point, it won't return to its original length, sort of like stretching taffy. So bad things start to happen beyond this point, which can allow relative motion between wheel surface and axle surface, bolts in shear again and failure can occur.
This is why its important to use a Torque wrench, on one of the most important connections on a vehicle, it keeps you from going too low and too high...