eli5 How are torque specs determined for various parts on a car? And what would happen if you increased them by something like 25% across the board?

Question

eli5 How are torque specs determined for various parts on a car? And what would happen if you increased them by something like 25% across the board?

In: Engineering

Answer 1

Vehicle OEM engineer here. To add to the good answers already here, many fastener torques are based on prior experience.

For example a new subframe with a similar duty cycle to a previous one would start with a common mounting fastener torque. Testing would look for movement or shuffling in the joint and correct any issues.

New designs would base initial torques and fastener sizing on calculation, competitor benchmarking, existing availability of parts and previous experience.

Critical fasteners will usually be calculated and FEA tested before tooling, and once prototyped typically checked with a load cell measurement for clamp load and variance.

As for overtightening, depends on the joint. Cylinder head bolts would probably fail, wheel bolts will probably be fine. Probably is the important term here as they’re all unique.