Definition of Nut/Bolt Torque

When fitting new tyres, etyres fitters all too frequently encounter wheel nuts and studs that have previously been over-tightened. It’s even more of a problem if you need to change a tyre in an emergency at the roadside, yet the nuts just won’t budge. It is often caused by the negligent use of the air driven impact-guns that tyre depot fitters routinely use. In extreme cases, however carefully a wrench is used, these nuts or studs are impossible to remove and break during removal. This is costly because the broken stud then has to be drilled out and replaced.

All car manufacturers specify the correct wheel nut or stud tightness for their cars. This is usually expressed in Newton Metres (NM) but sometimes foot/pounds (ft/lbs) is still used. This refers to the amount of rotational pressure needed to achieve the desired level of tightness. This rotational pressure is termed “torque”.

The level of NM torque required differs from car to car and the range is huge. A Peugeot 106 should be torqued to 90 NM whereas a 7 Series BMW should be torqued to 140NM. People carriers such as the Ford Galaxy need the studs to be even tighter at 170 NM and Ford Transit and Combi vans need a whopping 200NM.

If a tyre depot air gun has just been used on a Transit and you are having the tyres replaced on your Peugeot 106 it is easy to see how your wheel studs could be over-tightened. But you won’t know about it until you can’t get your wheel off when you get a puncture, or when the stud snaps when you next have tyres fitted or the car serviced.

This emphasises the importance of using a correctly-set torque wrench to tighten all wheel nuts and studs. This is why using a wrench, not an air-gun, is a vital part of the etyres fitting process.