Torqueing Nuts

If people give little consideration to their tyres, apart from price, then how much less attention do they give to their wheel nuts/bolts? Most people will just be happy if their wheel nuts are tight enough to keep the wheel on the car - and those nuts simple cannot be over-tight, can they?

Well, yes they can.

The issue of a loose wheel nut is pretty self- evident. If one wheel nut on a set is loose, then it puts additional strain on the remaining wheel nuts. Now, for some reason, that additional strain only very rarely causes a wheel nut to tighten itself. It usually results in a loosening. For most drivers that becomes a very obvious danger as the loose wheel vibrating on the hub transmits that vibration and possibly impacts on handling and steering control, so the driver will usually identify a problem and have it fixed.

With an over tight nut there is no evidence of a problem until things go wrong, and go wrong they can.

The first problem with over tightening a wheel nut is that the chances are they will all be over tightened, so on a wet and windy night when you get a puncture you can't get the wheel off and you have to wait for the AA or the RAC or whoever to come and sort a flat tyre. A repair most folks could do in less than the time it takes the fitter to arrive. That though is a minor problem.

The next issue is that when a nut tightens on a stud it can, if over tightened, stretch the stud. In itself not an issue, but the stretching of the stud weakens it. It is unlikely that it will weaken it below its breaking point, but repeated over tightening can do. The stud in the process work hardens and can shear. If one goes, so too might a second; that increases the likelihood of a third or fourth coming off. If you think that unlikely, then consider that trucks from time to time lose wheels from trailers when all the studs shear at the same time!

For those cars fitted with alloy wheels another difficulty arises. Alloy wheels are not quite as forgiving as steel wheels, and over tightening the wheel nuts can cause damage to the wheel centres, creating stress points that can lead to fracturing at worst, damaged wheel nut facings at best.

If your car uses wheel bolts rather than nuts, then you still have the same issues, plus the over tightening of the hardened bolts in the hub may strip the threads or even crack the hub.

Every tyre shop should have a reference chart to which they can refer for wheel torque settings. If the fitter runs the wheel nuts/bolts on with an air gun and hands you your car back, ask him to check the torque settings. However, remember that if the air wrench has set the torque higher than it should be, using a torque wrench will not identify that the nuts are over tight.

To read more on this issue click here.