Why it's important not to overtighten your wheel nuts

Having to replace a flat tyre on the side of a busy road is something all motorists would rather avoid. If you know what you’re doing and everything works the way it should, fitting a spare wheel should not take more than half an hour and you’ll be on your way. 

However, how would you feel in that scenario if you went to loosen your car’s wheel nuts, using the standard wheel brace supplied with the car, only to discover that the nuts were so tight you could not budge them? So tight that even placing your foot on the wheel brace and standing on it with all of your body weight could not crack them loose? Anecdotal evidence suggest this is not uncommon.

Needless to say, over-tightened wheel nuts can turn a simple wheel change into a nightmare. So, to ensure you don’t find yourself in this situation - and avoid potential mechanical damage you may not be aware of – here’s a few handy tips.

Why wheel nuts are over-tightened

This is often blamed on powerful pneumatic or battery-powered impact guns used by mechanical workshops and tyre retailers, inadvertently applying excessive torque through a hammering effect when tightening wheel nuts after vehicle servicing or fitting new tyres. 

Torque is the twisting force that’s applied when wheel nuts are being tightened. The amount of torque, measured in Newton metres or Nm, is specified by your car’s manufacturer and can usually be found in the owner’s manual. 

Each new car that rolls off an assembly line has its wheel nuts ‘torqued’ to the correct Nm settings.  However, if these factory settings are not maintained during ownership, wheel nuts can become either too loose or too tight.

Wheel nuts that are too loose can cause a wheel to start wobbling as it rotates, creating noises and vibrations which can be easily detected and usually cured by stopping and tightening them. However, if they have been over-tightened, it can create more headaches than just being stranded on the roadside.

Damage caused by over-tightening

This can cause stripped threads on wheel nuts and wheel studs plus stretching of the studs, which makes them weaker and prone to fracturing and eventual failure. This stretching can also cause the wheel nuts to work loose.

Disc brake rotors and brake drums can distort, causing steering wheel shake and shuddering when braking which can have knock-on effects in damaging other related components.

Alloy wheels, which are made from softer materials than steel, can also be damaged along with the aluminium dress-caps fitted to steel wheel nuts to improve their appearance. If the nuts are too tight, these caps can easily distort when force is applied to loosen them and end up spinning around on the nuts. 

The only solution then is to remove the dress-cap with a chisel to access the wheel nut, which not only destroys the dress-cap but also increases the risk of alloy wheel damage while doing so. 

How to avoid over-tightening

A cost-free (if not entirely accurate) way to check wheel nut tightness is with the wheel brace supplied with your car’s tool kit. 

Vehicle manufacturers design these tools to provide adequate leverage - and therefore the torque required - to tighten wheel nuts to the recommended settings. So, if you can loosen and tighten your car’s wheel nuts with the wheel brace, you can be reasonably confident that the wheel nuts have been tightened to, or close to, the correct torque. It also means you’ll be able to loosen them if you have to change wheels in our roadside scenario.

However, if you want greater accuracy, the best tool is a torque wrench. These are available from automotive accessory suppliers and hardware stores, with prices starting from around $50 for a basic version that would be adequate for this purpose.

A torque wrench allows you to select a desired torque setting and when tightening a wheel nut it will tell you (usually with a clicking sound) when the setting has been reached. Using this technique, four sets of wheel nuts can be easily checked within a minute or two.

This is a good habit to get into, particularly after your car’s wheels have been removed and refitted. Grit can get trapped between wheel nuts and the facings where they ‘seat’ on wheels, potentially creating false torque readings that aren’t indicative of actual clamping force. 

So, after checking the wheel nut torque settings after wheels have been refitted, it’s important to check them again with your torque wrench after about 50km when the nuts have settled, to make sure they are still correct.

Conclusion

The average car owner rarely if ever checks their wheel nuts, which is remarkable given the pivotal role they play in driving safety. After all, if tyres are the only thing between your car and the road, then wheel nuts are the only things keeping them there. 

So, it’s wise to make checking wheel nut torque settings part of your maintenance routine, particularly after your car’s wheels have been removed and refitted using impact guns, to ensure they have not been over-tightened.