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The spare wheel on my Mercedes A160 comes with its own set of wheel nuts and a message saying these must be used with the spare as it is a steel wheel whereas the other wheels are alloy - I can't imagine why this is so.

Peter

From the "Ask Jack" archives - 27 January, 2010

I'm sure you will find both the taper on the steel wheel nut and the wheel itself (where they come together as the wheel nut is tightened) is different to that of the alloy wheels and wheel nuts.

If you were to fit the steel wheel and use the alloy wheel nuts, the mating surfaces would be totally different and potentially the wheel could work itself loose or at best the nut would only be gripping the wheel at certain points and not mating perfectly as they would if both tapers were the same.

It is one of those scary things that can happen when owners change the wheels (from steel to alloy) on their vehicles. Often the spare is forgotten about.

In your case, Mercedes have provided the correct wheel nuts and instructions for the steel wheel, but for some owners of second hand vehicles there is always the possibility the nuts and instructions could get lost over time or simply not used if the spare needed to be fitted in a hurry.

Probably the biggest potential danger is if the steel wheel nuts were used but not replaced when the alloy wheel was refitted (such as after a puncture repair).