Spare tyre confusion

Posted on October 4th, 2017 by Rob Marshall


Many people are willing to pay extra for a spare tyre. Yet, even if they invest in one, many of our members have queried if they are still safe to use.

Is something better than nothing?

Air compressors and tyre sealant aerosols have limited use. While they may be able to plug a small leak, they are temporary measures, at best. Many tyre fitters refuse to repair a punctured tyre that has been filled with tyre sealant. Additionally, the sealer can find its way into tyre pressure monitoring sensors and render them inoperative.

Carmakers justify the lack of standard-fit spare tyres as a means of reducing weight, CO2 emissions and increasing fuel economy. For safety, the argument is that modern traffic conditions make it hazardous for DIY motorists to change a wheel at the side of the road. Both opinions have merit.

Different sized spares

To save cabin space, some cars are equipped with skinny spare tyres. These are designed to be used at very limited speeds (typically, a maximum of 50mph) for a limited period.

We have also heard cases of a ‘full-size’ spare wheel being sold for a car as a genuine optional extra, which is a different size to the other wheels on the car.

As it is an MoT failure to submit a car for its annual roadworthy test with different sizes of wheels fitted on the same axle, we have been asked if this makes spare tyres illegal.

The answer is that differently-sized wheels on the same axle are not illegal, provided that the odd one is marked clearly as being for temporary use – see picture. However, if submitted for an MoT Test, a fail would still result.