How to avoid failing your MOT on tyres

MOT Advice

Tyres are the only part of a vehicle which touch the road surface so play a critical role in the handling of your car, van or motorcycle.

Tyre tread depth

For cars and vans the legal minimum tyre tread depth is 1.6mm. For motorbikes it must be a minimum of 1.0mm. It is important to note that not all new tyres come with the same tread depth. The depth can be anything from 7-10mm but the average is around 8mm. Most new tyres will now come with an indicator between the treads, (a raised piece of rubber at the bottom of the groove) so if the surface of the tyre is level with the indicator you know it is time to get a new one.

It is not illegal to have mismatched tyres (having two different manufacturers) however we would advise you against mismatching across the same axis i.e. the two rear tyres being different tread patterns and the two front tyres being different tread patterns. The front is where all the weight is held and the back is what will swing out.

The best tyres should be on the rear as this makes for easier handling especially in wet weather, so if you get two new front tyres it’s best to get the older rear ones moved to the front.

Ply or cords exposed

The inside of a tyre is made up of ply and cords which can become exposed if the tyre has a cut. If the cut is 25mm or 10% of section width, whichever is greater, it can be cause for an MOT fail as a cut of this size means it is deep enough to be able to reach the ply and cords, if it has not done so already. If you notice this before your MOT it is advised to get the tyres replaced ahead of the test to avoid a fail, usually the garage carrying out your MOT can do this for you, but if you are unsure contact them to ask.

When you buy the replacement tyre it is advised that it matches the tread on the same axis, it is also important to make sure it is the same size as the others, and this is in line with the manufacturer’s recommendations.

Bulges, lumps and tears

Tyres can endure a lot of pressure in their lifetime as they bear the brunt of kerbing and pot-holes. Over time this can cause bulges in the rubber which essentially means it’s structural integrity has weakened and the air pressure is causing the visible lump. If this happens you should get it looked at by a professional tyre technician immediately.

Sizing

One of the less common MOT fails is when a tyre is fitted which is a different size to it’s partner on the same axis. This can cause the transmission on the front wheel drive to rotate at a different speed for each wheel. One way to put this into perspective is if you have a tyre 5mm higher it’ll be like driving with a brand new tyre and one bald tyre.

It is equally important to ensure if you are changing the size of your tyres to make sure you fit them with the same diameter that the vehicle was designed to work with. If the diameter is different to the manufacturer’s specifications it will affect the time it takes for the tyre to complete a full revolution and will in turn affect the readings of your speedometer and your gearing will be impaired.

If you are unsure about the size of tyre you need, please consult a tyre specialist who will be able to correctly advise you. We have a number of tyre specialists listed on our website and ready for you to book in or get a quote.