Motorcycle Tyre Tread Depth – What Is Legal?


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Last Updated: 26th October 2020

Having enough tread on your tyres will keep you safe and on the right side of the law.

It’s easy to check at home with or without dedicated tools so lets have a look at what you need to know.

What Is Tread Depth?


Tread depth is a vertical measurement from the top of a tyre’s tread rubber to the bottom of it’s deepest grooves.

Thread grooves are what give tyres their grip in wet conditions and their depth is how we monitor how much life is left in a tyre.

Once there’s under a certain amount of tread left, the tyre is unsafe (and illegal) to ride on.

Where Do I Measure Tread Depth?


Where to check motorcycle tyre tread depth

Depth measurements should be taken from a variety of grooves in different places across the surface of the tyre.

Road riding tends to wear out tyres in the middle first, with the grooves closer to the tyre wall often remaining nearly untouched.

Make sure you check the grooves down the centre line of the wheel.

Remember: the lowest depth you find is the true indicator of how much life your tyres have left.

How do I Measure Tread Depth?


Some manufacturers include tread depth indicators in their design.

These are raised areas inside the tyre groove.

When the wear gets close to these raised areas being level with the tread rubber, it’s time to change your tyres.

Other options for taking measurements range from digital measuring tools right down to using a 20p piece.

The 20p piece is an old favourite of UK riders.

Insert a 20p piece into the groove and take a side view.

If the outer band of the coin is covered by the depth of the groove, your tyres are good.

If not, it’s time to change them.

Tools

These methods are far from definitive and there are a range of inexpensive digital and analogue tread-depth measurement tools available online.

They generally work by placing the tool flat on the tyre then dropping a pin into the groove.

The tread depth will then be displayed in mm on a digital screen or analogue display.

This one (pictured below) is a well reviewed and very cheap.

What’s The Legal Requirement?


worn motorcycle tyre
This tyre is dangerously worn and needs replacing.

UK law demands a minimum tread depth of 1mm across ¾ of the tread pattern with visible tread on the remaining ¼ for bikes over 50cc.

Under 50cc requires all the grooves of the original tread pattern be clearly visible – if any grooves have worn smooth, your tyre needs changing.

Motorcycle MOT


Worn tyres will result in an immediate fail on your motorcycle MOT. Enough said!

What Causes Tyre Wear?


Ideally, tyres wear fairly evenly across their entire surface.

In practice this is often not the case.

The type of riding most commuters and casual riders do means that the treads closer to the tyre wall will wear out more slowly than those in the centre.

This is because we rarely lean into our turns knee-down with the edge treads in direct contact with the road.

Tyre Pressure

Over-inflation and under-inflation are the two primary causes of unnecessary, uneven tyre wear.

These will often manifest in a ‘squaring off’ off the top of the tyre and can cause handling problems – buy a gauge and check your tyre pressure often.

Suspension

‘Scalping’ is where indents and pits form on the front tire and is usually caused by problems with suspension.

Riding Style

Overloading your bike will also cause premature tyre wear, particularly if the weight is unevenly distributed.

Different riding surfaces significantly affect tyre wear. Riding on gravel can increase wear dramatically.

If you notice any kind of uneven wear on your tyres, point it out to your mechanic.

Age

Something worth mentioning is that tyres should be used within five years of their manufacture date.

This is because oils in the rubber can dry out and deteriorate over time, reducing their grip.

A tyre might look brand new, but not be road worthy due to age.

Every tyre has it’s manufacture date stamped on the tyre wall.

Conclusion


It’s pretty important to get this one right – both for safety and to stay on the right side of the law.

Once you’ve been riding a few years, you’ll get an idea of how long to expect from a tyre with your riding schedule.

Keep an eye on your tyres, consider investing in an inexpensive tread depth tool, and mention any uneven wear to your mechanic as soon as you notice it.