How To – Measure Your Tyre Tread Depth

Difficulty

What Do I Need?

Tyre tread depth gauge
20 pence piece (in a pinch)

Why Should I?

Following on from our summer article about the old black circles we thought we would do a quick how to on checking tyre depth, what with winter well and truly on our doorstep. Now this will no doubt be obvious to a lot of you but according to recent research a whopping 40% of British drivers cannot confidently carry out a tyre tread check. We’re not shaming here though and for those new to vehicle ownership it can be easy to overlook, especially where MOT exempt classics are concerned and there isn’t so much of an impetus to keep old faithful quite as faithful as perhaps you should.

As explained in the aforementioned Let’s Talk Tyres feature, decent rubber can make or break your classic. Quite literally. Not only that but tyres have a legal minimum depth which varies depending on the type of vehicle so being able to check them effectively will keep you in the good graces of the fuzz as well as away from any potential fines or points. For cars it’s at least 1.6mm throughout a continuous band in the centre 3/4 of the tread and around the entire circumference of the tyre. For motorbikes it’s even lower at 1.0mm although many experts believe double this depth is a much safer figure to aim for in both instances.

As tyre tread decreases and gets closer to the legal limit, stopping distances increase dramatically, particularly in wet conditions. A tyre’s tread helps dispel water away from the contact patch between tyre and road and with less tread depth, less water is expunged, decreasing grip. More tread means more grip which equates to better handling and increased safety, so regular checks are vitally important.

Talk Me Through It

NB: Remember, generally speaking it’s always good practice to replace tyres in pairs on opposite sides at the same time.

There are several ways to measure your tyre’s tread depth.

1) Use the built in tyre wear indicators. This is the easiest method, although it will only tell you when it’s time to fit new rubber, not the actual depth of the tread. Typically they’re small bars, a few millimetres wide, built into the tyre’s main grooves at various points around its circumference.

If the tyre tread is level or flush with the top of these wear indicators then your tyre has reached the legal limit and needs to be replaced pronto.

2) Using a tread depth gauge. Available in both analogue or digital formats they are simple gadgets that will display the exact depth of your tyre’s tread. You can even make one yourself should you wish.

Place the gauge into the groove of the tyre at various points around its circumference and take a reading at each spot. If it’s less than 1.6mm then that’s your cue to fork out for some freshies.

3) Use a 20 pence piece. Widely regarded as a good indicator of minimum tread depth the outer band or rim of the coin measures just under 3mm wide.

Place the coin into your tyre’s grooves, again at various different points and if the outer rim is not visible then your tyre is within the legal limit. If you can see it, however, then you’ll need to replace the tyre.

Conclusion

Tyres with decent tread are key to how your vehicle handles as well as how safe it is to use. No matter what the vehicle or tyre, it’s imperative to regularly check the tread depth. Best case you’ll get a fine, some points on your license and a telling off from PC Plod, worst case you’ll end up in an accident and potentially killing someone and/or yourself so even if you’re using the 20p method, get checking those tread depths.