Advice: Understanding road bike tyres

Tyres, if in good condition and well maintained, aren’t something we tend to give much thought. But if they’re not looked after, they’re the first things that will let you down across a whole range of situations.

They also affect your bike’s handling and overall running costs, so it’s important you have a decent understanding of what is, ultimately, the only thing between you and the road…

When it comes to choosing a set of tyres, you’ll need to know more than just the appropriate size to suit your bike. It’s important to have a clear understanding of what you need the tyre to do for you and how much money you’re prepared to spend.

Tyres are enormously complex both in terms of the actual rubber compound used to form the tread, the tread pattern itself, and also in terms of their internal construction.

The basic rule of thumb is that a softer compound will offer more grip but will wear more quickly, whereas a harder-compound tyre will last longer but offer less grip. An inappropriate tyre choice will result in uneven and or premature wear and will need replacing sooner than a tyre well suited to your needs.

Many tyre manufacturers offer a dual-compound tyre with softer, more grippy rubber on the edges (sometimes called the shoulders) and a harder-wearing compound in the centre (sometimes called the crown).

It’s a similar story when it comes to the construction. A range of manufacturing techniques can be used, with the most common being radial (where the ply radiates perpendicular from the centre of the crown) or bias (where the ply is laid on an angle).

The construction has a big impact on the stiffness of the tyre. A bias tyre will tend to have uniform characteristics from the crown through the side walls, whereas a radial tyre will have more flex on the shoulder of the tyre, which means it will warm up faster and give you a larger contact patch when the bike is leaned over.

As for the tread itself, the grooves in the tyre (or sipes) are there purely to disperse water. A common misconception is that the tread offers grip, in the same way your joggers might. But the more rubber you can get on the road's surface, the more grip you'll have, which is why racing tyres have no grooves at all.

Maintaining correct tyre pressures is probably the most important self-maintenance item to which a motorcycle rider can attend. Far from a set-and-forget job, it’s enormously important to ensure your tyres are inflated to the correct pressure. And rather than following the guidelines set out by your tyre supplier, it’s important to inflate your tyre to the pressures recommended set by the motorcycle manufacturer specifically for your bike (which always reflect the air pressure in a cold tyre – more on the impact of tyre temperature in a bit…).

Tyre pressures influence grip, the way your bike steers, the rate at which your tyres wear and can even alter the performance of your suspension, so it’s important to get it right and keep it right.

If your tyres are under-inflated, your steering will feel heavy and vague and the contact patch on the ground will increase, which will over-stress the carcass and result in premature and uneven wear. Alternatively, if they’re over-inflated, your optimum contact patch will significantly decrease, which reduces grip.

It’s a good idea to carry your own quality pressure gauge instead of relying on years-old service station gauges. Be aware that a tyre's pressure will read higher when the tyre is hot compared to when it’s cold, so it’s a good idea to get into a habit of checking your pressures at the same time – either before, during or after your ride – so you'll spot any anomaly more easily.

Most treaded tyres will feature wear indicators – small raised pieces of rubber set within a sipe, usually in a line across the shoulder of the tyre. Once the tread reaches the same height as these wear indicators, it’s time to replace your tyres.

Your pressures generally don’t need to be adjusted depending on the conditions, but you may want to up them slightly if you’re carrying a lot of luggage or a passenger for a decent period of time. Once again, consult your owner’s manual for recommended two-up pressures.

To the uninitiated, the letters and numbers stamped into the sidewall of a tyre don’t mean much, but there’s plenty of good info to be gleaned if you know what you’re looking at.

On the sidewall of most tyres, you’ll generally find three numbers separated by a forward slash, before two letters and another number – this is the size of the tyre.

For example, it might say 160/60ZR17. The first number, in this case 160, refers to the width of the tyre in millimetres from shoulder to shoulder. The number after the slash, in this case 60, refers to the height of the sidewall as an aspect ratio to the width. So the height of the sidewall is 60 percent of the aforementioned width.

The letters, though these aren’t always present, often refer to the tyre’s speed rating and construction. So in the case of ZR, the 'Z' tells us it’s rated to speeds in excess of 240km/h and the 'R' tells us it’s a radial construction. The last number, in this case 17, lets us know it’s suited to a 17-inch diameter rim. The sizes and how they’re represented will vary slightly between tyre manufacturers.

This article was originally published on August 27, 2018.