The huge choice of tyres in your local bike shop and the bamboozling jargon that goes with them can be a complete headache. Become an instant tyre expert with our plain-English guide to all things rubbery.
Sizes & Fit
Say you’re shopping for new tyres because not only can you see through the rubber on your old ones, but you can see through them if you hold them up to the light. The first thing you need to know is what size you want.
Tyre size is determined by the size of the wheel that the tyre fits, and they have to be the same.
If you read Sheldon Brown’s fabulously geeky pages on tyres (or tires, as he called them) you’ll learn that for historical reasons there are literally dozens of different wheel and tyre sizes. But only a handful are in common use, so to prevent our brains exploding, we’ll just talk about them.
Large-wheeled bikes have either mountain bike size tyres, generally called 27.5" or 29", or road bike size, aka 700C. As the name suggests, 27.5" tyres measure about 27.5" across. However, 700C don’t measure 700 of anything, though they used to in an archaic French tyre naming system.
To keep things nice and confusing, mountain bikes have recently begun to use wheels that are the same size as road bikes, 700C, but with much fatter tyres. These are known as 29-inch (and the bikes that use them are referred to as 29ers) because that’s roughly the size of the resulting tyre.
The most common smaller sizes are:
- 24-inch, used on ‘cruisers’ - large-wheeled BMX - and some kids’ bikes
- 20-inch, a very common size, found on BMX and some folding bikes
- 16-inch, used on kids’ bikes and many folding bikes such as the ubiquitous Brompton
- 12-inch, used on kids’ bikes.
The size will be marked on the side of the tyre, so make a note of it if you’re going shopping. If in doubt, write down all the numbers you can find, including any that are embossed into the tyre. These numbers include an international standard that precisely identifies the size.
The other part of sizing is tyre width. Fatter tyres can be run softer for more grip and comfort. That’s especially useful off road, where you sometimes need all the grip you can get.
On the road, it’s still worth seeing if wider tyres will fit your bike. Most road bikes, for example, come with 23mm wide tyres. Going up to just 25mm or 26mm increases cushioning and allows you to lower the pressure a bit. This can make a significant difference to ride comfort.
Grip & tread patterns
Tyres grip smooth surfaces, like tarmac, because of the way the rubber interacts with the road at a microscopic level. Unlike car tyres, road bike tyres don’t need patterned tread because a bike never goes fast enough to build up a layer of water under the tyre and skid. The best tyres for road use, therefore, have no pattern on the tread, or only a very light pattern.
Off-road, you do need the tyre to mechanically dig in and grip loose, wet surfaces. Different tread patterns work in different situations, which is why mountain bike forums are full of geeky blokes wanting to know what tyres work best in mixtures of 30 percent loam, 35 percent sand and 35 percent sheep droppings.
Propelling a tyre down the road uses energy because the rubber and casing absorb your effort as they bend and unbend where they meet and leave the road. The thinner the rubber and the casing are, the easier the tyre is to ride.
Higher pressure also makes for easier rolling, and so does a tyre being wider. It’s not obvious why, but this has been experimentally demonstrated over and again. What happens is that the patch of the tyre in contact with the road is more rounded if the tyre is wide, rather than being long and thin. That shape has the same area, but a shorter circumference, so less of the tyre bends and straightens as it rolls.
The downside of very thin casings and rubber is that they wear quickly and tend to be easy to puncture, and the downside of pumping your tyres up hard is that they can become harsh to ride, so you will have to find a compromise.
The air in your tyres lifts them off the ground and makes them roll smoothly and easily down the road. In the 1800s tyres were made of solid rubber; that made for a harsh and uncomfortable ride. The introduction of the air-filled (pneumatic) tyre is what made modern bikes what they are.
As we’ve just mentioned, if you inflate your tyres to high pressure, they will roll better, but too much pressure and they will get uncomfortable. Most tyres have a recommended range of pressure marked on the side, so experiment within that range until you find what’s right for you.
Incidentally, a floor pump with a built-in gauge makes it easy to pump up your tyres and keep them at the right pressure. You can get them from bike shops, or even from supermarkets.
Puncture prevention and resistance
Punctures are our oldest enemy. The best way to avoid them is to look where you’re going and not ride through patches of broken glass, but even the most aware rider occasionally gets unlucky. The most effective and practical puncture preventatives are layers of tough material built into the tyre itself. These may increase weight and make the tyre a bit slower, but the best ones - like the layer in Schwalbe’s Marathon tyres - are very effective.
Steer clear of solid or near-solid tyres. These are heavy, very hard to fit and have a very harsh ride. they’ll prevent punctures, but eventually they’ll also prevent you from riding.
Different types of tyres suit different uses, so if you’re still head-scratching, here some guidelines for the type of tyre you should be looking for. Overall size depends on your bike, of course.
Use: General commuting
Type: 700C or 26" tyres in 28mm or wider with some tread so you can take to towpaths and gravel trails and get out of the traffic now and then. Puncture resistant highly recommended.
Use: Fast commuting
Type: 700C or 26"-27.5" tyres with very light or no tread pattern for fast rolling. 25mm or 28mm is perfect for a bit of extra cushioning, and again we’d recommend some sort of puncture-resistance.
Use: General off-road
Type: Medium-tread mountain bike tyres in 27.5-inch or 29-inch size. Go for at least 2.0 inch width and don’t obsess about the weight of the tyre. Very light mountain bike tyres are intended for racing and can be fragile.
Use: Unladen road riding
Type: light 700C tyres. We like the extra cushion of 25mm wide tyres over the 23mm tyres commonly fitted to off the peg bikes. Doesn’t sound like much but those two millimetres prove size does matter.
Type: The fattest tyres your frame will take if you’re using a road bike; 1.25in or 1.5in ‘slick’ tyres if a mountain bike. If you’re carrying bags, then fatter tyres will help take the loads better. Take your road bike with you when shopping as there’s not space for particularly fat tyres in many modern road bikes.