All you need to know about bike tyres, plus how to choose and maintain your tyres

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Published: Monday, 26 August 2024 at 13:00 PM

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As your one point of contact with the road or trail, your bicycle’s tyres do a lot of work.

Tyres have to provide the grip you need without slowing you down unduly. They need to stay inflated and keep going for thousands of miles without needing to be replaced. They need to be comfortable, acting as a primary source of suspension, and they need to transmit your power and steering to the ground.

For a seemingly simple part of your bike, tyres are surprisingly complex, and a lot of R&D goes into bringing a new tyre to market.

They’re also highly specialised to suit the type of riding you do – whether that’s a time trial or a downhill mountain bike race. 

We’ll delve here into the types of bike tyre, the component parts that make them up and how to keep yours safe and working well. 

Types of bike tyres explained

The original bicycles back in the 19th century, including penny-farthings, had solid tyres. 

As you’d expect, their ride quality wasn’t great. It was John Boyd Dunlop who, in 1888, patented the pneumatic bike tyre and ushered in an era of smoother riding.

The air in a pneumatic tyre helps cushion the ride by acting as a spring, and does so with little energy loss, so you can ride faster too. 

Bike tyres have become ever more technical, efficient and adapted to their proposed use:

• Road bike tyres: Are designed for low rolling resistance, low weight and high grip on paved surfaces. The best road bike tyres are typically narrow and incorporate little tread. Winter or endurance road tyres are more substantial and include more tread. Specialist lightweight road bike tyres are used for time trials and triathlons
• MTB tyres: Provide grip on off-road rides, with a pronounced tread pattern and a casing designed to withstand impacts. The best mountain tyres are highly specialised for the different disciplines.
• Commuter bike tyres: Are typically wider and more robust than road bike tyres, have a tread and may include reflective details
• Gravel bike tyres: Come somewhere between road and MTB tyres, being wider than the former but narrower than the latter. Gravel bike tyres usually have more tread than road bike tyres and are, generally, designed to be used tubeless
• Cyclocross tyres: Offer grip for racing off-road, but are typically narrower than gravel bike tyres, to comply with regulations governing officially sanctioned cyclocross races
• Tyres for folding bikes: Are designed for the smaller wheels typical on folding bikes
• Electric bike tyres: Are engineered to handle the greater torque, power and weight of electric bikes. Tyre makers may have a separate range for fast electric bikes, capable of assistance above the normal 25km/h (20mph) speed limit
• Fat bike tyres. Fat bike tyres are, well, fat. They’re good for riding in sand, snow and bogs, but for other surfaces they’re heavy and slow
• Kids’ bike tyres: Come in smaller sizes to suit younger riders

How do bicycle tyres attach to a wheel’s rim?

There are three main types of bicycle tyre. All use different combinations of components to mount to the rim. A variant is the solid tyre, which we’ll also talk about.

Clincher tyres

The most common type of bicycle tyre is the clincher.

In this system, the tyre is an inverted U-shape with a rounded bead on the edge of the casing. The bead is held against the inside edge of the rim by the pressure inside the tyre, holding the whole tyre safely in place. For a standard clincher system, hooks on the rims help to keep the tyre on the rim. 

Air is held in an inner tube with a valve, which protrudes through the inner side of the rim to enable the inner tube to be inflated.

Tubeless tyres

Tubeless tyres are a variant of clincher tyres, where, as the name suggests, there’s no inner tube.

Instead, an airtight seal between the tyre beads and the rim holds air in the tyre. Liquid sealant, usually based on latex, is added to the tyre to help ensure it is airtight.

Unlike with a standard clincher, the wheel rim itself needs to be airtight. This may be through a continuous rim bed, or the rim may need to be taped.

A separate valve screwed to the rim is used to inflate the tyre.

Even in tubeless tyre systems, there are often hooks to the rims, which also help ensure tyre retention. But hookless rims are increasingly common, particularly in MTB wheels. These rely on tyre pressure and tight tolerances between the tyre beads and the rim to keep the tyre in place. 

Hookless rims are now a feature of many road and gravel bike wheels too, although they impose limits on the tyre pressure you can use, with ISO standards recommending a tyre pressure lower than 5 Bar/72psi. 

Tubular tyres

In a tubular tyre, the tyre casing is sewn together on its inner side, fully enclosing the inner tube like a sausage.

A tubular tyre is then glued to a rim with a shallow dished profile, which lacks sidewalls.

This enables the rim to be made lighter and there’s a degree of run-flat capability, both of which have made tubular tyres popular with road racers and cyclocross riders.

But tubulars are expensive, tricky to mount and even trickier to repair. Some types of glue used are toxic.

Rolling resistance has been found to be, typically, greater than tubeless tyres.

Tubs are now becoming a niche product, mainly confined to elite cyclocross competition, but a few exceptions remain in the WorldTour ranks.

Solid tyres

Another niche product, solid tyres – also called airless tyres – work with a clincher wheel rim, but are made from a material similar to running shoe soles.

The absence of air means no punctures, but solid tyres are typically difficult to install, their ride comfort isn’t a match for pneumatic tyres and their rolling resistance is significantly higher.

Bicycle tyre construction

Bicycle tyres are surprisingly technical. Tyre makers put a lot of research and development into their casings, rubber compounds and construction to optimise a new tyre’s performance for its intended use. 

That extends to all the components of the tyre, which we describe below.

Casing

The tyre casing, or carcass, is made up of one or more layers of fabric, usually nylon or cotton, which ensure the tyre’s structural integrity.

There are typically at least two layers, usually more, to ensure the tyre is robust enough for its intended use. 

The number of layers may vary across the width of the casing in some cases, with more in the sidewalls and fewer under the tread. 

How fine the material in a casing is will usually be expressed in threads per inch, or TPI.

Cotton tyre casings typically have much higher TPI counts than nylon casings. This results in a more supple ride, although cotton tyres’ longevity and resistance to cuts and abrasion may be less.

The TPI count is usually expressed as the sum of the threads in each layer of the casing, so a casing made up of three 40 TPI layers will be shown by a manufacturer as having a 120 TPI count.

Bead

In clincher and tubeless clincher tyres, a bead at the outer edges of the casing helps to hold the tyre in place. 

In a non-folding tyre the bead is generally made of steel wire.

In a folding tyre it is made of a non-elastic material such as aramid, Kevlar or carbon fibre.

Tubeless tyres need to have the best-performing bead material to ensure they don’t stretch off the rim.

The bead material is moulded within a layer of rubber to help keep it in place on the rim and, for tubeless tyres, keep the tyre-to-rim connection airtight. 

Tread

The tread is the part of the tyre that grips the road or trail surface. It’s made of a rubber compound, which will include additives such as carbon black to improve performance. 

While road bike tyres typically have little or no tread, the tread pattern varies by use, with MTB tyres usually having aggressive treads to ensure grip.

Gravel and cyclocross tyres may also have a significant tread pattern, depending on their intended usage.

The tread is typically fixed to the tyre casing in a process called vulcanisation, where heat and steam bond the two together.

The alternative is to glue the tread to the casing, which is used for most cotton tyres.

Compound

The rubber compound used for the tread will also vary depending on the tyre’s intended use.

Softer compounds may increase tyre grip, but at the expense of longevity.

The compound will typically include additives such as silica or graphene, which can reduce rolling resistance.

Sidewall

The tyre’s sidewall extends from the edge of the tread to the bead.

It’s comprised of the tyre’s casing fabric, but is usually coated with rubber to make it more robust and airtight. 

Other tyre construction features

There are other features that make up a bicycle tyre, which may improve its appropriateness for its intended use.

Puncture protection

Most bicycle tyres include a puncture protection layer under the tread. This is made up of a denser material, which is better able to guard against penetration than the casing fabric.

Materials used and their brand names differ by the tyre manufacturer, but Kevlar or denser nylon fabric are typical components.

It’s possible to add a separate tyre liner insert to a tyre to increase the level of puncture protection.

Some tyres designed for specific uses, such as lightweight time trial tyres, may omit the puncture protection layer.

Knobs and studs

Knobs are rubber protrusions in the tyre’s tread. They are most often found on MTB tyres and offer grip for off-road use. They may also be a feature of some gravel, cyclocross and specialist road and commuter bike tyres. 

The knobs’ pattern and their depth will vary with intended use. Knobs may incorporate siping – slits in the rubber to improve grip.

Specialist tyres for use on ice and snow may include metal studs screwed into the rubber studs to cut into the frozen surface.  

Reflective details

Tyres, particularly those designed for urban use, may include a reflective strip in the sidewalls to increase road presence at night.

Bicycle tyre sizes

There’s a huge range of bicycle tyre sizes – or more accurately internal diameter – depending on the wheel diameter they’re intended to fit.

Road bikes are typically fitted with 700c tyres, although in some cases smaller 650b tyres are fitted to smaller frame sizes.

Gravel bikes, too, may use 700c or 650b tyres.

MTB tyre diameters are usually expressed in inches, reflecting the origin of MTBs in the US. Their typical tyre diameters are 29 inches or 27.5 inches. 

These MTB tyres are equivalent in diameter to 700c and 650b tyres on road bikes, although tyres aren’t usually interchangeable between road bikes and MTBs due to the difference in tyre and wheel rim width. It may be possible to use MTB tyres on some gravel bikes though. 

Previously, MTBs rode almost exclusively on 26-inch wheels and tyres, but these have largely been superseded by the larger-diameter tyres on modern MTBs for their superior traction and roll-over. 

Commuter bike tyre sizes are also often expressed in inches, although confusingly 700c/29in tyres are sometimes marketed as 28in tyres when they’re designed for commuter bikes. You can also find 27.5in and 26in commuter bike tyres.

Some larger children’s bikes have 26in tyres, although 24, 20, 16 or 12 inches are more common sizes, reflecting the different-sized bikes required for younger children.

Folding bikes typically have small wheels and tyres too, with 20 inches a common size, although some folders – including Bromptons – use 16in wheels and tyres.

Fat bike tyres are massive. They usually start at 3.8in and can reach 5in wide. They typically hold low pressures and roll on 26in, or sometimes 27.5in, wheels.

Bicycle tyres and rim widths

The array of different tyre sizes and rims to which they fit means there needs to be some standardisation. That’s ensured by ISO standards, which in turn follow those defined by the European Tyre and Rim Technical Organisation, or ETRTO.

You’ll find ETRTO size markings on all bicycle tyres, even though they’re marketed by their more usual 700c, 27.5in, etc. designation. The ETRTO tyre sizes are defined by the the nominal tyre width in millimetres and the nominal tyre bead diameter, so a road bike tyre might have an ETRTO number of 25-622, indicating it’s 25mm in diameter and will fit on a 700c wheel. 

Why is it called 700c? Read our explainer for more detail.

Principal ETRTO tyre sizes

You can find a tyre in pretty much any width you choose. In contrast, there are specific tyre diameters, designed to fit properly on a specified rim height. Here’s a list of ETRTO tyre diameters and typical widths, along with the types of riding they’re used for.

Nominal versus actual tyre width

You’ll note the use of ‘nominal’ above. The actual tyre width for clincher and tubeless tyres will depend on the internal width of the rim.

This has steadily been growing for both road and MTB wheels. 

While 15mm internal width rims were typical for road bike wheels a few years ago, most road bike wheels now have internal rim widths of over 20mm, with many wheels from Zipp, for example, now measuring 25mm bead-to-bead. 

Older MTB rims might have measured around 25mm internally, while newer MTB rims are typically between 30mm and 35mm wide.

This internal rim inflation has resulted in actual tyre widths being significantly greater than their nominal widths, with a 28mm tyre often measuring over 30mm across when mounted on a modern road bike wheel.

To counter this, you’ll sometimes see width-as-measured, or WAM, quoted. Promoted by Gerard Vroomen, co-founder of Cervélo, WAM helps ensure your tyre will fit in your bike frame with adequate clearance.

Bicycle tyre inflation

Keep your tyres inflated to the correct pressure. 

Determining what this pressure should be isn’t easy. It will depend on factors such as tyre width, tyre type, the surface you’re riding over, whether it’s wet or dry and your weight. There are online tyre pressure calculators you can use: try those from Zipp or Silca.

Under-inflation will increase rolling resistance and risks damaging the tyre sidewalls. The tyre may be unstable when cornering and braking, and can even roll off the rim. 

Over-inflation risks a tyre blow-out or it blowing off your rim. It also lowers grip and makes the bike’s ride uncomfortable and jittery.

It’s worth investing in a floor pump with a gauge to get your tyre pressure right pre-ride, in addition to a mini pump to carry in case of a puncture while out riding. 

Essential bicycle tyre maintenance

Beyond keeping your tyres correctly inflated, there are some basic checks that you should carry out regularly to make sure your tyres are safe to use:

• Check for wear: Tyres usually have wear indicators in the tread. Often these are small dimpled depressions in the rubber. When these disappear, it’s time to change your tyres. If your tyres don’t have wear indicators, deflating your tyre and seeing how thin and flexy the centre of the tread feels provides an indication. If your casing is showing through the tread, you’ve left it too long, while for MTB tyres rounding-off of their knobs or a loss of grip are good indicators they are worn. In all cases, rear tyres usually wear quicker than front tyres.
• Check for tread damage: Check your tyre tread for cuts. You may also find small pieces of glass, flint or other debris embedded in the tread, or in the sipes in MTB tyres. Use the end of a sharp knife to prise these out before they can penetrate deeper into the tyre and cause a flat.
• Check for sidewall damage: You may get a cut in a tyre sidewall, but abrasion damage is more common. In both cases, this may cause a tyre failure, so it’s important to replace your tyre if the damage might be risking your tyre’s structural integrity. If an inner tube is protruding through the casing, you can insert a tyre boot to get you home, but replace the tyre promptly. Cracks in the sidewall may occur if the tyre is old or has been persistently underinflated.
• Check for damage at the bead: There might be damage at the bead, if the tyre has bottomed out on the rim. A more common cause with rim brake wheels is the brake pad rubbing on the tyre when braking. Make sure that your rim brake pads are properly aligned to avoid this and replace them if they are worn. If significant tyre damage has already occurred, replace your tyre.
• Keep sealant topped up: If you’re running tubeless, tyre sealant will dry out over time. Pop a tyre bead regularly to see if there’s still liquid sealant inside the tyre and top up if not. How often you need to do this depends on the conditions and the sealant you’re using; you may need to do this monthly or you may be able to leave it for six months or more. 

Knowing how to change a bike tyre is an essential skill for cyclists, both at home and when out riding. Make sure you have the tools needed: two tyre levers, a mini pump when out riding and a track pump for home use, a spare inner tube (even if riding tubeless), a puncture repair kit or a tubeless repair device and plugs, and a tyre boot. 

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