Mountain Bike Tires 101

Rubber Compounds

The rubber in most tires can more or less look the same, but it’s not. Most tire companies are offering many of their tires in more than one rubber compound, and each variation can ride pretty differently. Some rubber compounds are hard, which tends to make for a faster rolling tire that takes a long time to wear out. Some rubber compounds are softer, which tends to grip really well in corners and on slippery rocks and roots.

A lot of companies will use a softer rubber compound for their side knobs to improve cornering traction, but use a harder compound on their center knobs to help out with tire durability and rolling resistance. Some companies will also use multiple compounds with a single knob, building the base of the knob out of a harder compound, and then capping it with a softer, grippier rubber.

Rubber’s hardness is quantified as its durometer. There are a few different durometer scales, but bike tires are usually measured using the “a” scale, so you’ll sometimes see a bike tire’s “stickiness” referred to as a number with an “a” after it. A 60a tire is a medium-hard compound that should last a relatively long time and roll fairly quickly. A 40a tire is quite soft, and will give great grip at the cost of rolling resistance and durability. While not all companies will specify the durometer of their tires, most fall somewhere in the 40a to 70a ballpark.

A tire’s durometer isn’t the full story though — there are all kinds of additives that are put into the rubber that can make it behave differently. Companies use varying amounts of carbon black, silica, graphene, and an assortment of other materials to help improve the rubber’s durability, grip, or rolling resistance.

Most of the companies have a variety of marketing terms for their rubber compounds. Here’s a rundown of the most common ones with some quick descriptions:

Bontrager

Bontrager doesn’t have any special names for their compounds, but it’s not too hard to find the durometers of many of their tires. Their XC tires tend to be 62a for faster rolling. Some of the trail and enduro use dual compounds (61a in the center for fast rolling, 51a on the sides for grip). Their DH tires are usually a bit softer.

Continental

• Basic / Single – Continental doesn’t provide any information on their single compound tires, but guesstimates place them at the harder end of the spectrum – around 60a.
• PureGrip – Again, Continental doesn’t provide a whole lot of information about the compound. It’s grippier than their basic single compound tires, but not as grippy as their BlackChili compound.
• BlackChili – Unlike most other companies, Continental’s BlackChili compound is a single rubber compound that has some additives to improve tire life and rolling resistance, while at the same time preserving grip. I’d put in the same neighborhood as other companies’ trail oriented compounds (e.g. Maxxis 3C Maxx Terra, or Schwalbe TrailStar), but slightly slower rolling and marginally better durability.

Hutchinson

• RR XC – a harder compound is used for the base of the knobs, capped with a medium compound for traction, and a softer compound on the side knobs for added cornering grip. The priority is faster rolling.
• RR END – a harder compound is used for the base of the knobs, capped with a medium-soft compound for traction, and a softer compound on the side knobs for added cornering grip. This is an all-around compound that hits a middle ground on rolling resistance, longevity, and grip.
• RR DH – a dual compound tire with medium compound knobs in the middle and softer compound knobs on the sides to increase grip.

Kenda

• L3R Pro – a single, medium hard 60a compound for fast rolling while retaining decent grip.
• Stick-E – a single, medium soft (50a) compound for good all around grip.
• RSR – the race version of the Stick-E compound that’s even softer (42a) and grippier.
• DTC – a dual compound that uses the L3R Pro (60a) in the middle, and the softer Stick-E compound
• (50a) on the side knobs for good grip while preserving some durability and fast rolling.
• DH DTC – A downhill oriented dual compound. Medium-soft rubber in the middle (50a) and extra-soft rubber on the side knobs (42a). Priority is on grip, while preserving some durability.
• R3C – prioritizes fast rolling. Appears to be a triple compound with the base knobs built out of a very hard compound and capped with a hard compound in the middle and a medium compound on the side knobs.

Maxxis

• Single – a single compound throughout the tread. Usually a medium-hard compound.
• Dual – medium/hard compound on the center knobs with softer side knobs for better cornering grip.
• SuperTacky – a super soft, slow rebounding rubber that maximizes grip.
• 3C Maxx Speed – a harder compound is used for the base of the knobs. The center knobs are capped with a medium-hard compound rubber, and the side knobs use a medium compound rubber. This compound prioritizes low rolling resistance.
• 3C Maxx Terra – a harder compound is used for the base of the knobs. The center knobs are capped with a medium compound rubber, and the side knobs use a medium-soft compound rubber. This compound prioritizes all-around performance, and hits a middle ground on rolling resistance, longevity, and grip.
• 3C Maxx Grip – a harder compound is used for the base of the knobs. The center knobs are capped with a soft compound rubber, and the side knobs use an extra soft compound rubber. This compound prioritizes grip and traction over longevity and fast rolling.

Michelin

• Magi-X – dual compound, with a softer, grippier rubber.
• Gum-X – single compound that’s on the harder end of the spectrum.
• Gum-X2D – a harder compound is used for the base of the knobs, capped with a softer compound for traction.
• Gum-X3D – a harder compound is used for the base of the knobs, capped with a softer compound for traction, and an even softer compound on the side knobs for added cornering grip.

Schwalbe

• Dual Compound – a medium-hard rubber compound in the middle and a medium soft compound on the side knobs.
• PaceStar – a harder compound is used for the base of the knobs. The center knobs are capped with a medium compound rubber, and the side knobs use a medium-soft compound rubber. The priority is fast rolling.
• TrailStar – a harder compound is used for the base of the knobs. The center knobs are capped with a medium-soft compound rubber, and the side knobs use a soft compound rubber. This is an all around compound that hits a middle ground on rolling resistance, longevity, and grip.
• VertStar – a harder compound is used for the base of the knobs. The center knobs are capped with a soft compound rubber, and the side knobs use an extra soft compound rubber. This prioritizes grip and traction over longevity and fast rolling.
• GateStar – a harder compound is used for the base of the knobs. The center knobs are capped with a medium compound rubber, and the side knobs use an extra soft compound rubber. This is designed for four-cross racing, with fast center knobs and max grip in corners.
• Addix Speed – the new replacement for PaceStar – a harder compound that prioritizes fast rolling.
• Addix SpeedGrip – a new compound developed for all around trail use that balances grip with low rolling resistance and longevity.
• Addix Soft – as the name implies, a softer compound that prioritizes grip while still trying to retain a bit of durability.
• Addix UltraSoft – prioritizing grip above all else. Super soft and slow rebounding.

Specialized

• Gripton – Specialized uses this compound on a bunch of different tires, and it appears that the compound varies a bit depending on the application, so it’s not always clear what exactly this compound designation means.
• Numbered Durometers – on a many of their tires, Specialized is really good about stating what the durometer is. Sometimes it’s a single durometer, sometimes it’s a dual durometer.

Vittoria

Vittoria doesn’t have specific names for its different compounds, but it does have two tricks up its sleeve:

• G+ Isotech – this is Vittoria’s catch all phrase for their rubber compounds that they’ve incorporated Graphene into, which (according to Vittoria) allows the rubber to behave both as a softer and harder compound as conditions require.
• 4C – a 4 compound mix. The base of the knobs are made of a harder compound in the middle, and a slightly softer compound on the sides. Those bases are then capped with a medium compound in the middle, and a softer compound on the sides.

WTB

• DNA – a 60a durometer, harder compound throughout for fast rolling and longevity.
• Dual DNA – a harder rubber compound in the middle, with softer side knobs to improve cornering performance.
• Gravity DNA – the base of the knobs are built with harder 60a rubber, and then capped with a soft 45a rubber to improve grip.

A Side Note on Front vs. Rear

Like with tire width and tread pattern, some people will run a softer compound tire in the front. Front tires don’t tend to wear out as quickly, so the durability issues that come with a soft compound are somewhat negated. And the softer compound will increase traction for the front wheel where it matters most.

Bead Type

The bead of the tire is the stiffer bulge that helps lock the tire on the rim, and there’s basically two varieties: folding beads, and wire beads.

Folding beads (also sometimes called aramid or Kevlar beads) use flexible strands of aramid fiber or some other similar material. They’re lighter than wire beads, and the tire can be folded on itself relatively easily. The vast majority of higher end tires use a folding bead.

Wire beads are heavier and stiffer because they’re made out of steel wires running the length of the bead. You’ll generally find wire beads on less expensive tires, but you’ll also find it on many downhill tires. The stiffer bead can help make the tire more secure on the rim, so in applications where the weight penalty of a wire bead isn’t as significant (i.e. downhill), a wire bead tire can be a good option.

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