Muddy tires were yesterday

It's raining cats and dogs and the race track at the Swiss Cross-Country Championships in 2000 turns into a veritable mud bath. The tire choice: 1.5 inch wide mud tires with a high, open spike profile. Apart from the fact that the 26-inch wheel size has long since died out in racing, such tire dimensions are also unthinkable in cross country today.

If tires are fitted for mud races, the same treads are usually used as otherwise when a little more grip is required. The dimensions are then between 2.0 and 2.25 inches, depending on the manufacturer and taste.
The demands on traction, rolling resistance and damping have become so high that narrow tires with extreme treads can no longer keep up. However, one reason for this is that extreme races with a lot of grass have become rare - most cross-country routes are more weatherproof than they used to be.

But here too, there is no rule without exception. In the short track race at the World Cup in Val di Sole, Italy, Mathias Flückiger relied on the additional grip of tires with a 29x2.00 inch spike profile. The rain had previously turned the track into a slushy mud arena. In such conditions, narrower tires generally offer better grip than wider ones. The latter tend to float easily in mud.

Why wide?

Tires around 2.5 inches were established early on in downhill riding and are still considered the standard today. They offer better grip and more cushioning. With the advent of plus-size tires (2.8/3.0 inch) on trail to enduro bikes, the rethink in cross-country racing also began. Inspired by the "width craze", wider tires were suddenly being ridden where light and narrow had long been considered faster.

The 2016 Olympic Games were the impetus for the Swiss cycling association Swiss Cycling to carry out extensive tire tests. Roughly summarized, these showed that the rolling resistance of wider tires on wide rims is lower than with conventional tire and rim dimensions. The advantages of this were also greater than the weight reduction when using narrower tires.

In cross country, rim and tire widths have grown to such an extent that today they differ only slightly from those in downhill. Whereas Nino Schurter used to ride with 2.25 inch tires, today he rolls from success to success with 2.4s. Kurt Gross, Lars Forster's mechanic at Scott-Sram, reveals: "The air pressure has also dropped significantly. Whereas we used to ride with 1.5 and 1.4 bar on the rear and front wheels, we now fill the 2.4-inch tires with 1.25 and 1.15 bar. We achieve less rolling resistance and the riders tire less quickly."

Width comparison: The 2.4-inch wide Maxxis tires, as ridden by the athletes of the Scott-Sram team, measure between 60 and 61 millimetres, depending on the air pressure. A 2.5-inch downhill tire from the same manufacturer on the same rim width measures just over 62 millimetres wide.

The deep reach into the all-mountain drawer

The trend towards wide tires was not the only thing that was copied from all-mountain bikes. Wider tires also require wider support, as they would otherwise tip over in extreme lean angles - known as burping - or be too round, which would cause the tread to lose its effect. However, cross-country rims were always too narrow to provide sufficient support for the fat tires. So at the beginning of this trend, wider all-mountain rims were used without further ado and the additional weight was accepted.

Not all manufacturers are ready for wide yet - but the riders are

Some riders, however, are not yet riding at the current optimum. Nicola Rohrbach, for example, admits: "My tires are not yet tailored to 30-millimetre rims, but I still don't want to do without the advantages of the wider support."

He inflates the 2.2-inch wide Chaoyang tires to 1.4 bar at the rear and 1.3 bar at the front. On rough roads, he also uses tire inserts as puncture protection. Rohrbach also reveals that his tire sponsor is working flat out on new tires that are matched to the wide rims.

The situation is similar with Schwalbe tires. The current widest versions of the 29-inch cross-country models are 2.25 inches wide. "Some people like to ride them on the 30 mm rims, but Mathias Flückiger, for example, doesn't. He currently prefers to combine them with 25 millimeter wide rims, as the riding characteristics are better for him," says Thömus-RN team owner Ralph Näf. But wider versions for cross-country use are also set to come from Schwalbe soon.

In the BMC racing team, the athletes also ride on rims with a 25-millimeter rim width. However, they differ in their choice of tires. Chief mechanic Sylvain Gollay says that Titouan Carod and Julie Bresset are still riding more traditionally with 2.1 inch wide Vittoria tires. Carod in particular appreciates the easier acceleration of the narrower tires.

Meanwhile, Lukas Flückiger and Reto Indergand ride with 2.25-inch tires. Although they do not fully exploit the current possibilities of their team sponsors Vittoria and Cyp-Wheels in terms of dimensions, they have found their optimum in this combination. The difference to Carod's 2.1-inch setup with a measured width of 54 millimetres is just over three millimetres, which is already a significant difference.

The Continental tires of the Superior XC team, which includes Linda Indergand and Fabian Giger, are in a similar size range. Here, too, they rely on the results of rolling resistance tests, reveals mechanic and team co-owner Fabian Haug. The most common profiles, "RaceKing" for dry to medium conditions and "CrossKing" for wet conditions, are ridden in 2.2 inch widths.
The team also relies on 30 millimeter wide rims, explains Haug and adds: "In tests, our drivers clearly felt the difference compared to the 25 millimeter rims. The rollover behavior is better and burping also happens less."

Florian Vogel does his fast laps with prototype rims from Mavic. "These now also have an inner width of 30 millimetres. This allows me to ride with lower air pressure and the same rim tension," says the recent European Championship medal winner. The wide rims have clear advantages, Vogel continues: "At the World Cup in Andorra, I lost air and had to ride to the transition zone with 0.8 bar in my tires. Despite the low air pressure, I hadn't pushed the tire off the rim."

Tyres and rims are one system

The manufacturers are now busy tailoring tires to fit the wider rims, as in the Maxxis example. "Maxxis has adapted the shape of the new tire models to the rim shape of the XRC rim from DT Swiss. This is the ideal case, because the rim and tire have to be understood as a system," reveals Scott-Sram mechanic Yanik Gyger.

However, rim manufacturers also have a role to play in development. Producing rims that are as light as possible and laterally stiff enough is no longer enough. They have to be robust enough to withstand punctures undamaged. At the same time, they are also expected to have high damping properties so that as few vibrations as possible affect the body.

It is unlikely that the trend will soon be towards even wider tires. But we are approaching the Olympic year again and testing will continue - also in terms of rolling resistance. So there is still plenty to develop and optimize when it comes to tyres.