Will Shaw busts mountain biking's biggest myths
You have to have wide rims
This myth is seemingly supported by the industry moving to wider rims every year. Despite this, take a look at a World Cup Downhill or an EWS and you’ll see many riders opting for narrower rims. An example is the ever-popular DT Swiss EX471, which sports a 25mm internal width.
Without retreading old ground, wider rims provide better support for the wider tyres that are now commonplace from XC through to Downhill. A wider rim makes the tyre less balloon shaped and more of a supported profile. This increases lateral tyre support and allows for lower pressures with less risk of pinch flatting or burping.
Last year we visited DT Swiss’s headquarters in Switzerland. Andreas Tschanz, one of their rim engineers told us that rim width selection goes hand in hand with tyre selection.
“It's a combination of rim width and tyre width, so you cannot say what rim width is the best. Too wide and you no longer gain benefits, but it also depends on the tyres.”
So, are wider rims better? It really depends. We’ve found that around a 30mm internal rim width for 2.4” or so tyres is a sweetspot for everything from cross-country to aggressive trail riding. What about when you’re putting on a full-face? We’ve found a slightly narrower internal width (even just on the rear) paired with a sturdier tyre casing can result in less tyre roll as well as less mechanicals like pinch flats and cut tyres.
Lower tyre pressures are always better
Going hand in hand with rim widths, the idea that you want lower tyre pressures has gained traction in recent years. Despite the increase in grip, the lower you go, the higher the risk of pinch flatting. The potential for tyre roll and burping is also greater.
We’ve covered this myth in more depth in the past, and we found it’s best to do some experimenting with your setup. Factors such as where you’re riding, your riding style and what type of rim/tyre setup you have all play a role in determining the ideal pressure.
The emergence of tyre inserts has also encouraged riders to drop their pressures. We’ve been dropping our pressures between 2-4psi front and rear when using inserts such as CushCore.
One area where we’ve seen a shift to lower pressures as a result of rim and tyre widths is XC racing. Nino Schurter is now running 2.4” XC tyres mounted on 30mm internal rims and runs his pressures in the late teens. Only a few years ago pressures were closer to 30psi, internal rim widths were around 20mm and tyres hovered around the 2.0” mark!
Are lower pressures always better? It really depends. We would recommend dropping your pressures a couple of psi if it’s something you haven’t tried, as the difference in grip and comfort can be staggering. If you’re an aggressive rider who’s flatting regularly, an insert in the rear or a sturdier tyre casing are worth a look if you’re running rock hard pressures to compensate.