USA Cycling / UCI tire width rules for the cyclocross national championship

November 09, 2019

Probably the most common question asked by riders new to cyclocross is: "Can I use a mountain bike? Isn't it over the maximum tire width?" At local, casual, amateur races, the answer is almost always "yes" - bring whatever bike you have, come out, have fun, no worries about the size of your tires. 


These riders have those concerns because they've heard that that cyclocross has a maximum tire width rule - 33mm - and they're right, it's just that those rules are typically not in place at races that aren't held under the UCI umbrella. For the most part, this means that amateur racers never have to worry about the tire width rule - only elite riders who race at UCI-sanctioned events do. EXCEPT for national championships events. 

Not understanding the rules can be a serious "gotcha" and it's important to understand the details in advance. Even worse, the tire width rule, specifically in place at national championships, is enforced differently, or not at all, depending on your race category!

Three-tiered system

There are essentially three tiers - first, the "UCI" tier which applies to Elite, U23, and Junior 17-18 riders (max 33mm), "UCI Light" (35mm), for Masters categories, and "USAC" Juniors under 16 - for which there is no width restriction at all. 

Short summary of tire rules for the cyclocross national championship

  • Juniors under 16, no tire restrictions
  • Elite, U23, and Junior 17-18, max 33mm
  • Masters, max 35mm

In case you were wondering - no studded tires are allowed, regardless of category. So if the race happens to be on snow, leave the spiked/studded ice tires at home. 

Additional factors to consider

Tires are often wider than their label, and might violate the tire width rules despite their published width. So just having a tire labeled "33" or "35" isn't a guarantee of safety. This is most common when mounting tubeless tires to extra-wide rims, which can push the width of the tire slightly out of compliance. 

So if you're heading to nationals, which cyclocross tires are "safe" and pass the width rule?

Recommended Tires 

  • Tubular tires marked 33mm or less, which should include every common tubular tire designed for cyclocross racing from Donnelly, Challenge, Vittoria and so on should be safe for the "UCI" tier (Elites, U23, Juniors) as well as the "UCI Light" tier (Masters)
  • Tubeless tires specifically designed to be UCI 33mm compliant, such as the new Donnelly PDX WC. Gage Hecht recently rode these to 2nd at the UCI PanAm champs, so we know they're in spec and should be safe for both the "UCI" (33mm) and "UCI Light" (35mm) tiers. 
  • Tubeless tires marked 33mm for the Masters / UCI Light category, are likely to be OK - even if they inflate slightly larger than 33mm, they'll still be under the 35mm limit for Masters. That would include the Challenge Grifo/Chicane/Limus TLR models and Donnelly PDX, MXP models.

Which tires aren't "safe"? 

  • Any tire marked 36mm, 38mm, 42mm, or more. For the most part these are clinchers used for gravel cycling, it's unlikely such tires will be given a pass at a national championship event. Fine for training but don't expect to be permitted to race on them. 
  • Tires that are obviously way outside the rules, like any mountain bike tire in the "UCI / 33mm" or "UCI Light 35mm" tiers. 

Which tires are "borderline"?

  • Tubeless tires marked 33mm, especially if you've mounted them to modern, disc-only, wide tubeless rims that are common today but weren't 5 years ago, may not make the cut in the "UCI / 33mm" tier. Such rims change the shape of the tire, making it wider, violating the 33mm rule. They might also be just fine, but measure in advance to be sure, with the tire mounted on the actual rim you plan to use. 

The gauge itself is simple - I've seen officials using a "U" shaped wooden block (presumably with a 33mm or 35mm wide slot) in the starting grid. That's easy to approximate at home, before you choose equipment and travel. 

Finally if you want to read the fine print for yourself, check out the Cyclocross equipment FAQ at USA Cycling. 

Good luck!

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