JeffOYB

I've long heard it said that CX bikes are faster on a CX course than a MTB. So there's that.

Now why did UCI restrict tire width and even reduce it from 35 to 33? Are wider tires faster and thus 'cheating'? Where does the extra speed due to width end? ...Possibly wheels get faster as they become more like MTB wheels?

Feel free to spout here about CX vs MTB on CX courses and also about tire width...

I rode 28 tubies last year on my road bike. This season I finally have a real CX bike and am sporting 32 tubies. I've never tried 35's. ...I do have some cheap 35 clinchers and I recall they hurt my body to use them. But I wouldn't mind trying some sweet 35 handmades! I'm no UCI racer. I do love speed, flow and as much smooth cush comfort as I can get on a CX course, tho. Smoother equals faster to me. (I weigh 170 and ride my 32 tubies at about 25-30psi.) 35's seem like they might be smoother. I do have a pair of 38 Pasela clinchers I could try for fun. Those are sposed to be pretty nice tires. I've enjoyed them fairly much on gravel roads on heavy old steel bikes in the past. Might be fun to try em on my light new CX bike...

Andy_K 

To paraphrase the great Ulysses Everett McGill, it's a fool that looks for logic in the pages of the UCI rule book.

That said, if I had to speculate I'd say that they were trying to maintain the level of difficulty inherent to the nature of cyclocross. While it's true that wider tires are faster, especially in off-road situations, I think it's more likely that what's in view here is traction. Narrower tires require more skill in low traction situations. Limiting tire width forces riders to exhibit more finesse and thus keeps the sport truer to its roots. In this sense, I think that the tire size restriction is somewhat akin to the drop bar requirement.

There's a distinct challenge to cyclocross course design. Ideally a cross course should give cyclocross bikes an advantage over mountain bikes, but in the real world it can be tough to achieve that without having everyone complain about the race being a "grass crit." Course designers want to challenge riders and so they throw in lots of off camber sections, choppy descents and tight turns in sketchy conditions. A skilled rider can move a cross bike through these conditions with aplomb, but any hack can roll through them with a fat tired mountain bike.

At the amateur level the tire width limit is effectively a piece of trivia. In the races I've done there is almost always at least one person on a mountain bike with 2" tires. Once in a while someone will even bring out a fat bike. It doesn't matter. Ride whatever makes it fun.

JeffOYB

I was just wondering if basically a mtb would mop up the CX bikes hence the limits. Offhand it seems a little sad that this is so.

Maybe if there was more running the lighter CX bikes would win coz they're easier to carry. Ha...I don't mind CX bikes coming out on top even when if they do it by not being ridden!

I also don't really mind racing on gear that is supposedly slower. To me I suppose it's why I like CX: the terrain around here is so gentle that MTB's really aren't much fun to ride, but a CX bike can give a thrill even in a simple park: because, as you mention, they're trickier than a MTB for the given terrain.

Andy_K 

Most of the time, I think, cross bikes have a big advantage over cross bikes on a well designed cross course. There are a few courses around here where savvy riders will opt for a mountain bike, but in general I think mountain bikes are a handicap.

Erik Tonkin took second place in the A's at the first race of the year while riding a mountain bike and wearing a T-shirt and jeans. Mostly, I think, that's just because he's an animal and just plain fast. The race was mostly very flat and very fast, but it did have two steep-ish dirt climbs out of a little ravine where the mountain bike had an advantage. A lot of the people in the upper ranks could ride those hills on a cross bike, but I suspect the mountain bike made it a lot easier. But the course also had a lot of well-trimmed grass and pavement that had to have been better for the cross bikes.

One feature that can really put the hurt on mountain bikes is sticky mud. There was a race last year at a local motocross track where I decided to take my mountain bike out on the first lap, but I left a cross bike in the pit just in case. The mountain bike was great for a lot of that course, but there was a section of thick mud that stuck to my tires and turned the bike into a serious boat anchor. I couldn't wait to get to the pit and change it out.

grolby

The rule change was specifically intended to make it easier for less well-supported riders to be competitive with better financed racers. The logic being that, with a smaller range of allowed widths, fewer sets of wheels would be needed by everyone (remember, an elite rider on tubulars needs at least one set of wheels for every pair of tires). Performance didn't really have to do with it. It's a seriously misguided rule, as it does very little to mitigate the problem. The best-funded pros still have an enormous quiver of tire tread patterns to choose from and at least one spare for each tire. It's also frustrating, because the difference in volume between a 32 and 34mm tire is pretty substantial. Because a 32mm tire is so marginal, the racers who can't afford to have a full quiver of wheels are if anything even more screwed if forced to race the wrong tire for the conditions.

Personally, I don't think there should be any restrictions on tire width for cyclocross. I'm sensitive to the defense that cyclocross bikes should not become mountain bikes, but I don't think there's much danger of that. On a real CX course, there's a point well below MTB tire widths where I think the added mass and inertia will be more of a hindrance. I'm curious about where that crossover point is, but I don't think it's much above 700x35.

idc

Huh, I'd never read that. Interesting, and it makes sense.

I ride between 30mm and 33mm tires, but mostly ride on wider ZTR/Iron Cross rims - I feel sometimes that even 32mms (which measure out to about 34mm) feel almost too wide and actually slow you down. With narrower tires / higher pressure you're actually cutting through a lot of stuff and reducing rolling resistance - of course at the price of cornering/handling grip.

I imagine for most courses a CX bike will be faster than a MTB for a given rider between the barriers, run-ups, constant up + downs, and faster sections.

fietsbob

Not a Licensed racer in a UCI event ?, Why does it matter? ask the UCI rules Committee members If it burns your Soul not Knowing..

maybe Grolby can footnote that statement from the UCI documents,.. IDK.

Cyclocrossworld.com I saw sold a UCI Reg measuring width caliper , they play in the big leagues..




we just have a Crab shell width caliper to tell whether they have to be thrown back in the water.

grolby

The UCI rulebook does not give commentary on the rationale behind the rules. I remember when this rule change happened (it was pretty recent, early 2011 I think? Same time as the rule change to allow disc brakes). The discussion about this particular rule was largely focused on whether it would achieve the intention of making riders with less support more competitive. It was pretty much universally understood, from what I saw, that this was the reason for the rule change. So I'm a little surprised that no one seems to have heard that before.

But you know, if you're not racing UCI, it just doesn't matter. USAC has no width restriction whatsoever. I'm racing on 32mm tubulars because I anticipate upgrading to Cat 2 and being able to enter UCI Elite races (though that was derailed when I broke my collarbone last month) and don't want to have to purchase and glue a new set of tires if/when that happens... but if an upgrade doesn't seem fairly imminent, or there aren't UCI events in your region, there's no reason to handicap yourself with skinny tires.

LesterOfPuppets

I think it had a lot to do with the availability of nice XC 29er tires. People building monster cross bikes wit 48mm tires on that can really rail corners and float over rough stuff. Maybe it was sub-15 lb. MTBs they feared - Open ORA Ltd, anyone?

grolby

No. Tire width was already limited to 35mm in UCI races. Even without a limit, MTB-wide tires are probably well past the crossover point for cyclocross where big tires are more of a liability than a benefit. So far as I'm aware, "monster cross" is limited to a very specific contingent of North American enthusiasts who don't actually use them to race cyclocross very much. There are no tire width limits in USAC races, but you don't see a lot of MTB tires on non-UCI podiums.