Is a true 33mm CX tire faster in a CX race? (vs a gravel tire)?

[rothwem]

I’ve got a Crux from 2021 (the previous gen) that I’ve been using as a gravel bike for 4 years now and it’s pretty good at that. It’s got 49mm between the stays, and I run a 38mm Specialized Tracer on a 25mm internal rim that inflates to ~41mm. I wouldn’t hate a bit wider tire for gravel, but it is what it is. It works well.

I’m going to be racing 4-5 CX races this year, none of which will be observing the max width of 33mm, so I’m planning on just using my 41mm Tracers as usual. However, in talking with a couple guys I ride with, they all think I’m nuts for not “investing” in some 33s, with the belief that my 38mm tire is waayyyy slower. I’m not sure I’m sold, this sounds like old thinking to me. However, I’m finding myself with an extra road disc wheelset and I was thinking of giving it a try. So is a 33 “actual CX tire” any faster than a ~41mm tire in any CX racing situation?

[.RJ]

sounds like a bunch of roadie nonsense to me

I would wonder if a really good 33mm tubular might be a little better in some conditions, but I cant see a 33mm clincher being faster. Challenge sells the Grifo in 38mm tubeless, if i remember.

[prototoast]

The max CX tire size is a binding constraint of the rules, not an optimized value.

The widest tire you can fit in your frame that still gives you enough mud clearance for the conditions will be fastest.

[fredd]

yeah agreed that wider should be faster for most scenarios, you just wanna make sure that your tire is knobby enough for slippery races depending on where you are

[Gummee]

I don't like the way my '38c' Vittoria tubeless tires feel when turning on the CX course. The casing is marked as 40, but since 38c is legal, that's what the label says.

They feel like they're going to fold under at the pressures needed (appx 30psi) to smooth out the clumps of grass in the CX courses that I typically ride.

Straight ahead? Feel great. Turning? Ugh.

Add to that the toe overlap with the bigger tires and I'm going back to tubulars.

YRMV

M

[robt57]

Being a clyde @ 215 lb. My 33 is a 37 basically. I'd still use 33s if I hit a CX course, mainly because I have a few wheels with tubulars and few different CX tire.

The tubeless PDX tubulars have enough advantage over even a bigger clincher IMO. Not least of which is no burping or pinching if tubes are in play. But I doubt there is a tube to bee seen in a CX race for quite some time.

If anyone with more contemporary empirical CX experience wants to state contrary, I am ear wide open.

[superbowlpats]

I have both tubular (33C Limus and Baby Limus) and tubeless wheels for CX (38C Grifos). Unless the course has a horrendous amount of mud I'll take the 38C all day and every day.

[cgolvin]

Perhaps the mods should move this over to GD?

[rothwem]

Originally Posted by cgolvin

Perhaps the mods should move this over to GD?

Aw crap. Didn’t realize I’d posted this in the classifieds. Yes, please move.

[AngryScientist]

moved to GD.

I think it depends at least a bit on the course.

I do not think the blanket statement that the widest tire you can run with adequate mud clearance is universally the fastest tire for a given course.

[redir]

I thought that 32 was the widest allowed in CX but that may have changed since I was racing. They probably don't care for cat 4/5 though, check the rules. I used to have 4 wheel sets with various treads and sizes. If it's a packed hard dry course then a thinner tire with a file tread is faster. If it's a muddy course then the fattest knobby tire is best.

[Mark McM]

Originally Posted by redir

I thought that 32 was the widest allowed in CX but that may have changed since I was racing. They probably don't care for cat 4/5 though, check the rules. I used to have 4 wheel sets with various treads and sizes. If it's a packed hard dry course then a thinner tire with a file tread is faster. If it's a muddy course then the fattest knobby tire is best.

33mm is the maximum tire width for UCI cyclocross races. But in the US, most (local) races are run under USA Cycling rules. Under USA Cycling rules, only National Champsionships restrict tire widths to 33mm - and then only for Elite, Junior 17-18, and U23 races. Master National Championships restrict tires to 38mm. For other (local) races, you can use any tire width you want (and can also use MTBs or gravel bikes if you so choose).

As to whether a wider tire is faster in some cases, it might be interesting to look at why the UCI has a 33mm tire width restriction. When MTBs started being produced, it became obvious that these bikes with their fatter tires could be an advantage on certain courses, and in fact some racers would use mountain bikes in some races. But the UCI management is full of codgy old guys who didn't like the look of these new fangled bikes being used in "their" races. So to block the use of MTBs, they instituted a restriction on tire widths (and a few other new-fangled things), to makes sure that competitors used bikes "looked" like they "should" (whatever that means).

So the fact that the UCI (despite their backwardness) even had to create a tire width restriction means that some competitors wanted to use wider tires, and they wouldn't have wanted to use wider tires unless they were faster, at least in some cases.

[Gummee]

Originally Posted by redir

I thought that 32 was the widest allowed in CX but that may have changed since I was racing. They probably don't care for cat 4/5 though, check the rules. I used to have 4 wheel sets with various treads and sizes. If it's a packed hard dry course then a thinner tire with a file tread is faster. If it's a muddy course then the fattest knobby tire is best.

For UCI races, it's still 33c

For non-US cycling races, it's still run whatcha brung till you get to CX Nats and then it's the 38c limitation

HTH

M

[Mark McM]

Oh, and for a little irony about the UCI 'cross tire maximum width:

When the 33mm maximum width rule was created, this width was much wider than typical road racer used (but still a lot narrower than MTBs of the time). The 33mm width was for the entire tire, including knobs that stick out from the casing. Which means the casing width alone might be closer to 30mm or so. Today road racers are using 28mm and 30mm labeled tires on wide rims, which means the tire often expands out to about 32mm. So road racers may be using tires with more air volume than 'cross racers. (And there are no width limits for road racing, so road racers could use wider tires than 'cross racers if they wanted to. But that's UCI logic.)

[quickfeet]

I’m sure it totally depends on the course a the rider whether or not 33mm is faster.

Are you a good technical off-roader? If no, then a wider tire will help.

Is the course through the woods or on a rough course? If yes, then a wider tire will help.

Tires have a max size in cx because the point is to have less traction in certain conditions so you need to get off and run. There is a reason MTB racers have bigger tires. The goal is to stay on the bike in rougher terrain.

I saw Jonathan Page protest an early season cx win from Carl Decker in Utah around 2010ish because Carl rode up the stairs on a run up on the last lap. Page was definitely not doing that on 33mm tires.