UCI RACE TYRE WIDTH EXPLAINED
The hit and miss of racing cross with tubeless (and clincher) tyres has serious implications if you are racing UCI calendar events.
The UCI rules for CYCLO-CROSS state "For the cyclo-cross bicycle the width of the tyre (measured between the widest parts) shall not exceed 33 mm and it may not incorporate any form of spike or stud."
See ARTICLE 1.3.018 (Page 13) of the UCI CLARIFICATION GUIDE OF THE UCI TECHNICAL REGULATION
UCI races are Elite, Under 23 and Junior National level league (think UK National Trophy) and National Championship races, as well as World Champs and World Cup, plus DVV, Superprestige and loads of other races internationally which feature on the UCI calendar (see the calendar link above).
Amongst racers, new and experienced, there is a lot of confusion whether veteran and/or youth races at UCI events are covered by the rule, there are stories of tyre width gauges being seen and stories of tyre width gauges never being seen in these races.
The rules are clearly stated, if you you can find them, if you can figure out the language of the rules and what needs cross referencing.
To get clarification, after which the rules make sense, I contacted the UCI and British Cycling.
The UCI have told me that the Masters World Championships is the only non Jnr/U23/Elite event which they stipulate is covered by the rule, but that National Federations have discretion on how they apply the rule in their regions.
British Cycling have confirmed that they will be applying the rule only to Elite, Under 23 and Junior races at National Trophy / Champs.
It is definitely worth checking with the applicable National Federation if you are racing internationally, in the US they apply a 35mm rule to all races (including vet races) at UCI events.
How it works in practice is that on the start line and in the pits of races on the UCI calendar, a UCI commissaire checks each and every tyre with a width gauge. It's a go/no go test. If your tyres are too wide, you can't ride those tyres. You may be allowed to let a little air out and re-test.
But my tyres state their width on the side wall...
The effective width of a tubeless/clincher tyre is the result of the size of the tyre carcass, the psi, the width of the rim and the how far the side tread extends down the side wall of the tyre.
Is 33mm actually 33mm?
We measured a range of tyre brands both mounted and un-mounted;
|
33MM TYRE |
Carcass width measured un-mounted |
Carcass width measured mounted on LOWMASS
|
|
CHALLENGE OPEN TUBULAR |
94mm |
33.1mm |
|
SCHWALBE X1 ALLROUND |
85mm |
31.05mm |
|
VITTORIA TERRENO WET |
92mm |
33.5mm |
|
CHALLENGE LIMUS TLR |
94mm |
34.4mm |
| DONNELLY PDX WC | 88MM | 31.5mm |
|
CHALLENGE TUBULAR |
N/A |
33.04mm |
In addition to the variation in widths, each brand has its own bead shape which adds to the variability. Challenge's Open Tubular and TLR tyre are the same width un-mounted, but the TLR sits more than 1mm wider when mounted.
As per the rules, the widest parts of the tyre includes the tread.
While each brand's file tread, intermediate and mud tyres tend to use the same carcass, the side tread can extend wider beyond the carcass on some brand's tyres with a more aggressive side tread.
Tyre pressure plays a part too, tyre width increases by approx. 0.3mm per 10psi.
The wide rim trend is making matters worse
With cyclo cross bikes often borrowing road technology, the "wider is better" trend in road tubeless wheels means that many road/gravel tubeless rims (as well as 29er mtb tubeless rims) are either too wide to use for UCI events, or your tyre choice will be restricted.
A 31mm Schwalbe tubeless tyre on a 23mm internal width Stan's Crest rim only just passed at Nationals last year, and only by letting out more air than optimal. It turned out OK because the the rider was only 65kg and it was dry so the Schwalbe performed well. But what if it had been muddy? The only real tubeless mud tyre is the Challenge Limus TLR. He would have needed unfashionably narrow rims to run them...
From what we have seen, if your rim's internal width is greater than 20mm, you will be severely limited by tyre choice for UCI events.
Given all the variables, our advice is simple - if you are serious about racing, use tubular.
But unless you make the change to tubular, how will you know if your tyre and rim combination will pass?
You can use a vernier calliper to measure your tyre width, the offset side tread of many tyres can make it tricky.
We bought a 3d printed 33mm tyre width gauge with the idea to build a database of compliant combinations but there were too many variables of tyre pressure and people not knowing which wheel model (internal width) they have. Plus, the gauge was undersized and needed careful filling to get it to 33mm!
If you know your rim model / internal width - why not put 25psi in your tyres, measure its width, email us the measurement using hello@cyclocrossracer.co.uk and we'll compile the results.