Are Tour de France riders cornering on their tyre sidewalls? Prototype 29c Vittoria tyre suggests they might be

The Vittoria Corsa Pro is one of the best road bike tyres out there, and is seen fitted to a good few teams' bikes at the Tour de France and throughout the season. For the majority of the season so far, the pros have been opting for a 28c width, pushing up to a 30c occasionally - especially for those nervous about hookless rim compatibility - and even 32c for races like Paris-Roubaix. But while at the Tour de France Grand Départ in Florence, we spotted some riders on team Visma - Lease a Bike using an unreleased 29c width of the Corsa Pro. 

Are pro riders so sensitive to tyre width that Vittoria felt the need to create a tyre that straddles the existing 28c and 30c options? Not quite.

Tyres have, on the whole, been getting wider as the seasons go by. Free from the constraints of rim brakes, manufacturers of both frames and wheels have been pushing the envelope and wheels are now regularly aero-optimised for 30c widths. Visma was seen running a new set of Reserve wheels at the Classics at the start of the year with a wider internal width, with claimed aero benefits for those races where wider rubber is called for. 

The sidewall of these new prototype tyres also states that they are optimised for a 25mm internal width rim, and when I asked Vittoria about it the brand confirmed our suspicions:

“Technically, it is an actual 29mm on a 25mm rim, optimised in terms of casing shape and tread width to improve puncture resistance and cornering safety when using 24-25mm rims, while maximising the aerodynamic benefit on such wide rims.”

It’s no surprise to hear there are claimed aero benefits, but the mention of ‘cornering safety’ is what has piqued the curiosity most in the Cyclingnews tech team.

Two big selling points of wider internal rim widths include a less curved lateral cross-section, meaning a wider contact patch and thus better stability in corners, as well as a more stable tyre sidewall under hard cornering. As the sidewall is more directly atop the wall of the rim it helps to stop it from folding over, but this push to wider rims, combined with the continued use of 28c as the nominal standard width for pros has had an unintended consequence.

For the same tread width, if you widen the base of the tyre out, you also reduce the lean angle required to start cornering on the sidewall of the tyre itself. The only way around this is to use a wider tyre, which then starts to negate the benefits of the additional sidewall support, as well as adding weight. 

I suspect that this 29c width has, at least in part, been developed by Vittoria at the request of Visma-Lease a Bike to enable their riders to corner harder. I've put this theory to Vittoria, but I am yet to receive a response. 

There is already evidence of this happening with a very similar setup. Alec Briggs of British team Tekkers runs Reserve Wheels and Corsa Pro tyres and in a recent Instagram post, it’s clear to see just how far off the tread of the tyres he’s been going. One commenter asks “Rims too wide for the tyre?”, to which the reply was a pretty unequivocal “Yeah, basically”.

Expanding this thought out to UAE Team Emirates, we spotted Tadej Pogačar running 30c tyres in the opening stages of the Tour. It's not clear whether he is using 30c for every stage, though. The Enve rims the team uses are also wider than the norm, and it could be that cornering ability is the reason here, too, rather than simply a case of aero optimisation. 

Watching how hard the Slovenian was riding on the descent of the Col du Galibier on stage 4, it’s certainly not out of the question that it was at the forefront of the riders' minds during recon rides.