Bikes & Tech

Giro Tech: Rise of the 25mm tire

At the Giro the 23mm tire seems in decline, with many pro teams replacing this traditional favorite by its slightly fatter cousin, the 25mm

ROCCA DI CAMBIO, Italy (VN) — Alongside the influx of wider carbon wheels into the pro peloton has come a distinct trend away from the classic 23mm tubular – the tire size preferred by professional teams in just about every normal road stage for decades. It has long been the mainstay, viewed as the best compromise between aerodynamics, grip, rolling resistance and comfort.

In the last year or so that thinking has begun to change. Here at the Giro, the 23mm is in decline, replaced by its slightly fatter cousin, the 25mm. Many of the teams already recognized for more progressive technological mindsets have begun using fatter 25mm tires for regular road stages – no cobbles or gravel in sight, just smooth(ish) Italian tarmac.

These teams are also among those using the latest generation of wide rims available from companies like Zipp, Hed, Shimano and Bontrager.

The swap is usually spurred by mechanics and sponsor liaisons; it falls on their shoulders to convince their riders that a wider tire is beneficial. Among those with a penchant for tradition, it’s still a hard sell, and even within teams that have largely made the change there are still a few riders on skinnier tires.

“We use the wide tires on the wide wheels, it’s a better fit and more comfortable, “ explained Rabobank mechanic Joost Hoetelmans before Friday’s stage.

At the end of the day, each rider has the final say in what can be a very personal decision. Tires represent, after all, the thin line between themselves and the tarmac.

To convince their riders, mechanics are touting the lower rolling resistance often associated with sizing up, as written about extensively by’s own Lennard Zinn, as well as touting comfort over hours in the saddle. Cornering grip comes up as well – an important factor here at the Giro, which never seems to go in a straight line for long.

“You get more grip, more comfort; the guys like it,” Hoetelmans continued. “We never put more than 8 bar (116psi) in them, except for some of the Spanish guys, they really love high pressure. I don’t know why, but they do. So to make them happy I have to put more in. We run about 1 bar (15 psi) lower in the wider tires than in 23c tires.”

Rim manufacturers have begun to recommend the wider tires as well, as their own rims have widened 2-5mm in the last two years. Before, a 25mm tire dwarfed narrow 19 or 21mm rim beds, have in negative affect on aerodynamics and providing a less reassuring gluing surface – now, with many of the latest rims measuring 24mm or wider, a 25 fits the rim profile nicely. Though a 23 will usually test faster in the wind tunnel, the difference between 23 and 25 on a wide rim is usually quite small –apparently small enough to be outweighed by the other benefits.

On Shimano’s recommendation, most of the teams running the Japanese company’s wide 50mm prototype tubular rims have swapped to larger tires. Orica-GreenEdge has mounted Continental Competition 25mm tires; Rabobank has prototype 25mm Vittoria Corsa Evo SC’s glued on; Sky is running Veloflex 24mm tires, which measure out to 24.9mm.

RadioShack-Nissan is running 25mm Schwalbe Ultremo HTs on their 27mm-wide Bontrager Aeolus 5 D3 rims. Both Omega Pharma-Quick Step and Saxo Bank, which have been using Zipp’s wide 303 and 404 Firecrest wheels for the past two stages, are running what appear to be prototype Specialized tires. Though they are unlabeled, they measure out to 25.4mm wide. The Mavic tubular on the front of Tyler Farrar’s Garmin-Barracuda Cervelo R3 on Friday measures out to 24.2mm – a good match with what appears to be a new, wider version of the Mavic CC80 rim.

The Italian, French and Spanish teams seem to have stuck with 23c tires, at least for now. Teams like Lampre-ISD and Euskaltel-Euskadi (both on Vittoria Corsa Evo SC) have stuck with 23c, as has Androni, Movistar, and Ag2R. All these teams are sponsored by companies without an ultra-wide wheel.

To buck the 23c tradition teams have done their own testing, in addition to getting recommendations from their wheel and tire sponsors. Apparently they’re happy with the results, and with wider rims come wider tires here at the Giro, it seems.

That’s certainly something to keep in mind if you own a pair of the one of latest wide options yourself.