I was talking to Josh Poertner recently on the Marginal Gains Podcast and the issue was optimal tire width for road bikes. Josh said – from memory, and if I understood him right – that we’re closing in on the over/under on width, subject to road conditions and use case. What's pushing this toward "over" is Crr, and the "under" – that is, what keeps tires from getting too wide – is aero. It seems, if I understood Josh right, that tires just roll faster and faster as they get wider and I don't think that’s a well-known phenomenon.
This informs much more than just tire choice. If you look at new bikes designed today, have you noticed how often the fork blades and seat stays are set apart from the frame? I don’t know, but I suspect this gives the rider more freedom to select a wheel and tire that in combo presents a different – and often wider – profile to the wind. In other words, if you look at a bike as a unit rather than as a bunch of parts you could imagine a driving metric, and decisions made around it that affect the rest of the bike.
For example, imagine if that metric was tire size. Imagine that the one immutable fact is that I’ll be riding a 28mm or 30mm tubeless tire. This informs the design of the wheel. In my experience a wheel with an inner bead width 5mm narrower than the nominal tire size (the size on the tire’s label) makes a pretty good combo. The way the tire stands up in the rim, the aero profile (at least to my eye), the way the tire beads up upon inflation, all seems to sync well. So, now I have my combo: a 28mm tire in a wheel with a rim that has a 23mm inner bead width. Next comes the bike, which might now have set apart fork blades and seat stays and this seems to be the trend with tri (e.g., Kú Cycle and CADEX), as well as that new design Dave Koesel (Superdave on our forum) showed for a track bike. These new designs target one form of parasitic drag and you can even see this in the Canyon Speedmax.
As to tire size, I decided to stop guessing and just ask a half dozen folks I respect a lot about what’s being used in the pro peloton. These included folks at tire and wheel brands that get heavy use at the highest levels of cycling. The teams that are running Zipp wheels are now using tubeless 100% of the time. No more tubular. These would be Movistar, Q36.5 and Canyon-SRAM, and that’s in the Classics and in regular road races.
“In the Classics, tire sizes are actually bigger than 28mm,” for those teams according to a person familiar with what these teams are riding. “Most teams have been using 30mm to 32mm tires this season, depending on the severity of the course. Some teams were running 30mm up front and 32mm at the back, with some other opting for 32mm all around.”
On the road the majority of Zipps teams run 28mm tires most of the time, for all disciplines, from crits to stage races to even time trials. However, it should be noted that Zipp optimizes its wheels for 28mm (and wider), so to some degree the wheel provider informs tire size. But this works both ways. One very high-performing continental pro team reports to me that its riders prefer riding 30mm tires for road race, but really can’t because the inner bead width of the provided wheels are 19mm at the widest. Accordingly, part of calculus on tire width is the wheels the teams are supplied.
For those World Tour teams riding other wheels what I hear is that north of 80 percent of the peloton is now on tubeless full-time. “There are very few people left on tubular, but you still see people running clincher tires with super tubes.” (Such as those from Tubolito.)
“From what we’ve been told from various teams 28mm is more the norm than the exception for standard road stages,” according to Xavier Disley of AeroCoach. “Corresponding wider-width wheels,” he replied, are used “to accommodate these tyres aerodynamically.” For spring classics like Roubaix and Flanders it’s 30mm and 32mm tires, according to Xavier.
When I talk to tire brands what I hear is 28mm to 32mm for road. But the one area if disagreement is TT. Zipp’s riders are all on 28mm for TT, but Xavier Disley says that the fronts (for riders using wheels other than Zipp) are typically 25mm and even 23mm, while in the rear it’s 25mm up to 28mm.
As to tubeless, there are two ways to view the move toward this tech. One is that the tech is just better. The more cynical view is that R&D almost ceased for any tire type other than tubeless, which pushes riders toward tubeless. Xavier is still a fan of tubes for TT for this reason: “You can get more of a performance enhancement from being able to swap out your tyres depending on the exact characteristics of a race rather than having a tubeless setup that you’re not going to chop and change on race day. So for example for a really nice road surface I will ride Veloflex Records (dry) or Vittoria Corsa Speeds (wet), for worse surfaces I will ride Michelin Power TT (dry or wet), and then for real bad road surface and terrible conditions Continental GP5000 TT. You can’t do this with ease with tubeless setups; [it'd] be an absolute nightmare.”
I take it that sealant is the “nightmare” in this equation. If this is justification for tubes, do or will we triathletes change our race tires based on road or weather conditions?
Here’s a final thought from Xavier: “In 5 years time I would be surprised if every road stage was being ridden on 40mm tyres and corresponding giant wheels, equally no one wants to go back to 19mm tyres for road stages. Manufacturers are understandably pushing wider tyres and lower pressures to consumers because they are tangibly more comfortable and in the most part will make your regular rider a bit faster through Crr benefits and enjoy their ride more through comfort. Disc technology has allowed frame manufacturers to accommodate wider tyres easier than in the past which works in synergy with wheel manufacturers making wider wheels, so everyone has aligned on the issue a bit.”
This is a fitting note to end on because it dovetails well with what Josh said during our podcast, which (if I understood him right) is that the eventual best tire width for all road uses – considering Crr and aero and I assume other factors – may be as wide as 32mm (measured). This might be a 30mm nominal size depending on brand. If I parse Xavier Disley’s comments correctly he and Josh might be in violent agreement on this, for road race at least. It seems almost incomprehensible that the optimal tire size for road race is 30mm – with 28mm and 32mm as options for either smoother or rougher roads – nevertheless the usage data and the expert commentary upon which I rely so far points me in this direction (if I correctly interpret that expert commentary and pending further data from the front).
(PHOTO highest up courtesy Vittoria.)
