Gravel
Photo: Brad Kaminski | VeloNews.com

The Grind: The perfect gravel tire width

40mm is the new 35mm. Here’s why.

What is the ideal width for a gravel tire right now?

It’s a bit of a trick question, as the perfect tire set-up depends on where you live, how you like to ride, what event(s) you are targeting, surface conditions, and on and on. Many of us dork out and install specific tires for particular events. But if you had to pick just one width, which would it be, and why? When it comes to bike companies, they have to make this judgement call well before the bikes go out the door.

For 2020, the hot width is 40mm, according to custom research done for Bicycle Retailer & Industry News by 99spokes, which pulled data from 77 gravel models and found 40mm to be the median width.

It’s a big jump up from 5 years ago, when 32mm was the standard, or even from 35mm that was en vogue a couple of years ago.

I checked around with tire companies and racers like Colin Strickland, winner of the 2019 Dirty Kanza 200, and their perspectives lined up with the 99spokes data.

Gravel tire width trend chart
99spokes compiled all publicly available data from bike brands to track trends on gravel tire width

40mm: A good balance point

“The 38c (40mm) width is by far the most popular now, but things keep getting wider,” said Nathan Forbes, Schwalbe brand manager. “I think that a 42mm tire will be the most popular in the next two years, but only time will tell. We still have racers who want a 35c tire for certain events and other riders do as well if they don’t have the frame clearance for larger models, but those numbers are dwindling.”

At Vittoria, vice president of marketing and product Ken Avery also voted for the 38c as a do-everything width. “It’s a good balance point between road efficiency and off-road capability,” Avery said. “For what it’s worth, 38c measures 40mm on a traditional rim, but as rims are getting wider, this offers flexibility. The general rule of thumb is that the tire section width grows by 1mm for every 2mm the rim width grows. This means that if you were to run a more trendy 23mm wide rim — such as a pre-2017-ish 29er MTB rim — that 38c/40mm tire will actually measure more like 42mm.”

“The cyclocross riders may say that a 33 is faster, but most would run a larger tire if the UCI would let them,” Avery said. “MTB riders may say they like the comfort, and all-out traction of a wider tire. Both will likely gravitate back to a 38c for gravel use, once the dust settles. Some of this has to do with weight and contact patch size, while the comfort effect of the air volume also is a factor.”

“The bike industry will always push trends past their limit, and then correct back to what settles as the ‘standard’,” he said. “Plus-sized MTB tires are an easy example, where the trend went 3.0, to 2.8, to 2.6. In gravel, there will be a cross-over point, where gravel tires overlap with XC MTB tires. This point is right at the ‘2.0’ width mark for MTB. We already have seen numerous gravel riders on Vittoria Mezcal and Terreno 29×2.1 MTB tires, especially in the ultra-length events like Tour Divide.”

“If you want a short answer, I’d say that the longer the event, the wider the tire,” Avery said. “This allows for the added weight of supplies and gear, and also affords flexibility if your route gets a little gnarlier than you anticipated.”

Balancing racing ambitions with real-world riding

Down in Texas, Strickland agrees that the ideal tire setup completely depends on where you live and how your ride. “I learned my lesson about running light, fast tires at Land Run 2019 and SBT2019 with race-ending punctures,” he said.

But pushed for a single width, Strickland said 38mm, with a smooth center strip.

“While light cyclocross tires are tempting, more volume and tread dramatically reduce the probability of punctures,” Strickland said. “Myself and most people in the U.S. live a fair distance from the sweet gravel roads, so we all have to ride 30 minutes to an hour on tarmac to get there. This is why the slick center tread is key. You still feel fast on the road despite the extra volume. Also, you can jump on a ride with road bikes and not lose too much speed due to extra rolling resistance. There is no perfect gravel tire, but I have loved the Specialized Pathfinder Pro tubeless as a one-stop-shop road training and Texas gravel tire.”

Colin Strickland rolling away from the field to win the 2019 Dirty Kanza 200. Photo: Brad Kaminski | VeloNews.com

Trek road product marketing manager Anders Ahlberg voted 40mm, which is what Trek specs on its Checkpoint gravel bike. “We started that bike on 35s, but it was clear that riders wanted a little more versatility and capability,” he said. “Personally, I chose to ride 40s for Grinduro, and as much as I can say I was ‘under control’ during the singletrack descent, I felt like I wasn’t in too far over my head. On the other hand, at D2R2, I think you could have ridden 25s no problem, but I rode the same 40s there, and didn’t feel like I was too slow.  A 35 would have been super sketchy for me at Grinduro, and a 45 would have seemed like overkill at D2R2.”

At WTB, director of sales and product vision Johs Huseby is also betting on 40mm. “If designed correctly, it can still be fast enough, but gives one some good cushion, while still being efficient, but providing ample traction,” he said. “It allows the rider to go truly anywhere they want to go without feeling like they need to hold back. It will also fit on 98% of the ‘gravel’ bikes on the market.”

At IRC, marketing manager Steve Driscoll said — you guessed it — 40mm.

“The 40 is still quick enough to get the fast wind-up/acceleration, and can handle just about anything you can throw at it technically. In fact, we had several guys racing this year on 40s at Dirty Kanza, Steamboat, and Rebecca’s Private Idaho,” Driscoll said. “Now what would I pick? I’m a 36mm guy all day long. Although you lose a bit in the technical department, it’s a very snappy tire. For demand on bikes, I keep hearing the OE guys asking for wider and wider 45-55, and I think this big adventure push is a much smaller market than the big, epic event crowd for DK and Belgian Waffle Ride. My miss prediction was I thought the 650b market was going to be larger once people rode it, but now I’m even over the smaller wheel size. Riding anything over 50 miles just becomes too much work. Fun as hell in the techie stuff though.”

At Specialized, global road marketing manager Ben Edwards rejects the idea of one perfect tire.

“What we are seeing is gravel riders really starting to think about tire selection more like a mountain biker. Instead of choosing a single tire and just sticking with it, they are seeing what a huge impact the right tire will have on their ride,” he said. “It’s why we see riders looking for so much tire clearance in their frames. They may only use the max tire clearance of their frame a few times, but boy, is it nice to have it when you need it! If you need a high volume and you can’t sneak it in, you suffer.”

“This kind of thing is really the magic of gravel riding,” Edwards said. “It’s an equation to solve, not just the training, bikes and nutrition, but tires, too. No tire is 100% right for any course or ride, since the whole point is mixed surfaces. You just need to solve the equation to be on the tire that’s right for you, on most of the course.”

For the record, Specialized ships its Diverge gravel bike with 38mm tires, which measure closer to 40mm on the wheel.

Follow Ben Delaney on Strava.