Dylan Johnson on Improving Gravel Aerodynamics

Dylan Johnson recently worked with Silca in their lab to do some aerodynamics testing to see how a gravel bike could be optimized, using wind tunnel technology. And even he admitted that the results were surprising! You can watch the whole video here, and here, we chatted with him about a few other aerodynamic tips he’s picked up over the years of studying the science of wind. He’s so devoted to aerodynamics that he even raced a mountain bike that had been converted to what he calls a ‘Franken-gravel-mountain bike,’ swapping his flat bars for drop bars.

“I dove headfirst into the marginal gains territory, especially in the 2022 season,” he says. "I feel like I've always been a marginal gains guy. I used to think that weight was the most important thing. But I'm much less of a weight weenie now. As far as marginal gains go, aerodynamics is the most important of the marginal gains if we're comparing weight, aerodynamics, tire rolling resistance, drive train efficiency and weight of the bike.It depends on the course, obviously. But in a typical gravel race, though, if you're looking at those factors, aerodynamics is the one that's got the biggest impact. There's a reason why I spend the most time thinking about that one in particular."

Obviously, aerobars are the easiest way to add an aero element to your ride. But since many races don’t allow riders to use aerobars, there are other smaller gains to be made.

"As far as gravel racing goes, the biggest thing that I change is the tires, depending on the course. This has to do with aerodynamics, and it has to do with rolling resistance,” says Dylan. "The bigger the tire, the less aerodynamic it is. But generally, the bigger the tire, the better rolling resistance it has on gravel. So there’s a tradeoff. People assume that on gravel, the wider the tire is, the better the rolling resistance  and the faster it will be, but it's not without any drawbacks. The main drawback is that the wider the tire, the less aerodynamic. A wider tire actually takes up more area for the wind to hit. The wider the tire, the less well your aerodynamic profile rims work. If it's a rough course, that means wider tires will make sense, but if you have a smoother course and can get away with a narrower tire, it’s a good idea.”

On a hilly course, though, aerodynamics won’t matter quite as much. In those cases, Dylan thinks about bike weight as much as he considers the aerodynamics of the bike—though he prefers the more aero Factor Ostro in most races.

But what should you carry on the bike? For the exact stats on hydration packs versus bottles and which frame bag placement makes the most sense for the best aero gains, check out his video here: