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  • FartsWithAnAccent@lemmy.worldOPMtomicromobility - Bikes, scooters, boards: Whatever floats your goat, this is micromobility@lemmy.world•We Tested Four Popular Road Tire Sizes—Here’s Which Width Delivered the Most SpeedEnglish
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    3 months ago

    It’s safe to say that bike tires have been trending wider over the last ten years. Gravel bikes are now commonly using mountain bike tires, while mountain bike tires are slowly creeping towards 2.5 inches and wider. Even on the road, it’s safe to say that the 23 mm tire is well and truly dead, with 28 mm tires now being the default. While many riders are experimenting with and racing on tires closer to 30 mm in width.

    I was early to the wide-tire road bike thing, maxing out the clearance on my road bike with 32 mm Panaracer GravelKing slicks (that measured nearly 35 mm) back in 2020. For me, this was a big benefit of the move to disc brakes on the road. Wider tires meant more comfortable, more capable road bikes.

    In the five years since, I have actually moved back towards more traditional road tire sizes for a variety of reasons. The biggest was that I found tires much wider than 30 mm to be overkill for me on the road. When I wanted to ride mixed terrain, I had my gravel bike for that, but my road bike stayed largely on paved surfaces, where the larger tires felt heavy and unnecessary to keep on my bike all the time in the off chance I might encounter some gravel for five minutes along my route.

    tire testing

    Trevor Raab

    The second thing I realized is that I’m actually quite performance-oriented when it comes to my riding. Basically, the faster I go, the more fun I’m having. So, purely based on the feeling of speed and the fact that most modern aero wheels are optimized for 28 mm tires, I’ve generally stuck to 28 and 30mm tires on my road bikes since.

    My colleague Tara Seplavy recently published a deep dive into road bike tire sizes. She weighed, measured, and ride-tested Schwalebe’s Pro One tires in every labeled size from 25 mm to 38 mm. The story is packed with helpful information, insights, and advice on finding the right tire size for you. But it was missing an answer to the question my racer brain immediately went to. Which tire size is the fastest?!

    tire testing

    Trevor Raab

    So I grabbed the pile of tires and headed out to test and find out. The Test

    I did the testing on a closed 1-mile cycling loop near the Trexlertown Velodrome. This means I don’t have to worry about traffic or hitting the brakes. I used a set of Favero Assioma Pro RS-2 power meter pedals to maintain a consistent effort of 275 watts (4.2 watts per kilogram) over three laps (or 3 miles) for each test run.

    I tested the Pro One in four labeled sizes (700 x 25, 28, 30, and 32), all mounted to a set of Reserve 57|64 wheels. I picked these wheels because they use modern width and profile dimensions, with an internal width of 25.6 mm for the front wheel and 24.5 mm for the rear. Matched to an equally progressive external width of 34.3 mm on the front and 32.5 mm on the rear.

    Tire sizes were dictated by what was actually available (Schwalbe does not offer the Pro One narrower than 700 x 25) and what would safely clear my frame (which has pretty standard road bike clearance of 32 mm).

    tire test

    Trevor Raab

    I optimized tire pressure for each tire size using Silca’s Tire Pressure Calculator and measured each tire’s true size with a digital caliper. As expected, the labeled widths had little relation to the tire’s actual size once it was mounted and inflated on the wheels.

    tire testing

    Trevor Raab

    tire testing

    Trevor Raab

    During testing, the 700x32 tires inflated to 33.2 mm at the front and 32.8 mm at the rear. 700x30 came out to 32.1 mm and 31.2 mm front and rear. 700x28 inflated to 30.5 mm and 29.8 mm front and rear. While the smallest labeled size, 700 x 25, measured 28.8 mm front and 27.8 mm rear. The Results

    So which tire size was the fastest in my test? It was the narrowest. The labeled 25’s ( that measured 28 mm) were 17 seconds faster over 3 miles compared to the labeled 32’s (that measured over 33 mm). In terms of a speed difference for the same wattage into the pedals, I averaged 24 mph on the narrower tires compared to 23.3 mph on the wider ones.

    The two middle sizes followed the general trend: the narrower tire was faster, and the wider was slower. The 28 mm tires were 11 seconds slower than the 25 mm tires, while the 30 mm tires were 15 seconds slower over 3 miles.

    My Thoughts on the Results Plus Three Caveats

    So does this mean that everything you’ve heard about wider tires being faster is wrong? Yes and no. Really, the correct answer will almost always be, “It depends.” If you take anything away from this story, I hope that it’s always worth being skeptical of bold declarative statements of fact when it comes to what makes you faster on a bike.

    Yes, in my testing, the narrowest tire option was by far the fastest. Here are the three main reasons why this was the case. First, the surface I was testing on was fresh, perfect pavement. That favors the narrower options while negating the rolling resistance advantage of a wider tire. If the testing had been done on a rougher road, the results would have changed.

    tire testing

    Trevor Raab

    Second, was the speed at which I tested. At 23 mph, the most significant force acting against me is aerodynamic drag. That means even a minor reduction in frontal area, such as switching to a narrower tire, can have an effect. This again favors the narrower tire to be fastest in this test. Testing at a slower speed would have made rolling resistance a larger factor in the test, which again could have led to different results.

    Finally, there were the wheels I chose for the test. The Reserve 57|64 wheelset uses very modern rim dimensions with an internal width of 25.6 mm for the front wheel and 24.5 mm for the rear. Matched to an equally progressive external width of 34.3 mm on the front and 32.5 mm on the rear. These dimensions are optimized for a tire that measures 29mm according to reserve, which so happened to be what the 25 mm tires I tested measured out on these rims. Combined with the importance of aerodynamics, it meant that the narrow tires had another advantage. This means that testing with a different wheelset could have changed the results. Wrap-Up

    If there’s a single takeaway, it’s this: the fastest tire for you is the one you’ve tested on your roads, at your speeds, with your wheels and pressures. Lab charts and rules of thumb are helpful, but nothing beats a simple field test—fixed power, repeatable loop, controlled pressures, consistent setup—to reveal what’s quickest for your setup where you ride.

    And speed isn’t the only metric that matters. Even if a narrower tire wins in a straight-line aero contest on smooth pavement, wider options can be the smarter choice for real-world riding. They often bring better puncture resistance, more grip, and confidence in corners and on descents. Plus, lower rolling resistance on rough surfaces at appropriately lower pressures. Balance these gains against your goals and terrain. Start with what your rims are designed around, set pressure thoughtfully, then validate with timed runs. Let your data, not dogma, decide.

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