Gravel bikes wind tunnel tested MicroPaywall Test

Ten years ago, gravel bikes didn't know what they were. Some were bikepacking bikes, others mountain bikes with drop bars, others cyclo-cross bikes with new titles, and others were just a blended mix of everything.

But as races have grown in prominence and prize money has increased, competitors have become more… well, competitive. Flannel shirts and post-ride beers have been replaced by ice vests and high-carb recovery drinks. Talk of handlebar moustaches has been replaced by talk of handlebar width. And tyre width is everyone's favourite subject, from the amateur ranks right through to the pros.

As all that has changed, bike brands have scrambled to keep up, with riders wanting bigger tyre clearance, aero frames, narrow handlebars and more. And as a result, a new category of gravel race bike has formed.

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I've long been curious which of these new bikes is most aero, and I strongly suspect our readers are too, but there's a big caveat that's stopped us testing it 'til now: tyre clearance.

The term 'faster' doesn't solely come down to a bike's aero drag, and that's especially true on the rougher surfaces of gravel. A bike could have 40mm tyre clearance, be incredibly aerodynamic, but really slow on balance once you've factored in the rolling resistance against a bike with 57mm clearance.

We've long understood that wider tyres offer lower rolling resistance, but it wasn't until earlier this year, when we published a test that measured the combined differences of rolling and aero drag across different widths, that we could put some numbers against it.

We've got more tests planned in that field to refine our data and improve its accuracy. But for now, we're in a position to confidently measure the aero drag of gravel bikes with that context in mind. So that's what we did.

Just as with our road bike wind tunnel tests, we've taken a cohort of gravel race bikes to the wind tunnel at Silverstone Sports Engineering Hub to put them to the test.

The results

By our data, there's a clear advantage to any bike that can accept tyres as wide as 57mm, and slightly more again for those that can accept 61mm. But a bike with 53mm clearance isn't less good than one that can only accept 45mm tyres, because you can still run 45mm tyres in it.

I will reference the tyre clearance of each bike as results are published.

Bike only, stock wheelset

The graph above shows the CdA as it comes out of the wind tunnel software at each of the seven yaw angle plots. It's entirely normal for the CdA to increase at higher wind angles. Some bikes are able to use the sail effect to reduce drag when the wind comes from an angle, but chunky gravel bikes clearly aren't doing that.

Hover over (or click on) bikes in the key to highlight each one in turn.

The graph above is the result of the aforeshown CdA, weightings applied to reflect the real-world likelihood of experiencing each, and then using that average, I've solved for watts. It shows that the Argon 18 Anti Matter is fastest by 1.21w (+/- 0.26w error). The Crux 5 is next, despite being by far the lightest bike on test.

The Lauf Seigla, a Force-equipped bike with shallow wheels a round handlebar, separate stem and externally routed cables brings up the rear. I'm pretty surprised by the Basso Palta, which despite looking like a very premium machine, is both aerodynamically poor and heavy, at almost 8.5kg.

This is a slightly clearer graphic of the differences between each bike. Interestingly, our baseline Emonda ALR road bike is among the cohort, showing us that despite the obvious defecit of fat tyres, modern gravel bikes are able to hold their own against bikes - albeit basic ones - from a decade ago.

Bike with rider, stock wheelset

Above, we've plotted the same seven yaw angles, but this time for the bike with a rider - me - on top.

The first thing you'll call out is that the Emonda ALR is fastest. Don't read into that too much; being a road bike, the position was impossible to match against those of the various gravel bikes, so rather than get halfway there and still have rubbish comparability, we kept it as per our road tests. I stand by the notion that riders will generally be in a different position - shorter reach, taller stack - on a gravel bike anyway.

Emonda aside, a similar selection of bikes occupy the fastest spots, with the exception of the 3T, which had a very wide handlebar and a stem that couldn't be lowered without cutting the steerer, which we weren't permitted to do. Therefore, its position was a little higher and wider than the rest, and that has likely affected it here.

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