Elite gravel racers are increasingly shunning dedicated gravel tyres in favour of wider rubber designed for mountain bikes.
Proponents of this trend claim many mountain bike tyres – specifically lightweight options designed for cross-country (XC) racing – are faster than gravel bike tyres, despite the increased weight and aerodynamic drag most would assume they entail.
While not everyone is convinced, many racers at this year’s Traka told us they were keen to test out mountain tyres – provided their gravel bikes can accommodate them.
It was also a key tech trend at the 2024 Unbound gravel race, and one we expect to see repeated at this year’s event.
So, let’s take a look at who and what is driving this trend and what implications it might have for everyday gravel riders.
Is wider always faster?
Just as roadies have been endlessly debating whether wider tyres are faster in recent years, gravel racers are in the middle of an almost identical argument.
In the red corner, we have personalities such as Dylan Johnson – a professional bike racer, coach and influential YouTuber.
A long-time advocate of wider tyres for gravel racing, Johnson set out his argument in favour of Continental’s 2.2in Race King XC tyres on his channel earlier this year.
Comparing them to Pirelli’s Cinturato Gravel H tyre in 35, 45 and 50mm widths, Johnson tested the rolling resistance and aerodynamic drag of each setup at the Silverstone Sports Engineering Hub, before combining the two data sets to draw his conclusions.
While the mountain bike tyres were a clear disadvantage on paved surfaces, the data gathered on a simulated cobbled surface – which Johnson argues is far more representative of a tyre’s performance off-road – showed a significant advantage to the Race King tyres.
Of course, it’s fair to say Johnson wasn’t comparing apples to apples in his test. The Cinturato Gravel H tyre and Conti Race King tyres don’t share an identical construction, compound or tread, and there’s therefore more at play than tyre width alone.
However, Johnson contends this is the crux of the issue.
Though there are faster gravel tyres than the Pirelli Cinturato H, Johnson argues XC mountain bike tyres can be even more efficient than the fastest gravel tyres because they can be made with thinner casings.
This, Johnson says, is because the increased volume of XC tyres means they don’t need as much casing material or tread thickness to ward off punctures.
In turn, this enables them to be more flexible and to conform to imperfections in the trail surface more easily, lowering their rolling resistance.
Johnson’s wind tunnel testing also shows that, contrary to popular opinion, wider tyres aren’t always less aerodynamic than narrower ones. According to his data, the 2.2in Race Kings were actually more aerodynamic than the narrower, 50mm-wide Cinturatos.
Though Johnson concedes the XC tyres are heavier, he asserts that even when compared to the lightest tyre width (35mm), the weight penalty of XC tyres only has a marginal impact on performance – and is vastly outweighed by the benefits, in his experience.
Why aren’t all gravel pros using MTB tyres?
While squeezing the largest tyres possible into your gravel bike is a red-hot trend right now, not all racers are convinced it's the right thing to do.
In the blue corner, we have riders such as Nathan Haas – a former WorldTour road racer turned gravel privateer, who believes the added weight of mountain bike tyres is too big a disadvantage to ignore.
According to Haas, testing performed by his friend, and fellow former WorldTour racer turned gravel pro, Chad Haga, showed mountain bike tyres are a significant disadvantage compared to 40mm gravel tyres on long off-road climbs.
Haas acknowledges that, as Haga’s test was all uphill, it puts a spotlight on the weight difference between the two sets of tyres, and therefore doesn’t offer a complete picture of how each setup would perform over the course of an entire ride.
It’s also noteworthy that Haga tested tyres provided by his sponsor Maxxis, which – according to Bicyclerollingresistance.com (a lab which uses a steel drum to test a tyre’s efficiency) – doesn’t make the most efficient XC tyres.
It’s therefore possible he’d have gotten different results (and might therefore have a different opinion on the topic) had he tested the Continental tyres Johnson did, or another model.
Nevertheless, Haas argues that Haga’s testing has merit because climbs are so critical. As they’re where race-winning attacks are often made, optimising your setup to avoid getting dropped from the lead group in those key moments should be a racer’s top priority, he says.
Haas says the added comfort, grip and puncture protection of larger tyres would likely help more casual riders enjoy their riding more – he’s just not convinced they’re faster for elite racers.
Who’s right and what (if anything) does it mean for the rest of us?
We have, then, two contrasting arguments with no clear answer as to which is right.
As so often, the reality is that there’s no black and white answer, as there's no perfect gravel tyre for every situation.
Just as there are many kinds of gravel bikes, there are multitudes of gravel tyres and optimising for one aspect of performance typically means trading off something else.
Johnson, for example, acknowledges that while the XC tyres may offer a sizeable advantage on gravel trails, and are therefore the obvious choice for a race such as Unbound (the vast majority of which takes place off-road), his testing showed they don’t perform as well as narrower gravel tyres on smooth tarmac.
For races which feature a more even mix of on- and off-road riding, a middle-ground option (such as a 45mm-wide, lightweight gravel tyre) might offer the best balance of performance on both surface types, he says.
The takeaway is that it’s important (if you care about these things) to optimise your setup for the conditions you’ll be facing in any given ride or event – or be willing to accept compromises in performance for the sake of simplicity.
This is something we’ve seen 2024 Unbound 200 winner, Lachlan Morton, lean into in recent years.
For both last year’s race and the muddy 2023 edition, Morton used a 2.1in Vittoria Terreno XC tyre up front, paired with a 44mm-wide gravel tyre out back (which maxed out the rear clearance on his Cannondale SuperSix EVO CX).
For this year’s Traka 360 gravel race, however, Morton opted for 42 and 44mm Vittoria Mezcal tyres, front and rear.
As with the increasing size of road bike tyres in recent years, we suspect the adoption of XC tyres for gravel racing won’t simply be a flash in the pan.
In fact, we wouldn’t be surprised if bike and tyre manufacturers respond to it quickly, upping tyre clearance on gravel bikes, and creating gravel tyres in similar sizes and formulations to the XC tyres currently being co-opted by many racers.
So, expect to see wider clearances and tyres coming to gravel bikes near you soon.
