If you’re thinking of buying a new gravel bike this year, stop right now and check whether it has at least 50mm of tyre clearance. If not, don’t buy it.
While 40 to 45mm of tyre clearance was considered adequate a few short years ago, things are moving fast in the world of gravel riding and those bikes are now outdated.
Why? Because wider gravel tyres are potentially faster, grippier and more comfortable, and you therefore want to maximise your options when it comes to tyre selection.
Chunky cross-country mountain bike tyres have become one of the hottest tech trends in gravel racing over the past few years, and having just tried a set of 2.1in / 54mm Schwalbe Thunder Burts on my Kinesis GX Race, I’m convinced the hype is justified.
Of course, if – as I do – you already own a gravel bike that officially ‘only’ takes 45mm tyres or narrower, it’s still as good as it ever was. You may even be able to carefully push its limits on dry days.
But if you’re buying something new, don’t ignore this trend.
Gravel bikes with narrow clearances are obsolete
Since building up a gravel bike nearly two years ago, I’ve cycled quickly through a number of tyre sizes – always going larger.
Back in the spring of 2024, I started out on 38mm tyres – which seemed enormous compared to the 28s I have on my Giant TCR Advanced Pro Disc.
Through a mixture of testing new tyres and simply buying options off the shelf, I’ve since used 40mm Hutchinson Caracal and Caracal Race TLRs, 45mm Continental Terra Speeds and, in the last couple of weeks, the 2.1in / 54mm Schwalbes.
Each time, the step up in volume has felt like an upgrade in terms of speed, comfort and grip with few tangible drawbacks – even on the road.
In the case of the most recent upgrade, there was barely an increase in weight. The 45mm Terra Speeds I took off my bike weighed 555g per tyre, while the 2.1in / 54mm Thunder Burts weighed only 560 / 580g per tyre.
Getting to the nub of the issue, though, that low weight partly explains why the XC mountain bike tyre trend is so potent – the thinner, lighter casings can translate to lower rolling resistance compared to narrower gravel tyres that tend to use thicker, more puncture-resistant casings.
Factor in the better comfort and grip they also bring and you get a fantastic mix of characteristics for gravel riding.
Of course, if 2.1in tyres are ‘better’, you might reasonably ask 'well, what about 2.25in or 2.4in tyres?' and so on – and to that I’d say, 'Let’s try it and find out'.
I’m sure there’s a tipping point where having bigger tyres will simply weigh you down on climbs and cause more aero drag than you gain in rolling resistance, but exactly where the balance lies isn’t yet clear (and, as always with these things, it’s probably situation-dependent anyway).
Nevertheless, even given my relatively limited experience with gravel bikes, I’ve no intention of going back to anything narrower than 45mm at this point – unless I was riding on the kinds of gravel trails you get in Strade Bianche (which pro road racers typically race on 30 or 32mm road bike tyres).
It’s not only tyres that are getting wider
Another thing to consider is that gravel wheelsets have also been trending significantly wider recently – at least when it comes to racy ones.
Zipp boldly released its super-wide 303 XPLR aero gravel wheels in 2024, and it looks as if those have set the direction of travel for everyone else in this niche.
Hunt, for example, followed suit with its similarly deep and wide Limitless 40 Gravel Aero wheels last year, and Roval released its Terra Aero CLX wheels a few days ago.
All three wheelsets use rims shaped to be aerodynamic with big tyres and, as such, have greater internal and external widths.
A knock-on effect of the large internal rim widths, though, is a tendency to increase your effective tyre size by another few millimetres.
Those 2.1in Thunder Burts, for example, measure up at around 50mm wide on the 23mm-internal-width Fulcrum rims I have on my gravel bike, and the front tyre only just fits in the fork by the narrowest of margins (I will therefore have to switch to something narrower for muddy rides).
Ideally, I’d want to run them on wider rims, for a rounder, less lightbulb-esque shape and better aero performance, but in all likelihood they then wouldn’t clear the fork crown.
In this regard, my gravel bike (or its fork, specifically) has reached its limit. If wheels and tyres trend even wider in the future, I’ll need to upgrade to join in the fun.
Not everyone agrees, but that’s besides the point
I’ll happily acknowledge that not everyone is convinced by the ‘XC MTB tyres for gravel bikes’ trend.
Pro gravel racer Nathan Haas strongly asserts that he feels racers using them are optimising for the wrong things, for example, and that narrower tyres are almost always the faster choice.
Likewise, my colleague Warren Rossiter – one of BikeRadar’s most experienced gravel riders – is convinced the sweet spot for gravel tyres lies around 45mm.
This makes sense, because ‘gravel cycling’ is a very broad church, and the demands of the discipline can vary wildly from one area or riding style to the next.
Merida, for example, clearly designed its latest Mission gravel bike (which has ‘only’ 40mm of tyre clearance) with UCI Gravel World Championships-style gravel racing in mind. Typically, these courses feature fast, non-technical gravel secteurs mixed with stretches of tarmac, and run almost like Spring Classics road races.
In contrast, the Allied Able (which has a whopping 57mm of tyre clearance on 700c rims) targets the American gravel racing scene and races such as Unbound – where the vast majority of the course is off-road.
And both of those would be classed as ‘gravel race’ bikes.
My point, however, isn’t that you should use a specific tyre width for gravel, it’s that you should buy a gravel bike that gives you options.
A gravel bike with extra tyre clearance that you end up not using is far less frustrating than one that doesn’t have enough clearance for a tyre size you’d like to try.
Don’t buy into a tech dead end
To put it another way, a gravel bike with clearance for 40mm tyres now feels akin to a road bike with maximum clearance for 28s.
That bike could be fantastic, and you could experience most of the best road cycling has to offer, but much like a road bike with rim brakes, it’s a technological dead end.
As we’ve seen with modern, disc-brake equipped road bikes, which now frequently have room for 32 to 35mm tyres or wider, there are few downsides to having a bit more tyre clearance.
I’ve recently been testing the new Rose Shave FFX, for example, which ships with 28mm tyres but can accommodate 35s. It makes no tangible compromises in speed or handling compared to my Giant TCR that ‘only’ has clearance for 32s (quite the opposite, in fact – look out for a full review coming soon).
In my experience, the supposed benefits of things such as marginally shorter chainstays, or a slightly shorter fork trail, are far less apparent than the benefits of using the optimal tyre setup for any given ride.
Whatever kind of bike you ride, tyres are simply too important to compromise on.
