Gone are the skinny road tyres of old. How wide of a tyre you can run boils down to your bike’s clearance. Let’s look at what clearance is and why it’s important.
Bicycle tyre clearance is the distance between a bicycle’s tyre and any part of the frame or its components. As tyres go up in width, so does the amount of space they require to turn freely. And if they are too big, friction occurs between the tyre and frame around the chain or seatstays, the brake bridge, callipers (if still riding rim brakes) or the front derailleur, for example, as they turn.
Problems with tyre clearance happen not only around the rear triangle of a bicycle but at the fork, too. And it isn’t only about the tyre width but also height. It’s important to measure, observe, and listen to the space below the fork crown in between the fork blades where the tyres spin. If you’ve got rim brakes, this space is reduced from the start limiting your options.
For decades, you’d see nothing but skinny tyres pumped to rock-hard pressures in the professional peloton. Everyone believed them to be fast and aerodynamic. Pros racing 23-mm tyres, once thought to be mega-wide, for cobbled events such as the Paris-Roubaix, were considered slow. However, those riders were already onto something: improved comfort, handling and reduced rolling resistance. But how to convince an entire industry and culture? It took a while.
As the trend to wider rims and tyres in the professional ranks grew, bicycle manufacturers had to adapt their bikes to fit them. This meant greater frame and fork tyre clearance, characteristics that eventually trickled down to entry-level road bike price points on the sales floor of your local bike shop. Aside from comfort, improved traction and speed at lower pressures, we want to ride what the pros ride, right?
The road bike industry moving away from rim brakes helped improve tyre clearance significantly too since the callipers were eliminated from the brake bridge and moved to the fork blades. This opened up the space and gave brands and bike builders more freedom in their design possibilities.
We are discussing primarily road but going to disc brakes on mountain bikes gave them a massive boost, not only tyre clearance but suspension and improved travel opportunities. This move proved to be such an improvement disc brakes eventually made their way onto the road scene. We’re already seeing suspension models on gravel bikes and a dropper post may have led to victory in Milan-San Remo. Who knows what’s next?
Why it’s important
While it may seem like a seamless transition, going from skinny to wide, it isn’t always the case. Just because you want to run a wider tyre, it may not be possible with your current bike, especially if it dates to a pre-2013 model or if you’ve got rim brakes. Keep this in mind when purchasing any used road bike.
If you are new to the sport or are buying a road bike soon, wider tyres and rims are now fairly standard. What you want to check, however, is the bike’s specs. How wide of a tyre can it take? And consider what kind of riding you do?
This is especially important if you plan on having a second set of even wider wheels and tyres to do some gravel, bikepacking or cyclo-cross riding. You’ll want to go fairly wide, probably greater than 40 mm and not all models offer that option.
How to check compatibility
If buying new tyres, verify your rim and tyre combo first. Check with the bike, wheel and tyre manufacturers to be sure. The industry standard is to quote the maximum size tyre you can fit on a bike that leaves three to four millimetres of clearance above and on the sides of the tyre.
Three to four millimetres sounds like a lot to leave open but that free space is important for any flex that happens when sprinting out of the saddle or pushing hard on the pedals to get up that hill.
If riding in an all-road or gravel situation, that three to four-millimetre margin is necessary for any debris or mud that collects on the tyre too. You may squeeze one more millimetre in width out of the situation, but if you want to ride over 32 mm on your road bike, perhaps it’s time to consider adding an all-road, gravel or cyclo-cross bike to your stable.
Not all the same
Remember that clearance will vary by bike. I touched on this briefly already but it depends on the manufacturer and the bike’s usage. For example, the geometry of a racing-level gravel bike for the Unbound Gravel is designed for speed and a good bike handler, so the tyre clearance may only be up to 36 mm.
Whereas a recreational all-road or gravel bike, with a more relaxed geometry when speed isn’t as important, may accept tyres up to 48 or even 50 mm. If you aren’t sure about your bike’s clearance, a pair of digital callipers come in handy to measure any areas in question.
Measure the frame first, and then your inflated tyres on your rims to see if they’ll work. Listed clearance is pretty ambiguous. Your bike may accept up to a certain sized tyre but which one? You have to check.
If no information is to be found online, be careful your setup isn’t causing any rubbing. Friction could not only lead to the eventual frame or fork failure but damage your tyre too. It can cause a weak spot, which may bring about an eventual blowout. Something you don’t want to happen in the middle of nowhere or when bombing down your favourite descent.
Labels aren’t always accurate
The measurements printed on the tyre’s sidewall or product packaging may not be what they appear. Have you ever purchased a 25-mm tyre only to find out it’s actually more like a 28? This happens because current tyre sizing isn’t quite standardised, yet.
The industry is working on improving it and companies like WTB and Continental are leading the way with online compatibility charts. Once you have the rim and tyre width squared away, you can compare it to your bike’s clearance and be on your way.