As the adventure cycling category grows, gravel bikes continue to evolve. One of the best evolutions in gravel bikes is improved tire clearance. Tire clearance is important for a variety of reasons. Clearance translates to versatility, making a gravel bike a quiver-of-one bike. Run 30mm tires for all-purpose road rides. Run 40mm for all-purpose gravel riding. And run 50mm for adventure rides and bikepacking.
45mm WTB Riddler gravel bike tires
Of course, extra tire clearance also raises the question of how wide is wide enough for the riding you do most. While there is no magic answer to how wide a tire you should run, I advocate experimenting with tire width to see how it changes the feel of your bike and how it responds in different terrains and on different surfaces.
Tire Width and Terrain
50mm Panaracer Gravelking tires on loamy singletrack
The number one factor in guiding tire width choice is terrain — specifically, the road or trail surface types where you ride the most. It’s not rocket science: the rougher the surface, the better a wider, higher-volume tire feels.
While pavement is pavement for the most part, the term gravel means many different things depending on the region and even the season. One region’s gravel roads are compact, fast and ride great on 35mm slick tires, while another region’s gravel is chunky, loose and requires a 40+mm tire with a light tread.
And when it comes to mixed route rides where singletrack plays a role, a wide (45-50mm) tire handles roots, rocks and loose dirt much more confidently than a 30-40mm tire. Wide tires are all about air volume. More volume equals a cushier ride.
Overbiked or Underbiked, It’s Inevitable
For years, I’ve watched the local mountain bike scene gravitate towards more suspension and wider tires while the trails remain largely the same, leaving me with the impression that many riders are overbiked — meaning they have more suspension and bike tech than necessary to enjoy the local trails. Underbiking is simply the opposite. It’s intentionally riding a bike with little or no suspension or skinnier tires than considered standard for the given terrain and applies to mountain bikes and gravel bikes.
In reality, on a good, adventurous mixed-surface ride, you are likely to be underbiked (and/or overbiked) during some portion of the ride, depending on your tire choices. Choose bomber 50mm tires, and you’ll feel a little out of place on the pavement. Choose 34mm tires, and you’re going to feel underbiked on the singletrack connectors that link a ride together. It’s unavoidable. And it makes a ride fun.
34mm WTB Byway (left). 50mm Panaracer Gravelking SK (right)
How Wide is Too Wide for Gravel Bike Tires
A few years ago, I considered 40mm (1.5-inch) a wide tire on a gravel bike. Many bikes advertised clearance for 40mm, and you could often squeeze in a 42mm, which feels great for all-around gravel and mixed rides but leaves little room for mud buildup or fenders for winter riding.
Wide gravel bike tires equal confident descents
Today, more and more bikes offer clearance for up to 50mm tires — nearly a full two inches wide. However, just because a bike says it can take 50mm tires doesn’t mean you should always max it out or that it’s always helpful to run 50s. The extra tire clearance means you can run 40-45mm gravel tires and maintain good clearance for mud and debris. Mud clearance isn’t always a consideration. But for those who live in wet areas or where a single rain shower can turn roads into a muddy mess, the extra clearance can mean the difference between riding and walking. Just see the mud-caused chaos at the 2023 Unbound gravel race in Kansas.
So, Back to How Wide is Too Wide?
Of course, the answer to how wide is, it depends. However, the amount of frame clearance around your tires is a guiding factor. Obviously, your tires need to fit in your frame without rubbing. But within the limits of your frame, the right width is more nuanced.
Leave yourself just a few mm of clearance, and you risk muddy tires getting jammed up in your frame or an out-of-true wheel causing fit issues. In a dry climate with little fear of mud, a few millimeters on each side might be enough, as long as your wheels stay true. For those who routinely encounter mud, more than a few millimeters of clearance is a wise choice.
Why Go Wide?
Frame clearance warnings withstanding, I still advocate for wide tires. Wide tires mean more volume and more volume equals more comfort on any surface. High volume, 40-50mm tires make gravel riding and bikepacking adventures more fun.
Wide tires offer increased cushion, comfort and confidence on any unpaved surface. They extend your range to include more terrain and surface types, and unless you’re racing competitively, they don’t slow you down enough to be a concern worth worrying about. I would even argue that you can descend faster and corner more confidently with wider tires, making them faster than narrower tires. Wide, high-volume tires reduce overall fatigue and make long days easier on your body, regardless of tread pattern.
What About TPI?
Regardless of tire width, most brands offer tires in two types of construction: 60 tpi and 120 tpi. The term tpi refers to threads per inch used to create the sidewall. While 120 tpi sounds like a higher-density construction, the threads are thinner than those used on 60 tpi tires, so a 120 tpi tire is generally going to be lighter, more supple and a little less durable than a 60 tpi tire. That said, not all variables are equal between tire brands, so comparing thread count is not always a one-to-one comparison. For example, one company may add more rubber to the sidewall than another brand, causing their 120 tpi tire to be thicker and heavier than another brand’s 120 tpi tire.
You can generally count on 120 tpi tires to be lighter and more supple than 60 tpi tires, especially within the same brand. Rene Herse does a nice job of speaking about how tpi relates to tire construction and performance.
Go as Wide as You Can
Bottom line, I generally recommend running as wide a tire as your frame allows while taking local dirt, gravel and mud conditions into consideration. Wide tires make for fast, fun descents and extend your comfort over a long, adventurous day.
If you’re lucky enough to have two wheelsets, a frame with wide tire clearance sets you up for a quiver-of-one bike. Rolling a mostly paved route, pop in your wheels with 32mm tires. Getting adventurous, roll the fatties.
Tire Pressure and Tubeless Set-Up Tips
No matter what tires you roll, tire pressure makes a big difference. Modern mountain bike riders know less is more when talking about tire pressure. Of course, your weight, the road quality and tire width all play a role in guiding tire pressure. But don’t be afraid to run lower pressure than you might first think on your gravel tires. I rarely roll with more than 35 psi in any gravel tire, and I typically run as little as 18-25 psi on wider 40-50mm tires.
Going tubeless is essential for gravel riding. It will save you from pinch flats and punctures more times than you can imagine. If you’re new to tubeless tire setup, read our post on Tubeless Tire Tips and Tricks.
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