Greetings, fellow Mountain Biking enthusiasts. As you know, there’s no one right way to ride a mountain bike. You can bunny-hop over dilapidated trees and blast through rock gardens, or you can race your Zwift friends in your basement spin studio. Hell, do both. But if you’re itching to try out a new-to-you tread pattern, improve the technical skills in your portfolio, or just explore some unfamiliar substrates, choosing the right tire and width can help you avoid #FridayFail fame. We figure this is as good a place as any to make some mountain bike tire width recommendations, so grab a juicebox and let’s get started.
MOUNTAIN BIKE MULTIPLE CHOICE
Before we answer the question, “What width mountain bike tire should I use?” we need to nail down the wheel size you’re running.
• 26-inch wheels: The first mountain bikes were repurposed beach cruisers with 26-inch wheels. This size has fallen out of favor for most modern MTB applications, but they’re still a worthy option for smaller riders. And because 26-inch wheels are strong, responsive, and maneuverable, they’re great for all those BMX tricks the kids are doing on youtube.
• 29ers came next. Although they’re heavier and slower to speed up than smaller wheels, they offer a lower approach angle, greater momentum, and plush comfort. They also roll smoothly over the undulations and obstructions you’ll find on the trail. Still getting stronger and lighter, 29-inch wheels are becoming the preferred option for most MTB riders.
• 27.5” wheels sit right in the middle, also known as 650b. Quicker to accelerate and easier to toss around than 29ers, they’re also strong and durable like 26-inch wheels. If you’re too small for 29ers and looking for a smoother ride than what’s offered by the 26-inch size, consider this eager-to-please middle child.
WHAT IS YOUR DESIRED LEVEL OF RAD?
Once you’ve ID’d your wheel size, next up is figuring out A) the kind of riding you want to do, and 2) what surfaces you’re gonna ride on.
- Cross-Country riders tend to use tires measuring 29 x 2–2.4”. This range offers compliance and grip without being excessively heavy or cumbersome when you want to ramp up or down from speed.
- Trail is a wide-ranging category and the most common approach to mountain biking. Surly MTBs are right at home here, where the terrain is rough and varied, climbs are common, and the descents get technical. Trail riders are moving toward 29” wheels, but 27.5s still see plenty of action, and you’ll find widths ranging from 2.3–2.6”. These are fine for off-road impacts and exploring your hidden talents, but we like to go a bit plumper with 3” tires. The larger footprint means you can run lower pressures over loose stuff, and in general bigger tires provide more comfort for larger riders and heavy bikepacking loads. Finally, the pneumatic suspension built into a 3” tire provides serious benefits for the fully rigid rider.
- All-Mountain: There’s a good deal of overlap with Trail riding here, meaning Surly MTBs can play in this sandbox too, but All-Mountain riding zeroes in a bit more on descents. The bikes are comfortable and efficient for climbing, but the focus on rough, steep downhill sections means many riders look to narrower, faster-rolling tires in the 2.25–2.4” range. But if your rig can fit 2.6–3” tires, we love ‘em for all the reasons outlined in the Trail section above.
- The Enduro scene sees tires from 29 x 2.3–2.5”. Durability is a real concern for tires in this funhouse, and since Enduro races have climbing sections, rolling efficiency comes into play too.
- Tires for the Downhill discipline require a heavy-duty casing and come in the tidiest range of widths — usually 29 x 2.3–2.4” for the World Cup circuit. Everyday thrill seekers might go wider for comfort, but trimming weight in the tire department can make it easier to control momentum at speed. To really dial in performance, consider the “mullet” approach: a 29er up front provides a business-like angle of attack, while a more lightweight and playful 27.5” wheel parties in the rear.
- Bikepacking leaves a little more room for personal preference. For rolling efficiency and covering longer distances, 29-inch wheels fit the bill. But for a nimbler, more responsive ride, you might gravitate toward the 27.5” size. A tire width 2” or above will smooth out rough terrain, and going larger yet will provide extra cushion on rigid rigs.
GRAVEL, SAND, SILT, CLAY
Now that we’ve covered some different approaches to mountain biking, it’s time to get dirty. What’s the ground like where you’re riding? Tire Enginerd Charlie Denis tells us, “There’s a dump truck full of different materials you could be riding over — everything from sand to loam to clay and more. And it doesn’t matter what the substrate is so much as its particle size.” You’ll find the largest particles mixed in with gravel, followed by sand, then silt, then clay. As an added bonus, these surfaces often coexist, blurring the lines between one another while further complicating tire selection.
For the sand, silt, and dirt found on XC and MTB trails, a smooth tire that prioritizes rolling efficiency may let you down in the traction department, especially when you want to bite into corners.
Gravel introduces a choice, too. “Stay on top and scrape at the surface,” Charlie says, “or use very chunky meaty knobs to dig into the gravel and push it backward. The big knobs provide a stronger grasp, but balancing rolling efficiency and traction is tricky.”
Mountain bike tire tread technology takes all this into account.
GRIP IT AND RIP IT
“A tire without knobs is smooth,” says Charlie. “But another tire with too many knobs, well, that’s also smooth.” In between, knobs (or lugs) of different shapes and sizes are arranged into patterns that aid in:
- Digestion – Kidding. Just making sure you’re paying attention.
- Pushing shit out of the way
- Penetrating the substrate for grip
“Let’s say your tire and your bike are rolling in the direction you want. In order to speed up or slow down, you need something perpendicular to that travel path. A knob with a straight perpendicular face will help propel you forward. [But] If you turn that tire sideways in a straight cornering force, those perpendicular faces shift sideways too, and their propulsive effect diminishes. Those knob faces do nothing for ya, they just slide between the stuff.”
Zane Bushey, one of our tire product managers who contributed to this passion project, offers further explanation. “Long and short knobs in the middle of the tire, in the center tread, help propel and brake. As you go toward the sides of the tire, the knobs get slightly taller and longer to help improve cornering control. In between, we angle knobs in different orientations for specific outcomes.”
What about other tread features? Sipes — shallow lines cut into the surface of the knobs — help the rubber wiggle and conform to the ground so it can provide better grip. On center knobs, you’ll find sipes that are perpendicular to the direction of motion — positioned for better stopping and going. On side knobs, parallel-facing sipes come into play when you’re changing direction.
Ramping is another feature designed to improve knob performance. Stick a ramp on one side of a knob and rolling efficiency goes up. Leave a large vertical edge on the opposite side — no ramping — and braking performance is unaffected. If that sounds like the best of both worlds, perhaps it is.
Anyway, let’s look at some tires.
SURLY KNARD AND DIRT WIZARD
Knard is a fast-rolling tire that wants speed without sacrificing traction. It brings a tightly packed, square tread pattern for a tasty balance between propulsion, braking, and cornering. Designed for harder surfaces like gravel and general-purpose trails — as opposed to loose, loamy, chunky stuff — it puts you up on top of the substrate where sipes and ramps aren’t even needed. It comes in 41mm and 3” widths, as well as multiple diameters.
Dirt Wizard exists to transform shitty surfaces into happy magic fun time. Two rows of aggressive beveled knobs in the center grab dirt so it can accumulate on the tire and aid in braking. Large siped knobs on the sides assist with cornering even under wicked forces. Thanks to the rubber’s softer construction, the tire remains in contact with the substrate, adhering and conforming as you roll on through. Excellent for loose and messy stuff, the mechanical advantages baked into the tread provide traction and control on any off-road surface, whether you’re holding your line or cutting corners. Find it in 2.6”, 2.8”, and 3.0” widths, with multiple diameters including 26”, 27.5”, and 29”.
OK, HOW WIDE CAN YOU GO?
Someone out there is typing “can I put wider tires on my mountain bike?” right now, and our answer is “it depends.” To perform as intended, your tire needs to be paired with a compatible rim.
- If your rim is too wide for the tire, the side lugs will grab the ground when they shouldn’t. This will slow you down and make steering and turning unpredictable. In general, your ride will feel rougher than it should.
- Too narrow a rim will pull the side lugs away from the ground, diminishing traction when you need to dig into a turn. This scenario also puts extra pressure on your sidewall, often causing it to roll or fold. This can feel like slipping, which you may or may not enjoy.
- Our pal Charlie says the sweet spot for mountain bikes is “a rim width that’s about 50–60% of the tire’s width.” To work out this math problem, find the internal bead width of your rim. It’s measured in millimeters and should be on the manufacturer’s website. Once you have that number, divide it by .5 and then by .6 to find the range where your tire’s width should fall.
- Example: Let’s say your rim’s inner width is 40mm. Divide that by .5 and you get 80mm. Divide 40mm by .6 and you get 66.666mm. This means you should shop for a beastly tire between 67mm and 80mm wide. If you’re not into the metric system, that’s roughly 2.6–3.1”.
After ensuring optimal rim-tire compatibility, you need to know how big a tire will fit in your bike’s frame. You can find this information on the manufacturer’s website, such as SurlyBikes.com. If you’re looking at Karate Monkey, for example, the tire clearance is 29 x 2.5” or 27.5 x 3”. We don’t want your tire rubbing against the frame or anything mounted to it, so we leave 6mm of space on all sides of the rotating rubber. This often allows room for fenders, if you’re into those, or for whatever mud and crud you roll over on the trail. Other brands might approach tire clearance differently, but other brands are not Surly.
AND WHAT IF YOU WANT TO GO EVEN BIGGER?
If your bike frame will accommodate them, Plus Tires offer a larger footprint for greater traction and confidence. Falling somewhere between traditional MTB tires and Fat Tires, some folks consider a 2.6” tire a great Plus Tire. At Surly, though, we don’t call a tire “Plus” till it’s 3” wide or more. And since we started the whole Plus thing, we can do that. They usually pair up with 40–50mm rims and are compatible with 26”, 27.5”, and 29” wheel sizes.
Another step up takes us into Fat Tire realm — tires that are roughly 3.5” wide and up. Designed for winter riding, their volume, footprint, and tread patterns allow them to behave basically like a snowshoe. At low pressures, you’ll truly feel like you’re floating over the ground, as if carried by dozens of small but supernaturally strong fairies. Fat Tires also provide many benefits for general trail riding regardless of season. Take ‘em over mud, rocks, roots, or wet and sandy surfaces and marvel at your forward progress. Surly’s Fat Tire selection includes:
Nate, a 26 x 3.8” tire adorned with siped knobs, shoulder knobs, and superior crud-shedding abilities. Its tread pattern is similar to Dirt Wizard’s, but Nate is nearly twice as wide.
Edna, a 26 x 4.3” superstar capable of finding hidden fun on loose dirt, snow, sand, hardpack, and more.
Bud, a front-specific 26 x 4.8” tire with extra-tall siped knobs that conform to mud, snow, and worse while providing confidence for steering and braking.
Lou, the rear-specific mate to Bud. Also measuring at 26 x 4.8”, Lou’s tread pattern focuses on propulsion and braking rather than steering.
Since we’re talking about winter riding in a roundabout way, we should also mention studded tires. There’s simply nothing better than metal to provide grip on ice. Throw studs on your fat bike tires and the dreaded freeze-thaw-refreeze pattern will never again prevent you from enjoying your favorite frozen trails.
FATTIES FIT FINE
If you’ve been on or near a Surly bike within the last two-plus decades, you’ve probably seen the Fatties Fit Fine sticker affixed to nearly all of our chainstays. True since day one, this phrase means Surly bicycle frames are made to fit large tires. To learn how big meaty rubber might contribute to a more pleasureful mountain biking experience, head over to our youtube page.
ONE LAST TIP, SINCE NO ONE ASKED
Unlike the riffs of Lemmy Kilmister, tires deteriorate over time. Tubes leak. Sealant breaks down and weeps out. If you notice your tire isn’t holding air and a fresh tube or squirt of sealant doesn’t cure what’s ailing it, it may be time for new tires. Another way to tell when your tire’s best days are in the past is by looking for sipes. If your tire used to have sipes in the knobs but you can no longer see them, congratulations! You get to shop for new tires. We hope they’re fun.
That’s all for now, but we’ll see you around.