Thinking about riding fatter tires? Here’s what you need to know.

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PLUS SIZE CONVERSIONS! (26+, 27.5+, 29+)

Written by Craig Miller  – HB Cranford Lead Technician

Hello all!

It’s not news that many companies are now coming out with a wide range of tires in the 2.8” to 3.25” width. WTB started the surge with their 27.5×2.8” Trailblazer tire that was claimed to fit in most 29er frame and forks. Now, a lot of big name bicycle manufacturers (such as Salsa and Specialized) are designing their frames to take both 27.5” and 26×3” or 29” and 27.5+. As more and more tires and bikes continue to come out of factories, a lot of us that can’t afford the hottest new rig might be feeling a bit discouraged about not waiting those extra months for something new to hit the sales floor.

You may have just picked up a new 27.5” trail ripper or a 29” XC single track killer, but your friends with 27.5+ or fat bikes are blowing right by you in the rock gardens or rooty uphill sections where you might lose some grip. Or maybe you took your new fat bike out this summer, only to find that you couldn’t keep up with all of your friends with smaller wheel sizes on that flat, fast single track that we all love so much. Well, that is where a plus size conversion comes into play!


Image from QBP Call Up Sept. ‘15 issue

Thankfully, with all of the new standards and products coming out there are people like myself that like to push the boundaries of what can be done with the frame and forks that we currently have. As you can see from the image above, a lot of the tire diameters tend to overlap. Now, they’re not exactly the same, but they’re pretty damn close! You can convert a lot of 27.5 wheeled bikes to 26×2.8” or 3” for that added traction and float, and I haven’t found a single fat bike yet that couldn’t take a 29X3” or 27.5×3” tire. A smaller wheel and tire on a fat bike means a bit less weight, and a faster rolling wheel.

There is some measuring involved with figuring out if your trail/XC bike can handle a plus sized wheel and tire combo, but if you’re going from fat to plus sized it’s a matter of building a second set of wheels and getting the tires you’d like. There’s almost nothing that won’t fit. If you’re part of the first group, here are some guidelines:

  • Typically, if your bike can fit a 2.4-2.5” tire with your current wheel size, you’re most likely in the clear. If not, then it probably won’t work without some uncomfortably close clearances at the chainstay and I wouldn’t recommend it.
  • Time to get out your rulers and calipers! If you plan to go to 26+ from 27.5”, measure 335mm from the center of your axles and make a mark with tape or a dry erase marker on both sides of the fork and chainstays. If you’re going from 29er to 27.5+, you should measure 345mm from the center of your axles.
  • Now once you have everything marked, get out your calipers and measure the distance you have between your fork legs and chainstays at those marks. Measure the inside, we’re looking to see how much tire clearance you have.
  • If you have about 80mm of clearance at that point, we’re in the clear. You should have plenty of room for a 2.8” and possibly 3” depending on rim choice. If not, then unfortunately your frame will not be able to convert.

Okay, so now that we have those measurements documented somewhere, let’s discuss what it’s going to take to get you onto your new plus wheels! 2.8” to 3” tires are best mounted on 30mm to 50mm rims. The tires are much wider than standard tires, so they need a much wider rim. You can squeeze 2.8” tires onto a smaller rim, but you may notice some odd handling characteristics and the way the tire hooks into the rim wouldn’t be considered “safe” by many peoples’ standards. That, and you don’t get the benefits of higher volume and more float with a narrower rim. Talk to any of us at HB to discuss what rim options there are for the wheel size you’re going to. You’ll also want to discuss hub compatibility and hub choice with us while you’re at it.

Now I know this seems like a lot of work and more money to spend just to get you onto a bigger tire, but it’s far less expensive than buying a second bike. Plus, a spare wheelset is much easier to store than another bike and the benefits are huge. Who doesn’t love a smoother ride and more traction? Or a lighter bike and more speed?

To wrap things up, I think plus conversions are the easiest solution for someone looking to get better traction or a different ride feel from their current bike instead of having to shop for a new bike. I’ve personally converted 2 of my own bikes to plus and will be doing it to a third soon. I’m hooked on the benefits and feel. I think you probably would be, too. If you want check out or discuss everything before deciding whether to make the jump or not, call down to the Cranford location and ask for Craig. I can bring my bike to the store for you to check out and take for a spin, or even out to one of the many fat bike and plus bike demo days we’ll be having in the coming months.

P.S. Below are some links that you can check out to see technical specifications for certain plus sized tires, as well as a few articles that might help sway your decision.

QBP Call Up – On The Plus Side

QBP – Plus Size Tire Doc

Surly – Tire Geometries

Singletracks – Convert your 29er to a 27.5+ All-Trail Bike

The Radavist – Surly’s Dirt Wizard is the Shredliest 27.5+ tire I’ve ever ridden

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