By this point you’ve likely heard plenty of watercooler chatter (both excitement and complaining) about the latest crop of bikes with 27.5 wheels and tires ranging from 2.8 to 3.5 inches wide. If you’re looking for some backstory, check out Part 1 of this occasional series.
Here at Dirt Rag we’ve only had some short demo rides on these bikes at all, so we’re not prepared to pass judgement on any of them in particular—or the trend as a whole—but we’re trying to stay ahead of the curve.
In installment I’m going to look at the WTB Trailblazer 2.8 tire that kicked things off in the public eye last year when it debuted on the Rocky Mountain Sherpa prototype. We mounted up a pair to some of WTB’s own Scraper rims that have an internal width of 45 mm and seal with the excellent TCS tubeless system.
It’s so good, in fact, that in order to measure these tires I taped over the rim’s valve holes, mounted the tire and stuck a tubeless valve in. When I inflated it with a floor pump the beads snapped into place and the tire stayed inflated without any sealant in it for at least 36 hours. I wouldn’t recommend running these tires without sealant, but it was really impressive to see how well the TCS bead interface works.
Just like in Part 1 I wanted to see just how big these tires are in the real world. I grabbed the Feedback Sports calipers to find out. Mounted on the Scraper rim the Trailblazer measured 70.6 mm at the casing and 59.6 mm at the tread. The tread has a square profile, with the casing actually measuring out a bit wider than the tread. The sidewalls are much taller than a standard tire too. Flattened out and measured from bead to bead they are 170 mm, compared to 160 mm for a WTB Riddler 2.4 tire I measured.
Just as with the Panaracer tires I measure in Part 1, the rim makes a huge difference in the width of the tire. Mounted on a standard 21 mm rim the Trailblazers measured just 2.2 inches wide at the tread. They easily fit in a standard 27.5 frame and fork, but because the sidewall is so much taller I can’t guarantee they will ride very well.
One of the key arguments for the 27plus “movement” is that the wheel and tire’s diameter is very close to that of a 29er. In reality, these tires are a bit smaller. The 29×2.3 WTB Trail Boss pictured here measured 74.17 cm in diameter, while the Trailbazer is at 72.7 cm. It may not seem like a lot, but it is enough to drop your bottom bracket almost a centimeter if mounted in a 29er frame. Trust me, that’s a lot.
Speaking of, there’s really no guarantee that these tires are going to fit in existing 29er frames as many have championed. Neither tire is even close to fitting in my Santa Cruz Highball, though they both fit in an On One Parkwood frame I tried. Just as a lot of folks were shoving 27.5 wheels in bikes designed for 26-inch a few years back, I think there will be some experimentation and trial-and-error involved here, plus lists of “compatible” frames popping up in forums online.
Which brings us to the Boost system. The new, wider hubs and forks now coming to market are designed to accommodate these larger tires, as are many new frames.
Will the 27plus trend stick around in the long run? We’ll have to wait and see.