Boosting Off: Some thoughts on the new Boost axle standards.

The industry has just announced a new “Boost” standard, promising wider axle widths. Wideopenmag pen-pal Jon Rollason drops some home-truths.

Each spring, the Cheltenham and Winchcombe Cycling Clubs in the Cotswolds run HONC – a long byways and backroads reliability trial. Each year, looking around the starting line, you can see several gentlemen on 1990s Marin Mount Visions, with v‐brakes and the yellow and silver colours. Those bikes were state‐of‐the‐art for while. You wouldn’t buy one now. But those guys bought an awesome bike back in the late 90s, and they’re still going strong. Hold that thought…

…And so to the spurt of announcements from Trek, Fox and SRAM that Boost technology has made your state‐of‐the‐art bike obsolete.

boost reeba

In case you’ve missed this, Boost is a new divergence in bike components (it feels increasingly stupid to say “standard”). From Right Now, your rear hub is 148mm x 15mm, your front hub is 110mm x 15mm and your chainline is going to need to be stepped out 3mm from the bike’s centre as well to avoid the chain snagging on the tyre and getting all bent.

“This looks like the new normal.”

This is the new thing on all serious Treks, and SRAM have gone in hard, with their drivetrains, hubs and Rockshox forks making the switch at Sid, Revelation and (soon) Pike level. Fox have a Boost 34 fork as well. Shimano haven’t moved yet, but SRAM have so thoroughly slaughtered the Japanese in the OE market that that hardly matters. They’ll catch up in a year or two. This looks like the new normal.

boost X0 hub

You’re pretty pissed at this. Or a lot of you are. You’ve just kissed goodbye to 26” wheels and got used to 650b (even if we haven’t quite worked out how to say it). You’ve got your head around tapered fork‐steerers and given up on understanding how to buy a headset. You’ve realized that 20 or 30 gears was insane, you only needed 11 all along and jettisoned most of your drivetrain. Your 160mm travel, 650b wheeled, carbon‐fibre, 1×11, disc‐braked and dropper‐posted #enduro bike is perfect, and they all look surprisingly similar except for the labels and the garish neons. A huge step up has happened in the last few years – enough to persuade Pete Roggeman in to remark that “These are the golden days”.

“The more room you can create in the bike for the hub, the stronger a wheel can get.”

Had we reached a plateau of mountain‐bike perfection? We had not. The industry has charged on. You’ll have noticed two big things very much still in play: wheel diameter, and tyre size. We don’t have to go anywhere near “what is the best wheel diameter?” here. Suffice to say, the biggest objection to bigger wheels is that they aren’t as strong as smaller ones. That happens because longer spokes get fitted into the same width hub, and more acute spoke angles are the result. If you want a may‐pole to stand up, you pull on the ropes from further away. Want a rim to stay truer, you pull on the spokes from further away. If you think a 29er can be a contender if you sort the wheel‐strength issue out, you’re going to want a wider hub‐spacing. Ditto 650b, but with lower stakes. The more room you can create in the bike for the hub, the stronger a wheel can get.


SQ LabsLeaderboard

The other way of strengthening a bigger wheel is with awesome rimming (lol-Ed). Carbon fibre has suddenly and hugely successfully broken through into mountain‐bike rims. But guess what? Rims are getting wider. The 19mm internal rim widths of the past few years has given way to the 25mm of the Enve M70 Thirty, and with the wider rims, bigger, squarer profiles on bigger tyres. 2.35” tyre to go with your 160mm suspension? Of course.

But it wasn’t just sensible #enduro bikes getting bigger tyres. No‐one can avoid having an opinion on fat‐bikes (Wideopen editor Jamie insists they are ridden in his presence only in the dark), but those are for odd‐balls. The more interesting development happened when the drunken idiot‐savants at Surly dropped the Krampus on the world. Krampus may or may not be for odd‐balls, but it is designed to rip. The bike was the beginning of 29+ ‐ a 29er wheel, shod with a vast 3” tyre. It rocked, and was quickly copied on bikes for a certain sort of person, (the bearded sort, mainly). Surly bet on 650b being better if you made up the diameter with rubber, and tried to create 26+ with their Instigator 2.0 trail hardtail. That died on its ass.

But the idea that massive tyres were great was suddenly taking off. 27.5+, or “B+” was suddenly “a thing”: that is, a thing with a 27.5 diameter, 50mm wide rim supporting a 3” tyre. Awesome cornering traction. A smooth ride. Great rim protection. Good things.


But if you want those good things, the designer is going to need some more space for the hub, and some more space for the tyre. And so we are back around to Boost, and how annoyed you re that your current wheels won’t fit your next frame.

“Feel free to ignore the latest baffling and infuriating “standard” proliferation. Feel free to ride your bike.”

Let’s be clear: you do not need a 27.5+ bike. Not right now. Your bike is fine and dandy, and will last you 20 years with care. It is exactly as good as it was before 148 axle spacing. Feel free to ignore the latest baffling and infuriating “standard” proliferation. Feel free to ride your bike.

But the industry that brought us the amazing bikes we’re riding today has moved on again, to make the amazing bikes that we’re going to be riding tomorrow. When it’s time for your next bike, it’s going to have bigger tyres, and a wide stance. And it’s going to be even better than the one you’ve got right now.

You can read more about Boost over on SRAM’s website here.

Thanks to Jon Rollason for another awesome column. Jon is our long-lost-buddy who is now living and shredding in Hong Kong.