March 19, 2015

Ken, 148×12, the future, Keanu Reeves

As promised, here’s part 1 of my thoughts, musings, ramblings… incoherent gibberish about new axle standards.

I’m not even going into the new 110×15 fork standard right now, we’ll concentrate on 148×12.

First, remember: if you are buying a hardtail, a through axle has no actual benefit over a QR unless you weigh 400 pounds or are constantly forgetting to tighten your skewer. Your pathetic excuses for legs won’t get any more power to the ground than they did before – the rear end of a hardtail really doesn’t flex much, so adding a big fat axle make zero difference in how the bike rides. Of course, I build them all the time, and if/when I get around to building myself a new bike, that’s what I’ll do. Why? Because time marches on, and it’s harder and harder to get nice QR parts – just like it’s hard to find a really nice set of v-brakes these days. C’est la vie. Take the red pill. Or maybe the blue one? I can’t remember, the sequels have caused me to block all Matrix-related knowledge from my brain to avoid the pain.

142×12 came out about 3 years ago and quickly took the world by storm. Why? It promised a bit stiffer rear ends on FS bikes, compatibility via adapter for most existing hubs as the cassette and disc rotor stayed in exactly the same place, and something new to sell to the bike-buying public. Which I would roundly condemn, except that I’m one of the purveyors of said new stuff.

27.5+? My doing.

As a giant world of diverse wheel/tire and drivetrain options has opened up in the post-29er glasnost, lots of manufacturers realized that cramming 3×29/27.5″ tires into frames built around 73mm BB shells and 50mm chainlines (just a quick pause for a definition here: “chainline” here means the distance from the center of the frame to the center of the middle chainring, though these days that mostly means the *only* chainring. Here’s Sheldon Brown’s definition) would cause some terrible problems fitting everything where it needed to go. The chainstay, tire, and chainring all fight for space on a typical mountain bike frame (FS or hardtail) and if you have to give too much to the tire – you’ve either gotta lengthen the chainstays or do *something* to move the chainring out of the way. As more and more gears get crammed onto cassettes, the flanges of the hub have also gotten closer together (this has been going on for 20 years, really) which is generally bad, as the spoke tension between driveside/non driveside gets out of whack and the wheel gets less laterally stiff and weaker. Bigger rims (ie 27.5, 29) exaggerate these problems. Something had to give (well, ok, maybe “had” is too strong a word). Something is giving, anyway.

Enter “Boost” (why didn’t 142×12 get a cool name?) 148×12 rear ends. The idea here is that you move both the cassette and disc rotor outboard 3mm, and move the flanges out to match. Result, you can move the *chainring* out a bit to make more room for the tire, keep a decent chainline, and end up with a bit stronger rear wheel to boot.

Now, there’s another solution out there that I’ve been doing for over a decade along with a few other weirdos. It’s to stick with 135×10 (or now142x12) spacing, but move the *entire* rear end (meaning, the hub/dropouts/stays) about 5-10mm to the driveside (the exact amount depending on application). This gives you a great chainline for single ring bikes and loads of room for short chainstays and big tires. It’s also a near-dishless/even tension rear wheel. Great stuff, IMO. Cannondale ripped me off this year with their “AI system” (here’s C’dale’s explanation of the setup). Stupidmobile (you know, the 29er with 40cm chainstays?) was built this way. So are many bikes I build for customers, because it gives you a ton of benefits and really only has a few drawbacks. You can also do fun stuff like an 83mm low-q-factor fatbike by using various amounts of rear end offset (Felix’s runs a 135×10 rear hub offset 10mm).

Whew. Did that all make sense? No? That’s what I run into a lot. Many people don’t like the idea of asymmetry, so the whole idea is off the table. I think that’s a big part of the 148×12 idea – easier to explain, inherently less weird and threatening…but we don’t do normal and unthreatening around here!

Ken wanted it *all*. 148×12, lots of tire clearance (in his case 27.5×2.8-3 or so) and short, short chainstays (well, not totally insane – we did 41.5cm). So we went nuts and did an *offset 148×12* setup. In this case, it’s just 2mm of offset to get the chainline we wanted, but it still felt weird to take a brand new Anvil dummy axle and chuck it up on the lathe!

So long story short, Ken’s bike is weird but should be awesome. Your bike can be awesome too if you think outside the box a bit and let me get creative – it’s custom, folks. The world is your oyster.

Or we can just do 148×12, because what the heck, I already paid for the dummy axle, and the writing is on the wall…

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