People usually have this one sorted out before their conversation with us about wheels, but we get asked for our opinion on thru axle versus quick release all the time. Here are a few thoughts.
The two compelling things about thru axle are security of wheel to bike connection, and repeatability of rotor placement. With quick release disc builds, we've always supplied bolt on skewers rather than actual quick releases. This is because the brake force in a disc wheel pushes the wheel forward and down - out of the dropouts. On a rim brake wheel, that force goes in the opposite direction - up and back, into the dropouts. There's also the issue of the quick release lever potentially being next to a hot rotor. With a thru axle system, the entire axle goes - you guessed it - straight through the fork or frame, and the axle would have to come out before the wheel to bike connection was lost. It's harder to screw it up.
Mark's bike always look great. Thru axles both ends here
You might say "yeah, but only an idiot doesn't know how to use quick releases!" Guilty as charged, but my first time out with a new suspension fork several years ago nearly cost me my beautiful face, as the movement of the fork legs kept working the quick release loose. A bolt-on skewer stopped that issue cold, but from now on it's only thru axle suspension forks for me.
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On a quick release hub, the knurls on the end cap faces bite into the frame or fork to make a secure connection with the hub. That works well, but the knurls never quite line themselves up perfectly each time you install the wheel. On your rim brake bikes, you might have noticed this once or twice, and fixed it by loosening and then re-closing the qr. With discs, the rotor's clearance between the pads is much less than a rim's clearance between rim brake pads, and that fit becomes more exacting. A thru axle set up is more precisely repeatable.
I love this photo, and it shows the end cap knurls
While my current road disc bike has quick release front and back, and they work just grand, if I was getting a new disc bike - road, cross, or mountain - it would definitely be a thru axle front. The decision on the rear gets a bit murkier.
The quick release standard for disc rears is to have the dropouts 135mm apart, with 10mm diameter dropouts. Already on road bikes, which often have chain stays about 405mm long, the 135mm spacing causes some friction. First, it's hard to keep your heels clear of hitting the wider-spread chainstays (especially when you're a duck-footed freak like me). Second, the chain line gets more tortured as you shift to the outer cogs. Shimano says you need a 420mm chainstay for their drive trains to work correctly on 135mm rears. Specialized goes so far as to move the drive side flanges inboard on many of their disc hubs so that you can use the full gear range even with a 405mm chainstay. The problems with that are that you're somewhat limited to their hubs with their bikes, and moving the inboard flange in is precisely what you don't want to do from the wheel's perspective. For what it's worth, you can totally use a normal hub in these Specialized bikes, you just don't want to do any small-to-small cross-chaining - even if you are Andy Schleck.
Thru axle rears generally have 142mm dropout spacing, with a 12mm axle rather than 10mm. With long chainstays, hey no problem. On road bikes, it's complex. The overall width of the hub is the same on a 135mm QR hub as it is on a 142mm TA hub. On the QR hub, the outboard-most 3.5mm on either side ride in the dropouts, where on the TA hub the outboard ends of the hub nestle into a pocket/face on the inside of the dropouts. The 142-based frame will have a tiny bit more overall width. The hub shells are exactly the same, it's only the axle that will be different between a 135mm and a 142mm hub. The repeatability and security of attachment favor the thru axle rear just like it does on the front, so that's what we'd personally choose, all else being equal.
So the rear is a little bit more complicated than the front, but I expect that I'll see a new 135mm thru axle "standard" for road bikes when I go to Interbike in September. We'll need to give White Industries a little time to make the kit, but our CLD would be able to handle that format. And I thought this blog would be shorter than it was. Sorry.
13 comments
What is an example of a "bolt on skewer" versus a standard QR? Is that like the DT Swiss RWS skewers?http://www.dtswiss.com/Components/RWS/RWS-Thru-bolt
Those work nicely, I actually have one from an old mountain bike, but they are specific to a DT hub that accepts them. Bolt on skewers are simply 4mm rods (same diameter as a regular qr) but instead of having a cam lock lever you tighten them with a hex key. You can get a bit more torque and it's nearly impossible to screw it up, plus you aren't jamming your knuckles into the rotor.
The 'Big S' has taken a bit of stick on some forums for using this (thus far) unique "SCS" hub geometry, as customers have found that using normal mtb (or road) hubs result in the small cog contacting the rear derailleur drop out. To their credit, though, The Big S bikes I've tried with this arrangement shift and brake flawlessly. I read that this SCS hub geo is used because configuring a normal 135mm spaced disc hub, with the 415mm or shorter chainstays, collided with SRAM (and/or Shimano) specs. Wow…good times….Between the 135 and 142mm rear spacing, along with a bit of unique cassette spacing, and varieties of thru-axles, the current state of disc brake road bike standards are something akin to the Gertrude Stein quip: "there is no there there".
Another great article—thanks November! I just wanted to add my 2 bits that in addition to the stated benefits, thru axles—particularly for suspension forks—provide considerably more precise front end tracking than the old school 9mm axles with standard QR skewers. I'm guessing the larger axle (whether the older 20mm x 110mm or newer 15mm x 100mm) bolted through the dropouts helps keep the fork lowers aligned and working as a more unified system, compared to a narrower 9mm axle that's held in place by a relatively flimsy skewer system. Regardless of how or why, when I first replaced my 9mm std QR suspension fork with a 20mm thru axle fork back in '03, the front end held lines on technical trails like a hot knife through butter. Since the only variable that changed was the axle diameter (no difference in fork travel or stanchion diameter between the 2 forks, and the front wheel remained the same with convertable axle end caps), I attributed the much improved tracking to the thru axle. And for mountain bikes, I've ridden thru axle forks ever since then. Fast forward to today, and I wonder if there is such a noticeable difference in handling when comparing road disc std QR axles vs front and rear thru axles. I'm not sure if I push the limits of a road bike enough to notice the improved fork/frame lateral/rotational stiffness that thru axles provide. On the other hand, I bet thru axles would provide some improvement in cross/gravel bike handling when the race course or trail gets dicey. Bikerumor had a great article w graphics illustrating the difference between standard 10×135 QR rear axles vs the various thru axles available; essentially 12×142 uses same 135mm distance between the inner faces of rear dropouts as std 10×135 QR system, with an additional 3.5mm deep "recess" within each dropout to house the thru axle, aiding alignment (135 + 3.5 + 3.5 = 142). http://www.bikerumor.com/2014/12/19/2016-axle-standards-part-1-rear-148mm-thru-axle-coming-fast-its-about-more-than-just-better-wheels/ BTW, Mark's got a sweet FTB—those knobbies scream "traction!"
Rico – Yeah, Shimano says 415mm chain stays at least for 135mm dropouts. I have a data set of 2 instances where regular hubs worked, but both were on cross bikes (why they even need it on cross bikes I don't really know) so maybe it doesn't work on road? Or with some hubs? I use compact cranks so cross chaining small:small gives me chainring clearance issues anyhow. I don't know. But I think there is there there – I'm about to go ride my disc road bike all weekend and it's a lovely bike and I won't think about anything other than how nicely it rides and how stunningly awesome the Nimbus Ti CLD hubs that will be on it are.Another Dave – Thanks. Definitely suspension forks get stiffer with thru-axles. No doubt at all. The action that loosened my skewer in my example most def wouldn't have happened with a 15mm thru. I didn't bring it up in this one because length limit the huge majority of our wheels go into bikes that don't have suspension forks, but while I think in a road or cross bike if you found the right bike and it had qr, you could easily live with it, on a mountain bike, I think you're punching yourself in the face (perhaps literally) if you go qr.