It's all in the Details

A while back, Shimano and Fox teamed up to create the 15mm TA standard for suspension forks. (EDIT: More to that point of history, check out this article over on NSMB from 2010.) Up till then, Rock Shox had pioneered the 20mm thru axle, but these forks were really biased towards the freeride or DH segments. Shimano and Fox teamed up because there was a need for a fork that was both light and stiff, but not necessarily as stiff as a DH fork and certainly not as light as a XC racing rig. I like to call this a “Mountain Bike”. Remember those?

So before all this 15mm TA business happened, I was still riding 26″ mountain bikes, and I was running a Rock Shox Revelation. 1.125″ steerer and a 9mm quick release hub. Out of curiosity, I found a lightly used Pike with a 20mm TA. Luck would have it my wheel set was sporting a set of DT Swiss / Hugi hub set and the front hub could be converted to 20mm TA with the swap of the end cap kit. That first ride kind of changed everything – not just from a performance stand point regarding the fork, but from a stiffness and control in tech stand point. The front end just stuck to the line I aimed it at… This changed everything.

After our move to NH a few years later, I found myself curious about the big wheels. 29″ wheels that is. New to the area, I also did not have any clue where any of the single track was. 29″ wheels made perfect sense: Build up a bike that could carry some speed and those big 29″ wheels could handle dirt road and trail duties without sucking the life force out of me as 26″ wheels tend to do on long spans of road. I found a Surly Karate Monkey frame/fork, built it up as a single speed and began exploring. Rigid is of course fun, but suspension is even more fun. So once again, I found myself with a Rock Shox fork beneath me but it was a QR version (I don’t think Thru Axles had totally come into vogue “just” yet? They were present, but the hook hadn’t been set, yet.). Right around this time I also found myself looking over Ted Wojcik’s shoulder every friday and we built a frame together as I had drawn it. A great learning experience and a bond of friendship was forged too. But I recall the hubbub that abounded when Shimano and Fox introduced their 15mm TA. Yet another standard was created when there already existed one. A trend in the cycling industry that seems to be rehashed over and over again! But, all this new technology getting thrown around aside, some things stick while others fall away. The ones that stick typically are the ones that make sense in the long run and have a clear performance advantage.

Fast forward and I’ve built out the shop and have begun building bikes under the name 44 Bikes. Experimenting with different tube sets, tube diameters in combination with 44mm head tubes and tapered forks/15mm TA’s, it became crystal clear just how much of a performance advantage these new suspension forks had over the old ones I had ridden for years. Brake induced fork flutter was pretty much gone, that washy feeling under hard braking in corners was pretty much gone, when I pointed the bike at a line of tech, the bike responded with a lot of confidence and control… Etc. Etc. And etc. I was sold. Quick releases on a suspension fork were out. Thru Axles were “THE HOT SET UP”. Check it out. A little weight penalty yes, but that old quick release just is dwarfed by a Fox 15mm TA:

15mm TA / QR 100

Manliness aside, the connection that a thru axle brings to the table is a solid one. Which brings me to the subject at hand, and the recent uproar of “talk” regarding thru axles and road bikes. What I want to speak about is more on the mountain side of things primarily and draw parallels that show how the performance of certain set ups can be improved. Way up there at the top is technically my 7th mountain bike prototype. It sports a QR 135mm rear. I love this bike. But with the advent of 12x142mm TA’s for the rear, and having ridden one on my single speed due to the ease of swapping the dropout inserts made by Paragon Machine Works, it has become clear (once again) just how much of a performance advantage a 12x142mm TA in the rear can offer. Power through the pedal to the rear end is incredible. On a steel hardtail, I “thought” this would translate to a really stiff rear end. Quite the opposite once out on the trail. The stiffness actually translates to power transfer (according to my opinion) and on longer rides the resiliency that steel is known for is still there all day long. But the thru axle further triangulates the rear end and kind of ties the two dropouts together in a way that creates this solid, power transfer system. Here’s one of the business sides of the old QR 135 setup:

Proper

One thing about this set up is when it’s in combination with disc brakes. If the QR isn’t tight enough, under heavy braking, the wheel can become slightly ajar or come out of alignment in the dropouts. So you gotta keep that QR tight (not gorilla tight) but tight none the less. On a TA, you can get them tight, but just tight enough by setting the adjustment of where the threads engage (Shimano’s set up). The thru axle still has a cam of sorts on the end so you still draw the two dropouts towards each other. But since the axle goes all the way through and is encapsulated by the dropouts, even if the TA is slightly loose, there is just no way that wheel is coming ajar. You’d have to physically unthread and pull the axle halfway out for that to happen. So there’s that factor to think about. Here’s the business end of a TA on my latest prototype which replaced the one above:

Proper

I know I’ve heard some talk about repeatability of alignment between wheel sets with wheel swapping and quickness of swapping wheels. Those two things I kind of view as marketing hype. For one, each hub manufacturer adhere’s to their own set of guidelines for tolerances. A “plus or minus” of a given measurement. I’ve had two identical hubs from the same company that both would require a subtle adjustment at the disc brake caliper – just a simple realignment of the caliper. They still worked, but the rotors rubbed on one wheel while it did not on the other. The whole quickness of wheel swapping I see like this: With a TA, you must unthread the thru axle, then pull it all the way out, set it down somewhere for safe keeping, or hold on to it in one hand (and make sure no dirt gets on the thread if you do set it down), then drop the wheel out. On a quick release wheel, you flip the QR, loosen the nut a few turns and pull the wheel out. Hence the terminology: “Quick Release”. So you could argue there is an extra step with a TA that requires you to remove the thru axle while a quick release remains in place. This is splitting hairs though, I know that. But both can be done quickly and painlessly by a skilled mechanic or an experienced rider. The clear advantages are in the performance attributes spoken about above when it comes to power transfer and reliability of alignment under heavy braking long term when in combination with a disc brake set up. And for your viewing pleasure, here’s what both a QR 135mm looks like next to a 12x142mm TA:

12x142 TA / QR 135

When translating this over to the road and especially dirt roads with loaded bike packing set ups, and your bike is sporting disc brakes, there are clear advantages. Traditional caliper or canti-lever brakes and thru axles? Not sure there is a real, quantitative need there? And it’s more to do with where the applied braking forces are in relation to the wheel honestly – on a traditional Canti-lever or caliper brake, the brakes are being applied from both sides of the wheel – on a disc brake set up, which is asymmetric, you’re applying brake forces only on one side and it’s more likely to “pull” the wheel towards the disc brake side and hence the need for something a little more stout at the connection point: The axle. (There’s physics there, of which I vaguely recall from college and high school… Something to do with axis of rotation and applied force with relation to the axis of rotation – I’m no scientist apparently, but I think we all get the basic take away.) From a builder perspective, there is little room for error when building a thru axle compatible fork or frame. But from a user stand point, I can see where a more solid connection through a triangulated rear end of a bicycle which is loaded down with a bike packing set up will allow for more power through to your pedal stroke creating more efficiencies with less power loss. Each pedal stroke over 100, 200 or 1000 miles plus adds up. And if you are going the distance, each pedal stroke matters with forward motion. Or have a quick release loosen up on you or not be tight enough with a loaded touring set up with disc brakes? CX Racing set ups with disc brakes with greater power transfer? These are clear performance advantages. Small ones, but like any system, it’s the sum of it’s parts. All these little things add up. Shave some weight here, add some stiffness there. Again: it all begins to add up.

Are thru axles here to stay? Yes, they are. The bigger question however is where do the belong? Just like the whole DH segment vs the Trail segment where the question becomes “Just how stiff does stiff have to be?” you need to ask yourself just how much performance do you need and if you are running disc brakes or cantilever brakes, how solid of a connection do you need. Either set up be it disc or cantilever can be handled with by a quick release. They’re light, they’re simple and they’re not broken. But if you want just a touch more performance and want the self assurance of a more solid connection, the a thru axle may be the right set up choice for you. Personally, I think it all comes down to your set up, what kind of terrain you’re riding and how you’re riding. This starts to paint a picture of your needs and requirements for your build. These are the questions I ask myself with each client: What are you riding? How are you riding? What do you need? Those same questions you should ask of yourself when choosing your set up and deciding if disc brakes make sense and with disc brakes do thru axles make sense.