Thru Axle Hubs
by John Neugent
John Neugent probably knows more about bicycle wheels than anyone else alive. Maybe more about bikes as well. He's spent his life in the bike business, at every level. He now owns Neugent Cycling, a firm devoted to delivering world-class equipment at the lowest possible price. If you are in the market for a set of wheels, please, check out John's site. He really knows his stuff. —Chairman Bill
Thru Axle Hubs:
About 15 years ago, I invented a quick release skewer that opens outside of the pesky fork bosses (known as lawyer lips in the Bike Industry). It was my intention to get filthy rich by selling the design to every bike maker in the world. I failed miserably at both.
The fork bosses are there because if a quick release is not properly used the wheel can fall out. Add to that the fact that it operates on a cam, whose function many people don’t understand, and it is reasonable to believe it’s a problem.
About the same time I was developing my new skewer, there was a good amount of Internet chatter (almost all outside of the US) about the fact that a disc brake on the front wheel has a tendency to throw the front wheel out of the fork when applied. The rotor is grabbed behind the axle creating a fulcrum forcing the axle down and out. Or so they say.
Purists among us just say tighten the quick release properly and you won’t have a problem. But, as Richard Prior said, “You know how dumb the average guy is? Well half the people are even dumber!"
I don’t know if it has anything to do with this, but about the same time, thru axle hubs started appearing on bikes. Back in the good old days, changes to hubs, bottom brackets, and headsets didn’t happen. Bike shops hated changes because it meant they had to stock more parts for repairs. Shimano could get away with it but dealers hated it when they did.
But then for some inexplicable reason (inexplicable only means “I” don’t understand), people started changing everything. In a new product frenzy caused by overstaffed development departments, marketing guys, and a need to be different so you can charge more for your products, the Bike Industry fell into a neurosis of individualism.
And, my friends, that’s where we are now. This makes Bob Dylan look like a conformist.
To give these neurotics credit, much of what we have today is better. But I think the title of this article is Thru Axle Hubs so let’s go there.
A thru axle hub
Despite what some makers want you to believe, hubs are extremely simple – an axle, bearings, and a hub shell connected to spokes. What various companies did was create larger axles. The larger the diameter of the axle the stiffer it is. On the front wheel, especially with a suspension fork (whose legs operate individually) this is a big deal. Credit the neurotics. The problem is that we have a neurosis of individualism so that there are multiple designs.
At the Sea Otter a couple of years ago I asked the head of one of the biggest hub makers in the world “What is going on?” He said “Chaos.”
It would be one thing if there were big performance difference between the different platforms but that doesn’t seem to be the case. As is so common in all industries, marketers will claim huge differences that really don’t exist. Is a 12 mm thru axle stiffer than a 9? Sure. Does it make any real difference? I doubt it.
The good news for you and for most everyone else is that the hub makers saw this coming. One of the very interesting parts of the industry is with the people who manufacture the products. Go to a good hub factory in Taiwan (where the vast majority of quality components are made) and they will know long before anyone else what the big bike companies are interested in making because they are most likely part of the development. So, over the course of the development cycle (one or two years) hub company “A” gets asked about 9, 12, and 15 mm front thru axles and 10-135, 12-135 and 12-142 rear axles by their 10 top customers. What is “A” hub company going to do? Make a hub that works with all of them by exchanging end caps.
As a point of reference, a normal quick release front axle is 9 mm. The thru axle versions are 9, 12, and 15. The standard rear axle is 10 mm with an over locknut dimension of 135 mm on a Mountain Bike and 130 on a Road Bike. The thru axle versions are 10-135, 12-135, and 12-142.
The thru axle itself replaces the axle (thus the name) so essentially functions both as an axle (sliding onto the slip fit of the hub bearings) and the quick release. They definitely are stiffer and therefore add a certain amount of performance because of that, but they are also a little bit heavier and slower. Because they are more difficult to install incorrectly, they also might be safer (for some folks).
So while the thru axle virus was infecting the Mountain Bike market, it mutated into the Cross, Road, and Gravel Bike market along with the disc brakes it accompanies. The UCI seems to feel road discs don’t belong - largely, I believe (which has little currency in today’s market) because riders don’t want them. The bike companies and their suppliers love them because it creates new business – a reason to buy a new bike.
There is one very good reason to get a Road Bike with disc brakes, in my opinion, and that is it eliminates the possibility of a carbon rim overheating – which is very real. I find almost all knowledgeable riders understand this possibility and properly fan their brakes and avoid it for the most part but since carbon rims and bound together with glue, it’s possible to heat the rim enough to melt the glue. On carbon tubulars it’s also possible to heat the rims enough so that the glue holding the tire on melts – causing the tire to slide and the stem to break.
I know the thru axle is not a disc brake but they seem to go hand and hand. I do not believe we will see large scale use of thru axles on Road Bikes until and unless the top pros use them so for most people this is not a big deal. If my wheel sales are any indication, thru axle sales are a tiny portion – but you never know.
Thanks for reading —John Neugent
John Neugent was was one of the first to establish quality hand wheel building in Taiwan around the turn of the century. He now owns Neugent Cycling, a firm devoted to delivering world-class equipment at the lowest possible price.