The rapid growth in disc brakes for road bikes has catalysed the uptake of thru-axles. Marc Abbott asks if this mountain bike technology will soon replace the humble skewer
When Tullio Campagnolo invented the quick-release skewer almost 90 years ago, even he, as the father of Italy’s groupset giant, couldn’t have imagined that his simple idea would become the industry standard.
Designed for race use, where time is everything, a system that allowed a wheel to be dropped out for changing (or, in Campagnolo’s case, flipping, to use the secondary gear on the other side of the hub) was always likely to gain favour. As with so much race technology, the humble quick-release filtered down to the bikes we grew up riding.
But leaps forward in bike design often demand new approaches. The advent of disc brakes on road bikes has necessitated a change in thinking when it comes to maximising stiffness and minimising losses, provoking manufacturers such as Focus, Boardman and Colnago to take their lead from the dirt bike world.
Their use of a thru-axle, a pin that needs to be pulled completely through the spindle before the wheel can be removed, has sound foundations.
“The big advantage is the stiffer load path between the caliper and rotor,” says Keith Bontrager, arguably the godfather of modern mountain bike development, and now component developer for Trek.
“Flexing in the axle or dropout on the brake side will allow the rotor to shift and contact the brake pads, causing the brake to drag. It’s noticeable when climbing out of the saddle. The large axle and rigid connection between the axle and dropout minimises that.”
With such a clear performance benefit, surely everyone is swapping to thru-axles? Not so, says Zipp’s wheel development director Michael Hall: “Zipp continues to design wheels/hubs that allow the rider to easily change between quick-release and thru-axle.
“Our 77/177D disc brake hubs are actually supplied to the customer with both quick-release and thru-axle end-caps, so they can make the decision.”
Which, for now, means the customer looking to upgrade still gets a choice. But what’s the flip side?
“The disadvantages are that [the thru-axle] can add a bit of weight, and removing and replacing a wheel becomes more time-consuming,” says Bontrager. “That time issue is a minor annoyance for most riders, but pro teams will have to work out a way to swap a wheel quickly in a race. It might mean bike swaps become more common.”
The increased use of disc brakes prompts a broader question: how much will frame and wheel design change?
“Thru-axles are something new that will change bike and frame design,” reckons Hall. “As for wheels, disc brakes open up opportunities for advancements in rim design, since we are not as limited by a brake caliper or chainstays. For instance, rims can certainly get wider.”
Bontrager takes the position that mountain biking has done the hard work for us, adding: “There are a few things that change when you design a disc wheel or thru-axle, but most of those have been addressed with off-road wheels and are well understood.”
The key question is, if there’s a clear performance benefit to be had from switching to a thru-axle setup, will that be reflected at your local bike shop?
“Stocking both will require the dealer’s inventory to be a bit deeper,” says Bontrager. “That might make getting a specific spare tougher in some cases.”
Bontrager also highlights the more secure nature of the thru-axle: “[US firms] may move away from quick-release to reduce the problems with product liability… Incorrect use of QRs continues to be a problem in the States.”
It’s time to take a long, hard look at ourselves and ask whether it’s weight or stiffness that’s the most important factor in our bike-buying decision. Rim brakes with QRs will have their place for years to come, but if you want to make the switch to disc brakes, bolt thru-axles are the obvious, future-proof choice.
Yes: Keith Bontrager, father of modern MTB and component developer for Trek
“It’s likely that thru-axles will become the industry standard eventually, down to a certain price point. I don’t know what the timeline will be, but if it’s anything like the wheel size thing in mountain biking, where the 26-inch option was rapidly removed with the introduction of 650b and the 29er, I think it could happen quickly.”
No: Michael Hall, Zipp wheel development director
“We want to provide the best options for our customers. Zipp continues to design wheels and hubs that allow the end user to easily change between quick-release and thru-axle. Our most recent disc brake hubs, for example, allow the rider to change between quick-release and thru-axle simply by swapping the end-caps by hand.”