22 March 2009

bikefix Exclusive: Thru-Axle Standards for Everyday Riders

With 15mm and 20mm thru-axles becoming increasingly common on all-mountain, cross country and 29er mountain bikes, we thought it would be good to take some time and let you know about bikefix's experiences and views on the matter. New standards can be confusing, and to top that off, the issue of what axle size issue is best for a given application is not completely settled. The first thing I feel compelled to say is that both 15mm and 20mm are far superior to the old standard 9mm for mountain biking. Why? Thru-axle setups are stronger, safer and stiffer than the traditional quick release, while often only adding a bit of weight

Starting last summer, Fox and Shimano introduced the 15x100mm thru-axle (15QR) as a way to get most of the strength and stiffness of the (already established) 20x110mm thru-axle format without (as much of) the associated weight. In response, some companies (notably Rock Shox) opted to lighten their 20mm systems as much as they could. What is available now are two different axle sizes that feel remarkably similar on the trail with similar weight premiums. We expect that the next generation of 15mm thru-axle forks and wheels will be able to shave a bit of weight from the initial offerings. While there may be some weight to be saved in the 20mm format, its likely to be less than from the 15mm and we will probably see these two formats move further apart than they currently weight-wise (for a given use).

I love the way all these stiffer axles ride. For XC, Trail, and All-Mountain use it is hard for me to tell the difference between the two. I’m guessing that the 15mm standard will blossom in use and be found from lightweight race forks to beefier trail and all-mountain equipment. The original 20mm axle is an accepted standard and will likely remain the province of downhillers, but I think the lightweight 20mm thru-axles will be players in the 5in. travel trail and all-mountain market.

Because 15mm and 20mm forks can be built very close in weight, the system weight difference will come from the wheels. A lot of the reasoning behind Fox/Shimano's adoption of a smaller 15mm axle is the fact that it can be made to work with existing 9mm quick-release hubs' shells and bearings. This means that smaller hubs and bearings than would be possible with 20mm axles can be used with the 15mm through-axles. So, while a 15QR Fox 32 fork (with axle) is about 105g heavier than its 9mm equivalent, the accompanying Shimano hub is about 55g lighter- for a 50g net weight penalty. Over at RockShox, their 20mm Maxle Light-equipped Reba with hub is about 125g heavier than the 9mm equivalent- that's largely because a 20mm thru-axle hub (without axle) weighs about the same as the same hub with a quick release skewer. Racer-only 15QR XTR wheelsets have been spotted, and Mavic's bikefix pick Crossmax ST is already available in the 15QR (Charlie already has a set on test). Of course, there will be exceptions- WTB's 20mm front hub is reportedly only 6g heavier than their 15QR hub, but that kind of parity can only be achieved by using smaller bearings with the larger axle.

In the end, both formats vastly improve on the good old quick release. I like the way both systems work. The Fox axle is super-simple to use but requires some attention the first time you set it up. The new Maxle Light from Rockshox is considerably better than the standard Maxle and works just as well as the Fox 15mmQR, but is even simpler to set-up initially. As I said, I don’t think the dust has settled regarding these formats and we probably will see some more changes, but the standards themselves are likely here to stay- and well worth it. As time goes on, the formats are likely to settle a bit- with fork and wheel companies aligning themselves with one format or the other. We're not saying that anyone should go out and upgrade right away, but when the time comes for a new fork and wheels, definitely go with one of the larger axle formats.


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