So, the freehub and cassette system has been with us for over 25 years now. Is it time for a change? Kappius Components think so, and while their $999 hub might be a touch spendy to instantly consign the current system to the annals of history, its design is based on some sound engineering and could be the shape of things to come. Let's have a look at how it works.
We've seen in recent years how parts of the bike we hadn't considered can suddenly become the focus of development. The bottom bracket is a prime example. Sealed square taper units ruled for many years, then all of a sudden we had Hollowtech 2 and outboard bearings, we had press fit and BB30, we're just getting our head round BB386... that's a lot of design thinking going into two bearings and a tube. Will hubs be next? Kappius think so, and they're ahead of the the curve with a brand new system already in production.
Father and son team Russell and Brady Kappius are not happy with the current setup, and that's been the driving force behind the development of the Evolution hub. "I wouldn’t have moved forward with the Evolution hub if I didn’t firmly believe I could make a significant change for the better", says Russell in his design philosophy. So, what's to change?
Well the freehub, for all its ability to make the process of swapping cassettes a fairly simple process, places serious design limitations on the hub itself. Chief among them is the placement of the wheel bearings, which on the drive side of the rear wheel have to be inboard of the cassette, and in many cases that means they're even inside the wheel flange: almost on the centre line of the wheel itself. In an ideal world, says Kappius, the bearings would be as widely spaced as possible to make for a more stable load bearing structure. We've seen exactly that progression with bottom bracket bearings moving outwards to create a lighter, stiffer platform.
The freehub system also places constraints on the size and positioning of the drive transfer system; normally this is a tooth/pawl system and sits inboard of the cassette, again near the centre line of the wheel. The small diameter of the drive transfer system also means that it's transmitting very high loads, making it prone to failure.
So, how does the Evolution hub differ? Well, there's no freehub. the hub body extends all the way to the dropouts through the middle of the drive cluster, allowing the bearings to be placed as widely as possible within the space available. This means that the forces the axle has to cope with are reduced, allowing a lighter axle to be used, and the wider base of the wheel hub makes for a more rigid structure.
The drive system is mounted externally on the hub body and a series of splines engage with the drive cluster. It's larger than the tooth and pawl system of a freehub (57mm compared to 35mm) and it's placed further out on the axle to keep all the wheel forces as close as possible to the 'ideal trajectory' which Kappius define as a straight line from the centre of the rim to the outside faces of the hub. The drive ring engages 240 times in a revolution, almost four times as many as even a Chris King hub; there's 60 teeth and 8 pawls (using rare earth magnets instead of springs) that are offest such that two are engaged at opposite sides of the hub at any one time. The greater diameter, and the positioning of, the drive ring mean that the drive cluster can be made lighter but the whole system is stronger. The conical internal face of the cluster narrows to a cartridge bearing in the far end and the whole thing attaches to the hub body with an 18mm cone spanner; there's no need for chain whips. The drive clusters are currently engineered from SRAM Red and XX cassettes.
And the benefits? Stronger, lighter hubs that deal much better with the forces involved in driving a bike forwards. The design incorporates a wider hub body and bigger flanges along with the new drive system, with disc mounts incorporated into the flange design instead of using a separate mount, driving weight down. Current production hubs are about 270g but Russell is confident that weights as low as 200g are possible once production ramps up. That's comparable to the very lightest hubs out there, but there are also big gains in reliability too. The oversized drive ring (for which Kappius has a patent) has to cope with lower forces and should be much more durable. It should, says Kappius, "last forever". Here's hoping. Currently the hubs are available in 135mm and 142x12 for mountain bike frames, but Russell is looking at road bikes too. Although his opinion is that road bikes will adopt 135mm spacing soon.
"I'm very much a proponent of discs on all bikes, and am actually riding a Specialized Crux with BB7s right now, with my hubset," he says. "That said, I don't intend at this point to have a 130mm disc rear hub, but rather a 135mm. I'm betting that is where we end up once the 130/135 choice is made. And heck, I can interchange that wheel from the Crux to my Cannondale Flash 29er with just a cogset swap. But if it looks like frame manufacturers decide on the 130mm spacing for disc road wheels then I'll support it. It's pretty easy to do."
The major downside for now is the cost: at $999 with a drive cluster, it's a pricy thing indeed. But these are early days and small runs; assuming that the feedback is positive it'll be interesting to see whether the design principles in the Kappius hub get more widely adpopted. "Time for the bicycle hub to catch up with the other exciting cycling technological advancements", says Russell. Maybe he's right.
Dave is a founding father of road.cc and responsible for kicking the server when it breaks. In a previous life he was a graphic designer but he's also a three-time Mountain Bike Bog Snorkelling world champion, and remains unbeaten through the bog. Dave rides all sorts of bikes but tends to prefer metal ones. He's getting old is why.