Cutaway: Chris King Road & Mountain Bike Hub Comparison, Plus Ceramic Bearing Closeup
With the introduction of Chris King’s Campagnolo-compatible freehub and ceramic bearings option a bit a go, it gave us a chance to look a bit deeper at the R45 road hubs and see what makes them different from King’s standard hubs.
The road hubs use a smaller setup with a 45-tooth ring drive, hence the model name R45. The change from their standard 72-tooth version was to reduce size so they could make the hub shell smaller. They also wanted to reduce the noise. But the big techie reason has to do with degrees of engagement differences between road bikes and mountain bikes.
“When we had to shrink everything for the R45, if we had wanted to put 72 teeth in there we’d have had to shrink the teeth. Our goal was to limit it to a half inch of pedal movement,” said Brian Schultz, product engineer. “With road gearing, 45 teeth ends up with
7.5º 8º of rotation, giving a maximum of half an inch of pedal movement with standard gearing.”
The bearings are built into the drive shell differently, too. On the MTB hubs, there’s a needle bearing in the center of the freehub body because it handles radial forces well (as in forces that are perpendicular to your axle…like dropping off a rock). That’s good for mountain biking and such, but they have a bit more drag.
“With the road hub we went with ball bearings because they have less drag,” Schultz said. “The slotted spring you see in between the two sealed bearings introduces preload for the bearings inside the freehub body. The preload takes out the play in the bearings since they’re angular contact sealed bearings, not radial, and can be adjusted as they wear in via the adjusting clamp on the exterior of the non-drive side.
“The Campy version differs from the standard R45 in that it uses two same-sized bearings in the freehub body because of the deeper splines. With the regular R45 hub, the outboard bearing is a bit larger because Shimano/SRAM freehub bodies don’t need such deep splines.”
The Campy’s axle is also slightly different to accommodate the smaller bearings, so if you were to switch from Shimano to Campy, you’d need to replace the axle and freehub body.
The mountain bike hubs (and all of their other hubs for that matter) use a 72-tooth ring drive engagement system and 19.5mm axle. The R45 hubs use a thinner 17mm axle.
Where the road hubs use a spring between between the two sealed bearings, the mountain bike hubs use a spacer with flared ends between the sealed bearing and needle bearing. On the outboard side, the Seal Ring threads in to compact it all and keep the angular bearings tight. The Seal Ring also incorporates a rubber mud seal to keep the crud out, hence the name.
The Road hubs all have a slightly thicker spoke flange with a bit more “meat” above the spoke holes to handle radial lacing, something that’s not recommended on their regular hubs, especially not for disc hubs.
Close up of the Campy freehub body. Them’s some deep splines.
A closeup look at their ceramic bearings.