We’ve had a couple weeks to test out the new Soul Kozak road hubset which retail for $400 with either Campy or Shimano freehub bodies. For the front hub Soul Kozak brought the flanges in for increased aerodynamics while the rear hub gets both magnetic and bearing upgrades. The head of our custom wheel building program, Troy Watson, pulled them apart, rode them (laced to ENVE 45s with Sapim CX-ray Spokes) and gave us his thoughts.
The Soul Kozak Magnetic Rear Hub
The rear hub has been completely redesigned from their previous road offering. The big difference is the move from a 3 pawl drive system to a magnetic mechanical diode system that Soul Kozak first used on their MTB disc hub. The system is very similar to DT Swiss’ star ratchet but with a few differences. The drive ring’s teeth are machined vertically into the side of the freehub body and are one piece not a separate. The other half of the drive ring is a machined steel piece that is floating side to side in the hub shell. The floating drive ring and teeth machined into the side of the freehub body are forced together by opposing magnetic forces. The hub body and floating drive ring have magnets in them that are pushing against each other. The magnets are used instead of springs, so it is one less moving part to fail or need maintenance.
There are some other design features of the rear hub that need addressing. The freehub body is steel not aluminum but the hub is only 212g. So it is slightly lighter weight then the DT Swiss 240 hub which uses an alloy freehub body and smaller bearings and axle. Also the Soul Kozak uses very large 6903 size bearings. There are a few hubs that are using the 6903 size but usually only one or two. The Shimano hub uses a total of four 6903 bearings, two non-drive side and two in the freehub body. The Campagnolo version uses two 6903 bearings on the non-drive side and and two 6803 in the freehub body to accommodate the smaller diameter freehub body. The trick they used goes back to the steel freehub body. Since steel is stronger then aluminum they were able to machine the walls of the freehub body thinner and squeeze the large outside diameter of the 6903 bearing into the freehub body. The only downside is that doing that made it so that a standard lockring no longer fit the freehub body so they made their own 4 gram (11 tooth) alloy one, which they include with the hub.
The Soul Kozak Aerodynamic Front Road Hub
The most obvious thing about the front hub is the narrow flange spacing, but there are some other things as well. The hub has a 17mm axle and large bearings but only weighs 75g. The 17mm axle is needed for stiffness because of how far the bearings are set in away from the dropouts. The flange spacing is 28mm center to center of flange, which is 8 to 10mm narrower then the average hub. Most hubs are in the 34 to 36mm range with a few being even wider at 38 to 40mm.
The narrow spacing is to help with aerodynamics. The spokes are almost completely shielded by the rim. Bladed spokes are also work better the closer to vertical they are based on the air flow direction they actually see. The narrow flange spacing will reduce lateral stiffness but these were mainly designed for deeper section rims where the smaller rim spoke circle diameter will bring the bracing angle back up closer to what a regular hub with low profile rim would be. If you were to take an average front wheel like a Shimano Dura-Ace hub laced to a HED Belgium C2 rim you would have a spoke bracing angle of 7.2 degrees. Now compare that to the Soul Kozak front hub laced to a Enve Smart System 60mm front rim and you will have a bracing angle of 6.3 degrees. So yes the average front wheel will be a tiny bit stiffer but the Soul Kozak /Enve front wheel will be significantly more aero with pretty much the same stiffness.
Thoughts on our Test Rides
The very notable first impression we have of the hubset is that when coasting the powerful magnets used to engage the freewheel make a very loud noise. For more info on the ride we’ll be posting a long term update in the future since this hub is largely designed around durability and strength. We don’t feel that there’s anything to worry about as we’ve ridden narrow flanged aerodynamic front hubs before with no problems. And with the rear hub being steel and using larger bearings we believe we’ll like it more, in terms of durability, than the 2011 rear hub that it replaces.