I posted this in the powertap thread in the XC forum but I figured it would interest people here as well.

Quote Originally Posted by WR304 View Post
Coffee King (CK) pointed out that wheelbuilder.com now have a Powertap 142x12mm axle conversion kit available. The conversion kit allows you to use your existing Powertap hub with newer bikes such as the Specialized Epic and Trek Superfly 100 which have 142x12mm thru axle rear dropouts.

Once converted the Powertap hub can also still be used with standard 135mm QR rear dropouts by simply swapping the end caps.

Wheelbuilder PowerTap MTB 142mm x 12mm Axle Conversion

There isn't any mention of warranty on the product page so it would be worth checking what implications this has before ordering. I'd guess that swapping the axle will probably void any existing warranty on your Powertap hub.

Pictured below: Wheelbuilder.com 142x12mm axle Powertap hub conversion kit
Saris told me that having wheelbuilder do the conversion did not void the warranty on the hub. So that's good to hear. I asked Saris if they offered 142x12 or if they could convert it for me and they said no, go to wheelbuilder so they are clearly 100% aware of what wheelbuilder is offering. According to wheelbuilder they actually worked with Saris on some of the hubs, providing input on flange dimensions and things like that.

So I basically did the same thing as WR304 with my powertap for my new bike. After sending it to Saris for new internals I took the SL+ 2.4 Disc, powertap hub straight to wheelbuilder.com to get it converted to 142x12. However after getting the wheel built up I realized I hit a big snag. The rivets on the rotor (between the carrier and the rotor itself) rub the frame on my Pivot Mach 5.7 Carbon's integrated post mount. Apparently this is a problem on some carbon Specialized frames (the epic I think wheelbuilder said?). I'll call wheelbuilder and saris tomorrow to see if they have a solution.

Honestly this rotor carrier seems like huge overkill. It's a rear rotor so it doesn't get that much force, it has 8 bolts holding it on the hub at a pretty large radius with a 4mm thick piece of what looks like aluminum. By comparison the front rotor I'm using is also a two piece 160mm but by formula and the bolt circle diameter for the six bolts is much, much smaller and the aluminum is only 2mm thick. Realistically this all shouldn't matter much as the friction between the rotor and the hub will be holding it in place rather than a shearing load on the bolts themselves. My biggest challenge here is going to be trying to mill this thing perfectly flat so the rotor remains true when mounted to the hub. I plan to remove 1-1.5mm of material.

To clarify I won't have to mill down the whole face of the rotor carrier, just the circled area. The hub is actually machined out between the bolt holes so there is no need to cut between them.

Honestly though the tolerances on the frame, especially in the drop out area don't seem to be fantastic. For instance the threads on the axle that came with it seems to rub the inside of the hole in the frame that it travels through to bolt into the derailleur hanger no matter how I try and fiddle with the derailleur hanger when I bolt it to the frame so I'll try this in another 5.7c frame tomorrow to see if that fixes it.