Bike: 2002 Fatboy

I recently attempted to assemble a second rear wheel assembly; Rim, bearings, Belt Sprocket, Brake Rotor, and Tire. This would allow me to simply swap out an assembly when needing new rubber than mount a new tire on the removed assembly at my leisure.

Sorting through all the parts I've squirreled away over the years, I found everything I needed but became confused when mating up a Brake Rotor. I had a new, still in the box rotor which was marked "Front". I have always assumed that the rotors for this bike were identical and interchangeable. Wrong!

Digging through my parts again I found another rotor which was stamped with a Harley part number. Referencing my Parts Manual, I identified it as a rear rotor. Comparing the two rotors on the bench, I found two differences.

(1) The bolt holes in the rotors are counter-sunk creating inboard and outboard mounting positions. The rotors have slots cut into them for heat dissipation. These slots are slightly angled. Since one rotor is mounted on the left side of the bike and the other on the right, mounting a front rotor on the rear would reverse the direction of the slots. In my mind this would be Cosmetic Appearance only and would not make any difference since you cannot view both sides of the bike at the same time.

(2) The second difference is that the rear rotor is slightly thicker than the front. The difference is so small I only noticed it after measuring with a caliper. The rotors are also stamped with Minimum Thicknesses.
Rear = .205
Front = .180


So my curiosity is peaked. Does anyone have experience swapping rotors front and rear. Logic tells me that a front rotor could work on the rear but a rear rotor mounted on the front might drag.

 

I havent tried this swap, but a few other things to conisider.

are the bolt sizes for the front and rear rotors the same size? I can't remember off hand.

if the rear is on the front, i think as long as you spread the caliper apart as far as it can go before mounting it, the pads should self adjust to the proper spacing once you apply the brake the first time and prevent dragging. just like it would if you put new brake pads in.

not 100% sure on either, cuz i'm not at my bike to look at mine, just some stuff to consider.

 

I'm running a rear wheel on the front of my train, thus running a rear rotor as well. No issues with the thickness, but hardware is very different. 5/16" for the front and 3/8" on the rear IIRC. Since I'm running a rear rim straight up, my front brake is on what should be the pulley side of the wheel. The pulley hardware is 7/16" IIRC. I had to have the rear rotor mounting holes milled slightly larger to accept the pulley side hardware.

The slots and mounting side make no difference, other than aesthetic.

 

Jreichart,

Understand your conversion. Certainly would have made your life easier if you had access to a solid Front wheel. Back on subject, you've proven that a rear rotor can in-fact be utilized on a front wheel with no caliper or brake pad clearance issues.

So I ask myself, why didn't Harley just make the rotors uniform and interchangeable? Must be a marketing strategy!

Another topic. I also have a Train which I've customized. I'd like to see a few photos of yours and what you've done. I once tried mounting a 140 series tire up front but it developed strange, scary handling characteristics. Email me direct at olongapo2@gmail.com