bikerumor monday mystery bicycle part picture

Photo from the collection of Jason Woznick of Fair Wheel Bikes. If you think you know what this is, post your answer in the ‘comments’ section– the correct answer will be posted there on Tuesday!

To send in your own Mystery Pic to be considered for the Monday feature, click here and attach your photo with all pertinent information.


  1. Those are definitely AC cranks, but I don’t see the logo, so they might be the generic UMC version. BTW – don’t ride them, I broke two sets on the driveside, crankarm just snapped in half leaving a very jagged edge that made a scar I still have today.

  2. I think I remember these as AC experimental or low run production cranks. IIRC, they took their standard cranks and milled out the rest of the windows but halted production after high failure rates.

  3. definately AC cranks! I remember lusting over those as a teenager, then magic motorcycles came out and AC were a thing of the past.

  4. Answer from Jason:
    Titus cranks. (these will be confused with AC cranks which are very similar since these were made by AC, but the machining on the cutouts are different between the two.)

What do you think?