I just made an interesting observation about rotor rings and the old biopace and I was wondering if anyone else had similar experiences. Bottom line, as much as Rotors are touted as the new great, expensive thing, they are really identical to biopace.
I have been riding Rotor Q rings for about a year now and logged a few thousand miles with them on my road bike. Although I do not find them “smooth” as others claim, they have all but eliminated my knee pain. So now I am looking to set up my CX rig with the Rotor Q ring single front setup (I am also somewhat admittedly influenced by Vos after watching her decimate the Worlds field with these rings).
A fiend of mine told me to just install my old biopace rings. He contended they are oval and therefore the same. A quick internet search indicates that this is not true and that the biopace rings are actually the opposite as the Rotor rings are designed to decrease the effective chain ring size when your pedals are in the non-power section of your pedal stroke (roughly at 12 and 6 o'clock) in order to help you speed through that part and apply power where it counts, while Biopace rings increase effective chain ring size when the pedals are in the "dead" zone of your pedal stroke.
To prove to my friend that I was right, I decided to compare them side-by-side. I have 42T version of both so I just lined them up. I was amazed. They really are identical. If you rotate the biopace counterclockwise 2/5’s (or two bolts holes to the left) then it is the same as the Rotor ring when in the 5 position. Both the overall shape and teeth line up to a millimeter.
I was wondering if anyone else has tried using the old biopace as a substitute for Rotors?
Biopace overlaid on Rotor ring
Rotor ring overlaid on biopace on crank
Biopace overlaid on Rotor ring on crank note the indicator that should be inline with the crank arm is two bolt holes to the left
brokenman, did you end up trying this experiment? for one ring prob it can work great, maybe gets dicey if you did a biopace double and a 10s or 11s chain? did you just up the price for biopace cranksets on eBay? too bad there isn't a 135mm biopace to put on a buffed C-Record crankset!
did you end up doing this BrokenMan? Guess it matters how the spider is oriented on a crank.