Rotor 3D+ Mtb Cranks and Q-Rings Review

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Background Reference:

Traditional Elliptical Chainweels

Around the turn of the century, shortly after the development of the chain driven bicycle, someone came up with the bright idea of elliptical chainwheels. The idea was that the large radius of the chainwheel would drive the chain when the cranks are horizontal and the small radius would pull the chain when the cranks are vertical.

The theory was that while the cranks are horizontal you can pedal more efficiently, and thus can push a higher gear. When the cranks are vertical, you get a lower gear due to the smaller effective radius of the chainwheel. The lower gear is easier to push, and you get through the dead spot sooner. This is the basis for the Q-Rings design.

Biopace

Biopace is a patented non-round chainwheel design made and licensed by Shimano. It looks the same as Elliptical but it acutally is the exact opposite of the classical elliptical design. The product of extensive research and computer-aided design, Biopace chainwheels have the small radius engaged when the cranks are horizontal, the large when they are vertical. This is because the Biopace design is based on a dynamic analysis of the motion and momentum of moving cranks and legs, unlike the static, geometric analysis that produced classical ellipticals.

The theory is that during the power stroke, when the cranks are more or less horizontal, you are using the power of your legs to accelerate your feet, which get going quite fast in the lower gear provided for that part of the stroke. Biopace relies more on momentum to get around the pedal stroke instead of optimizing for the power of the user.  Biopace is really a flawed theory and venture and have alienated many users from trying standard elliptical designs.



About the author: Francis Cebedo

The founder of mtbr and roadbikereview, Francis Cebedo believes that every cyclist has a lot to teach and a lot to learn. "Our websites are communal hubs for sharing cycling experiences, trading adventure stories, and passing along product information and opinions." Francis' favorite bike is the last bike he rode, whether it's a dirt jumper, singlespeed, trail bike, lugged commuter or ultralight carbon road steed. Indeed, Francis loves cycling in all its forms and is happiest when infecting others with that same passion. Francis also believes that IPA will save America.


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  • Chris says:

    So their bb will allow you to run a 30mm spindle thru a standard bb shell? Also, it appears that the spider can be removed from the crank arm. Is this correct? If yes, one could then run a spiderless chain wheel say from HBC and have a wicked light set of SS cranks!!! Hmmm, if that is the case then I am thinking that I need to save up some money!!!

  • euqi santos says:

    just would like to ask if you sell roto rings only without the arms compatible for shimano 3X10 cranks?

  • RanDog says:

    Same Question, in my case just the 2 inner q-rings for FC-M980 XTR TRIPLE, Do You Make Them?
    I have an earlier M970 with Q-rotors, only the two inners on my old 9spd would work on my Spark, but thats all I really needed for my XC use.
    Thanks
    Randy

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