Monday, March 10, 2008

12 Non-Circular Chainrings

Bobby with unconventional chain rings at TOC '08 : Courtesy Eddy58

Last Sunday, as I watched the "Race to the Sun" Prologue TT on Versus, I observed Bobby Julich had the funky looking non-circular chain rings on his Cervelo. Okay, so whats new?

There seems to be a very comfortable relationship between him and O.Symetric. Julich reported once that he believed the chain rings gave him an extra 5 seconds per kilometer in his time trial runs.

Notice that in the beginning of this post, I said non-circular. Its safe to say that it is a custom made shape to Julich's biomechanical situation. There have been a few elliptical and oval models in the past. One of the best known initiatives was Shimano's oval Biopace of the 80's. Others who followed suit include the independently operated Power Cranks and Rotor Cranks with their elliptical Q-Rings. Another drastic idea was to use a spring mechanism with the circular crankset so that energy could be returned back at the dead centers to aid in power delivery.

In the 360 degrees of circular pedaling movement, there are two "dead centers", each occurring when the crankshaft is near the 6 o clock and 11-12 o clock positions. In these spots, it is difficult for the human body to produce much crank power since the tangential pedal force direction (shown below) is perpendicular to the preferred force direction of the legs. Thus, when one leg is vertically up and the other down, tangential forces cancel and a situation known as "Power Vacuum" occurs for a very short period of time.

Non-circular chain rings aim at reducing the dead centers by changing the shape of the pedaling path and manipulating the gear ratios so that a rider can minimize time spent in these dead spot and approach pedaling power potential.

Pedaling Forces : Analytic Cycling

It makes sense to me but I can't speak for these types of chain rings since I don't have them. It seems to me that they must be custom made to a rider's pedaling technique to provide any objective feel for higher power. Otherwise, any noticed variation is simply an unwarranted placebo effect. Other known issues are linked to nonrhythmic movement of the knee, front shifting and chain suck.

Apart from the mechanical side, there's also a small self-esteem issue for me to be maverick at the local circuit and ride strange looking stuff. I'm not Cipollini, but neither do I have the capacities of Julich. At the moment, I like what I use and prefer the idea of fully developing my upstroke phase to accelerate through the bottom half of the pedaling circle. This should account for any power variations at the dead spots.

What do you think of non-conventional chain rings? If anyone has had a direct experience, it'll be nice if you share with us some numbers related to the improvements or any other disadvantages you may have observed.


  1. Ron - I use Q Rings on my bike. The thing I like about them is that both chainrings are fully adjustable meaning you can accelerate or retard the rings by just moving the bolt pattern one way or another. They tell you to start on position #3 and ride for 400 miles and to then adjust based on your needs. I personally find 3 to be good. As for performance, there is definitely a noticable difference, but it is not when you are burning down the road at 125 rpm. It is under heavy load, particularly climbing. I feel like my pedal stroke is more circular rather than push push push push. Just my observations, but I am happy with them and will probably stick with them as I change bikes.

  2. I have them on my TT bike and road bike. The TT setting is 4, for a more forward position and the road bike is on 3. To me they make the bike feel silky and smooth and during climbing it feels like you can really power up without frying the legs during longer climbs. Improved a cceleration is also noticable. I love them.

  3. Ron,

    I came into a bio pace on a bike I picked up in the late 90's. I didn't notice any difference.

    I'm of the same mind as you that stroke improvement removes the dead spots.

  4. I use Q-rings.

    I did a 20 minute TT the week before getting them, and a 20 minute TT the week after. I noticed a 5.3% increase in power, which was exactly in line with what rotor predicted. It's hard for me to argue against this. I think I'll be getting a set for my TT bike.

    Front shifting is definitely less smooth, but I don't shift my big rings that much anyway.

    The biggest surprise is that even though they look weird, you don't feel any different riding them.

    As for just developing a smoother pedal stroke, I'm not convinced. You just physically don't have as much muscle to push at 12 o'clock or 6 o'clock. You can minimize the deleterious effect, but if you don't have as much muscle there, you don't have as much muscle there. I don't think any amount of practice pedaling in circles can eliminate this completely, but combined with Q-rings, it seems like you may be able to nearly completely do away with the dead spots.

  5. Luke - You claimed an increase in absolute power of 5% in CP20. What if this change was just from an increase in say, fitness, rather than any change in equipment? Did you also check to see sometime down the road whether this figure still held?

    I think a better parameter to judge will be power output vs heart rate or better still, lactate concentration in the blood, all on a protocol like a Conconi or Wingate test... which can be difficult to do outside a lab setting.

    It seems to me as if adaptation rates will vary among people depending on their riding experience and pedaling style. People who have used conventional cranksets for a long period of time , or those who've gotten pretty comfortable applying unusually large upstroke forces on the pedal
    may find the sudden change in pedaling technique hard to adjust to. On the other hand, novice riders may actually adapt easier and hence, perform better.

  6. Yes, it is possible that the 5% increase in power is due to fitness, not the Q-rings. However, over the course of a week in which I got more (not less) tired, it seems unlikely that I would get that much stronger.

    A lactic acid test would absolutely be better, just not feasible outside a lab. I included the results I did to give a little credence to the studies Rotor did (including lactic acid tests). Their power numbers matched what I found. Doesn't mean the rest of their results are legit, but it indicates it at least a little to me.

    Going back to look at heart rate, the differences in heart rate were statistically insignificant.

    Adaptation rates will of course vary - I've been competitively cycling for a few years, but not decades. I mostly included that to give an idea of how different the pedal stroke is - namely, not different at all.

    I'm going to keep updating my review at Technical Cycling as I use these. I hope to later include a test where I go back to standard rings, and do/don't see a power drop.

  7. I meant

  8. Luke - Thank you for the link. Regarding your results, if they can be replicated again or pushed further another time, there'll be plenty of reason to think that they're working out for you.

    Chris - I'm surprised you have a set of Rotors yourself. I agree with you, they could be more beneficial to you in low speed-high torque scenarios like climbing a hill. I hope they work out for you.
    One thing - the next time you do seated climbs on those rings, see if your arms are doing more work than you think they should. I'm just curious.

    Todd - Thanks.

    Blue - I think the book "Bicycling Science" by David Wilson has blasted the story on Biopace pretty much forever. There is no evidence that they made any significant difference to performance, and they are no longer widely available.

  9. Thanks for bringing up BioPace, by the way. I have used that in the past, and while it certainly felt both weird and fun, it certainly didn't seem to actually help anything (did anyone else think that riding these was sort of fun though?). These are markedly different than that, however. They operate on a completely different principle, as I'm sure you're aware.

    I just took a rest week, and my wattage jumped by a surprising amount so I won't be able to update the Q-rings review too much for a couple weeks until some of this rapid changing drops away (at
    Technical Cycling, now that my ability to link things has stopped failing me - I'll put at least some more info up tonight). I haven't seen any studies over time with this, so I'm a bit curious to see how much of it is placebo effect, and how much is legitimate biomechanics.

    One point worth making - they certainly don't seem to make you slower, whether or not their positive effects are significant or not.

  10. I had a rental Bianchi once with BioPace chainrings and just found them to be very strange. My feeling is that since not everyone pedals the same way, the dead spot is bound to be different, hence the adjustability of the Q Rings. I did go on to buy a Bianchi but I had the shop switch the BioPace rings for standard circular ones. But as you know, there doesn't seem to be anything that has not already been invented in cycling over the last 125 years!

  11. Ron,

    I have a hard time with this stuff. In 1973 I turned a 56 minute TT over 25 miles with a steel road bike, no aero bars a cloth cap turned backwards and wool jersey and shorts at 17 years of age.

    Yes I like the gear that is out now but I still manage to better guys my age with all the gear.

    I went to get spacers today for my stem and the LBS gal asked me if I wanted carbon. My reply was those are for guys with 0-6% body fat.

    Sometimes I think the gear gets carried too far. I still won't use aero bars and turn good times 10k 15:30. Not bad for 51 and overweight.


  12. Sprocket - People have always come up with amazing ideas to go unconventional, pedaling with compressed air, linear drives etc all come to mind.

    Blue - I agree, fit, function, performance and comfort overwhelm any fancy equipment out there.


Thank you. I read every single comment.