"oval" cranks

welsh_14

I've noticed while watching the tour de france that a few riders have oval like cranksets rather than round. As a mountain biker I've never seen this before. So I wondered what the benefits of this is over a "normal" round crankset?!

Monty Dog

I suspect you mean oval chainrings like Osymetrics? The chainrings are shapes to optimise the power transfer during the pedal stroke i.e. larger diameter when leg is delivering peak muscle power, conversely, smaller for recovery phase of stroke. The original concept was developed by Shimano and called Biopace about 25 years ago - the problem with these was that the ring shape was 90 degrees out of phase and hence fell out of favour.

Gizmo_

Q-rings also - as seen on Wiggo's TDF bike, I think: http://www.rotoruk.co.uk/qrings.html

It's a clever concept.

solosuperia

Monty Dog wrote:

I - the problem with these was that the ring shape was 90 degrees out of phase and hence fell out of favour.

I never realised this was the problem, did have "Biopace" rings back in the day and couldn't get on with them. I wondered at the time why I could not get a smooth pedalling action.

I am assuming from what you have said that by moving the rings through 90 degrees has that problem has been solved.

Tell me do Wiggins and his ilk use them 100% of the time or only for mountains?

welsh_14

Yes that was exactly what I meant!
Interesting to know thats what they are for. Wonder how much difference an average rider would notice from these or whether its something on the pros would notice!

Monty Dog

From memory, the Biopace concept was that the ring was smaller at the point of peak power, but it just felt weird - the name lives on as the term using for a 'bobbing' you get when riding some suspension bikes. Wiggins and Millar are both proponents of oval chainrings - the downside is that the front mech shift can be tricky as you can jam the chain between the ring and front mech cage.

rolf_f

SoloSuperia wrote:

Monty Dog wrote:

I - the problem with these was that the ring shape was 90 degrees out of phase and hence fell out of favour.

I never realised this was the problem, did have "Biopace" rings back in the day and couldn't get on with them. I wondered at the time why I could not get a smooth pedalling action.

I am assuming from what you have said that by moving the rings through 90 degrees has that problem has been solved.

Biopace was fine. I certainly had no problems with it. TBH, I wonder if the ovalisation was too subtle to make that much difference - the current ovalised rings are far more extreme in shape.

Anyway, Sheldon is worth a read on it.

http://www.sheldonbrown.com/biopace.html

I think people tend to assume that Rotor rings are just 90 degrees out of phase of 'the original arrangement' which they assume was Biopace. Unfortunately the original arrangement predates Biopace by decades and itself was out of phase with Biopace by 90 degrees. What this does mean, unless we start talking 45 degree phase shifts (which could be reasonable), is that what Rotor are doing now has been already done before! It either matches Biopace or Biopaces predeccessors.

amaferanga

I've only noticed oval rings on the TT stages. My own experience of oval rings is that they make no real world difference and for road racing they're just not worth it.

BelgianBeerGeek

+1 to Rolf's comments. I still have Biopace rings on my old Raleigh (currently in bits in the attic). I too never had any issues with them and agree they are perhaps too subtle.

I think the jury is still out on what, if any, benefits are made. I think that if there were real gains then everyone would be using them.