Paris - Nice time trial.

[Johndec]

Hi. Just watching a reply of the last stage of Paris-Nice, the 10k time trial. Do I need new glasses or is Wiggins riding a bike (Di2) with non circular crank rings? They appears to have a slight oval shape to them to correspond to his pedal downstroke.

[RonK]

Hi. Just watching a reply of the last stage of Paris-Nice, the 10k time trial. Do I need new glasses or is Wiggins riding a bike (Di2) with non circular crank rings? They appears to have a slight oval shape to them to correspond to his pedal downstroke.

Probably - they are in common use on TT bikes and some riders even use them on their road bikes.
They were introduced by Shimano about 20 years ago. I had a bike fitted with their Biopace chainrings.
They are claimed to help pedal through the dead spot at the top of the pedal stroke.


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[toolonglegs]

Yes oval chain rings, but very different orientation to the ones of 20 years ago

[Johndec]

Thanks Ron. Just did a bit of googling and it appears they have been around for about 20 years. Never noticed them before and it appears Wiggins is a big fan of them. He might be onto something. He won the TT

[JV911]

wiggo uses O.symetric chainrings

[population100]

They can (apparently) hamper shifting. I believe Wiggins dropped out of the 2009 world TT championships due to mechanical problems shifting from large to small chain rings.

He seems to have fixed that now though.

[toolonglegs]

High point of the oval on old Biopace is in line with the crank arm... these days they run it a 90 degree angle.

[JV911]

these days they run it a 90 degree angle

yep and adjustable in the case of Rotor

mine shifts prety well but maybe not as crisp as a traditional chainring (given the distance between the derailleur and the chainring is not constant)

[toolonglegs]

these days they run it a 90 degree angle

yep and adjustable in the case of Rotor

mine shifts prety well but maybe not as crisp as a traditional chainring (given the distance between the derailleur and the chainring is not constant)

Not 90 degree adjustable though... unless you want to put them on the wrong bolt holes .