Paris - Nice time trial.
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Paris - Nice time trial.
Postby Johndec » Mon Mar 12, 2012 6:46 pm
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.
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Paris - Nice time trial.
Postby RonK » Mon Mar 12, 2012 6:56 pm
Probably - they are in common use on TT bikes and some riders even use them on their road bikes.Johndec wrote: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.
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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Last edited by RonK on Mon Mar 12, 2012 6:59 pm, edited 1 time in total.
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- toolonglegs
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Paris - Nice time trial.
Postby toolonglegs » Mon Mar 12, 2012 6:59 pm
Yes oval chain rings, but very different orientation to the ones of 20 years ago
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Re: Paris - Nice time trial.
Postby Johndec » Mon Mar 12, 2012 7:03 pm
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
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Re: Paris - Nice time trial.
Postby population100 » Tue Mar 13, 2012 10:05 am
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.
He seems to have fixed that now though.
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Re: Paris - Nice time trial.
Postby toolonglegs » Tue Mar 13, 2012 6:06 pm
High point of the oval on old Biopace is in line with the crank arm... these days they run it a 90 degree angle.
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Re: Paris - Nice time trial.
Postby JV911 » Wed Mar 14, 2012 12:32 pm
yep and adjustable in the case of Rotortoolonglegs wrote:these days they run it a 90 degree angle
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)
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Re: Paris - Nice time trial.
Postby toolonglegs » Wed Mar 14, 2012 4:13 pm
Not 90 degree adjustable though... unless you want to put them on the wrong bolt holes .JV911 wrote:yep and adjustable in the case of Rotortoolonglegs wrote:these days they run it a 90 degree angle
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)
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