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Technical FAQ: Biopace chainrings and other gearing questions

  • By Lennard Zinn
  • Published Jun. 10, 2014

Using Biopace cranksets

Dear Lennard,
Bradley Wiggins used Biopace chainrings in the crucial time trial in the Amgen Tour of California. He quoted an advantage of some 40 seconds over the course. With the amount of data collected and analyzed nowadays, this is no longer subjective.

I was given a Biopace crankset a long time ago and tried it for a while. With multiple bikes, the differences switching is just too small and takes away from the enjoyment.

With the new 10- or 11-speed rear cluster, it is now possible to tailor a particular chainring for different terrain with no downside. What about running a triple crank with a smaller Biopace chainring just for climbing?

I am a firm believer that there is nothing new under the sun. Do you know what the wisdom is for people that have tried this?
— Curious Bill

Dear Bill,
There is an extremely critical distinction between Shimano Biopace chainrings and the Osymetric chainrings used by Wiggins in his 2012 Tour de France and Olympic victories and by Chris Froome in the same Tour, as well as the Rotor chainrings used by other top riders. However, I was under the impression that Wiggins used round chainrings in the Folsom TT in the 2014 Amgen Tour; here it is in action.

Biopace, like the Houdaille Powercam crank concurrent with it back in the early 1980s, gave the rider a smaller gear during the power phase of the pedal stroke and a higher gear over the top and bottom of the stroke. In other words, the time spent in the power phase was reduced, and the time spent at the “dead spots” was increased. This never was shown definitively to offer an advantage.

Conversely, Osymetric and Rotor chainrings give the rider a higher gear during the power phase of the pedal stroke and a lower gear over the top and bottom of the stroke. In other words, the time spent in the power phase in increased, and the time spent at the “dead spots” is reduced. There is modern power data indicating that there is an advantage to be gained with these chainrings. The downside is that they do not shift as well as round rings, and with electronic shifting in particular, which gives the rider no option to fiddle with the lever and get the desired shift, they can be problematic. This is one theory about Wiggins’ legendary throwing of his bike. There can also be a problem with insufficient stiffness of the Osymetric rings for extremely powerful riders.

So no, I don’t think that there is any wisdom in attempting what you are proposing, as I don’t think Biopace works. However, using an inner Rotor or Osymetric ring with a round outer ring could work, but don’t know if you can find one for the granny position of a road triple crank.

I did race one of my cyclocross bikes with a Rotor inner chainring and a round outer ring. I raced with Rotor chainrings on all of my cyclocross bikes, but generally I ran a single front chainring. With my Campy Record EPS-equipped bike, though, I could not run a single chainring, as removing the front derailleur for the electronic shift system totally screwed up the rear shifting. But it didn’t shift worth beans on a pair of Rotor chainrings, so I just used a Rotor inner ring and a round outer ring and was almost always on the inner ring in cyclocross races. And having the big ring was nice for riding to the races.

You are right that there is nothing new under the sun, though; you need only look at the first photo here to see that.
― Lennard

Configuring non-Firecrest Zipp wheels

Dear Lennard,
I have read some of your articles. It seems like the best solution to be able use my 2011 non-Firecrest Zipp 404 wheels with a new 2014 Cervelo P3 Di2 Ultegra system is to put a Campy freehub and cassette on my Zipps and run it with the Shimano drive train. Will the wheels need to be re-dished?

Do you have any other suggestions on how to get around not having to purchase new wheels?
— Linda

Dear Linda,
Yes, using a Campagnolo freehub body and 11-speed cogset is a solution that will avoid having to get a new set of wheels. No, the wheels will not need to be re-dished.
― Lennard

More on mixing XTR Di2 and road Di2

Dear Lennard,
When you say there are not enough clicks on a Di2 chainring lever to shift a triple, what does that mean? I’ve always assumed that Di2 levers have two buttons — up and down — and I got the impression the newest versions will just keep shifting until the derailleur runs out of gears. Is this not true?
— Steve

Dear Steve,
Yes, it’s true. That was a brain fart on my part. I was speaking as if it were a cable-shift lever.

You could run the XTR front derailleur on the XTR triple crank with an Ultegra Di2 or current Dura-Ace Di2 lever. Shimano has made it possible for some time to reprogram the levers so that the right lever shifts the front and the left lever shifts the rear. So obviously, there is no limit on how many gears it can shift other than what the derailleur is limited to.

Here’s an answer from a Shimano spokesman to the same thing:

A reader asked about installing the XTR Di2 on a tandem for use with a triple. If the reader used the XTR M9000 triple crank, he/she would be able to actuate that with a road Di2 lever using the new XTR Di2 M9050 front derailleur. Unfortunately, if he used it with a standard road triple, he would be outside the Shimano recommended compatibility parameters. Though it may be possible.

― Lennard

More on QR skewers

Dear Lennard,
A few other often missed problems with in-line type quick releases that I see on a regular basis are:

1. The nylon/plastic cup that the lever cam rides in is constantly under compression and each time the lever is closed it becomes more compressed. After a relatively short period of time, the nylon cup can be deformed so that it no longer functions as originally designed and more and more force is required to secure the wheel each time the lever is engaged.

2. The lever (usually aluminum) pivots on a chromed steel end. Too often this chromed steel pivot is corroded and dry, thus making it feel as if the lever cam is achieving the goal of a securely held wheel when, in fact, the operator is feeling the high level of friction between the two materials. A drop of lube in this spot will allow the lever to operate with less friction and more confidently secure the wheel.

And as others have mentioned, I only recommend internal cam quick releases with horizontal dropouts.
— Mike Varley
Black Mountain Cycles

FILED UNDER: Bikes and Tech / Technical FAQ

Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance and Zinn and the Art of Road Bike Maintenance, as well as Zinn and the Art of Triathlon Bikes and Zinn's Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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