Bicycle Mechanics - Swapping Biopace chainrings for round ones

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.



PDA
geoduck
09-20-04, 10:55 AM
Remember Shimano's Biopace chainring idea? :D

Well, I've salvaged a set of cranks from an old clunker I had sitting in the basement, and they have Biopace chainrings. I want to use the cranks on a singlespeed mountain bike I'm putting together, but of course I need to lose the stupid elliptical rings.

My question: looking at the crank arm spider, it appears that the locations of the stack bolts are in an elliptical array as well. But when I measured, it appears that there is approx. 3.5" when measured between any two bolts, so maybe it's an optical illusion created by the elliptical chainrings.

Does anybody know for certain if the chainring bolts for a Biopace set may in fact be set up in an elliptical array, or would they likely follow some other standard for late 1980s mountain bikes?

Thanks!

_'duck

rykoala
09-20-04, 11:09 AM
The chainring bolt pattern is standard. You can still use them in the singlespeed conversion. They are NOT a bad thing. Sheldon Brown uses Biopace on a fixed gear! Save yourself some money and keep them. Forget all the hype about them hurting knees. They don't. I myself was curious about using them for tours, here's the thread. I'm convinced:

http://www.bikeforums.net/showthread.php?t=66334

BTW Biopace rings are NOT elliptical. They will NOT hurt your knees like elliptical rings will. Nor will they significantly change chain tension on you.
geoduck
09-20-04, 11:39 AM
Thanks for that, Rykoala. With this project (ss buildup), I'm finding that first-hand experience is as good as gold.

Well, if Sheldon's done it, I sure can try it. I've ridden Biopace before, and I was not fond of how it felt. Aching knees were never an issue, but then again it was 10+ years ago. Come to think of it, I think it was only the granny ring which was Biopace. Maybe it won't feel as funky on the big ring, which is the one I'll likely use on the ss.

And since I'm trying to do this conversion on the super-cheap (as in zero dinero) cobbling together old parts, it won't hurt to try!

Edit: thanks for the correction. Biopace chainrings ARE NOT elliptical.

John E
09-20-04, 12:37 PM
My mountain bike came with a 38T Biopace middle ring, which I replaced with a 40T round. Both used the then-standard 110mm BCD.