Can you replace just the chainrings on a biopace crank? If not, what are good options for an 87 of the same vintage?

Yes you can. Probably just regular ole 130bcd crank.

I put round rings on a touring Biopace crankset, using the sizes I selected for the 110/74 BCD. You can so the same with the 130 BCD road Biopace cranks.

BTW- make sure you make note of the orientation of how your Biopace rings are installed- just in case you decide to put them back on (for whatever reason and however doubtful that may be )

Been there ... done that. One of the first changes I made to my mountain bike was to replace the 38T biopace middle ring with a 40T round one (110mm BCD). I recently replaced the 48T outer ring with a 46 (both round), so I am ironically now back to 38T (round this time) for the middle ring, to maintain my favored 1.5-step 8-tooth drop.

Yup. Standard cranks and spider. You can mix Biopace and standard round rings too, although some combos work well and others don't. It can be tricky to adjust the front derailleur to get reliable shifts without dropping the chain.

It's easy to return the Biopace double to the default configuration -- the locator pin is intended to go one way. However you can reorient/index the oblong chainrings however you like, within the limits of the five available positions. I found some alternate orientations I liked, while others felt weird. Eventually I returned the Biopace 52/42 rings to the default position. Suited me well when I used 'em a couple of years ago.

FWIW, subjectively speaking, the 42T small Biopace ring felt "smaller" to me, more like a 39T. On climbs it didn't feel like mashing with a 42T standard round ring.

I also preferred shorter cranks with Biopace. Usually I'm not picky about crank length. I ride 170, 172.5 and 175. But longer cranks felt weird to me with Biopace, very herky-jerky. Switching to 170 cranks resolved that issue and my cadence felt "right" again.

It's very subjective but I liked Biopace when I used it for a year in 2019. Only reason I'm not using it at the moment is I disassembled that bike to rebuild it and still haven't finished the rebuild. I plan to switch that bike ('93 Trek 5900) to Dura Ace cranks, 53/39 to match the Ultegra 53/39 cranks on my 2014 Diamondback Podium. But I might swap the Biopace over to my Ironman, with 170 cranks.

If you like the concept, other companies made oval rings. Check the Bay for Sakae Ovaltech or Sugino Cycloid.

The late Sheldon Brown was a big fan of Biopace rings. Per his website, seems that's to be expected - according to him, Biopace is "easier on your knees" and allows "healthy, efficient pedaling at slower cadences than is possible with round chainwheels".

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

All my bikes have been equipped with round chainrings since new, but I have to admit that Biopace rings do sound interesting. I've picked up a couple of sets of Biopace rings along the way (and am debating picking up another I've got my eye on). A set may end up on the oldest bike the next time it needs a new chain so I can give them a try.

One size does not fit all. I tried the 38T Biopace middle ring that came with my mountain bike and never got used to the pedaling cadence.

or SunTour Blaze

I have kept the Biopace chainrings on my 1989 Schwinn Circuit, because like the Sante groupset on it, it's part of the bike's original equipment. I tried it in the original configuration, and I noticed a 'surge-y' feeling when going up a 2-3% grade. I currently have both rings rotated one spider arm clockwise, which makes the orientation more like the current thinking on oval chainrings, and I don't notice the same feeling, though of course this is totally subjective. But I'm leaving it like this.

I just picked up a 1985 Centurion Ironman that also has Biopace chainrings, so I'll experiment more when I'm finished with the rebuild.

I keep my old Windows 98SE system alive because it has an email from Sheldon counseling me about Biopace......I do miss the wisdom and the man.
Always been a fanboy. Much easier on my old, beat-up knees. Whenever possible I include them in a build, most recently a early/mid '80s Klein Performance built with Shimano 6204 cranks and 50/38/28 Biopace rings. Even got them to index with brifters. Wasn't easy and I do not recommend it, but it works for me and it can be done.

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Yup, I noticed that surging too in some chainring orientations, especially with longer cranks. And it felt better to me in "harder" gears and a slower cadence than I normally used.

That's what Biopace was designed for---lower cadences of the sort employed by the majority of casual and non-racer cyclists, aka the majority of cyclists, period.

All of the other eccentric chainring designs, starting in the 1930s, if not earlier, and continuing to the present day, were designed for high-cadence, racer-oriented use.

Excellent advice. Though applicable Shimano Service Instructions of that period do often cover how to install Biopace chainrings, not everyone is going to have that kind of documentation readily available (and perhaps won't know where it can be found). Documenting the orientation in some way before removal thus seems a very good idea if you don't have access to period Shimano documentation concerning Biopace, or if you've installed them in an alternate configuration that you like better.

Added: turns out that the older Shimano docs covering Biopace installation are harder to find than I remembered. If anyone's interested in having a copy of those instructions for future reference, do an internet search for "SI-T-30A-000-00-ENG" and choose the entry from "si.shimano.com" covering a number of FC-M### cranksets. That document explains how Shimano recommended orienting Biopace chainwheels during installation.

My late’80s Schwinn LeTour is equipped with the SunTour “Blaze” groupset and has OvalTech chainrings. I assumed that the designers consulted with kinesiologists RE: the best / most effective orientation of the ovalized chainrings so I’ve always made sure to note the position whenever I’ve done any disassembly.

In 2006 I picked up a 1st generation Colnago Technos frame. It was so gaudy (to me) that I went full tilt bozo on the build.



I had an NOS 1987 Shimano Deore M730 MTB gruppo that I'd gotten dirt cheap on eBay so I used the 175mm cranks with 28-38-48T BioPace chainrings, the derailleurs plus I had as set of road wheels built using the Deore hubs. It was intended to be an old man's climbing bike and it did the job. It felt better climbing than my other triples but I wasn't sure whether it was the BioPace rings, the 175mm cranks or both.

In 2010 I got an almost NOS 1988 Peugeot Biarritz with a Shimano 600 Ultegra gruppo. It came with 42-52T BioPace chainrings. (eBay photo with speedo wires and Nitto Technomics tall boy stem which were immediately removed)




In researching BioPace chainrings back then I put together this Flickr album with photos I lifted from the internet. It shows various generation Shimano BioPace rings plus Sugino, SR and Stronglight versions. Some of the info may not be correct but that was 11 years ago.... No 2nd editions or editing!

https://www.flickr.com/photos/282672...57625130627294

On a subjective note, I've been riding 48T, 49T or 50T large chainrings with 38T or 39T small rings for years. I found that the climbing effort on that Peugeot with the 42T BioPace ring and 24T or 28T rear sprockets had the same feel as a 38T round ring! Better comparison than with my Deore MTB cranks.

BTW, BITD I could spin 90 rpm all day! For the past 15 years, I'm happy to hit 60 rpm. The suggestions that BioPace rings were designed for "average" riders seems to hold true as most complaints that I've read were by more aggressive riders.

verktyg

mine too

Had to run out to the garage to be sure my LeTour hadn’t “gone missing” ! I’m neither here nor there RE: elliptical chainrings. If the bike came with them, I leave them on. If I’m building from the parts bin, I’d use whatever brand elliptical chainring that had the number of teeth that I wanted and fit the crank spider. If a round chainring better met the needs, I’d use it. Not being a competitive rider, I’m not so sure I’m realizing the “benefit” of ellipticals but I certainly don’t notice any detriment.