My 7 speed bike has the Shimano 600 Ultegra FC6400 crankset. It uses the 52/42 Biopace chain rings with a 130mm bolt circle diameter. I would like to switch to normal round rings. What are my options as far as compatible rings? Can I use newer models without issues, or do I have to look for 7/8 speed specific versions?

Thanks in advance for any help.

Any round 130mm BCD chainring will fit. I'd recommend a 50/38t combination.

Sugino still makes cheap alloy rings that will work on the 7 or 8 speed. the new 10 speed rings will have a different offset but will probably work but will cost about 3x as much and the teeth are narrower because of the narrow chains used.

I'm looking at this for the big ring: EBAY

I need to find the same for the small ring.

Any comments?

I'd recommend the 52/42 that was originally specced for a much likely narrower 7spd range; typically 21 or 23-13 rather than the 23 or 25-11 of modern 10spd drivetrains. Those ratios worked in the 80s, and I can't imagine why they should have stopped working.

The larger rings also have the slight advantage of making your ratios marginally closer.

The eBay chainring looks like a decent buy. Those lift pins will noticeably improve your shifting.

Send me your Biopace! Unfortunately I don't have any round rings to trade, otherwise I'd offer.

By"the same", do you mean you want the same series/finish for the small ring? Or, so you just mean a smaller, silver ring with ramps/pins? I cannot tell exactly what ring that is, as the description doesn't say, and the picture won't show us any of the descriptors that shimano stamps on their rings. I wouldn't overthink that stuff.

In terms of what ratios you want to get, it depends a lot on what cassette or freewheel you're running, what kind of geography you ride on, what style of riding you do, your strength as a rider, personal preferences (do you like to mash, or do you like to spin?), etc. I've been digging the 50/39 for road use lately, with a 12-25t 10speed cassette. That probably doesn't help you at all, unless you're just like me.

For your sake, let's hope you're not...
-rob

PS- the 39t would be easiest to source, but you can easily find the other sizes discussed, if you try...

i knew somebody was going to ask for those biopace rings!

-rob

I've always used those rocket rings or "origin 8" I think they're called now. They're cheap and work just fine.

My surly has 9 speed rings and a 7 speed cassette and chain -- works flawlessly.

Thanks so far for the input. I used to race many years ago and I have two sets of wheels, both cassettes, and I have all the cogs to get from 12 teeth to 26 teeth. So I can set up almost anything I need from there. I am more of a spinner and we have our fair share of moderately hilly terrain. But right now I ride mostly for fitness.

I'm not sure I am going to give up on the biopace just yet, but I want to try the round rings. I'll ask about the series of the Ebay ring. As for the smaller ring, I just meant tooth count. I'm not to hung up on making everything match. I'll keep my eyes open.

a 38~39 /48 will work as well as a 42 /52 and I agree Sugino chainrings would be least cost, new,
though Vuelta and Salsa thru QBP are good too,
7xxx a bit harder alloy..

and there are also Surly Stainless chainrings long wearing ..
made for single speeds but will work on older derailleur bikes too .
as long as your expectation for instantaneous shifting is realistic, as it must be..
.... patience, grasshopper ...

an alloy outer and steel inner may be ideal ,
as most people ride a lot on the inner chainring ..
at modest speeds and efforts.

Try rotating the BioPace 144-degrees clockwise (2 holes). It will do the opposite of Shimano's intention and even out the torque-variations around the pedal-stroke. I've found that it really helped me get a more even roar out of disc-wheels in time-trials. Several pros use modern version of oval rings and they have oriented this way as well.

I was about to say - give up on the Biopace unless you rotate them...

Shimano did it exactly wrong. Doing it right can actually be good for a few extra percent... https://www.noncircularchainring.be/

Here's a picture of Bobby Julich's O'Symetric rings:

https://www.bikecult.com/works/chainring/ringtwo.jpg


Notice that the large portion of the ring pulls on the chain at the downstroke. This increased radius slows down the crank and reduces torque on the downstroke. Then on the dead portions at the bottom, the smaller radius speeds up the ring and increases torque in those areas.

Some articles:

Bike Radar - Non-round chainrings making headway in the pro ranks
VeloNews - Olympic Tech: Bobby J and his funky chainrings

I stopped reading after the authors said "Shimano's disaster" -- I've never read peer-reviewed literature that is written like that.

They might as well have said "Shimano did some stupid sh*t, like back in the 80's or something and that's what we're..."

Uh, that's not overstating it at all, given that non-round rings can potentially be of benefit and Shimano queered the pitch for a couple of decades, by doing it, as I said, exactly wrong. As in, couldn't have been wronger.

I figured it out for myself in about 1992 and rotated my Biopace rings. It's obvious.

Although that piece is a bit informal in tone for its format, the actual content seems quite sound. I found it quite informative.

Standard Sugino or Vuelta SE rings will work fine. They are free of ramps and pins.

Sugino's are available in many places.

https://www.vueltausa.com/components/...mm-38-60t.html

I do! PM me.

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