Are 22 tooth (or smaller) and 32 tooth rings available for Bio-Pace cranks on a mountain bike? I would like 22/32/38 crank rings. All I can find are 28/38/48 or 51/52. A 30 tooth middle ring from a road bike might be an option - if I can ever find one.

Why? You ask? My knees and hips are shot, thanks to a hereditary bone defect.

If I remember correctly (which isn't assured) Bio-pace mtb cranks used classic 110/74 BCD. If so, the minimum size rings are 24 and 34t (maybe 33t) respectively. But that's for round. The shape of a Bio-pace would increase the minimum size somewhat, but don't ask me how much -- it was a long time ago.

Have you check EBay ? Biopace is an old system that never caught on . It was around in the early 80's . you might find Old / new stock on EBay .

Below lifted directly from Sheldon Brown (Biopace Chainwheels)


"Biopace chainrings are no longer made, but they are found on many bicycles from the 1980s and early 1990s. Biopace chainrings turn up in substantial numbers on eBay.

50T, 48T, 46T, 44T, 38T and 36T chainrings were made in the 110mm bolt circle diameter; 28T and 26T chainwheels in the 74mm bolt circle diameter. These chainrings were generally used in triple cranksets: the 74mm bolt circle is only used for the innermost chainring of a triple. However, the outer chainring may be left off or replaced with a chainguard/protector plate (like a toothless chainwheel) for a wide-step double.

Sizes 53, 52T, 42T and 40T (that one only in steel) were made in the 130mm bolt circle and were generally used in racing doubles, though some cranksets have a 130mm outer and 74mm inner bolt circle. Few front derailers could handle a 52T outer and 28T inner Biopace chainwheel, though."

Looks like I'm going to have to go with a more modern crank. Oh well. Any idea if a 1x9 or 1x10 setup with a 22 tooth front would be viable? Would a 22 tooth front cause too much torque (in the larger rear cogs) and break the chain or damage the hub or freebody? A 22 front 40 rear sounds ... "interesting" and might prevent some uphill walks. I hate walking ...

While my knees and hips are shot, I am worried about torque because I can still press 1,000 pounds with my legs. I use the "standard" 170/172.5 crank arms that came on the bikes.

The 74 BCD will take a 24t ring. a 24-30 will give you a 21 inch gear. It's pretty low for a road bike and a little high for a loaded tourer.

Have you considered using shorter cranks?

Just get a modern mtb triple and get a large cassette for the rear.

Wich one is better. and make the bike go faster. Biopace crank 52/42 or crank 53/39. The 52 tooth crank is much slower than 53 tooth crank. In both cranks used same cassete

Neither of them. The rider makes the bike go fast, not the gears. Give it up and ride your bike more.

Because of their shape, I think the smallest 110 BCD ring in Biopace was a 36T, and 40T in 130 BCD. I don't think a 1x10 system would be a step in the right direction at all -- what freewheel/cassette are you using?

If you wait about 15-20 years from now you can buy new Biopace chainrings, as Shimano will bring it back again with other manufactures jumping on the wagon. All telling us how good it is.
Comes around about every 50 years.

No but is fine to play with different type basic round rings alot of the time even stock on Biopeace MTB's the small was a round you can use a small of 24 fairly easy.

I fully expect that in 15 to 20 years I will either be pushing up grass or in a wheel chair. Either way, my riding days will be over.

Nope . as said above.. the biopace granny gear was a 28,26?t because the bolt circle was a 74mm & it still could not be smaller than its bolts to hold it on..


now If you take the Design to one of the eager to please manufacturers at the next Taipei Trade show, with a big bank loan letter of credit
I imagine they will give you a batch quote to manufacture a few thousand of them , and once the CAD CAM program is sorted out.
when you sell through the 1st batch .. the next thousand will cost less,


an electric Motor.

Correct.

IIRC, 28T was the smallest Biopace ring offered. But there's no reason why the OP couldn't use a smaller, round 74mm BCD ring instead.

Subject to 24t being the limit.