Chainrings needed for half-step plus granny gearing

[junoak04]

I am repairing/upgrading my old 1988 Cannondale ST 1000 touring bike, which had a great half-step plus granny 18-speed setup. I've replaced the freewheel with an IRD 7-spd 13-15-18-21-24-28-32 freewheel, which will work great with my 28-44-48 Biopace crankset--except these rings are worn enough to probably cause chain suck problems soon. But since the crankset is old and has 74mm bolt circle diameter for the inner ring and 110mm bcd for the outer rings, I haven't been able to find replacements I know will work. Can anyone help? I see 3 possibilities.

Does anyone know where I can find a 74mm bcd inner ring with teeth from 24 to 28T--either round or Biopace; plus 110mm middle and outer rings with either 44-48T set or 46-50T? All 3 rings need to be either round or Biopace.

I have found Sugino rings, but I'm not sure the 44 or 46T will work as a middle ring; does anyone know? In addition, these have no ramps or pins to aid shifting. Would that make these noticeably poorer shifting than the original Biopace setup?

Finally, if all else fails, does anyone know where a more modern crankset (with different bcd) can be purchased with either a 24-44-48T; 24-46-50T; 28-44-48T; or 28-46-50T set of chainrings?

THANKS very much for any help anyone can provide!

[DaveM]

Google. I think all the things you're looking for should be readily available. However, it might be tough to find biopace chainrings except on ebay. The pins/ramps do aid shifting a little. But probably not major.

If you're replacing all three chainrings, it might be cheaper to buy a new crankset anyway. Note that a new crankset might call for a different length bottom bracket.

[GeorgeET]

The 1988 bike is not that old. I just replaced a center ring on my bi pace bike with a new round one I got on ebay. Works fine. I replaced the 28T granny bi pace with a 24 when I first got the bike so if you have problems finding one contact me off list.

It was 28,38,48, now its 24 ,38,48.This is a 91 Schwinn MB.

Ye google. Check Nashbar too.

[junoak04]

(08-26-2010, 08:48 PM)DaveM Wrote:  Google. I think all the things you're looking for should be readily available. However, it might be tough to find biopace chainrings except on ebay. The pins/ramps do aid shifting a little. But probably not major.

If you're replacing all three chainrings, it might be cheaper to buy a new crankset anyway. Note that a new crankset might call for a different length bottom bracket.

Thanks, Dave; I appreciate your help!

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(08-27-2010, 03:49 PM)GeorgeET Wrote:  The 1988 bike is not that old. I just replaced a center ring on my bi pace bike with a new round one I got on ebay. Works fine. I replaced the 28T granny bi pace with a 24 when I first got the bike so if you have problems finding one contact me off list.

It was 28,38,48, now its 24 ,38,48.This is a 91 Schwinn MB.

Ye google. Check Nashbar too.

Thanks, George. A 24T round inner isn't hard to find; nor is a 48T round outer. It's a 44T middle that I can't find--except for a Sugino standard with no ramps or pins.

[GeorgeET]

Ye, this a 110mm 5 bolt crank, correct?

Did not see any 44's bb in my brief search. Did see a few complete cranks but thats extreme, unless you really want this. :-))

Consider other combinations, the 4 tooth jump is not that much. Nice Bike hang onto it.

[junoak04]

Yes, it's a 5-bolt 110mm crankset. Four-tooth jump is what I need for the half-step setup that I like. It seems clear that no one uses that sort of setup anymore, since 8, 9, and 10-speed cassettes are now the standard, but it works great with a 6 or 7-speed freewheel. Anyway, thanks again for your help!