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Old 08-01-08, 10:43 AM   #1
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Compact double with 7-speed friction?

I'm thinking about ditching the MTB triple on my Bridgestone XO-4 and replacing it with a compact double. I'm running a 7 speed rear in friction mode. My question is, if I put on a crankset made to run 10 speeds, will I have to use a 10 speed chain, and if so, will that cause trouble with the 7 speed rear? Should I just leave well enough alone? It's definitely rideable as is, but there are times when the 42 x 12 high isn't enough, and I'm never on the granny ring.
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Old 08-02-08, 08:51 AM   #2
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You probably won't need a 10-speed chain and a 9-speed chain will do but either will work with your 7-speed cassette or freewheel.
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Old 08-02-08, 11:42 AM   #3
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You probably won't need a 10-speed chain and a 9-speed chain will do but either will work with your 7-speed cassette or freewheel.
Thanks; that's pretty much what I thought. I believe on balance I'm going to just ride the cranks that are on it, at least for now. It mostly just stays on the 42 ring; the cassette is a 12-21. I still have a 96" high which is generally enough for me. I also like the fact that this is a $65 Craigslist bike, and apart from the new cassette and a few parts (drop bars, saddle, dt shifters) I had lying around, that's all I have in it. For under $100 it's become my go-to bike for daily rides, errands, locking up, etc. Rides like a champ and I don't mind leaving it in the garage.
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Old 08-02-08, 05:03 PM   #4
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I'm thinking about ditching the MTB triple on my Bridgestone XO-4 and replacing it with a compact double. I'm running a 7 speed rear in friction mode. My question is, if I put on a crankset made to run 10 speeds, will I have to use a 10 speed chain, and if so, will that cause trouble with the 7 speed rear? Should I just leave well enough alone? It's definitely rideable as is, but there are times when the 42 x 12 high isn't enough, and I'm never on the granny ring.
You're already running a compact double. All you have to do is ditch the granny gear. Now you have a 110 BCD spider. Use the next size smaller spindle. You shouldn't have to change anything else. Good luck

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Old 08-02-08, 05:57 PM   #5
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How about an 11-19 cassette instead?
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Old 08-03-08, 01:14 AM   #6
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You're already running a compact double. All you have to do is ditch the granny gear. Now you have a 110 BCD spider. Use the next size smaller spindle. You shouldn't have to change anything else. Good luck

Tim
Actually, the bcd is 58. I may take off the granny as you suggested - I certainly can't see any need for it. The chainline on the outer 2 rings is acceptable as is.
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Old 08-03-08, 04:03 AM   #7
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Actually, the bcd is 58. I may take off the granny as you suggested - I certainly can't see any need for it. The chainline on the outer 2 rings is acceptable as is.
58 has to be the inner/granny BCD. I was talking about the outer chainrings. http://www.sheldonbrown.com/gloss_bo-z.html#bcd

If you're looking for something like a 50/36 then it would be cheaper to just buy a new crank. Chainrings cost almost as much as new crank. I was thinking you had something like a 48/38/28 crank. In which case you could loose the granny respace the crank and save a few bucks over a new crank. Good luck in whatever you do.

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Old 08-03-08, 06:57 AM   #8
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You may be able to find the chainrings you need on eBay. You can go as low as 34T on a 110mm BCD, and something like 48-34 should work very nicely.
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Old 08-03-08, 10:28 AM   #9
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58 has to be the inner/granny BCD. I was talking about the outer chainrings. http://www.sheldonbrown.com/gloss_bo-z.html#bcd

If you're looking for something like a 50/36 then it would be cheaper to just buy a new crank. Chainrings cost almost as much as new crank. I was thinking you had something like a 48/38/28 crank. In which case you could loose the granny respace the crank and save a few bucks over a new crank. Good luck in whatever you do.

Tim
No, I'm telling you for true this is a compact mtb crankset with a 58 bcd spider, measured at the outer ring. The stock rings are 42/34/24. From what I can tell, the biggest ring available for it is a 42, which is what I have. Anyway, like I said I've decided to just ride it the way it is. Ideally, yeah, a 46 or 48 would be marginally better, but I'm working on the fine art of making do, at least where this bike is concerned. Thanks for all the help.
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Old 08-03-08, 11:37 AM   #10
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Originally Posted by jbonamici View Post
No, I'm telling you for true this is a compact mtb crankset with a 58 bcd spider, measured at the outer ring. The stock rings are 42/34/24. From what I can tell, the biggest ring available for it is a 42, which is what I have. Anyway, like I said I've decided to just ride it the way it is. Ideally, yeah, a 46 or 48 would be marginally better, but I'm working on the fine art of making do, at least where this bike is concerned. Thanks for all the help.
What kind of crankset is this? Pictures, please.

Most 5-bolt "compact MTB" cranks have a 58mm diameter bolt circle on the granny ring with a 94mm bolt circle for the outer and middle ring. Either you've mis-measured or you have a very unusual crank.

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Old 08-03-08, 03:39 PM   #11
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What kind of crankset is this? Pictures, please.

Most 5-bolt "compact MTB" cranks have a 58mm diameter bolt circle on the granny ring with a 94mm bolt circle for the outer and middle ring. Either you've mis-measured or you have a very unusual crank.

Jeff
I was thinking that myself. But, what do I know. Check the link I posted earlier to Sheldon Brown's site on BCD's. He doesn't mention 58mm as being an outside measurement. Could be he is measuring the distance between chainring bolts not the actual diameter.

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Old 08-03-08, 06:57 PM   #12
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Yeah, you guys are completely right, and I'm nominating myself for idiot of the day. I was measuring incorrectly. It's a 94. Thanks for setting me straight.
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Old 08-03-08, 10:43 PM   #13
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Yeah, you guys are completely right, and I'm nominating myself for idiot of the day. I was measuring incorrectly. It's a 94. Thanks for setting me straight.
Darn you! I was trying to for that nomination!

(Just bought some new spokes at the bike shop. I gave them the wrong measurement because I put the wrong hub into Spocalc. Sheesh... you'd think that after 30 years of working on bikes I'd learn.)
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