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Old 03-23-06, 01:18 AM   #1
moki
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gearing for a double crankset

I'm building up my beat up Maiposa as a light touring bike and need some help.

Yes, I searched. Yes, I know I should get a mtn triple up front and something wide (12-34) in the back.

However, I have DA indexed downtube shifters (7 speed) and brake levers already. I live in the prairies, so super low-end gearing isn't so important.

I need: derailleurs, a rear wheel, and either a cassette or freehub for sure, and probably chainrings.

I'm thinking: old shimano mtb derailleurs, but am unsure of their compatibility with indexed downtube shifters.
Do the derailleurs have to be 7 speed?

What size chainrings (I have a road double crankset w 52-42 rings, whcich will be waay too tall)? Any decent, inexpensive brands/models?

Is a freehub or cassette better? I figure Harris cyclery can sort me out, if my LBS can't.

Thanks
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Old 03-23-06, 02:27 AM   #2
NoReg
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Cassette is probably better for 8, just because there aren't many freewheels in that size. There is lot of 7 freewheel stuff around. You can get a rear Phil hub from Rivendale for just over 100 in a 7, which is a pretty great deal. Freewheels are fine no mater what, but Phils have hardened axels which reduces the longer un-supported shaft problem. If you want LX then you might as well go for cassette since the axle can bend in either format, but are probably better in the cassette. Mostly it is a mater of what you like, can pay for, and what you know how to fix.

You can easily run a touring bike off of a double, as far as the gearing range is concerned. To give an example, touring bike builder Beckmann prefers a range of 30-90 gear inches, he says he has never had to go lower than 30 inches. I definetly like 20 inches. On my bike the two lowest rings, a 24 and 36, give me a range of 22 to 90, The other chain ring give me a 96 gear, and a 114. That isn't the whole story, but it is the whole story the way a lot of people have their bikes set up.

Gearing 24-36-48, 11-30

59.6 89.4 114.2
50.4 75.7 96.7
43.7 65.6 83.8
38.6 57.9 73.9
32.8 49.2 62.8
28.5 42.8 54.6
25.2 37.8 48.3
21.9 32.8 41.9

I'm not recomending that set-up, but it is failrly typical.

Gearing is a very personal mater, but if you can borrow a bike and throw 60 pounds on it, you will quickly get the feel of what gears you really need.
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Old 03-23-06, 02:42 AM   #3
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Since you don't want to get rid of your crankset, but rather change chainrings only, the smallest you can go is a 38 with your existing crankset.
At least if you had a smaller double spider you can get the small ring down to 34 and perhaps run a 48 big ring with that.
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