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Another Gearing Question

Old 10-07-11, 03:19 AM
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Another Gearing Question

Right now the gearing on my Bridgestone T700 is as follows:

Front: 50-44-28
Rear: 14-17-21-26-34

With this I have a lot of unused gears (too low). There are not many hills around here so I really don't need gearing this low. I was thinking of replaceing the 44t up front with a 40 or 42t and replacing the freewheel with a nos 14-17-20-24-28 so my new gearing would be:

Front: 50-42-28
Rear: 14-17-20-24-28

I think this would give more useable gears, or am I wrong?

I would still have the 28 Granny up front as a bailout.... Make sense or waste of time?

Last edited by Capecodder; 10-07-11 at 03:23 AM.
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Old 10-07-11, 04:20 AM
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Your 34/28 gives a bottom gear of 22 inches, which is nearly down to Frank Berto's old "go anywhere with the kitchen sink" design, which got down to 19 inches, I think. Your pattern is a decent approximation of a half-step plus granny, which is one of the standard setups that gives you a full set of distinct gears. The other one is called a one-and-a-half or an Alpine. The evenness that you do have is because the step ratio between cogs is even, except for the jump from 26 to 34.

Your suggested freewheel, the 14-28, is a nearly perfectly even spread, with an ideal step ratio of 1.189 and a standard deviation of only 0.0217. it gives you a bottom gear of 27 inches, better than what you have now. This new freewheel is a great basis for either a half step or Alpine. For a half-step you want the chainwheel step ratio to be half of the freewheel's, or 1.095. For that I'd go with a middle chainwheel of 46 teeth rather than 42, retaining the 50. For an Alpine I'd go with a 52-40 in front, for a front ratio of 1.30.

Both of these schemes will give you 10 distinct, non-redundant gears without using the granny.

After you go to the 14-28, you can increase the granny ring to 32 or 34 if you want to tighten up the total range even more. I don't know how deep of a bailout you need.
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Old 10-07-11, 08:53 AM
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Originally Posted by Road Fan
Your 34/28 gives a bottom gear of 22 inches, which is nearly down to Frank Berto's old "go anywhere with the kitchen sink" design, which got down to 19 inches, I think. Your pattern is a decent approximation of a half-step plus granny, which is one of the standard setups that gives you a full set of distinct gears. The other one is called a one-and-a-half or an Alpine. The evenness that you do have is because the step ratio between cogs is even, except for the jump from 26 to 34.

Your suggested freewheel, the 14-28, is a nearly perfectly even spread, with an ideal step ratio of 1.189 and a standard deviation of only 0.0217. it gives you a bottom gear of 27 inches, better than what you have now. This new freewheel is a great basis for either a half step or Alpine. For a half-step you want the chainwheel step ratio to be half of the freewheel's, or 1.095. For that I'd go with a middle chainwheel of 46 teeth rather than 42, retaining the 50. For an Alpine I'd go with a 52-40 in front, for a front ratio of 1.30.

Both of these schemes will give you 10 distinct, non-redundant gears without using the granny.

After you go to the 14-28, you can increase the granny ring to 32 or 34 if you want to tighten up the total range even more. I don't know how deep of a bailout you need.
IMHO an excellent reply.

Capecodder, If your going to picnic/light tour I'd go with the Alpine, plus it'll look at home on the T bike.

Brad
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Old 10-07-11, 03:40 PM
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Thanks guys..... I think I'm going to give the Alpine gearing a try.
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