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another gearing question (searched the forum i promise and still confused)

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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

another gearing question (searched the forum i promise and still confused)

Old 07-03-10, 05:15 PM
  #1  
nicknyce26
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another gearing question (searched the forum i promise and still confused)

just got a fixed gear bike and it appears to have 50x16 gearing. I took the advise I found on here and hopped on my mountain bike and found the gears that i pretty much stick to on my daily commute to work. On the mountain bike I stick on the middle chainring which is 32t and the rear cog is between 14t,15t, and 16t. From this would the best gearing for my fixed gear bike be 32x15. I get confused at all the gaer ration calculators any help would be appreciated. My daily commute is 24 mile round trip thanks.
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Old 07-03-10, 05:32 PM
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elemental
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If your fixed gear has 700c ("road") wheels and your mountain bike has 26inch ("mountain") wheels, you'll need to take this into account as well. To accurately convert, you'll need to know the wheel and tire size for both bikes as well. Assuming the mountain bike is on 26" wheels with reasonably-sized tires, you're in the mid-fifities, which is on the smaller side for gearing (but there's nothing wrong with that). To get a ratio like that, however, you're probably going to want to go with a much smaller chainring.

I would start with the smaller chainring. I am using a 39T on the bike I just built, and I like low gears. If you wanted the equivalent of 32x15 with a 50T, you'd end up running something like 50x24, which would be a little ridiculous.

Last edited by elemental; 07-03-10 at 05:41 PM.
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Old 07-03-10, 05:50 PM
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Screw what the MTB felt like. You are on a much more efficient machine now and your body will feel it.

Look to gear inches. You need to aim for somewhere you feel comfortable. I run just over 80 gear inches. You could start with between 67 & 70 and go from there. To calculate your gear inches go here and play around with gearing:

https://www.machars.net/bikecalc.htm
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Old 07-03-10, 05:55 PM
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First, your gear inch on the mtn bike is around 54~56, I am not sure because I dont know what your mtn bike is. Your FG GI is 82 G.I.

You can probably handle 60~65 gi since your fixed is lighter and since there isnt a deraileur.

Since changing your crankset is expensive, id recommend getting a 20t cog (surly) which will bring your GI down to 65. (50x20)
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Old 07-03-10, 06:29 PM
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Originally Posted by Dr. Banzai View Post
Screw what the MTB felt like. You are on a much more efficient machine now and your body will feel it.
Not necessarily true. The 39x17 bike I'm riding is a 29er with 2.1" knobbies (haven't gotten around to ordering slicks yet), and in terms of efficiency it's not noticeably different than my other 29er (1x9). It would be helpful to know what sort of bike we're dealing with, though. I do agree that 55 GI is probably smaller than you'll end up with, regardless.


Originally Posted by squeegeesunny View Post
Since changing your crankset is expensive, id recommend getting a 20t cog (surly) which will bring your GI down to 65. (50x20)
Chances are unless the crankset is some sort of B.C.D. monster a smaller chainring alone would be fine. They do cost a little more than cogs, but it will be a lot easier to experiment with 15-16-17T cogs than giant ones, and aesthetically speaking 50x20 is not going to be pretty.


Assuming this is a road bike, I would order something like a 44T chainring and 17T cog, which will put you in "normal" drivetrain territory. This isn't the 32x15 on your mountain bike, but it's still on the smaller side of gear combos. If you don't like it, you can easily go to smaller or larger cogs as you see fit. The whole setup should only cost about $50.

Last edited by elemental; 07-03-10 at 06:38 PM.
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Old 07-03-10, 07:27 PM
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sorry my mountain bike has 29x2.10 (700x54c) inch wheels and the fixed gear has 700x23

Last edited by nicknyce26; 07-03-10 at 07:33 PM.
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Old 07-03-10, 08:48 PM
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Originally Posted by elemental View Post
Not necessarily true.
It's physically impossible for an MTB knobby to have the same rolling resistance as a 700x23. It is also physically impossible for a fully kitted out MTB to be aerodynamically better than a stripped down road bike. Shall we move on to bike weight? Shall we discuss riding position? How about parasitic losses through the MTB dérailleur?

You may not consciously feel it but the efficiency increase is certainly there. Capitalise on it.
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Old 07-03-10, 09:55 PM
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Originally Posted by Dr. Banzai View Post
It's physically impossible for an MTB knobby to have the same rolling resistance as a 700x23. It is also physically impossible for a fully kitted out MTB to be aerodynamically better than a stripped down road bike. Shall we move on to bike weight? Shall we discuss riding position? How about parasitic losses through the MTB dérailleur?

You may not consciously feel it but the efficiency increase is certainly there. Capitalise on it.
It would have behooved you to read the next sentence as well as the first:

Originally Posted by elemental
Not necessarily. The 39x17 bike I'm riding is a 29er with 2.1" knobbies

Last edited by elemental; 07-03-10 at 11:41 PM.
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