nicknyce26

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.

elemental

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.

Dr. Banzai

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

squeegeesunny 

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)

elemental

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.


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.

nicknyce26

sorry my mountain bike has 29x2.10 (700x54c) inch wheels and the fixed gear has 700x23

Dr. Banzai

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.

elemental

It would have behooved you to read the next sentence as well as the first: