I'm converting a 15 speed vintage bike to a single speed and I need to know a good Gear Ratio. I live in a very flat town if that makes any difference. I'm new at this so please help me. I would also like to know how to find out what size bottom bracket i need.

I lived in downtown Milwaukee for 8 years and with the exception of a couple hills, it is exceptionally flat. I ran a 48x16 (go ahead and start talking about "skid patches" kids, I dont ride around skidding everywhere...) for a 78ish gear inch and had no problems. Felt right to me. Your mileage may vary..

Please see this URL to assist in your selections:
https://www.sheldonbrown.com/gears/

[EDIT]
oh and if you do start talking skid patches, it could be known that i *am* an ambidextrous skidder

44x16 or 46x16

For flats, I'd use either 46 x 16 or 48 x 16...

single speed or fixed gear?

What does everyone think of 46 x 17 for mostly flat commute? Too small, or ok?

Can you explain how the gearing differs from fixed to single?

Cause I have a single speed right now running 42/19. And I'd like to try some thing different. And soon I will also be getting a set of wheels with a flipflop hub that I plan to run SS/fixed.

there difference is that one coasts and one... doesnt

and powerband, 46x17 is a completely worthy gearing. if you are reasonably strong you can still bomb hills (and with that gain ratio, much faster than people who see a hill and downshift), but you also retain the luxury of not having to spin like a madman down any sort of decline.

happy colored marbles.

haha, funny guy.

Besides the obvious of coasting. Will the GPI still be the same for fixed or SS if running the same size wheels?

i have a 52/15 ratio


is that skid-possible? should i get a smaller teeth crank? :[

yeeeeuh, same gears just different mechanicals at the hub/cog level.

gasian, anything is "skid-possible" if you're strong enough and throw your weight around properly. it takes practice and is easier to learn how to do it with a lil baby gear and move up. i could probably skid a 39/19 with my shin while sitting, for example. 52/15 is pretty tall for street riding in general though, but hey if you have the balls go for it. i dont.

I has 48 x 16 with 172.5 mm cranks. I'm finding that I can't push it comfortably over about 110 on the rollers, and downhill I'm getting pushed out of the seat trying to spin over 145, tops out about 38 mph and I have to put back pressure or get tossed out of the saddle (Happened only once so far).

Would going down to 165 mm let me spin faster? I'm thinking of hunting up a 47/17 for the flipside and changing up my 16 for a 14 too. What kind of average/top cadences would I see with that setup?

thanks cizz

i can't skid with that ratio for my life. how many teeth crank do you think would work well for a semi-beginner?

i'm thinking maybe a 46T ish?

46 is probably more managable than a 52 for learning to skid. a pointer if you may... go find some gravel road or some slick grass in a park (maybe after it rains) and practice your technique there until you are able to ride it out to a stop. then move to the street where the resistance is much greater. youll eventually get it to pop and then you're golden. as far as _how_ to skid, that is a thread that has been beaten to death years before i ever joined this forum; i would recommend the search function atop the page.

id go w/ a 46 T
i use a 42x14 and a 50x18

Most say a good place to start is 70-75 gear inches. The 3 fixed gears i have range from 69-73 gi.

Go 52/17.

Thanks a bunch, cizzlak! Very helpful posts from you.

well 42/19 would be way too much pedaling for fixed. While the "easier to pedal" ratio is perfect for single speed since you can coast once the cadence gets too high. "typical" fixed ratio would be somewhere around 48/17. that's what i run and i often find it to be too much pedaling, but i everytime i climb a hill i'm reminded why i keep it. A friend of mine says that he averages about 21mph with this ratio and maxes out at 34mph (he has a computer). obviously these aren't accurate and change from person to person, but this can give you an idea of a "common" ratio.

If its fixed and flat and you like to cruise pretty fast, go 49x16. If its SS/FW, run a flip flop hub with the 16t fixed cog and with an 18t FW. You'll love it. Since its flat, you wont have to worry about mashing up hills like around here.