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Discussion Starter · #1 ·
Hi all you single speeders,
I am building up my first single speed, which is a blkmrkt mob( http://www.blackmarketbikes.com/mob.html ).
It seems like most of the single speeds on here are xc bikes, but hopefully you can all help me. I have a 36 tooth ring up front, and need to decide what to run in the back.

So; 26 inch wheels, 175 mm crankarms, 36 tooth front sprocket, and a dirtjump and street appropriate gear ratio. What size rear cog would you recommend? Right now, I am thinking 19,20, or 21 tooth. And for the record, I tend to run pretty low gearing, and just spin faster.

Thanks everyone.

EDIT: in case it matters, I am 5'11" ish and 165 pounds.
 

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Your fitness level and the kind of riding. For me my XC SS stuff is pretty flat so I run 34:17 with no trouble. I think if you ride in a place that has relief it is tough unless your fit.
 

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Discussion Starter · #5 ·
Fitness level: pretty darn good, but as I said above, I like to run lower gears and spin faster than most people I see.
Terrain: dirtjumps, some trails, pretty hilly (santacruz mountains) and street whenever I can.

On my (beater) bmx bike, I have a 44 x 16 tooth setup which is exactly 55 gear inches, and it feels very nice. 36 x 20 (on the 26 inch wheels) comes out at 47 gear inches. However, while running a casette, 36 x 21, and 36 x 19 are both much lower than 55 gear inches. And, with 21 or 19 rear, it feels quite nice. But to get 55 gear inches, I feel like it is geared too high.

So why does 55 gear inches on the bmx feel nice, but not on the mob? (and yes, it is calculated for wheel size differences, and crank lengths have no effect on the calculators)

Thanks man.
 

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crank length makes a difference in real life though. 175 cranks are 3% shorter than 180s. the difference between a 19t and a 20t is 5%. that explains the difference right there.
 

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If you like to spin a bit and your terrain is challenging I'd vote for 36/20. Second choice would be 36/21. Most of us ride 32/18 (26" wheels and 175mm crank arms) here and it seems ideal for rolling trails with some moderate climbs. I prefer a high cadence too and I've tried 32/19, but it's just a wee bit low for me.

Personally, 36/19 would be higher than I'd want.

I don't know who these people are running 2:1 and greater. I can't push that.

LB
 

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is the terrain that you ride bmx the same as the mob? I would think you'd want a similar gear inch if it is. But I'm guessing you might hit more (hilly) single track on the mob. If so I'd go with 36x22. Just depends how much walking you like versus speed on flats/downhills.
 

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Discussion Starter · #10 ·
I normally ride dh/fr, so I walk almost all uphills (except fireroads). It definitely will be on trails more than street stuff (the nearest actual city is a 25 minute drive). I just ordered the 20 tooth, so I will update this on how it feels.

Thanks everyone.
 

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Discussion Starter · #12 · (Edited)
Alright....it's in.

I tossed the cog on there, and got the bike running. I (somewhat) unfortunately had to use a chain tensioner, because with the gears I am running, the axle needs to be pulled way back in the dropouts to make the chain taught. And the half-link chain was the wrong width, so it didn't work. With the chain tensioner though, I can run the wheel slammed in the drop out, and have a tight chain....so that's good.

But the 20 tooth feels very nice. It would be too small for downhill, and even some normal trails, but for popping 180's and doing footjams and stuff.....its very nice.

So far it's all good.
 

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Discussion Starter · #13 ·
Well, I got a bit more riding in on it yesterday. From a standstill, it accelerates pretty easily up to speed. Rolling along, if you give it a good kick, it also speeds up quickly. The top speed is a little bit low, but I don't really need it any higher....its not like I am going to be bombing any DH trails on my 4 inch steel DJ bike.

I wouldn't want the gearing any lower, and I don't want it any higher.....so that makes it just about perfect.
 

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I suppose one gear cannot be perfect in all scenarios. If it was, they wouldn't have invented derailleurs. But I'm glad that the 20T seems to be what the best cog for your setup. Thanks for the update!
LB
 

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Discussion Starter · #17 ·
Like I said before, I spin much faster than everyone else I ride with/know. Plus, their really aren't that many dj's that you need to be going 25 miles an hour into. Just a nice pump into the lip will get you the height you need for most. And for street kinda stuff, it feels really nice.
 
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