# Help me understand: Changing rear cog on a SS



## ZmyDust (May 13, 2011)

Noob question here: I just got a 2011 monocog 29er SS. The bike is perfect on the trails :thumbsup:

However, Im going to be doing some flat road commuting in the next few weeks and the 33:16 is a little low on the pavement. I find myself pedaling like a mad man to get speed then coasting. I'd like a higher gear for the road. 

Correct me if I'm wrong, but I can just change out the rear cog to an 18t or 20t to "gear up" a bit? With this setup is there any need to change the front cog for what i want to do? Is the new cog and maybe a chainwhip the only components I'll need to convert? Any other changes to the ride I should expect if I change to 33:18 or 33/20?


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## Stevob (Feb 27, 2009)

going the wrong way dude. you need smaller on the rear, or bigger on the front, to achieve what you want.


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## Stevob (Feb 27, 2009)

you'll also need a tool to remove the cassette lockring.


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## ZmyDust (May 13, 2011)

Ah I was afraid I was understanding wrong. So should I go down to a 14 or up on the front? The rear looks like alot less time in the garage the night before a ride...


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## henrymiller1 (Apr 25, 2008)

You need 36x16. i rode w/ 34/18 then 34/16 now 36/16 is magic number. I tried 36/15 and it kicked my ass. or my knees.


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## Stevob (Feb 27, 2009)

Try changing the rear first anyway. Chances are that a 14t will suffice. If you decide to increase the front chainring, then you may have to add links to your chain as well.

FWIW, 33/14 = 2.357:1 and to get approximately the same ratio by only changing the front, you'd need a 38t chainring (38/16 = 2.375:1) , which as I said above, will probably necessitate extra chainlinks.


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## ZmyDust (May 13, 2011)

Thanks for the replies folks. I will prob try a 14 in the back before changing the front.


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## ts818 (Jun 6, 2011)

Before you go out and buy yourself a new rear cog, count the teeth on the back sprocket, my new monocog 29er that i got two weeks ago, has a 20t in the back, im assuming yours does as well. I just bought a new chainring from bikebling, a 36t. (I went for the front chainring over the rear cog as a matter of aesthetics, i got a blue e.thirteen sprocket)

But assuming I'm not going off the deepend with this and you have 33:20, the 18t rear (33:18) would bring you to around 53 gear inches, alot of guys do 32:18 which is quite different. I would say you would want to think about getting a 19t rear, or think about a front chainring which is a more delicate tuning than the rear cog. You can do the math at Sheldon Brown's Gear Calculator. (google search it I can't post links)

Or if you can wait a half a week I can tell you if the 36t I got was right, or if i should have gone higher or lower. I'm second guessing myself thinking I overdid it and should have went with the 35t.

This is all assuming you want to find that happy medium between trail riding and road riding, if not go with a 16t or 15t in the back.


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## alexrex20 (Dec 20, 2005)

14t cog would give you plenty of speed, but make sure you air up the tires to max psi or it will be more of a workout than it's worth to get those extra mph.


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## TiGeo (Jul 31, 2008)

Yeah - the 'Cog should come stock with a 20t in the back and a 32t in the front - that is why you are spinning out on the road. A 14 or 15t should give you a much higher road gear. Remember, you may have to remove a few chain links as the r. wheel will slide way back in the dropouts.


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## ZmyDust (May 13, 2011)

Wow I'm glad you guys are here to set me straight. I had read somewhere online that the cog came stock 33/16 but apparently too lazy to go to the garage an count myself. 

TS818 - looking foward to how you like your 36t up front. How many chain links if any do you thin you'll have to add? 

Right now I'm leaning towards a 16t to start. I'll prob end up with a box full of different cogs as time goes on to change for diff conditions. 

Thanks again guys. Anybody else feel free to chime in with suggestions!


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## alexrex20 (Dec 20, 2005)

You need to check your chainring and cog to make sure. 33/16 is a very tall gear for a 29er.


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## manual63 (Nov 5, 2006)

*I would leave the front alone*

Mostly for ease. It is a pain to change the front and it will require a much longer chain. If you dump the rear to 14T, which is what I would recommend for road 33:14, then you will actually shorten the chain. This means you MIGHT have to take out a link....not sure because I don't know where your wheel is positioned in the dropout.

I suggest getting 2 chains with a quick link.....that would be SRAM.....

One shorter chain for the 14T and one longer chain for the bigger gears that you run in back for off-road. The reason you want 2 chains is because adding and removing links all the time weakens your chain over time and on a singlespeed, you put a lot of pressure on the chain and it can come apart under pressure.....which will send you flying over the bars if you are not careful.

For my singlespeed, I have a 26", I run a 33 up front and a 16 in the back for most off-roading. In my toolbox I have 14 - 22 tooth gears, yep.....each increment. I don't ride my mountain bike on road much because I do have 2 road bikes, one a singlespeed. If you find yourself switching back and forth a lot, I recommend just getting a different bike for road riding......if you can afford it. Not everyone can so you gotta get by with what you have.

Good luck and have fun singlespeeding.......I love it!


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## manual63 (Nov 5, 2006)

To figure out gear inches, so you know how much harder it will be going from one gear ratio to the next, you want to do the following.

Front chainring divided by rear cog size.

Then times the wheel Size in inches (700c is close to 27" for road applications).

My singlespeed road bike is a 47:19.

(47/19) * 27 (about) = 67 (rounded)

If you run a 33:14 on your 29er....

(33/14) * 29 = 68 (rounded)

So a 33:14 with big off-road tires might be a bit of work if you are a newbie to singlespeeding. You might want to consider a 15t in the rear.

With a 29er for off-road I suggest an 18T so you have 33:18. If you push a lot harder than that, like with your 16T you could have knee troubles, just my opinion.

Do the math.

(33/16) * 29 = 60

I suggest around a 52 for off-roading and if it's hilly, that is a little steep.

(33/18) * 29 = 53

You could even go 19T in the rear.

It's easy to see how big of a change you can get by only changing out the rear cog. Find the off-road gear inches you are comfortable with and then the on road gear inches you are comfortable with. Then all you have to do is some simple math to figure out what cogs to use.

I know the gear inches I prefer for each trail I ride. At our local Lebanon Hills trail I like to run around a 46 and at Theodore Wirth I like a 52. On a 26" bike that is 32:18 and 32:16 respectively. But if I ride someones 29er, or when we go test the f-bom 29er once the prototype is done, I can easily figure out what gears I want to run on that bike with some simple math.


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## ZmyDust (May 13, 2011)

Thanks for the breakdown.Unfortunately I'm not in a position to by a road bike at the moment. I like the current 33/20 for trails but I think im going to attempt a 33/16 setup for flat road. If it's too tall for me like somebody suggested I'll get a 18t.


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## Godless Communist (May 8, 2007)

ZmyDust said:


> I'll prob end up with a box full of different cogs as time goes on


Yep, you''ll eventually amass a small collection!

Consult one of the many gear inch calculators available online, like this one: http://cycleseven.org/bicycle-gear-inch-calculator

In my experience, for everyday paved cruising, a gear combo that gives you 63 - 65 gear inches works pretty well. For true offroad riding, I'm in the high 40s or low 50s. For "serious" road riding with skinny tires, 70 +.


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## ts818 (Jun 6, 2011)

Ya Zmydust, i'll let you know. I actually looked today and was wondering if the 36t will even fit, you'll notice it is quite tight down there. But I'm still wondering if your looking for that happy medium or if you just want real power on the road.

I think the 33/20 is perfect for trails, but I wanted more on the road and just figured it would be harder work on the trails, but not impossible. If that's what you're looking for then ya I can let you know.

FYI,
I'm 6"2' 185#s this is my first mountain bike,
the last six years i was on a k2b (bmx) with a 20" 44:16 coming in at 51.4 gear inches,
the 36:20 on the monocog brings you to 52.2 gear inches
stock is 33:20 coming in at 47.8 gear inches
and all the rear cog supporters at 33:18 thats 53.2 gear inches

so depending on how i like it i would either go farther up to 33:18 or slightly down to 35:20, e.thirteen sells odd tooth chainrings

and as for chain links i'm hoping I wont have to add any, i've been riding like crazy and already stretched my chain so that the dropouts are all the way back


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## Stevob (Feb 27, 2009)

approx 3mm (1/8") axle adjustment for every increment in chainring or cog size, shorten for adding teeth, lengthen for subtracting teeth.


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## ZmyDust (May 13, 2011)

TS- for my first order I want to test this thing out fast on the road. See what it can do and I can do on it. I'll try balance later. Gonna start with an 18 and 16 rear cog. 

This is also my first mountain bike (11 monocog 39er). Im 6'5 255 lbs. I havent been on anything except booze food and other stuff for the past 5 years. Very little exercise..I've had it almost a month and can't get enough. I ride somehow every day. Trails when I can but easy stuff so far. I get a heck of a cardio workout hauling around a half a mile loop in my neighborhood on and off the sidewalk from the road. Great for cornering and leaning practice. 

Thanks everybody who has posted. You guys rock!


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## ts818 (Jun 6, 2011)

So i've been riding the 36t for the past two days on my monocog and its just amazing. I've commuted twice and i can tell noticeable differences. It's not a racer on the roads by any means but that feeling of going nowhere is mostly gone. I road trails yesterday and i couldnt have been happier. They were hardpack and i was flying through them. This leads me to believe that I found the perfect gearing for me. Sure if i was on a loamier trail it might be slightly tall gearing but it'll be fine. There weren't any climbs i couldnt do.

Considering that,
The 36t at 36/20 is basically equivalent to getting a 18t rear at 33/18. So the 18t should be a pretty good gear for trails, and the 16t will probably be good for the road, you may want a lower one in the future, especially if its flat where your commuting. Enjoy the new ride!


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## bwheelin (Apr 4, 2008)

ZmyDust said:


> Ah I was afraid I was understanding wrong. So should I go down to a 14 or up on the front? The rear looks like alot less time in the garage the night before a ride...


i was in your position last week. i had a 32/16 and it wasn't what i needed when i was on the pavement. i was going to change the cog to a 14 but ended up changing the chain ring from 32 to a 38 and it feels much better. everyone is different though.


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## ZmyDust (May 13, 2011)

Guys help me out. You all know these bikes so well. If I'm ordering rear cogs (16 and 18 to start), should I get size 
1/2 x 1/8 
or 
1/2 x 3/32?


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## jollybeggar (Feb 2, 2004)

3/32 is standard 9spd, 1/8 is heavier popular with BMXers. I'd go with 3/32 just because it's more common and you can use quick links.


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## ZmyDust (May 13, 2011)

Thanks guys. I've got a Avenir 18 inch and 16 inch rear cog, a Pedro's Trixie tool, and a Camelbak MULE on the way. Looking forward to getting out there and trying some alt gears.


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