# Thread: Question for Gearing Wonks

1. ## Question for Gearing Wonks

I'm building a new 29" SS. On my old 26" SS, I ran a 36 x16 with 175 mm cranks. My new drivetrain will have a 32 chainring. Before I blow the bank on an Eno freewheel, I wanted to know what cog would mostly closely match in gear inches to my 26"(or gain ratio or whatever relationship you want to use...). I have really liked the gearing so far and want to come close to that feel with my new ride. And let's say I will be using similar sized tires to keep it consistent.

Thanks JK

2. According to my calculations with some assumptions...

26x2.125" tires @ 36x16 175mm ==> 58.5 gear inches
29x2.1" tires @ 32x16 175mm ==> 57.3 gear inches

Close as I can get you...

3. http://www.sheldonbrown.com/gears/

What he said... 32x16 will be basically the same.

4. Or you could go to an 18 on the back (36/18) for the same ratio but that would be more expensive if you are using a White Industries freewheel.

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Calculating Gear Ratios from 26 to 29
(Need to know how to do basic algebra)

If the height of the tire from the rim is kept constant, calculating gear inches in not necessary. The rim diameter at the tire bead of a 29er is 622mm and for a 26er it is 559mm. 622/559=1.11. So a 29er with the same drivetrain will be geared 11% harder.

Changing chainring: (36/16) = (x/16)1.11
Changing cog only: (36/16) = (36/x)1.11

Solve for "x".

5. ## calculation?

Who said anything about calculation?

http://www.jpmartineau.com/iphone/bi...ar-calculator/

Originally Posted by Thor29
Or you could go to an 18 on the back (36/18) for the same ratio but that would be more expensive if you are using a White Industries freewheel.

------
Calculating Gear Ratios from 26 to 29
(Need to know how to do basic algebra)

If the height of the tire from the rim is kept constant, calculating gear inches in not necessary. The rim diameter at the tire bead of a 29er is 622mm and for a 26er it is 559mm. 622/559=1.11. So a 29er with the same drivetrain will be geared 11% harder.

Changing chainring: (36/16) = (x/16)1.11
Changing cog only: (36/16) = (36/x)1.11

Solve for "x".

6. ## Or just use this easy rule of thumb...

For a given chainring size, run two teeth larger in the back to replicate a 26 ratio.

So, if you ran 32x16 on a 26er at a particular trail or race, run 32x18 on a 29er...

Joe

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