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Discussion Starter · #1 ·
I am thinking about running a Rohloff Speedhub on my new 29er frame when it comes.

All started when I opted for Rohloff sliding dropouts a little while back.

I want to set the bike up for ocasional singlespeed use and have a very nice chainset I want to use.

If I want to run with a 36t front chainring what size sprocket should (or can) I use when on a 29er with 2.1" tyres.

Thanks,

P::..
 

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Discussion Starter · #2 ·
Now I have had a think about this a bit more. Let me know if I am on the right lines.

Most 26" MTB wil run 42/16 with a Rohloff Speedhub.

This gives a ratio of 2.625

Dia of a wheel 26*Pi = 81.68

81.68 * 2.625 = 214.4

Dia of 29" wheel (Aprox I Know) = 29*Pi = 91.11

214.4/91.11 leaves a gear ratio of 2.35:1

So will 36:15 (2.4) be a reasonable gear?

P::..
 

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Cassoulet forever !
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in a first approach, yes.

You can also do the dirty 10% tip :
42|16 - 10% -> 38|16
(close to your result)

For more precision, I think you need a better value for the real diameter of the whells.
Best way would be to calculate with the lowest gear your want.
 

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Have you checked out Sheldon Brown's online gear-inch calculator?

https://sheldonbrown.com/gears/internal.html

36x15 Speedhub gearing will get you a gearing equivalent to a 22x33 granny combo, and a half tooth lower than a 44x12 high gear. Therein lies the Speedhub gearing conumdrum: do you take an even lower gear at the expense of spinning out at the top end, or vice-versa?

Here are some Gear Inch numbers to compare (and remember that Gear Inches take wheel diameter into account):

Speedhub & 29"er [36x15]
102.6 (high) | 19.5 (low)

Speedhub & 26" [36x15]
91.3 (high) | 17.4 (low)

Derailleur & 26" (44/32/22 x 11/34)
103.8 (high) | 16.8 (low) | 17.8 (22x32)

============================

Other Speedhub / 29"er options:
[36x16]
96.2 (high) | 18.3 (low) < equivalent to a 22x31T granny on a 26" derailleur bike

[36x17]
90.5 (high) | 17.2 (low) < equivalent to a 22x33T granny on a 26" derailleur bike

[34x17]
85.5 (high) | 16.3 (low) < equivalent to a 22x34T granny on a 26" derailleur bike

 

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Discussion Starter · #5 ·
Cheers,

As I am going back to gears more for the high gears than the low I think 36:15 sounds right for me. Although the low gears will be nice again too! Before I went singlespeed my bikes were all set up 2x9 (without a granny ring)

Not like I am going to be stuck with it if it doesn't work out!

The only thing holding me back is the price and the weight. £750 for the OEM1 Disk in black is a lot when I can get a full XTR groupset with disks for less.

P
 
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