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Discussion Starter · #1 ·
Hello,

I am going to customize the drivetrain on my 29er. I plan to use a custom front crankset with 20/30/40 gearing. I was wondering if I would be better off with the 11/34 or 12/34 XTR model. My goals are to get equal gearing range to a 26 while getting the best gear transitions given these options. All 9 speed. I do not plan to use a 12/36 as it is way too heavy for my liking. Any advice would be appreciated. Thanks.
 

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I run a 12-34 and really like the ratios, no big 20-17 tooth jump in the middle of the cassette.

But if you're bike's going to see commuting/training/group ride duty on the road, I'd go 11-34, the 44/12 gear combo on my bike is just barely enough to hang on the local road group ride or when doing sprint intervals on the road.

Just riding dirt? 40/12 will be more than enough.
 

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The gain ratio is going to be closer to a 26" if you go with the 11-34. I ride with a 44T big ring and prefer the 12-34. I like the gear transitions on the 12-34 better and don't need an 11T with the 44T ring. Given that you are dropping to a 40T, you are going to need the 11T to get the same ratio, so you are going to have to pick your poison.
 

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Discussion Starter · #7 ·
This bike is dedicated to off road riding and never used on the road. But I do see the point in the top end possibly being too low with a 40/12. But I will say that in all my years of riding off road rarely to to the top combo even on flats. I ride East Coast trails--they are short steep climbs that come up very fast and frequently and I don't get many long downhills at all.
 

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AFAIK you'll get closer ratios with the 34-12, which to me is better and worth loosing 1 tooth on the high end - I say 34-12.

40/12 will still give you 96.7 gear inches, where as 44/11 on a 26" would give you 104 gear inches. So to do 25 mph with the 40-12/96.7 gear inches gearing you'd be spinning somewhere around 87 RPM, need faster 30mph=104 RPM, 35mph=122 RPM.

On a roadie doing 122 RPM with a compact crank 50/12 will net you 43mph.
 
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