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Gear Ratio/Inches Comparison Chart--26, 27.5 & 29er with Cassette/Chainring Combos

Okay so I created a chart to compare 27.5 and 29 inch wheels to 26 providing both a gear ratio relative to the 26 inch wheels and gear inches for the 1x11 or 1x12 Cassettes (SRAM in this chart) and the old XTR, 3x9 with 26 inch wheels I used to ride. Although obviously you can compare different combinations of cassette/chainring teeth combos and wheel sizes.

The left and right columns illustrate SRAM 11 or 12 speed cassette setups with 27.5 and 29 inch wheels respectively--the center column is for 26 inch wheels with XTR 3x9 setup. I included varying size chainrings but obviously for the SRAM setup you can only use one chainring whereas the old XTR you'd shift among three chainrings.

For example, the lowest gear on the old XTR set up I had yielded a .706 gear ratio and 18.4 inches with a full pedal stroke. To get about the same on my XX1 11 speed with 27.5 inch wheels, I used a 28 tooth Chainring, which yielded .705 gear ratio and 18.3 gear inches--very similar.

So if you moved up to 29 inches and a 12 speed, you'd use a 32 teeth chainring to get about the same gear ratio/inches--that would yield .714 gear ratio and 18.6 gear inches.

Looking to move to a bike with a 1x12 and 29 inch wheels so I'll probably go with a 30 tooth chainring because I ride a lot of uphill and found myself using the that 42 tooth chainring most of the time. Rarely ever use the high end gears unless I'm on a street peddling home, which doesn't happen too often.

Anyway I attached the comparison I used to help me decide and figured it might help someone else. Did this on Excel and I think its right but if anyone notes a math error let me know and i'll fix it.
 

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Ok, good start. Figure in tire size? And the cassette and chainrings could have more in them. My 2x11 has 26/36 chainrings, and the 11 T cassette is pretty common. Cheers.
 

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Ok, good start. Figure in tire size? And the cassette and chainrings could have more in them. My 2x11 has 26/36 chainrings, and the 11 T cassette is pretty common. Cheers.
No I did not consider tire size. For gear ratio it wouldn't matter right? For gear inches I was more concerned with "relative" to the other setups so I figured tire size would be close. You'd obviously have more inches per full pedal if you calculate in the tire size.

Plus its also not an exact measure. Even with identical gear ratios they'll be a difference based on tires, wheel size, bike geometry, etc. But for me it was more deciding what chainring would be best. Obviously be better to just try it but I have four rings now (28 to 34) and I rarely use any other except the 28 (and then only the 30) on my 1x11 with 42 inch granny. So I wanted to make an educated guess rather than buy 3 or 4 rings and try it.

I'd be happy to calculate someone's gear inches if they wanted by giving me the exact diameter of their tire.
 
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