What's the range on granny gears - the innermost, smallest front chainring?
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1There's always the "24-inch" gear -- i.e. two feet. Can climb almost any steep hill.– darkcanuckCommented Oct 22, 2010 at 16:48
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3 Answers
The Mountain Tamer Quad lets you get down to a 16-tooth granny gear, although in the fourth position.
For the upper range, it depends on the crankset - if you limit it to only rings in the third position I suspect a 74BCD 30-tooth would be the largest commonly available. If you include the inner ring of a double crankset they can be as large as chainrings are made - 60-tooth rings can be purchased and you can get plans to machine your own chainrings up to 92 teeth.
Gearing is commonly described in Gear Inches and to clarify, having your chain in the smallest front ring and the biggest rear cog results in the smallest gear.
Chainrings
The smallest chainring I've seen on a 5-arm crankset is a 20T, although 24T is a lot more common.
8-Speed cassettes
Shimano had a line called "Megarange" that was 11-34T. I believe it's no longer manufactured but you can find them online sometimes.
SRAM has a cassette in the PG-850 line that is 11-32T that I believe is still available.
9-Speed cassettes
Shimano has a number of models that are 11-34T and one model that is 12-36T.
10-Speed Cassettes
I believe the biggest you can get is 12-27T.
IMPORTANT NOTE: Not all front or especially rear derailleurs will be compatible with these large range rings and cassettes. Check with the manufacturer - most have spec and compatibility docs online.
Out of curiosity I used a gear calculator to figure out what the gear inches would be if you actually configured a bike and could ride 20x36 on 700c wheels...an incredibly small 14.7 inches. That means every pedal revolution you travel about 46 inches, just over half the circumference of the wheel.
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3Would be helpful if you could offer an explanation for gear inches in the terminology thread; what higher or lower values translate into for the cyclist, how it's calculate, etc... Commented Oct 22, 2010 at 2:57
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+1 to @meagar's comment. Stuff like gear inches, chainring, cassette, et cetera, can all get entries in the terminology thread. @Gary.Ray, nice answer! Commented Oct 22, 2010 at 3:10
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1My mountain bike had a 24x34 gear on 26x2.00 wheels, which according to the calculator is 18.2 gear inches. At 60 RPM, that gives 3.3 miles (walking speed). As silly as it feels to go that slow, it can be nice to have the option. :)– amcnabbCommented Jul 27, 2012 at 22:28
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Minor point, back in 2010, Campy did have a 13-29 10s cassette. Of course, most people don’t use Campy. These days, I think there are 12-30 10s cassettes for Shimano or Shimano-style freehubs. The answer has become a bit more complex on the rear side because of the rise of gravel bikes. Commented Dec 27, 2020 at 17:51
My Giant Yukon came with a 22 tooth inner chainring and a 32 tooth cassette although now I have a 34 tooth cassette on there. It is nice for climbing up hills although you can still begin to struggle above 20%. The legs will turn the gear easily enough but you'll still get puffing and panting to maintain a reasonable cadence. You can get these new 40, 42, 50 and 52 tooth cassettes available. I'd love to try 22/52, that would be the rock crawler of bicycles.
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53 tooth cassettes are available from aftermarket manufacturers as well. Now, that would be fun! Commented Dec 28, 2020 at 1:29
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Interesting to see the difference in trends and available options between now and a 10 year old question– Nate WCommented Dec 31, 2020 at 20:56