Take the 2-minute tour ×
Bicycles Stack Exchange is a question and answer site for people who build and repair bicycles, people who train cycling, or commute on bicycles. It's 100% free, no registration required.

What's the range on granny gears - the innermost, smallest front chainring?

share|improve this question
    
I edited both the title and the question to clarify what I think you were trying to get at with this question - feel free to roll back or re-edit if I missed the point. –  Gary.Ray Oct 22 '10 at 4:00
    
actually, the other way! I'll fix. :-) –  Jay Bazuzi Oct 22 '10 at 15:03
    
There's always the "24-inch" gear -- i.e. two feet. Can climb almost any steep hill. –  darkcanuck Oct 22 '10 at 16:48

2 Answers 2

up vote 2 down vote accepted

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.

share|improve this answer

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.

share|improve this answer
3  
Would 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... –  meagar Oct 22 '10 at 2:57
    
+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! –  Neil Fein Oct 22 '10 at 3:10
1  
Added the terminology entry and linked it above. –  Gary.Ray Oct 22 '10 at 3:53
    
My 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. :) –  amcnabb Jul 27 '12 at 22:28

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.