[Leon94]

I happened to find this website that gives a pretty technical description of BMX sizing and gearing. The website is intended for bmx racers, but still valuable whether you are on the track, street, or park.

http://supertrakbmx.com/content/view/3/5/

 

[jasride]

Hell yeah, good find. All that gearing probably pertains more towards a racer than anyone but everyone should know a little about what gearing they're using, although I'm sure this topic has been posted a few time before.

just to keep it simple, the formula is:

(sprocket size) divided by (rear cog size) times (tire diameter) = gear inches.

I guess they recommend staying anywhere between 50 to 55 gear inches, but I know a few riders who choose to ride more towards the upper 50's close to 60 gear inches.

 

[t1maglio]

To bad that site is old school and doesn't get into the smaller gears.

So on a 24" bike I was told that 27x11 or 25x10 would be good. According to their numbers I should be thinking 27x12 and 25x11. That might be kinda slack, but considerably closer to my 36x13 on my 20" then those first numbers. A 23x10 or 30x13 seem pretty close to ideal.

 

[sittingduck]

http://sheldonbrown.com/gears/

 

[Graydog]

Bike school has a very easy to use gear calculater
www.bikeschool.com