Gear roll-out is the distance the bike will travel with one revolution of the cranks for any particular gear ratio. I believe it's also called "gear development".
Gear roll-out chart.
http://www.analyticcycling.com/Power...Gear_Disc.html (SCROLL DOWN)
You can use it to determine what gears you need for any particular speed or rpms.
For instance, you might wanna know what revs you'll be doing at a particular speed.
For example: "what revs will I be doing at 60kmh (37.29 mph) with a 52/12 gear ratio"
So, you go to the chart which tells you your 52/12 gear ratio = 9.135 meter roll-out...then.....
60 kmh / 60 = 1 km in one minute
1 km x 1000 = 1000 M in one minute
1000 / 9.135 = 109.47 rpm
You can obviously do this the other way around. For example, you might wonder "hmmm...if I was riding at 105rpm in my 52/12 gear, how fast will I go?"
So, you go to the roll-out chart which tells you that 52/12 has a roll-out of 9.135 meters.
Therefore: 105 x 9.135 = 959.175 meters per minute.
Therefore 959.175 x 60 = 57550.5 meters per hour
which obviously = 57.55 kmh
It is also used for juniors because they have gear limitations to reduce the chances of injuries.
This is different to the old "inches" calculation, which is (# chain-ring teeth / # cog teeth) x 27
eg: (52/12) x 27 = 117 inches.
Last edited by Fat Hack; 08-19-04 at 11:02 PM.