Gearing Questions

hey, to figure out wich gear will be 'easier' to pedal, you have to calculate the gear ratios for each gear setup. To do this, you take the number of teeth on the chainring and divide by the number of teeth on the freewheel cog. The closer this number is to 1, the easier the gear will be to pedal. Hope this helps.

-Ben 😎

This is the formula for working out gear "inches", even though they're not real inches -- it really just provides a comparison.

Note: 27 is the old wheel size.

(30/21) x 27 = 38.6 inch gear

(39/26) x 27 = 40.5 inch gear

so, there you go; not much differecnce.

The other way is gear rollout or gear "developement", which is the distance that you travel with one revolution of the cranks in any particular gear :

http://www.analyticcycling.com/PowerMeasAnalyGear_Disc.html Scroll down for the chart. As you can see, this chart doesn't have a 30 tooth chainring, so you can roll it out yourself in your driveway.

There's also Sheldon Brown's gear calculator, where you can input your own chainring sizes:http://www.sheldonbrown.com/gears/

surfrusty said:

I have a choice between 2 diferent drivetrains. And I want one that is going to not kill me on the climbs as I'm kinda still starting out. The lowest gear on one is a 30 (front triple) and a 21 (rear cog). The other is a 39:26. Which is the lower gear? Which will be easier on the hills and how do you calculate that?

Thanks!

If you go to Sheldon Brown's site as suggested you can put in MPH at say 80 rpm pedal cadence. If you do that then you get:

30/21 = 8.9 MPH at 80 rpm cadence
39/26 = 9.4 MPH at 80 rpm cadence

for comparison a 39/27 is 9.0 MPH, so the triple with the 21 gives you an effective 39/27.

Keep in mind also a cassette with a 21 as the largest cog will have much closer spaced cogs than one with a 26. Closer spaced cogs on a cassette give you more fine tune control on gear selection.

coatimundi01 said:

hey, to figure out wich gear will be 'easier' to pedal, you have to calculate the gear ratios for each gear setup. To do this, you take the number of teeth on the chainring and divide by the number of teeth on the freewheel cog. The closer this number is to 1, the easier the gear will be to pedal. Hope this helps.

-Ben 😎

Acutally, the lower the number the easier, .8 is easier than .9... it just happens that most bikes do not have gears that low...

All information is correct as posted. It is as simple as dividing the number of teeth on the crank gear by the number of teeth on the free wheel. The larger the result of this equation means the greater the effort required. Of course, if you have the strength, this results in going faster 😄

If you don't like mathematical equations stop reading now. and skip to the bottom 🙄

If you have a tolerance for detailed calculations, you can create a nice spreadsheet to compute speeds for different cadences and the various gear combinations. The complete equations for converting cadence and gear sizes into speed goes like this:

C = cadence in cycles per minute
T = number of teeth on front gear
t = number of teeth on rear gear
Pi = 3.1415926....(the ratio of circumference to diameter for a circle :eek: )
assuming a 700 mm tire diameter, speed, V, can be computed by the equations

for miles per hour

V= C x 60 (T/t) x Pi x 700/(25.4 x 12 x 5280)

or for kilometers per hour

V= C x 60 (T/t) x Pi x700/(1000 x 1000)

So for a cadence of 90 cycles per minute,
the 39:26 ratio gives a speed of 11.1 mph;
the 30:21 ratio gives a speed of 10.5 mph.
Therefore 30:21 is easier, but slower.