View Single Post
Old 11-11-2015, 08:26 PM
bluegoatwoods's Avatar
bluegoatwoods bluegoatwoods is offline
Motorized Bicycle Elite Member
Join Date: Jul 2012
Location: Central Illinois
Posts: 1,576
Default Re: Attention! Little math help here!

Okay.....well......I'm a bit rusty on that stuff. But I ought to be able to get you someplace.

Let's set your 25 mph cruising speed as our benchmark.

You're doing 25 at X engine rpm --it doesn't matter exactly what the value of X is --with a 44 tooth sprocket. I've already forgotten what your sprocket choices are. But did you mention a 56 tooth? Let's go with that.

To figure out how fast you'd go at X engine rpm you'd need to figure 25 x 44 divided by 56......equals.......mumble, mumble......lemme find a paper and pen.........just a minute........I'll be right back......

okay...25 x 44 divided by 56 equals................Infinity???!!!!

Oh, mannnn!!!......I'd better get a calculator........

25 x 44 divided by 56 equals.....19.6 mph at X rpm.

Maybe I made that more complicated than it needs to be. When calculating results of different sprocket sizes just take the ratio of the sprocket you've got against the sprocket you're considering. In this case the ratio of 44/55 which equals point 8. So with a 56 tooth sprocket your speed at X rpm will be point 8 times your speed with a 44 tooth sprocket.

Or you could calculate your torque at X rpm using the inverse. 56/44. Which equals 1 point 27. So at X rpm, on a 56 tooth sprocket you'd have 1 point 27 times the 'pulling power' that you'd have on a 44 tooth.

Unless that Mogollon Rim is very, very steep you probably don't need a sprocket any larger than 56.
Reply With Quote