reduction ratios

[ZKDX]

i'm playing around with some calculations using a spreadsheet i pulled from the net somewhere. Anyway, i'm trying to decipher the definitions of the spreadsheet names and my manual. Spreadsheet needs the following:Primary Trans Ratio, Transmission ratios, and Total Reduction. Is the primary trans ratio my rear/front sprocket, the transmission ratios the spec for each gear, and the total reduction the same thing as my final reduction ratio?...i'm a bit confused with all the lingo!

 

[ZKDX]

sorry....also meant to ask---where can i find what kind of rpm my kdx200 will produce?

 

[Rich Rohrich]

This might help answer a few questions. http://www.ericgorr.com/techarticles/mototech_march_2000.htm


Also if anyone is interested, DRN member Dave Petersen (96whyzee125
) made up a really nice spreadsheet to do gearing calculations. He was kind enough to give me permission to share it with anyone who would like it. If you guys are interested I can put it up on Eric Gorr's website so you can download it.

 

[ZKDX]

rich, please post spreadsheet, if you don't mind

 

[Rich Rohrich]

I'll upload it tonight and post the link here.

If any of you guys D/L it and use it don't forget to send Dave - 96whyzee125
a PM thanking him. :thumb:

 

[BRush]

On a bike (well, at least on my KDX) the final, or overall ratio is calculated like this:

Final Ratio = Chain Ratio * Trans Ratio * Primary Ratio

The primary ratio is the reduction before the transmission. You’ll have to determine by what the spreadsheet is doing to see if “total reduction” corresponds to chain (e.g. sprocket) ratio or not.


On my ’96 H model . All the data for the primary and trans ratios were found in the service manual.


Example:

Primary reduction ratio. This is 63/22 or 2.864

Transmission ratio, which of course depends on which gear you are in:

1st gear = 35/13 = 2.692
2nd gear = 28/14 = 2.000
3rd gear = 23/15 = 1.533
4th gear = 21/17 = 1.235
5th gear = 25/24 = 1.042
6th gear = 20/23 = 0.870

Chain ratio, which depends on your sprockets. Stock is:

47/13 = 3.615

Final Ratio = 3.615 * 0.870 (6th gear) * 2.864 = 9.007

If you know the final ratio, your engine rpm, and your rear tire diameter then you can calculate the theoretical ** speed for that gearing.

MPH = (RPM * PI * D) / (Final Ratio *1056)

Where D = wheel diameter in inches


** (“theoretical” is code for saying that we’re just having fun with math here and you ain’t never gonna get your KDX to do 110 no matter what size sprockets you slap on :confused: )

 

[23jayhawk]

I put together a reduction model last year for the KDX, but could not figure a way to post it anywhere. Gives ground speed and RPM for any combination of countershaft and rear sprocket, given a tire diameter.

Guess I need to get around to building a web page. :cool: