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bryant
Member
Here is what they call a JACKSHAFT CALCULATOR. Forgive me if this is already on the thread. I haven't read all the post. Its ok I guess but I like jpilot's best. This is on ebay.
http://reviews.ebay.com/JACKSHAFT-CALCULATOR_W0QQugidZ10000000005700013
Tom
http://reviews.ebay.com/JACKSHAFT-CALCULATOR_W0QQugidZ10000000005700013
Tom
danlandberg
Active Member
Question. Should you count the teeth on the crank shaft gear & the teeth on the clutch gear and put those readings into box #1 Then input the tooth count of the drive & driven sprockets in box #2 to get an accurate rpm to mph? My speedo is right on (clocked by a road side speed trailer) When I input just drive & driven #s + tire size and a guesstimate rpm, It tells me I'm going 70 mph +.
srdavo
Well-Known Member
yes!!
danlandberg
Active Member
Thanks Dave! It comes out like I guessed (RPMs to MPH) I cruze at 28 mph & guessed it at 6000 rpms when is calculates at 6500 rpms. I was close!
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AussieSteve
Active Member
G'day Dan. To save counting, there are 20T on the crankshaft cog and 82 on the clutch, then 10, of course, on the countershaft sprocket and ??? at the rear, (44T?).
The best way to calibrate your speedo, (although it sounds like it's good now), is to put the valve at the bottom and mark the spot on the floor, then, with your weight distributed on the bike as it would be when riding, roll forward one turn and measure the distance and enter that figure into your speedo as 'circumference'. If your speedo needs 'diameter', or for accurate calcs in the Gear Ratio Calculator, divide the circumference measurement by pi.
(Under load, my 26" front wheel is actually 25.57".)
As an aside, for anyone with a shift kit, you can still use this calculator for four ratios by combining the first two and entering them as the first ratio in GearRatio.exe.
ie. 20T to 82T = 4.1:1 and with standard countershaft and shift kit 10T to 17T the ratio is 1.7:1. Multiply 4.1 x 1.7 and enter that as the first ratio - 6.97:1. (1 tooth to 6.97 teeth)
The best way to calibrate your speedo, (although it sounds like it's good now), is to put the valve at the bottom and mark the spot on the floor, then, with your weight distributed on the bike as it would be when riding, roll forward one turn and measure the distance and enter that figure into your speedo as 'circumference'. If your speedo needs 'diameter', or for accurate calcs in the Gear Ratio Calculator, divide the circumference measurement by pi.
(Under load, my 26" front wheel is actually 25.57".)
As an aside, for anyone with a shift kit, you can still use this calculator for four ratios by combining the first two and entering them as the first ratio in GearRatio.exe.
ie. 20T to 82T = 4.1:1 and with standard countershaft and shift kit 10T to 17T the ratio is 1.7:1. Multiply 4.1 x 1.7 and enter that as the first ratio - 6.97:1. (1 tooth to 6.97 teeth)
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danlandberg
Active Member
Hi Steve to late already counted L.O.L. And that is the way I programed my speedo. Rolled the bike one complete turn to get the measurement. 
AussieSteve
Active Member
You're way ahead of me. Good one.
The gear ratio calculator is excellent, especially with shift kits and the multiple ratios.
Beats doing it manually with a calculator.
The gear ratio calculator is excellent, especially with shift kits and the multiple ratios.
Beats doing it manually with a calculator.
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