Gearing Help
Bighead, that is an awesome platform you have to start with!
For the gearing calcs you'll need a few things up front, like desired top speed, circumference of the tire you plan to use, and the max engine rpm you intend to run at. You'll also need the primary drive (crank gear/trans input gear, top (5th or 6th)gear, and final drive (sprocket) ratios; these should be in the Kawi service manual.
Then it's just a matter of dividing the engine max rpm down through the ratios to get your tire rpm. You can take a guess at what sprocket ratio to start out with, or use the existing ones as a baseline. Then you take the tire circumference and calculate how much ground the tire will cover for one rotation. Once you have the wheel rpm you can get the mph at a give engine rpm. Below are calcs I did for adding a jackshaft to the MowCart.
In your case the engine pulley/transaxle input would be represented by the Kawi's primary reduction between the crank gear and trans input gear, the intermediate drive ratio would represent your top (5th or 6th) gear ratio, and my input reduction would be ignored. Final drive ratio represents your countershaft and wheel sprockets. If you just plugin your numbers and start out with what is on the bike you'll be able to determine which sprockets to use.
TIRE CIRC. 64" ENGINE SPEED- 3600 RPM
ENGINE PULLEY 3.5 DIA CIRC. 11.0
PRI. INT. PULLEY 2.75 CIRC. 8.64
PRIMARY DRIVE REDUCTION .785:1
4586 RPM
SEC. DRIVE PULLEY 3.75 CIRC. 11.775
SEC. DRIVEN PULLEY 2.75 CIRC. 8.64
INT. DRIVE RATIO .73:1 (Primary Reduction Ratio between crankshaft and trans input shaft) 6282 RPM
INPUT PINION REDUCTION 2.31:1 (Not Used in this example)
2719 RPM
6TH GEAR RATIO .60:1
4533 RPM
FINAL DRIVE RATIO 9.89:1
458 rpm
X 64" per tire rev.
=29331 in/min.
X 60
=1759879 in/hr.
/63360 in/mi
=27.7 mph
I actually have a spreadsheet for this somewhere in our racing archives; I'll try to dig it up; it works a lot faster than this.
Burn Rubber! (Or Dirt)
Bighead, that is an awesome platform you have to start with!
For the gearing calcs you'll need a few things up front, like desired top speed, circumference of the tire you plan to use, and the max engine rpm you intend to run at. You'll also need the primary drive (crank gear/trans input gear, top (5th or 6th)gear, and final drive (sprocket) ratios; these should be in the Kawi service manual.
Then it's just a matter of dividing the engine max rpm down through the ratios to get your tire rpm. You can take a guess at what sprocket ratio to start out with, or use the existing ones as a baseline. Then you take the tire circumference and calculate how much ground the tire will cover for one rotation. Once you have the wheel rpm you can get the mph at a give engine rpm. Below are calcs I did for adding a jackshaft to the MowCart.
In your case the engine pulley/transaxle input would be represented by the Kawi's primary reduction between the crank gear and trans input gear, the intermediate drive ratio would represent your top (5th or 6th) gear ratio, and my input reduction would be ignored. Final drive ratio represents your countershaft and wheel sprockets. If you just plugin your numbers and start out with what is on the bike you'll be able to determine which sprockets to use.
TIRE CIRC. 64" ENGINE SPEED- 3600 RPM
ENGINE PULLEY 3.5 DIA CIRC. 11.0
PRI. INT. PULLEY 2.75 CIRC. 8.64
PRIMARY DRIVE REDUCTION .785:1
4586 RPM
SEC. DRIVE PULLEY 3.75 CIRC. 11.775
SEC. DRIVEN PULLEY 2.75 CIRC. 8.64
INT. DRIVE RATIO .73:1 (Primary Reduction Ratio between crankshaft and trans input shaft) 6282 RPM
INPUT PINION REDUCTION 2.31:1 (Not Used in this example)
2719 RPM
6TH GEAR RATIO .60:1
4533 RPM
FINAL DRIVE RATIO 9.89:1
458 rpm
X 64" per tire rev.
=29331 in/min.
X 60
=1759879 in/hr.
/63360 in/mi
=27.7 mph
I actually have a spreadsheet for this somewhere in our racing archives; I'll try to dig it up; it works a lot faster than this.
Burn Rubber! (Or Dirt)