I have no tach so I have had no idea what RPMs I was turning.
Cold weather and snow ruined my bike riding so I did math.
My tires are 26"x2.3" and measure an actual 26.5" high.
I have the "as issued" 44t rear sprocket, and 10t front.
The engine gear ratio is 20:82.
Much of you who have built "80cc" kits have the same specs.
My tires are a bit oversize but we are only talking 200 rpm at max speed.
So the math is:
tire-dia x pi x 25.4mm/inch / 1000 = distance of wheel rotation in meters
speed in kph / 60min/hr x 1000m/km / distance of wheel rotation = wheel RPM
(wheel sprocket / shaft sprocket) = 44t/10t = 4.4
(clutchgear teeth / drivegear teeth) = 82t/20t = 4.1
Wheel RPM x (wheel sprocket / shaft sprocket) x (clutchgear teeth / drivegear teeth) = Engine RPM
So, as first mounted and new, I got 40kph top speed or 5700rpm
As it wore in, speeds picked up to 50kph or 7150rpm
With some tuning and head work I can often see 60kph or about 8600rpm
my strongest torque is at about 35kph or 5000rpm
torque drops off fast under 30kph or 4300rpm
9000rpm is 63kph and I touch it occasionally but the vibes are terrible.
Aiming for 50mph? 80kph is about 11500rpm
60mph? 100kph will buzz this combo to 14000rpm!
Even with a 36t sprocket if I can still spin 8600rpm I will be lucky to see 73kph.
Steve
Cold weather and snow ruined my bike riding so I did math.
My tires are 26"x2.3" and measure an actual 26.5" high.
I have the "as issued" 44t rear sprocket, and 10t front.
The engine gear ratio is 20:82.
Much of you who have built "80cc" kits have the same specs.
My tires are a bit oversize but we are only talking 200 rpm at max speed.
So the math is:
tire-dia x pi x 25.4mm/inch / 1000 = distance of wheel rotation in meters
speed in kph / 60min/hr x 1000m/km / distance of wheel rotation = wheel RPM
(wheel sprocket / shaft sprocket) = 44t/10t = 4.4
(clutchgear teeth / drivegear teeth) = 82t/20t = 4.1
Wheel RPM x (wheel sprocket / shaft sprocket) x (clutchgear teeth / drivegear teeth) = Engine RPM
So, as first mounted and new, I got 40kph top speed or 5700rpm
As it wore in, speeds picked up to 50kph or 7150rpm
With some tuning and head work I can often see 60kph or about 8600rpm
my strongest torque is at about 35kph or 5000rpm
torque drops off fast under 30kph or 4300rpm
9000rpm is 63kph and I touch it occasionally but the vibes are terrible.
Aiming for 50mph? 80kph is about 11500rpm
60mph? 100kph will buzz this combo to 14000rpm!
Even with a 36t sprocket if I can still spin 8600rpm I will be lucky to see 73kph.
Steve
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