I replaced item 14 in this diagram with the 17/49. It was originally 51/15 I haven't changed item 12 yet. I believe it is 52/16.
www.partsforscooters.com/scooter-parts-diagrams/50cc-4-stroke-QMB139-Gear-Box-Parts_2
I have seen a formula to calculate a GY6 ratio of clutch rotations to tire rotations. So I can calculate the improvement from my previous and current ratio but I don't know where to go from there. How do you convert that ratio to actual MPH limits?
Here's what I think you would need. Basically I take 51 and divide it into 15 which gives me my old secondary gears ratio of 3.4 and then I take my primary gear ratio of 52/16 = 3.25 and times the two ratios together for an overall previous ratio of 11.05 rotations to 1 tire rotation... I think.
So if I use the new gears ratio in place of the previous gears we should see 49/17 = 2.8823529412 x the primary gears ratio of 3.25 = 9.3676470589 to 1 tire rotation.
I have removed almost 2 rotations from my work per tire rotation. I should be seeing a speed increase...?
So if I am currently roughly 9.4 to 1, how do I calculate that into the bikes top speed using a 10" rim with a Pirelli 3.50 x 10 tire. I think the tire circumference would be calculated 3.5"(height) x 2 (top&bottom side wall) + 10" (rim) = 17" diameter x 3.14 = 53.428571429". I should be able to take the amount of inches in a mile and divide it by the tires circumference to see how many revolutions the tire must make to go one mile. So 63360" / 53.428571429 = 1185.8823529 tire rotations per mile?
Ok thats about as far as I can figure. What the next step to calculate my top speed?