I'm too lazy to look through the whole thread again.
Sprockets depend on a number of variables.
1. Gearbox Ratio in each gear
2. Primary Gear Ratio
3. Horsepower
4. Tire Size
5. State of Tune.
You need to figure out the above variables and then plug them into my speed calculator:
7.5 HP is capable of 55mph.
Honda50.com Gear Ratio - Speed Calculator
You'll notice I only have Honda and Japanese combinations from the pulldown menu. There is a 100% chance we will not ad any of the chinese "flavor of the day" gearboxes/engines because they change too fast, and we have no interest in them. However, you can get the ratios and plug them in manually.
One of my old combinations was as follows:
Honda Monkey 4 speed gearbox with a 1.043 4th Gear Ratio
67/18 Primary Ratio
88CC BBK, Race Head, 20mm Carb, Good exhaust - Around 7.5HP
3.5X10" tires
I ran a 35T rear sprocket, and a 15T front sprocket, but did run a 16T on occasion. I liked the 15T better with the 4 speed.
on any of the chinese motors, I expect them to run out of steam before 10,000 rpms.
The more horsepower you have, the taller gearing you can run. If the bike falls flat in top gear, either your front sprocket is too big, or your rear is too small.
Alot of sprocket choice is personal riding preference. Just my 2 cents.