KDXRIDER.NET

https://sprocketcalculator.com/

Does this online calculator seem accurate? I have 13/46 that gives me a sustained top speed of about 50mph according to my phone gps. Using the calculator, I see that a 15/42 would be 26.4% increase to about 63mph. I use it to check fields some miles away and rip around on gravel roads mostly. As it is, it's geared way too low and second gear is how I would like first gear to behave like. According to the calculator, the 15/42 would allow me to use the same chain.

Has anyone dual-sported their bike or otherwise set it up for gravel roads? I will do a steering stabilizer if it get's too twitchy which I suspect will happen.

Try gearingcommander.com

You can punch in the year, and engine and play with the gearing. It loads stock gear and mph automatically. It says an H series 200 with stock gearing is at 68.4 mph at 8000 rpms in 6th. It's 69.9 with 13/46 at 8000 rpms in 6th.
My 220 with stock gearing has hit 70 mph but it didn't have much more in it. MAYBE 75.
If your phone gps is accurate and you're getting 50 mph top speed it's not running right. Is your main jet the correct size? Have you done plug chops?
I don't think we have room on the swingarm/chain guide to go with a 15 tooth sprocket. What year is your bike?

I was wrong and my front was a 12. I put a 14 on so it's now 14/47 and has the 110/100-18 rear tire. At 60mph on a flat gravel road it seems about as high as I dare rev it; it has power to go faster but it's revving pretty high. I have a mini-tach I can put on it. What is max RPM? Could it be that someone changed gear sets?? The clutch feels good and no sign of slipping.