Most states have minimum seat height regulations. 20 inches? Your race chassis won't pass inspection even as a motorcycle. The PCX125 is redline AND horsepower limited to 62 mph. It gets 105 mpgUS at best. Not 130. I get 90 mpgUS on my CBR250R. And 98 mpgUS on the PCX150. The PCX150 will hit the higher redline at 66. Still too slow. There are parts available to increase the final gearing but you would have to stack two different kits to make any real change. You might get 15% longer gearing but the 125 doesn't make enough power to take advantage of it.
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The Honda PCX / Honda Forza Forums • View topic - Gears for higher top speed
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Go with a CBR250R drive train if you want to cruise at 70 mph.