Hey Scootmeister, I'm using an 11t-34t rear cassette. The bicycle chainring is 24t. The engine sprockets are 11t/72t.
(34/24) x (72/11) = 9.2727. Multiply that by the 5:1 pocket bike gearbox to get 46.36:1
Top speed is limited by the driver's fear, lol.
With 15:1 in eighth gear, I stay below 45mph. I'm usually in 7th gear @ 17.72:1, between 35mph-40mph.
There are no isolated long stretches of flat road where I can really open her up.