try a 15-42 combo and a 2nd gear start

 

Yes I agree with 15/42 with a 20" tire
That calculates to about 58mph at 6800rpm in 5th gear

We all have a tendency to overrev, and even though the motor can rev to 8500 easily, it is way over/past the torque curve.

This of course is based on a tire with no growth. If you are using a tire that grows, calculating the gearing must be difficult.
You almost have to buy the tires and have a tach to know where you are at. Then gear accordingly.
I do not have a tach and that is why I am searching for information of this subject.
Thanks for the info so far.