Gear Ratio??



-So I have a 25cc Homelite trimmer and I'm planning on doing the direct chain drive thing. I've found couple of clutches and sprockets for the system, but I'm not sure what a good ratio would be.
-I figure the engine will spin at about 8000 RPM and I have 23" tires. Using a gear ratio of 6:1 I will get a top speed just under 30MPH.
-Do you guys think that this setup will have enough torque to get me started or should I try to go 10:1 which would give me a top speed just under 20MPH?
I don't understand your ratio calculations.

8000 RPM
23 inch tires
6:1 reduction

8000 RPM/6 = 1333 RPM at the axle

1333 Revs/Minute * 23 inches diameter * 3.14 (pi) * 60 minutes/hour = 5.78 million inches per hour

5780000 / 12 inches per ft / 5280 ft. per mile = 91.2 MPH... !

(maybe you forgot to multiply the tire diameter by pi?)