X2: good starting point is 1st gear × axle ratio = 10 or more, especially for a small engine with mixed use.
Easy math, using "calculator" function:
Enter the axle ratio (3.55, etc.).
Press "1/X".
Result × 10 is 1st gear ratio.
10 ÷ 3.55 = 2.82:1.
10 ÷ 3.23 = 3.10:1.
10 ÷ 3.73 = 2.68:1.
10 ÷ 4.11 = 2.43:1.
OK with less than 10:
big motor/light chassis
heavy flywheel
highway only
Needs more than 10:
small motor/heavy chassis
big cam
aluminum flywheel
traffic only
