Lilone,

18x6W or 18x4W will do it. Any more pitch than that and your in high gear. Try to get a 18x4W if you can. The less the pitch the lower the gear just like in a vehicle. What your doing with the 18x8 is like trying to start out in a car in 5th gear. Doesn't work well does it?

JMHO,

Gibbs