Smaller diameter for acceleration and bigger for top speed ..... if ground clearance is an issue then a gearing change may be your only option ..... I don't know what ford box your car has but the type 9 is much used in competition and I'd guess the internal ratios could be changed to give you just the gearing you wanted (maybe higher first and lower fifth) ..... is there any scope through mapping etc to boost the torque (even at the cost of ultimate power) ? ....might help you pull the higher gear
K
