Final gear ratios - Tires and wheels
I know there is a lot of people that love the big tire or wide tire look on vehicles. Truth is final gear ratio is very important to the vehicle so it can reach optimal cruising RPM's and not be struggling. Like for the 2nd Gen Dodge Ram trucks optimal final ratio to the ground is about 3.73:1. That puts you right at 66 MPH with perfect 2,000 RPM on the tach which happens to be right at the top of the torque curve. When you increase the tires size say to 37" with 3.55 gears in the axle your final gear ratio to the ground is now 3.00:1 which is way too tall and the truck struggles to be even in over drive. So guys with 37" tires should consider either 4.10 gears or 4.56 gears and that bring you back close to the 3.55 to 3.73 ratio realm again to the ground. The few people I've been working with on this all report better MPG number as well as performance.
Looking cool does cost more than set of tires and wheels. You have to invest in much more to make sure the final ratio is correct typically a Dodge Ram 4WD is about $4,000 for front and rear ring and pinion.