[Blue Bomber Man]

For the savings of gas alone updating your rims to lightweight alloy wheels will probably never return a financial payback to you (Unless you can get a decent price for selling your old rims)

To get an idea of the impact of lighter wheels, take your vehicles weight and divide it by your HP. This will tell you how much weight each HP drives. Say you have a 100 hp car that weighs 2000 lbs. Works out to 20 lbs/hp. So cutting 20 pounds from your car would be the equivelent to improving your engine by 1 hp.

Now this isnt really a comparison of apples to apples because the wheels are rotational mass. I think the conversion is roughly 4:1 so if you cut 20 pounds of wheel mass it is the same as cutting 80 pounds off the car

As far as aerodynamics they are probably all horrendous and you can always slap a moondisk on if you dont mind the looks of them

So clearly it will help with performance (which is why racers use light wheels) and I am sure it will help with mileage some, but I dont think it would be very significant...perhaps one mpg maybe two.