Quote:
Originally Posted by stroker87
your right its the WEIGHT difference pick up a stock 17" wheel then a 22" wheel you'll see what i'm talking about I've had a few set of rims (8 and counting) on my suburban and most was the same over all tire height so the speedometer would ready correctly but the weight of the bigger or even just a different wheel that weights more in the same size is what kills mpg
my stock tire size is 265/70/17= 31.7 Overall Diameter
my aftermarket wheels have 305/40/22= 31.6 Overall Diameter but weight a lot more then the stock rim/tire combo so mpg suffers
the more they weight the more power it takes to turn them even if they are the same size
if you typed your current tire size correctly you should be getting better MPG that size 265/50/20 is a 30.6 Overall Diameter witch is smaller then the stock 20 inch size that is 275/55/20 and that is a 31.8 Overall Diameter tire
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Remember the wheel and tire are rolling weight and so with that in mind, there is only a small portion of it that is actully suspended and adding weight to the vehicle. It is not the weight that you are dealing with as much as it is the circumference that you have to get the wheel to turn effectively to make it work. Turning a small gear is easier than turning a larger gear with the same output ratio from the tranny. That is why drag racers go for the different lower gears for different length tracks
You are right, my tire diameter is smaller than the monsters that were on the truck when it was stock. That smaller diameter along with my 3.42 gearing makes the application of torque to the ground much easier, since the smaller diameter essentially changes the gear ratio to a lower gear.