I have the american racing supersnake wheels, they look great but are heavy. Rear 20x10 is 36lbs, and front 20x9 is 34lbs. On the highway on a long cruise, I am now getting 5mpg less. How does it effect performance?

Is it worth the money going to light weight wheels.

 

It depends on how you use the car.

On a road course it means less acceleration out of the corner, and it makes things much harder on your brakes. Lighter wheels are better for racing, but again, depends on how you use the car.

I'm surprised to see you're loosing that much MPG. Are the tires high rolling resistance? Just the weight alone should not add up to 5pmg less.

 

Driving long distance at 70mpg I can get 27-28mpg on the track wheels. On the supersnakes I am getting 23mpg top.

 

Wrong thread. Sorry

 

It's really not possible that a total increase of only around 40 pounds - whether sprung or unsprung - would cause that much difference in mileage. A wild guess would be that maybe the two sets of wheels/tires are different sizes (overall diameter not width)? Then the difference becomes a function of an inaccurate odometer because of the different number of wheel revolutions per mile... the actual gas mileage is about the same but the calculation is thrown off by the odometer difference.

 

Also, rolling resistance between one tire model and manufacturer and another can be significantly different causing noteable difference in fuel economy.

John

 

I thought the stock tire with wheel was around 40+ pounds?

 

Pretty sure the stock wheels alone are around 35 pounds each, depending on which stock wheels you are talking about

 

Indeed. The Brembo wheels are 31lbs each. the 255 tires are additional 30 lbs or so.

 

My 19" wheels with tires are about 60 pounds.

 

The obvious question - old tire size vs new tire size. If the diameter of the tire changed that can account for some of the mileage change. What's the new tire size?

 

This. If you didn't tune the car for larger diameter tires, the car will think you are doing less miles than you really did and thus showing worse gas mileage.

Also if your new tire has a larger contact patch with the road you have more friction with the ground. This will lead to a decrease in efficiency, so less MPG though it would take some truly massive tires to see that significant of a drop. Your spedo will be off as well if you didn't program the new tire size.

Not likely it's an issue of weight.

 

+1

+1 here too

All of that.

 

Unsprung/rotating mass is often estimated to be 4x as significant as mass anywhere else on the car.

It requires more energy to accelerate which penalizes any time you change speeds (up or down) and because of the greater inertia of the suspension system, the suspension will react more slowly to bumps and surface imperfections which makes the ride rougher and handling poorer.

Light wheels are ALWAYS better (so long as they're strong enough to do the job )

 

Agreed... unsprung weight is important for handling and suspension responsiveness. But a relatively small difference in unsprung mass will have little effect on fuel mileage - certainly not 4 mpg (~17%). Even if each wheel/tire was 10 lbs heavier and your 4x figure is accurate, that would mean having a 160 lb passenger would also knock 17% off of the fuel mileage which we all know is nowhere near reality.

 

Absolutely.

As others have guessed above, difference in the diameter (and therefore the mileage calculation) likely explains a lot of/most of what the OP is seeing.

 

Just don't run slicks on enkei pf01's - I've cracked two wheels now at the track

Back on subject, -5 mpg isn't from the wheels. Wider tires, different driving winter blend gas maybe.... Once you're at speed the weight of the wheel really makes no difference for highway mileage. Stop and go mileage would suffer a bit

 

I don't disagree here at all. The penalty for heavier wheels is technically limited to the added energy required while imparting acceleration either in the rotational access, acceleration of the whole car-system or for acceleration in the direction of suspension travel.

That said, how many of us actually change wheels and end up with a tire package that offers lower rolling resistance?

-5mpg would require an absurd amount of friction increase from wider/stickier tires but there's almost always some kind of measurable fuel consumption penalty with a tire upgrade.

 

how do I tune the car to use the aftermarket wheels? I think that is mostly the issue as when I hand calculated it I was getting 27mpg on the hwy.

I really like my supersnake rims and do not want to have to replace them with another set, any ideas?

 

Hmmmm . . . . "tuning" in this case simply corrects the math that the car's computer is using to display speed and distance traveled on the speedometer; so that does not explain the difference between the dash MPG read-out and your hand calculated result because they should both be using the same number for miles.

But to answer your question: you need a hand held tuner; you go in to the tuner and "load custom tune" or whatever it is in that model of tuner; then before loading the tune, you go in to "adjust parameters" and select the correct "revolutions per mile" for the tires that you have on the rear wheels. The best place to get the "revolutions per mile" number is from the manufacturer's web site for the exact tires that you have, or from another source of the same information such as Tire Rack.

Or, not sure if maybe a dealer can do it for you?