Alloy Wheels

[rty]

I read somewhere that switching from steel rims to light alloys can slightly increase gas mileage. Has anyone experienced any mpg gain?

[TrailDust]

Originally Posted by rty

I read somewhere that switching from steel rims to light alloys can slightly increase gas mileage. Has anyone experienced any mpg gain?

IMHO the fuel savings would be negligible, but I suppose there are some vehicles it could make a very slight difference. Then again, who am I to talk as part of the reason I removed the 3rd row seat (55 pounds) and also don't lug around the 2nd row padded console (15 pounds) from my Highlander was to save weight and eke out every smidgen of fuel mileage I could...but it didn't cost anything to do it either....

TrailDust

[IronNam]

depends on how much weight you lost, im not sure how much steelies weight, around 30 pounds average? there are wheels that weigh in about 8lbs forged and with about 80lbs lost on your vehicle, especially ont he wheels, your engine wont have that heavier engine load also.

1lbs = 10 lbs rotational force if i remember

[EvoFire]

Steel wheels weigh a lot, I've been thinking about it as you can definitely feel the car being faster/slower from weight of the wheels. I've also been thinking about the weight as a function to mileage, though there doesn't seem to be much calculations or posted info on this subject.

[touringcamry]

It will take a very long time to recoup the cost of the wheels in terms of fuel savings if that's your main objective. Decent lightweight rims, 18lbs or less for a 17, cost maybe $300 and up each without a tire.

You might see a 5% gain but even that I speculate is optimistic. There is potential that you won't have any gains or that you could be worse off than when you started especially if you're getting bigger wheels.

[IronNam]

bigger isnt neccesary, just different material for same size would be good still.


look, if you have a bike, find a way to put half a pound on each one of those spokes, and try to pedal


that will be your control...


then take those weights off, and bike again


im sure there will be a difference

[msanford]

Originally Posted by rty

I read somewhere that switching from steel rims to light alloys can slightly increase gas mileage. Has anyone experienced any mpg gain?

My winter steelies are lighter than the stock alloy wheels.

Oh, right, you asked a question, too. Like others said, it depends how much weight you lost. This is a total off-the-cuff estimate, but you will probably lose the same amount of weight by burning half the fuel in your tank.

Want better mileage, don't fill all the way.

[rty]

I was thinking more of the effect of less force being required to turn the lighter wheels rather than less total weight.

[msanford]

Oh yes I know you were referring to the wheel's rotational inertia, but as much of a knee-slapper that my answer wasn't, it's probably more important than the wheel's RI.

But, to answer your question: if you assume that a wheel is a solid disk (which of course it's not, but close enough) you can calculate its moment of inertia as I = (mass • radius^2)/2.

So, for two 16" wheels, one 15 lbs and one 25 lbs, you'll get a net gain of 1280 inch-squared-pounds, per wheel, by reducing the mass of the wheel. This really only matters on the driven wheels.

But since the moment of inertia of a rotating disk is a function of the radius squared, you'll get a bigger bang for your buck by reducing the wheel's radius than it's mass. Better, do both.

Now, reducing the wheel's radius will usually increase the tire's profile, increasing the amount of rubber that has to deform every time the wheel turns, decreasing rolling resistance, etc. This is probably a negligible offset, however.

[Zembonez]

There is technically a gain in handling and efficiency anytime you reduce rotational mass and unsprung weight. It is doubtful that you would ever notice a difference at the pump.

Curb appeal would be improved drastically.

[msanford]

Zembonez has the right idea