A 25 pound aftermarket wheel can actually take less energy to rotate than a 20 OEM wheel, for example...

Go to a sporting goods store and pick up a 28oz wood baseball bat, and swing it around a few times, now pick up a 35oz wood baseball bat and swing it around a few times. although its just 25% heavier, it feels more like 75 to 100% heavier. But now take that same 35oz wood baseball bat and swing it from the other end... it feels like its about 5 ounces as most of the weight is near the axis...

Now look at the Z06 or C6 OEM wheels that have the fat part of the spokes towards the center, and the spokes thin out as they go away from the wheel, this provides most of the spoke mass near the axis and where the load is greatest, and the thin part of the spokes far away from the axis in effect turning the 5 baseball bats backwards..

Ping became famous doing just the opposite with golf clubs by moving the weight to the perimeter of the clubs so when you miss hit the ball it doesnt rotate as easy and slice the ball.

My examples might be a bit exagerated, the the concept is intact.

I wonder if a wheel balancing machine like at discount tire spins up the tires to balance them at the same rate, maybe you could time it and see if 2 25# tires with different spoke configurations spun up in the same amount of time, then possibly use some common wheel and tire combination as a reference and compile a data base of times for other tire combinations. Possibly GM did it right and gave us the best combination from the factory. MeekRN™

 

Interesting thought.....

 

I thought tire machine spun the wheels to 70 mph and then took the reading. So the size of the rim would not matter, since the shaft is moving at 70mph.

The rotations per mile would be different, but the speed would be the same, NO?

 

Once spun up, yes Buda he is talking about the time it takes to spin each one up to that 70 MPH. His hypothises is that if the mass is closer to the center it should take less time than if the mass were located farther out. Makes sense !

Another Buda

If you are running runcraps It don't matter as their weight is so great that I suspect that it will be a wash in the end.

For best results go to a lighter tire. Based on this a pound less would be a significant saving!

 

Well, I be danged. We have some people who really put some thought into their think. Great analogy. And, your simple generalization is quite applicable. In general, the heavier the design, the thicker the outside bulk/hull/barrel, and, the larger the wheel diameter, the more energy needed for polar moment (higher rotational mass). But, this is why wheel manufacturers struggle to design custom wheels that are not only larger in diameter, but, lighter in weight (as much as possible) to reduce the effects of higher rotational mass.

 

Just spoke to my brother who is some sort of mad scientist. He said in theory you would be correct, as rotational mass needs more energy to be propelled the further away from center it gets. Then he went into a whole bunch of mad scientist ramblings about all the other factors that could make it not note worthy. Alls I really got was that the sustained energy to keep it moving, because of the rotational mass, would be less...

In other words, it would take less to spin it up, but more energy to keep it spinning. But in reverse, more energy to get it spinning, but less energy to keep it spinning...

Peace
Willfulone

 

Just add more horsepower and don't worry about it!

 

It is true, that the moment of inertia depends on how the mass is distributed about the axis. There is a greater moment of inertia if more mass is farther from the axis than if the same mass is distributed closer to the axis . Ahh-umm, WTF As above add more ponies and watch friction make smoke.

 

I think this wheel weight thing is of little matter to most of us but have to put .02 in. Don't think anyone has mentioned that in the "weights & measures" it shows that the run flats is one place you can save weight. So if you take them off it probably more than offsets the new weight of most repo's.

Otherwise think about your wheel as another gear. The bigger it gets the less revolutions per minute at the wheel. It's a form of gearing up or down you rpm at the wheel which probably affects your take off and your top speed similar to different rear ends. .02 not to worry