18" wheels heavier than stock?

MuuMuu101 said
This is not the case... However, just because the wheel and tire is lighter doesn't mean you're automatically going to have less losses and an increase in performance due to weight alone (not taking into consideration grip, contact patch, compound, sidewall flex, etc). What really matters when it comes to wheels is the mass moment of inertia. Essentially, it's how much energy it takes to revolve an object around an axis. Basically, the farther away the mass is away from the center of an axis, the harder it is going to be to rotate that object. Although your 18" wheel may weigh the same or less as a steel wheel, your tire for the 18" wheel may weigh more than the one for the 15" wheel causing more mass to be farther away from the center. Thus, an 18" wheel vs. a 15" in wheel with the same overall tire size may have a larger mass moment of inertia than the 15" wheel.

That being said, I'd rather have a 17"+ wheel over a 15" wheel any day. There are so many more benefits than the loss produced by rotational mass.

This is true, but consider that I was not comparing apples to apples with a 225/60/15 vs 275's and 295's.

For example, a 295/50/15 BFG T/A tire weighs in at 32 lbs. Even if you assumed the 15x9 or 10 that you'd need to mount it weighed the same 25 lbs as the 15x7, that would make for a 57 lb wheel. That's almost 8 lbs heavier than the 295/35/18, and I would guess that the moment of inertia would be higher as well.

Sidewalls are not a constant thickness, they taper and carry a lot more weight as they move away from the rim. To truly figure out the moment of inertia you'd need the weight distribution of the tire.

Of course, not all tires are as heavy as the BFG T/A's either. Still, I don't think that the moment of inertia discussion is as clear cut as it might seem on the surface.