On a tuner-tv show a few weeks back, they put larger brake rotors on a car and a cat-back exhaust then discovered a net loss of horsepower on the dyno. On the show, after trying various things to figure out what happened, where they expected more hp, they learned the loss of hp at the wheels was directly due to the greater reduction of hp due to the higher inertia of the rotors than by the increase in hp due to the exhaust. I understand this but wanted to add this observation to changing wheels. The larger rotor places mass to higher radius than before, which increases rotation inertia. My take on this would be that a larger diameter wheel and tire puts mass further out in radius much like this rotor change did. Thus,even with a lower overall weight, it is the new distribution of the weight radially the affects power at the wheel. Simply reducing the weight may not be beneficial after all.
BTW, the exhaust mod raised hp by 5 and the rotor change was a loss of 12 hp as measured on this show. They used a static chasis dyno. I wish that I remembered the name of the show.

 

From what I've been reading, most of the weight difference here is in the runflats vs std. tires not the wheels. This makes sense because the runflats need a lot of material in the sidewalls to support the car weight without air in the tire.

 

I'm curious to the weightdifference between run-flats and regular tires. I have run flats and would never trade them for normal tires anymore. In case of a tireblow the runflats will provide more control I think.

 

I'll weigh the runflats when I replace them with winter tires in December.

 

I'll weigh the runflats when I switch them out for winter tires in December.