Originally Posted by bnj
I'll begin with your first claim: How much is a significant weight reduction? Then, how much is exactly the weight reduction in a tire that is exactly the same, except being non run-flat instead of run-flat? Take for example potenza RE050A vs RE050A RFT 225/40-18 (typical tire in a Bmw from factory).
To be honest, I don't know the exact weight difference... but I do know that it is significant and on the order of several pounds.
You should be aware that since it is weight located at the outer most area of each wheel, this extra weight will generate a lot of intertia (think of how fast the wheel rotates at, say, 60 mph). Losing rotating weight is one of the effective ways to improve your car's performance both in a straight line and in corners. In addition, the reduced weight will give the suspension a better ability to react to changes in the road surface hence improving handling, feel, and ride quality.