Herm said:
How did you guys come up with 50lbs extra for the larger tires?
This is where I am a little confused. I would tend to think the alloy wheel material would be less dense than the rubber sidewall material, meaning that 17" wheels with 50 series tires would be lighter and have a smaller rotational inertia than 16" wheels with 60 series tires, assuming the outer diameter was the same.
But I admit that intuition can be dead wrong. It would be interesting to weigh them and compare. I suppose Tony has already done that with different wheels. Do you have weights, Tony? Does anyone have a way to measure rotational inertia?
For reference,
here is a discussion about weights of Porsche 16- and 17- inch wheels with 245mm width tires. It seems that at that width, the 17" wheels weigh about 1 lb. more than their 16" equivalents and the 17" tires weigh slightly less. Nothing definitive there, but it seems like we could be talking about less than 5 lbs. difference, total.
For further reference,
here is a specification table for Michelin Energy Saver A/S tires showing different weights for different tires (expand the table to see weights). Unfortunately, I don't see the P215/50R17 size listed there nor do I see two sizes that I consider to be the same width AND the same height that would allow weights to be compared properly. I do see a P225/50R17 that weighs LESS than a P205/65R16 (22.2 lbs. versus 22.8 lbs.).
I guess my conclusion is that 16" alloy tires/rims are likely slightly lighter than 17, but probably by less than about 5 lbs. total for the car. If anything, the overall weight probably depends more on WHICH tire and wheel are chosen, as some will certainly be lighter than others.
I suppose if you go with 17" you may be paying more for tires, however.