BFG KDW2:
225/45 YR17 - 24 lbs 25.1" OD
225/40 YR18 - 28 lbs 25.1" OD
225/35 YR19 - 24 lbs 25.2" OD
Fuzion ZRi:
225/50 WR16 - 24 lbs 24.9" OD
225/45 WR17 - 25 lbs 25.0" OD
225/40 WR18 - 24 lbs 25.1" OD
225/35 WR19 - 24 lbs 25.2" OD
Goodyear GS-D3
225/50 WR16 - 24 lbs 24.9" OD
225/45 WR17 - 23 lbs 25.0" OD
225/40 WR18 - 24 lbs 25.1" OD
225/35 WR19 - 24 lbs 25.2" OD
Where's your magic weight loss? The data don't lie. It seems that the loss of sidewall would lose some weight for you, but it just doesn't work, mostly because the steel bead gets longer as the sidewall gets shorter. You happen to be gaining a tiny bit of overall diameter with these sizes, but it's pretty negligible: 0.4% per step.
Also, you obviously got different tires with your wheels. One lb on your overall setup isn't going to make as big a difference as new or different rubber, a wider or flatter contact patch (did rim width change?), or your better driving with more experience.
So, you definetly save weight by going with a smaller rim. This will make you faster, all other factors being equal. How serious you are about your drag times vs. street pimp factor is probably the deciding factor. For road race, you will get better response with a thinner sidewall, which can make you faster. GRM had an article about this topic, where they compared different size tires on a Honda. The problem I see with the article is that they added tire and rim width as they increased the rim diameter. It shows a speedup with low-profile tires, but they only went to 17", IIRC - and there was a bigger increase between 15-16 than 16-17, indicating diminishing returns, which are to be expected. I'd wager that a test between sizes on a Contour would show that the fastest setup is a 17", but it could very well be a 16 or 18, and vary significantly depending on the car setup, and the tire chosen for the test.
But most of our cars are on the street exclusively, and the few that see the drag strip, autocross, or road course don't spend a large percentage of their lives there. So for the use of the car most of see, the difference is slim to nill. I run 16s because - a) they are at least as fast as any other size within my abilities to wring the last bit out of them b) I got them for cheap c) tires in 16" are cheap. I also prefer smaller wheels look-wise: 225/45R17 on a BBS-style wheel is what I'd roll if money was no object, but the way I go through tires the savings are big. If you have the money for large wheels (maybe because you manage to make summer tires last more than 5k), and you like the look, then that's great for you. But a smaller wheel will result in a lighter total combo, and the tiny sidewall on huge setups is not a real advantage.
