Understood. California and other places can be a pain when it comes to car modifications. Especially when you factor in needing CARB certifications for modifications and altering any of the catalytic converters in the exhaust system can be deemed not road legal. It always blew my mind living in California that even though it has such a huge automotive enthusiast footprint, it's such a pain to own a modified vehicle.

I mentioned the header for as a comparison though in regards to "bang for buck". It doesn't really apply to the OP since he already has forced induction. So, $1,000 for a header and tune yields a change that is easily noticeable according to everybody that does it. People say time and time again that it's probably the best modification for the money.

In comparison, wheels and tires, which will end up costing around the same, if not more (depending on brands) will make a noticeable difference as well. Is it the same as a header and tune? Eh, probably not; but I'm willing to bet it would still be worth it in the end.

I went from 17x9s with 215/45s to 18x9.5s with 265/35s and I definitely felt the car was more sluggish after doing so. I'm actually going back to 17s now.

If you're looking for responsiveness and quicker spooling/revving coming out of corners you'd be better off getting a light clutch/flywheel setup rather than changing the wheels. That is, assuming you don't already have a decent aftermarket clutch/flywheel.

Quantifying this for his use would involve doing some timed acceleration tests from a dig and from a roll at various speeds/RPM, and seeing the repeatable differences. The second test would be stopping distances. I think no one goes out to buy heavy wheels and light wheels just to test. They just go out and buy the light ones.

That may have to do with the tire itself as well.

The size and grip of the tire has much more effect than the weight of the rim - but a heavy rim vs a light rim will feel different. Really depends how you drive and what application (autox, track, street, mudbog) to see if the difference is worth the added expense.

Note that some very lightweight rims are designed for track use - ie smooth surfaces without potholes! The wheels may work great on a track but on real streets could have a higher failure rate - either cracks or bends. And of course not all lightweight (or heavy!) wheels are created equal.

I see a bunch of people running very wide wheels = heavy. Even with lightweight wheels, a 9.5" wide rim will be much heavier than an 8" wide one. And then tires too - wider tires equals more weight.

So when deciding if light wheels are worth the expense, think about grip as well, and how much tire you actually need. And then remember a Pilot SS in 235 width might have the same grip as an S-Drive in 275 width. And remember more width doesn't automatically equal more grip.

Lots of factors. I'd say research and buy the right wheel / tire setup that is right for your application.

Seriously guys, go look up the Grassroots Motorsports article on this exact subject.

They have quantitative evidence, track times, dyno, etc.

I don't think RPF1s are a good choice for the twins. They are light, but they deform easier. This is not very good for hard cornering ...

In general, going as much light as possible is not always a good rule. Weight is a factor, but another factor is stifness! You have to find a golden rule between both .

People here don't seen to like that information.

One cannot simply claim to be a professional in a field they have yet to become qualified in, let alone have any experience in....