WDKWANG

The DA integra stock tire size is 195/60-14. The tire diameter is 23.3" and tire sites recommend that you do not go beyond a 3% tire diameter difference. So that leaves me with a maximum play to 23.99" if I want to upsize to 16" rims.
I intend to fit lightweight 16x8 wheels but the issue is that I want to get the most amount of grip possible. Right now, it seems that the best options from tirerack.com is the Kumho Ecsta XS (Extreme Summer tire) at 215/45-16 with a 23.6" tire diameter, which is only a 1% diameter difference, or the BFGoodrich g-Force T/A KDW 2 (Ultra High Perf. tire) at 225/45-16 with a 23.7" diameter.
The Kumho's are 2 performance categories above the BFGoodrich's, but can it overcome the 10mm difference?

Another question is what if I just go purely by tire choice and put correct tire sizing as a secondary priority, how much of a problem can I expect?
Going with 225/50-16, the options of having the famed Bridgestone RE-11, Dunlop Star Spec, Hankook R-S3, and Yokohama AD08 are now available but at a tire diameter of 24.9", which is a 6.4% difference. At this point, while I'll be going 64mph when my speedometer is reading 60mph and it only gets worse as speed increases. I also imagine that the handling/feedback would take a hit with a higher profile tire, regardless of how hard the tire's advertised sidewall is.

I have a 370z running with Bridgestone RE050A 245/40-19 in the front and 275/35-19 in the back. Since having this car, I've learned a lot about how tires aren't just tires and that there are many influential factors in how the car handles. When I put on the winter Blizzaks, or now running cheapo Hankook V12's in the rear, I can really feel the difference in grip/handling/feedback compared to the hard Bridgestone's.
I just want to bring the Integra's more up on par with the Z. Thank you, and sorry for the long post.

0doc@tirerack

Based on our measurements (and customer feedback) the 225 (even in a 23" diameter) will most likely need a fender lip roll and/ or suspension mods to fit without rubbing. The Kumho XS is a great tire in dry, but weak in wet traction so we normally recommend it as a "track only" tire (unless you seldom see wet roads in your daily commute). I'd normally recommend going down to 205/45R16 to get some better options, but that size can only go up to a 7.5" wide wheel. If you haven't bought the wheels yet, consider that size as you can get the Bridgestone RE11 and the BFG GForce KDW2 in that size that are almost as good as the Kumho in dry but much better in wet.

WDKWANG

I don't have an issue with fender rolling if needed; I actually prefer the tire poke look. Going back to the main questions, do you know if a 225mm lower performance tire can overcome a 215mm higher performance tire? Also, how much of an issue am I expecting with an increased tire size from stock 23.3" to 24.9", aside from a speedometer correction. Thank you

TunerN00b

That one is easy.

No.

Compound matters significantly more than any other factor in terms of traction.

0doc@tirerack

Yep,

I'd much rather have the better compound in a 215 than something weaker in a 225................