No doubt about it, a tire on an under powered car that has good/great compound will def benefit and perform better with a narrower tire, essp something like a NA civic.
I choose the 235 because I'm using a hard compound designed more for life than performance, and I value straight line traction a bit over everything else given the power the car has.
Without a doubt, these tires when new, got better traction in a straight line vs the stock ones. They never had the cornering speed the stock tires did. Because they are taller, they also require a bit more power to turn due to gear ratio change. But when your biggest issue is 3rd gear burn outs exiting the corner, how wide the tire is becomes something to think about.
In a perfect world, I'd put some ultra expensive $250 per tire, stock sized tire on the front of my car every 10k miles ( my stock set lasted 14k miles ). But I got rid of a G35 that ate $305 a piece rear tires for something that would be cheaper on expendables and be just as fast. The G35 needed tires ever 15-17k miles on the rear and about 25k miles on the front and they were not cheap at all. My fist rides on $76 a piece front tires and bald rear ones ( soon to be replaced with something cheap as well ).
If i was going to road race the car, I'd have special wheels/tires for road course duty. Now that i know the driveline shatters when its given power on street tires at the drag strip, I'll buy some slicks before I go back. If i did autocross on the weekends, maybe i would spend the cash on the $250 a piece 10k mile tires, but i don't.
I needed a tire that got me some traction, was cheap, and that I could sleep well at night after brutally abusing them. (Stand by for a video later). These 235/40-17 did/do that.
Seems everyone on this forum ( and almost all current fist owners ) have a different use and purpose for the car than I do, so I don't recommend my tire to anyone else. It also lost some of its amazing turnin which makes the car so fun stock.
A 235 will fit on the stock rim, but unless your pouring some power to it and your broke ( like me, lol ), then you have lots of better options at 205/215 IMO.
An aftermarket wheel is super worth it, if you buy it for weight instead of price or looks.