I am in the market for new wheels and tires. What is a good offset for 18 inch wheels to keep them inside the fender lip? Also, what is a good size tire for an 18x7 wheels? Stock off set is 41mm right? Anyone?????
Proper offset is really determined by rim width... and also tire section width.
Nubz is wearing 18x8 +35 with 225/45ZR18 tires. No rubbing issues even at race track-speeds, but it comes pretty close. The wheel/tire can fully compress and camber into the wheel well, but there is less than 0.5" of clearance on the outboard edges and with the inboard spring-perch. If there is not enough air pressure in the tire and it starts to bulge, it might not clear the fender... so I am very diligent about running 38.0 psi front and 38.5 psi rear.
You should be fine with 18x7 +35, though a lower offset like +30 or +25 might make the rim appear more "flush". If you're buying aftermarket mass-produced wheels, you won't have much choice in offset selection.
For a 7" wheel a 215/45ZR18 tire would fit nicely, MAYBE a 225/45ZR18, but I would not go too far beyond that. A 235/40ZR18 might be pushing it to the point where the tire wears prematurely.
Also keep in mind that a 225/40ZR18 from one manufacturer may actually be noticeably wider or taller than a 225/40ZR18 from another manufacturer. Tread pattern will also affect the "actual" width of a tire.
If you can swing it, I would recommend going to a used-tire shop and mounting 2 tires of the exact size/model that you plan to buy. See if the shop is willing to let you test-drive the tires and give them right back, you pay for mounting/balancing of-course.
It's a relatively cheap experiment so you don't buy new tires that will cause rubbing.
stock offset is 38mm an a 17x7 wheel. If you want to stay INSIDE the fenders, don't get a lower offset than 35 on an 8" wheel. But like judy said, you have to pay attention to tire size as much as wheel size and offset when you get near the fenders. Also, whatever size of wheel offset you get, the rears will "tuck" more than the front unless you stagger the width/offset. The rear track is narrower than the front. Are you lowering too?
I personally wouldn't go to 18" wheels around here, because of the shape the roads are in. They just wouldn't last too long. Even 17" are pushing it here. That has to be considered in the purchase of new wheels. That's quite an investment you're about to make. My wheels are 17X7 Daytona's with 38mm offset.