yikes.. okay ill try some basics first. There are others who can probably explain it better.
19 vs 18 is the diameter of the wheel..
9.5 and 10.5 are the width of the wheel. Now keep in mind, width is measure from the inside where the tire hoods to the barrel. If you measure the very outside of the lip, most wheels are generally about 1" wide. Aka a 10" wheel, with the lil lip section would measure around 11" wide.
Not all tires will fit on all wheels.
OEM 370z sport tires are 245/40/19 front and 275/35/19 rear.
the 245 is the width of the tire in mm. The 19 is the diameter. The 40 is the ratio of the side wall from the width. So the widewall is 40% of the width which in this case would be around 98mm which is about 4 inches.
The 275 is again width of the tire in mm. The 19 is the diameter. The 35 is the ratio of the side wall from the width. So the sidewall is 35% of the width which in this case would be 96.25mm which is close to the front. This basically shows that your front are about the same overall size as the rear except for the rear are wider by 30mm.
Offset is how many millimeters away from the center of the wheel the hub is (where it bolts to the car).
+47mm for the OEM sport 19" front means that the hub is 47millimeters towards the outside of the wheel.
lets say a 10" wheel is around 250mm wide (25mm x 10).
on a offset of 0. there would be 125mm of wheel on each side of where the wheel bolts to the car.
so a +47 means that now, there is 78mm on the outside and 172 mm on the inside.
Generally for our cars you want no more than 95mm wheel on the outside for the front.
and around 135mm on the outside in the rear. THis is for the wheel to be FLUSH with the fender with no lowering of the car running OEM camber and running proper width tires. (according to whats ive seen.. others may slightly differ)
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