Being fairly new to cars and specs and so on, I've heard many ppl mentioning 245/40/18 front and 245/45/18's and 275's and stuff like that. Can somebody clarify what each number means and the units?

I can guess that 18 would be a 18" rim.

In addition, what would be stock for our g35? Is there a generally agreed/acceptable limit?

thanks in advance

 

Coupe or Sedan?
This tool will show you some size differentials,etc.
http://www.miata.net/garage/tirecalc.html

 

245/40/18

245mm width
40% of width (245) = profile or width of sidewall
18"

stock is 225/45/18, 245/45/18
since 18x8 wheels, (18" x 8") you're pretty much stuck with these sizes
for optimum fit.

 

Sry, i meant coupe.
So the rear wheel is wider at stock then?
What do you mean we're pretty much stuck with these sizes?

I still don't quite get the middle number, ie 40% of width (245) = profile or width of sidewall, is that the part that is not counted in the tires?

 

Take a look at this information from Tire Rack:
http://www.tirerack.com/about/techcenter.jsp

 

An alternate front size is 245/40/18 which is pretty close to the stock 225/45/18 diameter. I intend to get that size when my Pilot Sports wear out...

 

Thanks a lot ppl