Originally Posted by Feanor
I'm a bit puzzled about the offsets being different though - I thought they had to be the same?
Or do the offsets differ depending on the wheels that the car comes with? To be honest though I don't really understand what the offset measurement really means.
Regarding the mounting specs, it sounds like you're saying that the info on the website is wrong?
As for the tyres being taller, do you mean the profile is bigger? IE the /xxR figure? (eg /45R or /50R)
In simple terms, the offset number determines how far in or out the wheel will sit on the car. A lower offset will have the wheel sticking further out, a higher offset will have the wheel sunk in.
The offset number will differ from car to car. Some cars require a higher offset up front + lower offset in the rear while other cars require similar offsets front and rear. Wheel width is also a number to take into consideration. An 18x8 ET35 & 18x9 ET35 will have differing outer and inner positons - the proper front outer position and rear outer position will differ from car to car. Thus there are no universal requirements such as the offset being the same front and rear.
Profile number does not necessarily determine the thickness of a tire. Let's use a 225/45/18 for example. The thickness of a tire is the section width (225mm) multiplied by the profile number as a percentage (.45). Thus the tire thickness of a 225/45/18 would be 101.25mm (about 4") thick.
So by stating taller tires he means the thickness would be greater, creating a larger outer diameter. E90 18" tire thickness would be 225*.40 = 90mm while 18" F30 tire thickness would be 225*.45 = 101.25mm. So yes, F30's require larger/taller tires