Coupe this - that's not how profiles work
Jive - that's the width...
I don't get what either of you are talking about.
profile is a percentage of the tyre witdh:
eg. 225/50/16 will give a sidewall height of 50% of 225 = 112.5mm
and if (for arguments sake) a tyre size is:
385/35/18, the sidewall height is 35% of 385 = 135.75mm
Therefore, "low profile" does not always equal skinny side walls.
Example:
stock skyline R33 gtst tyre size is 205/50/16 (by memory)
therefore total rolling diameter is:
16" ----> 406.4mm
add sidewalls (two sidewalls) = 2 x 205 x 50% = 205mm
equals 611.4mm.
if then you go to an 18" wheel, you will have to drop the profile to match the rolling diameter, working backwards
say we want to fit a 235 width tyre:
18" ----> 457.2mm
therefore the sidewalls must be 611.4 - 457.2 = 154.2
therefore each sidewall is 77.1mm
as 77.1mm is a percentage of the width, the profile is 77.1/(tyre width)
profile = 77.1/235 = 32.81%
However, as tyre profiles are in 5% increments, you must use a 35 profile.
As a 235 doesn't come widely in a 35, the fitment is a 40 profile.