[vujade]

a positive offset wheel is a wheel where most of the wheel is under the arches.
a negative offset wheel is a wheel that looks like a deep dish

if you are running a 4.5" wheel now with a 23mm offset & you are
changing to a 5.5" wheel with a 40mm offset, this setup will give you 4mm more clearance then you had previously with the old setup.

Now taking the 4mm extra clearance & subtracting it from the 10mm extra your track is going to stick out because of your mods, this will make your car an extra 6mm (about 1/4") wider per side.


To figure backspacing:

Backspacing is figured by dividing the wheel width in 1/2, then applying the offset to that number.

For instance, lets say you have a 7" wide wheel with a 52mm offset.
7 divided by 2 = 3.5"
Now take the 52mm (about 2") & add that to the 3.5"
2" plus 3.5" = 5.5"
So you end up with 5.5" of backspacing on a 7" rim