Don't the rear windows have to let in 75% of light (i.e., be 25% tinted or less) to be legal?
Very very shiney car. Completely mint. 8-)
No the rears can be 100% if you like, have had that on a few of my cars.. What you have state is only applicable for the front 2 side windows... BUT if you are going to get the fronts done have them checked first and see what the standard window tint is, then deduct this off the 30% rule.
E.G.
Standard windows 8%
Rule 30% - 8%
Get fronts then tinted 22% ONLY
OR In another term..
Front Window: 75% transmission of light into cabin
Front Sides: 70% transmission of light into cabin
Rear Windows: No specific limit of light into cabin
But also remember if you have tints on any window you must inform your insurance, due to it is a modification THAT can be classed as an impairment of vision out of the car.