I would go with Trularin's advise, because backspacing kept buggering me around as well.
just consider that your 235 adds just above 1/2" to the rim and the 275 about 3/4".
1 degree of camber though let's the tire tilt inwards by 3/8".
I posted measurements of the TRIGO here:
http://www.clubcobra.com/forums/t509...-&pagenumber=2
"Cobra wheels have 3.1/2'' backspace I am told.?"
I took some measurements from the TRIGO set. I never really got used to "backspacing" or "offset":
25.4 mm = 1" (sorry for metric values)
front nominal width 7.5"
total width: 214 mm
wheel mounting face towards brakes: 92 mm
center section thickness: 67 mm
take wing nut off and measure to outside: 55 mm
wheel mounting face to outside (towards fender): 122 mm
rear nominal width 9.5"
total width: 264 mm
wheel mounting face towards brakes: 92 mm
center section thickness: 67 mm
take wing nut off and measure to outside: 105 mm
wheel mounting face to outside (towards fender): 172 mm
Dom