there are tolerance issues with the actual rolling circumference of tyres . it is only around half inch tolerance . 275/40 R 20 front with 315/35R20 rears have a quarter inch difference . ok so 275/40R20 is 2287mm , 315/35R20 is2290mm ,295/40R20 is2337 , that is a 2 inch difference in rolling circumference so go ahead and destroy your diff`s, transfer case and transmission Mr smart arse .