I'm sure I could find this if I search, but I don't have time.

I've got 245/45/17 on the front, I'm about to purchase 315/35/17 to put on some 17x10.5. It's ok to have 45 on the front and 35 on the back due to the different width correct?

 

i have 45 on front and 40 on back.. havent ran into a problem.. u should be fine
245 45 17 front 275 40 17 rear

 

you should be fine. the 45 and 35 is the tire's aspect ratio.. for a 245/45-17, that means the tread width is 245 mm, and the sidewall is 45% the tread width (45% of 245 mm). that's why when you gowider on the tread width, you go down on the aspect ratio, otherwise you end up with a tire that's way too tall.

 

+1 to the 10th powerrrrr

 

It's the perfect combination if you are staggering your tiresbecause it will not throw off your speedometer.
245 x .45 = 110.25 height.
315 x .35 = 110.25 height.