I really hate how my front tires are bigger than the back. I have a 285 17 in the front and a 285 18 in the rear. It looks bad IMO. I was wondering if I could bump the back tire up a size or two? My only concern is that the car is lowered. The fenders are already rolled and it has launch bags that could help little if needed. Here is a pic. I would really like a 315 or 295 or something taller. The rear wheel is 10.5 wide. What would fit and look good on the car?

 

Just go with a the first number has nothing to do with sidewall. Bump up a size, and match the front. In otherwords, if you have 275/40r17's in the front, get 295/40r18's in the rear. I think Nitto has some 305/45r18 DR's for a descent price, the rears would be a tad bigger, but would look better.

 

how about just putting the 17" wheels on the rear

 

Please be careful with what you say, you can't bullshit a bullshiter

Section Width
Following the letter(s) that identify the type of vehicle and/or type of service for which the tire was designed, the three-digit numeric portion identifies the tire's "Section Width" (cross section) in millimeters.

P225/50R16 91S

The 225 indicates this tire is 225 millimeters across from the widest point of its outer sidewall to the widest point of its inner sidewall when mounted and measured on a specified width wheel. This measurement is also referred to as the tire's section width. Because many people think of measurements in inches, the 225mm can be converted to inches by dividing the section width in millimeters by 25.4 (the number of millimeters per inch).

225mm / 25.4 = 8.86"

Sidewall Aspect Ratio
Typically following the three digits identifying the tire's Section Width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio.
P225/50R16 91S

The 50 indicates that this tire size's sidewall height (from rim to tread) is 50% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the lower the sidewall. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm. By converting the 225mm to inches (225 / 25.4 = 8.86") and multiplying it by 50% (.50) we confirm that this tire size results in a tire section height of 4.43". If this tire were a P225/70R16 size, our calculation would confirm that the size would result in a section height of 6.20", approximately a 1.8-inch taller sidewall.

the 2nd set of (295/## 18) has everything to do with the sidewall, which is based on the the first set of (###/35 18)
i would say a 295/35 18 is better but your still at 26" total dia...
but becasue your front is a 285/40 17 which is about 26.1" total dia... and you are on a 17" wheel the fronts will still "look bigger" over the 295/35 18.

because a inch larger wheel at the same dia... will have less sidewall.

a 305/30 18 is more tire and side wall but bumps you to 27" total dia...
this may actually look better for your current setup up.
but i would recommend the 295/35 18, and when the fronts wear out run 275/40 17 which is 25.7" total dia... up front
that is my opinion.

 

Just go with a 285/40/18 tires in the rear.

 

Looks like a damn Truck Tire on the front compared to the back.No offense.Would look better Swaped fronts with backs or new tires for back but the fronts are still just too big.

 

The rears are 285/40/18s now. Im thinking maybe a 305 ?

 

Uhhhh ok captain bullshitter I kinda messed up the first sentence but i should have been more through with my explanation, but what I was getting at was the fact that the second set of numbers has the most effect on the sidewall... though the first set of numbers has a bit of effect as well. I realize the same diameter wheel with a larger rim takes away sidewall.