The first number in a tire size is the width of the tire in millimeters. The second number is the aspect ratio, which is the height of the sidewall as a percentage of the width. The third number is the wheel diameter in inches.
In this case, the 205-70-15 tires are 205 millimeters wide, with a sidewall height of 70% of the width, and they are designed to fit on a 15-inch wheel. The 255-70-15 tires are 255 millimeters wide, with a sidewall height of 70% of the width, and they are also designed to fit on a 15-inch wheel.
The difference between the two tire sizes is that the 255-70-15 tires are 50 millimeters wider than the 205-70-15 tires. This difference is too great, and using the larger tires could cause several problems.
First, the wider tires could rub against the fenders or other parts of your vehicle, which could damage the tires and the vehicle. Second, the wider tires could make your vehicle more difficult to steer and handle. Third, the wider tires could increase the fuel consumption of your vehicle.
For these reasons, you should not replace 205-70-15 tires with 255-70-15 tires. If you are not sure what tire size is right for your vehicle, consult with a qualified tire expert.
