Diameter

• A R245 tire is a radial tire with a wheel diameter of 245 mm, or 30.46 inches. A R265 tire is a radial tire with a wheel diameter of 265 mm, or 31.65 inches.
  
  

Speedometer

• A tire larger than the manufacturer's recommended size will make the speedometer read slightly slower since there is more distance covered by the turn of the wheels. A smaller covers less distance with the turn of the wheels, so the speedometer reads slightly faster.
  
  

Wear and Tear

• A larger tire such as the R265 will experience less tire wear in the same distance and under the same conditions as will a R245. The larger tire has more surface area to meet the pavement, which reduces the amount of wear any particular part receives.