Are Car Tire Sizes the Same?
3 Answers
Most car tire model markings appear as 175/70R1477H, where 175 represents the tire width of 175mm, 70 indicates the aspect ratio of the tire section is 70%, R stands for radial tire, the tire diameter is 14 inches, the load index is 77, and the permissible speed rating is H. The international standard car tire code expresses the section width and aspect ratio percentage in millimeters. This is followed by the tire type code, rim diameter (in inches), and load index (permissible load capacity code). Tire sizes are printed on the sidewall and can be represented in two ways, such as 34*7 or 7.50-20. The former denotes high-pressure tires, while the latter indicates low-pressure tires. Additionally, many other markings are printed on the sidewall, for example, D is used for light vehicles, F for medium vehicles, G for standard vehicles, and H, L, J for large luxury and high-performance vehicles.
I just realized there's a significant size difference when changing tires. Even for the same model, front and rear wheels may use different sizes. For example, the SUV I drive has 225-width front tires and 255-width rear tires. Engineers say this improves braking performance. Most regular family cars use uniform sizes for all four wheels, but performance vehicles intentionally differentiate. Never choose cheaper tires with wrong specifications - those numbers on the sidewall like 215/65R16 all represent different parameters. A friend of mine opted for non-compliant tires to save money and clearly felt insufficient grip when driving through water, making emergency lane changes particularly dangerous. When replacing tires, always check the vehicle manual or original specifications. Wrong sizes may cause the ABS system to misjudge speed values. Pay extra attention to matching issues when switching to winter tires each year, otherwise the tire pressure warning light on the dashboard may stay on constantly.
With 20 years of experience in car repair, I've seen all kinds of tire issues, and size differences are more complex than you think. Manufacturers match tire sizes based on load capacity and power, with rear tires on rear-wheel-drive sports cars typically being 10%-15% wider than the front ones. When replacing tires, just looking at the brand isn't enough; you must check the tire specification code. I once inspected a damaged car for a client where the previous owner had installed smaller tires, causing a speedometer deviation of 30 km/h. Even a 1 cm difference in tire width can affect steering precision and unsprung mass. While it's trendy to fit large rims with low-profile tires, excessively increasing the wheel diameter can cause friction with suspension components. Also, remember to check the production date on the tire sidewall—rubber hardens after three years, compromising safety.
