What is the size of a 400-12 tire?
3 Answers
400 represents the tire section width of 400mm, and the following 12 indicates the rim diameter of 12 inches. Tire size specification example (taking 195/55R15 as an example): The international standard tire code represents the section height and aspect ratio percentage in millimeters, followed by the tire type code, rim diameter (inches), load index (allowable load mass code), and allowable vehicle speed code. For example, 175/70R1477H, 175 represents the tire width of 175MM, 70 indicates the tire section aspect ratio is 70%, meaning the section height is 70% of the width, the rim diameter is 14 inches, the load index is 77, and the allowable vehicle speed is grade H. Notes for replacing car tires: When selecting tires, the specifications of the tires should be the same as the previous ones and must match the other tire on the same axle, such as speed rating, load index, tread pattern, brand, size, etc., to ensure safe driving. The valve stem should also be replaced because after changing the tire, the aging cycle of the new tire and the valve stem may differ. During the new tire's cycle, the valve stem might develop issues, which are not easily noticeable, so it's best to replace the valve stem when changing the tire. Installation direction and inflation: If using the original equipment tire, follow the manufacturer's installation requirements. For non-original tires, the side with the production date usually faces outward. If it's a directional tire, align the arrow on the wheel with the car's forward direction during installation. During inflation, you can fill the tire to the maximum allowable pressure and then reduce it to the manufacturer's specified standard pressure.
When I first encountered this tire size, I found that 400-12 actually represents a very straightforward specification: the 400 at the front refers to the width of the tire in millimeters, meaning the tread width is approximately 40 centimeters wide; the 12 at the back refers to the diameter of the rim in inches, equivalent to a rim size of about 12 inches. This design is commonly found in small and medium-sized vehicles, such as tricycles or small agricultural vehicles, because the wide tread provides better grip, making it suitable for driving on uneven roads. When helping a friend inspect his old vehicle, I came across this size—it’s bulkier than standard car tires like 195/65R15, but it’s durable and highly adaptable. However, when choosing tires, always remember to check the vehicle’s manual or consult a professional mechanic to avoid installing the wrong size, which could affect driving safety and potentially cause the wheels to make clunking noises. In short, understanding tire sizes is the first step in vehicle maintenance—don’t slack off!
Having driven for twenty or thirty years, I'm quite familiar with tire sizes. The 400-12 specification means a tire width of 400 millimeters paired with a 12-inch rim. This type of tire is mostly used for agricultural vehicles or small trucks, like those utility vehicles often seen on rural roads. The wide tires provide stable handling on muddy roads. I remember when I first learned to drive, I also used tires of a similar size. They're sturdier than typical family car tires but consume more fuel. Nowadays, they're rare on the market, and you'd have to visit specialty stores to find them. When selecting tires, make sure to measure the rim size accurately—mismatched sizes can lead to accidents, such as excessive bouncing or unstable braking. It's advisable to regularly check tire pressure and wear. A correctly sized tire can ensure your safety for a decade.
