Motor Expo 2026

Many people wonder... whether it is necessary to use the same brand and model of tires on all 4 wheels. To answer briefly before explaining the reasons: “it is necessary.” When it says 'the same model for all 4 tires,' this means most cars in the world, with some exceptions in certain sports car models where the front tires are a different size from the rear tires. However, only the size should differ; they should be the same model and brand as specified by the car manufacturer.

If we drive a car in perfect condition on a flat, windless road, and keep the steering wheel steady, allowing the car to go straight, we will notice that when there is a crosswind or a sloping road, our car will move diagonally from its original direction without us moving the steering wheel even slightly to turn. The reason why the wheel can roll diagonally when there is a side force, even though the wheel axis remains in its original direction, is because our car's tires are flexible and can deform. The angle that arises from the difference between the direction the wheel is rolling and the actual direction of travel is what we call the slip angle (SLIP ANGLE). Its value, whether large or small, depends on the tire's structural design, rubber compound, tread pattern, and tire pressure, as well as the amount of side force applied. If this force is high, our wheels will definitely roll significantly diagonally from their original direction. Aside from the values of the side force and tire pressure, it must be said that the slip angle varies between different tire models and brands (which differ in structure, rubber compound, and tread pattern). This angle has a profound effect on the car's stability. Manufacturers must choose appropriate tires and adjust the suspension system to work “in sync” so that the car has good road holding, stability, and safety.

Users have the duty to strictly follow the tire specifications set by the car manufacturer. The car owner's manual usually only specifies the tire size and maximum speed rating. For certain high-performance car models, manufacturers will specify the exact ”brand” and model of the tires. Otherwise, it is “left to be understood” that all 4 tires must be of the same brand. When car factories adjust the suspension system to ensure road holding and safety under the condition that all 4 tires must be the same model and “brand,” car users must strictly adhere to this.

In cases where it is not possible to comply, only the difference between the front and rear tire pairs is permissible! And there is a very important condition: tires with a wider slip angle should be placed on the front wheels. 

The problem is: How will the car owner know which tire model has a wider slip angle? There is an easy way to observe it, but it requires some effort: try placing one pair of tires on the front and drive, observing the car's responsiveness to the steering wheel. Afterwards, swap these tires with the rear pair (don't forget to adjust tire pressure). Drive again and observe which setup responds to the steering wheel worse or more sluggishly; that setup is the safer one.

I reiterate... This problem is life-threatening. If used under normal conditions, it might be fine, but whenever an obstacle needs to be avoided at high speeds, the car's behavior will change so rapidly that the driver won't be able to correct it in time, even if they have racing-level skills. This is especially true for those who mix radial tires with conventional structures; radial tires (with narrow slip angles) must only be placed on the rear wheels. Those who do the opposite are unnecessarily risking their lives due to negligence or ignorance. It is truly a life-threatening matter.  

Source: www.autoinfo.co.th / Formula Magazine

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