Changing tire sizes good or bad idea

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In almost all cases it is recommended that you stick to the factory-size for your car or truck's tires. This is because many components of the vehicle were specifically designed for that specific size of tire. This mainly has to do with the diameter of your tires.

For example, if you get a larger tire with a larger outside diameter, your car will travel farther before the tire completes an entire rotation. Since your car's computer determines many things based on tire rotation, such as:

Speedometer
Odometer
Anti-lock brake system
Torque
Traction control
Gearing settings

A change in tire diameter means that incorrect information is going into your car's computer. Your car's computer relies on correct information from the tires in order to respond well in emergencies. For example, over-sized tires could make your anti-lock brakes fail to engage properly.

When changing your tire size might be acceptable

It's possible to change the size of your tires without actually changing the diameter. One example is if you want larger rims - you can buy tires that compensate for the larger rims by reducing the "height" of the outer tire. This is why the tires of cars with large rims have a much thinner "band" of rubber along the outside of the tire.

Other times you might want to change the size of your tires is when the factory-recommended size is rare (and thus expensive) and you want to find a more affordable option. Generally, you don't want to go with tires that have a diameter that is more than 3% different from the factory tires. It's also a good idea to consult with a trusted mechanic before switching to larger or smaller tires.

Don't want to do the math? Use a Tire Size Calculator

Calculating the diameter of the rims vs. the overall diameter can involve a lot of math, which we won't go into here. A much easier and convenient path is to use a tire size calculator, which does the math for you.

Remember, your car was designed for optimal performance with a specific size of tire. Whenever you change the size of tire, you are compromising the performance and possibly the safety of your vehicle, so only change tire size after carefully researching and considering all your options.