Can a car run with a spare tire that has a smaller diameter than the original tire?

[Chris]

It can be driven for a short period of time, but not for long-term use. Here is a detailed introduction about car spare tires: 1. Overview: A spare tire refers to the backup tire of a car, and its specifications should be the same as the original car tire specifications. Some vehicles use spare tires with special color rims, compact spare tires, folding spare tires, or run-flat tires to remind the owner to check and replace the faulty tire in time. 2. Precautions: A spare tire is actually for emergency use and is not intended for long-term use. Regardless of the width of the spare tire, manufacturers have specific production and usage requirements. Since the spare tire is not used for long-term driving, it does not wear out. Therefore, a tire that has not been worn is different from a tire that has been completely worn out. Using a spare tire on the car itself poses certain safety risks.

[Jessica]

I've seen many car owners casually driving on smaller spare tires, only to run into trouble. As someone who often helps friends with car repairs, I must say that compact spare tires can indeed cover short distances, but there are specifics to consider. A smaller diameter means a shorter wheel circumference, causing imbalance between the left and right sides of the vehicle—this leads to odd steering feedback, instability during turns, and potentially delayed braking. More critically, speed readings become inaccurate—actual speed may be slower or faster than displayed, increasing the risk of speeding tickets. Prolonged use may also wear down differential and suspension components, resulting in costly repairs. That’s why I emphasize keeping speeds under 80 km/h and using it strictly for emergencies to reach a repair shop. Regularly check the spare tire’s pressure to prevent aging and leaks. Ultimately, a spare tire is an emergency tool—don’t push its limits.

[LeMila]

Having driven for 20 years, I once experienced a flat tire and had to use the compact spare tire, which was noticeably smaller in diameter. At that time, the car felt slightly tilted when driving, and both acceleration and braking were less responsive than usual. I learned that prolonged driving under such conditions could affect the vehicle's electronic systems, such as causing the ABS to malfunction. For safety, I only drove 15 kilometers to the nearest repair shop, keeping the speed below 60 km/h. Spare tires are designed as a temporary solution and are not meant for long-distance or high-speed driving. Now, I check the spare tire pressure every three months to ensure it can support me in case of an emergency. I recommend everyone develop this habit to prevent minor issues from turning into major hazards.

[MacAvery]

Using a smaller spare tire can indeed serve as an emergency solution, but details matter. When there's a diameter difference, the vehicle's left and right wheel speeds will be inconsistent, potentially interfering with the anti-lock braking system. The actual distance traveled becomes shorter. I usually limit the speed to 80 km/h and only drive short distances to avoid damage. The key point is to check that the spare tire specifications meet the manual requirements—don't overlook this.