Driving on a spare tire is a common temporary solution to a flat, but it is not a substitute for a full-sized tire and can negatively affect your vehicle if used improperly. Spare tires, especially the most common type, are designed with compromises in size, construction, and durability compared to standard tires. These compromises save space and weight but introduce limitations that restrict them to short, low-speed emergency use. Understanding your specific spare tire type is the first step in using it safely.
Understanding Spare Tire Types
Spare tires typically fall into two main categories. The most common is the compact temporary spare, often called a “donut” tire, which is noticeably smaller and narrower than a standard wheel. This type features lightweight construction, shallow tread depth, and requires a high inflation pressure, generally around 60 psi. A full-sized spare tire matches the dimensions of your vehicle’s regular tires, though it may have a non-matching wheel or different tread pattern. If the full-size spare is an exact match, it can generally be used like a normal tire, but compact spares are intended only for limited operation to get you to a repair shop.
Key Safety Limitations
Compact spare tires have severe restrictions on vehicle operation. Manufacturers generally recommend a maximum speed of 50 miles per hour (80 km/h) and a maximum driving distance, typically between 50 and 70 miles. Exceeding this speed limit can cause the tire to overheat due to its lightweight construction, increasing the risk of failure or a blowout.
The smaller size and reduced tread depth of the temporary spare decrease traction and stability compared to a standard tire. This reduction affects handling, making steering less responsive and the vehicle less stable, especially during cornering. The difference in traction also compromises braking performance, potentially increasing stopping distance. It is advised to avoid highway driving and use caution in adverse conditions like wet weather.
Mechanical Risks and Prompt Replacement
Using a spare tire for an extended period induces mechanical stress on the vehicle’s drivetrain. The primary concern is the difference in tire diameter, which causes the spare wheel to spin faster than the other tires on the same axle. This continuous difference in rotational speed forces the differential to work constantly to compensate, generating excess heat and premature wear.
The size mismatch also interferes with modern safety systems that rely on consistent wheel speed data, such as the Anti-lock Braking System (ABS) and traction control. These systems may interpret the spare tire’s different rotation rate as a loss of traction, causing them to activate inappropriately or trigger a warning light. Prolonged use places strain on the transmission, suspension, and wheel bearings. The spare tire should be viewed as a short-term emergency tool, and the original tire must be repaired or replaced immediately.