donut spare
A type of spare tire. The undersized spare wheel (tire and rim) provided by automotive manufacturers in lieu of a full-sized tire, for use in emergencies, when one of the regular ones can no longer be used.
donut spare: the skinny emergency wheel you shouldn't drive far on
A donut spare is a compact wheel assembly, typically 15 to 17 inches in diameter, designed to fit under the floor or trunk of a vehicle as temporary replacement for a punctured or damaged full-size tire. It consists of a narrower tire (often 125 to 155 mm wide, compared to 205 mm or more for standard tires) mounted on a lightweight steel or alloy rim. The tire itself is usually a bias-ply construction rather than radial, prioritizing compactness over performance.
Manufacturers introduced donuts as a weight and cost reduction strategy beginning in the 1970s. A full spare tire and rim assembly can weigh 40 to 50 pounds; a donut weighs roughly half that. This lower mass cuts vehicle weight, improves fuel economy figures, and reduces manufacturing cost. Modern sedans and crossovers almost universally ship with donuts rather than full-size spares, though some performance vehicles and trucks still carry full-size wheels.
Speed and distance restrictions
Donut tires carry strict limitations. Most manufacturers specify a maximum speed of 50 mph (80 km/h) and a maximum distance of 50 to 70 miles (80 to 110 km). These limits exist because the narrower tire deflects more under load, generating heat and increasing blowout risk; the lighter construction tolerates less abuse. Exceeding these boundaries has caused tread separation, sudden failure, and loss of control. Many drivers ignore these warnings, leading to roadside failures and accidents.
Handling and traction suffer noticeably on a donut. The narrow contact patch and softer sidewalls produce increased body roll in corners, longer stopping distances (especially on wet pavement), and reduced grip during acceleration. Traction control and stability systems may behave unpredictably when three full-size tires and one donut are installed, since the spare rotates at a different speed and produces different slip characteristics.
The donut's practical value is as a get-home device: drive slowly to a repair shop or tire replacement facility rather than wait for roadside assistance. Some drivers and fleet operators now omit spares entirely in favor of tire repair kits and portable electric pumps, viewing the donut as obsolete. However, for drivers without roadside assistance coverage or in remote areas, even a donut remains preferable to immobility.