Railway tires

The steel wheels of steam locomotives are usually fitted with steel tires to provide a replaceable wearing element on a costly wheel.

(Some trains, mostly rubber-tyred metros and people movers, have rubber tires, including some lines of the Paris Métro, the Mexico City Metro, the Caracas Metro, the Montreal Metro, Sapporo Subway, and the Santiago Metro).

A different form of damage to railroad wheels takes place if violent wheel slip occurs. The friction caused can heat the wheel (and rail) enough to cause heat damage.

Replacing a whole wheel because of a worn contact surface is expensive, so steam locomotive driving wheels are fitted with replaceable steel tires. The tire is a hoop of steel that is fitted around the steel wheel. No obvious fastening is generally used to attach it. As with wagon wheels, the tire is held in place by an interference fit - it is made slightly smaller than the wheel on which it is mounted. To install a tire it is heated until it is glowing hot. Railroad workshops generally have special equipment to do so. As the tire heats, it expands, making it big enough to fit onto the wheel. After placing it on the wheel, the tire is cooled, and it shrinks onto the wheel. When cold, friction between the tire and the wheel is such that the tire will not budge, even under extreme forces.

Removing a tire is done in reverse - the tire is heated while on the wheel until it loosens.

Tires are reasonably thick, up to about an inch thick or more, giving plenty of room to wear. If a tire wears out of shape, or gets flat-spotted, but has a reasonable amount of material remaining, it can be turned on a wheel lathe to refinish it, reshaping it to the correct profile.

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