Railway Tires - Installation

Installation

Replacing a whole wheel because of a worn contact surface was expensive, so older types of railway wheels were fitted with replaceable steel tires. The tire is a hoop of steel that is fitted around the steel wheel centre. The tire is machined with a shoulder on its outer face to locate it on the wheel centre, and a groove on the inside diameter of the flange face. The inside diameter of the tire is machined to be slightly less than the diameter of the wheel centre on which it is mounted, to give an interference fit.

The tire is fitted by heating to a controlled temperature, avoiding overheating. This causes the tire to expand. The wheel centre, usually already mounted on the axle, is lowered into the tire which is flange side up. The tire cools, and the retaining ring (a shaped steel bar rolled into a hoop) is fitted into the groove. Hydraulically operated rolls swage the groove down on to the retaining ring.

The tire is primarily held in place by its interference fit. The shoulder on the outside and the retaining ring also keep the tire in place if the interference fit is lost. This is most often due to severe drag braking down a gradient, or due to an error in the machining.

Removal of a worn tire is by machining out the retaining ring and heating the tire to relax the interference fit.

Some steam locomotive wheels had tires bolted through the rim, or with a second smaller shoulder machined on the inside face of the tire. This shoulder was severely limited in size as it had to pass over the wheel centre for assembly.

tires of different designs were fitted to wheels with wooden centres (Mansell wheels in the UK) and to various other types.

The use of tires is becoming obsolete. The utilisation of traditional freight wagons was often so low that tires never needed renewal, so it was cheaper to fit a one-piece ("monoblock") wheel. Monoblock wheels are lighter and offer better integrity as there is no tire to come loose. Modern flow-line repair lines are disrupted by the inspection of the wheel centre once the tire is removed, possibly generating extra rectification work, and the need to make each tire fit its allocated wheel centre. Monoblock wheels are now more economical.