Installation

The steel wheels of steam locomotives and other older types of rolling stock were usually fitted with steel tires or tyres (in British English

British English

British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

, Australian English

Australian English

Australian English is the name given to the group of dialects spoken in Australia that form a major variety of the English language....

 and others) to provide a replaceable wearing element on a costly wheel.

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 tyre 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 tyre is machined to be slightly less than the diameter of the wheel centre on which it is mounted, to give an interference fit.

The tyre is fitted by heating to a controlled temperature, avoiding overheating. This causes the tyre to expand. The wheel centre, usually already mounted on the axle, is lowered into the tyre which is flange side up. The tyre 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 tyre is primarily held in place by its interference fit

Interference fit

An interference fit, also known as a press fit or friction fit, is a fastening between two parts which is achieved by friction after the parts are pushed together, rather than by any other means of fastening...

. The shoulder on the outside and the retaining ring also keep the tyre 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 tyre is by machining out the retaining ring and heating the tyre to relax the interference fit.

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

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

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

Causes of Damage

The most usual cause of damage is drag braking on severe gradients. Because the brake blocks apply directly on the tyre, it is heated up, relaxing the interference fit. It is not feasible to fit the tyre with such a heavy interference as to eliminate this risk entirely, and the retaining ring will ensure that the tyre can only rotate on the wheel centre, maintaining its alignment. In rare instances the rotation could be so severe as to wear the retaining ring down till it breaks, which could result in derailment.

Severe braking or low adhesion may stop the rotation of the wheels while the vehicle is still moving can cause a flat spot on the tire and localised heat damage to the tire material.

Tires are reasonably thick, about 3 inches, giving plenty of room for wear. Worn tyres or tyres with flats are reprofiled on a wheel lathe if there is sufficient thickness of material remaining.

Non-steel Railway Tires

Some trains, mostly metro

Rubber-tyred metro

A rubber-tyred metro is a form of rapid transit system that uses a mix of road and rail technology. The vehicles have wheels with rubber tyres which run on rolling pads inside guide bars for traction, as well as traditional railway steel wheels with deep flanges on steel tracks for guidance through...

s and people mover

People mover

A people mover or automated people mover is a fully automated, grade-separated mass transit system.The term is generally used only to describe systems serving relatively small areas such as airports, downtown districts or theme parks, but is sometimes applied to considerably more complex automated...

s, have rubber tires, including some lines of the Paris Métro

Paris Métro

The Paris Métro or Métropolitain is the rapid transit metro system in Paris, France. It has become a symbol of the city, noted for its density within the city limits and its uniform architecture influenced by Art Nouveau. The network's sixteen lines are mostly underground and run to 214 km ...

, the Mexico City Metro

Mexico City Metro

The Mexico City Metro , officially called Sistema de Transporte Colectivo, is a metro system that serves the metropolitan area of Mexico City...

, the Caracas Metro

Caracas Metro

The Caracas Metro is a mass rapid transit system serving Caracas, Venezuela. It is constructed and operated by Compañía Anónima Metro de Caracas, a government-owned company that was founded in 1977 by José González-Lander who headed the project for more than thirty years since the early planning...

, the Montreal Metro

Montreal Metro

The Montreal Metro is a rubber-tired metro system, and the main form of public transportation underground in the city of Montreal, Quebec, Canada....

, Sapporo Subway, Seattle Center Monorail

Seattle Center Monorail

The Seattle Center Monorail is an elevated monorail line in Seattle, Washington, that runs a little over one mile along Fifth Avenue from Westlake Center in Downtown to Seattle Center in Lower Queen Anne...

, Taipei Rapid Transit System

Taipei Rapid Transit System

The Taipei Metro, more commonly known as the MRT or formally as the Taipei Rapid Transit System, is a rapid transit system serving metropolitan Taipei in Taiwan. The system is built and operated by the Taipei Rapid Transit Corporation and consists of 89 stations and of revenue track...

 and the Santiago Metro

Santiago Metro

Metro de Santiago is South America's most extensive metro system with 5 lines, 108 stations and 103 kilometres of track making it the second longest in Latin America after that of Mexico City. The metro system serves the city of Santiago, Chile. Three of the lines are rubber-tyred...

.