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A wheelset is a pair of railroad car, railroad vehicle Train wheel, wheels mounted rigidly on an Axle#Vehicle axles, axle such that both wheels rotate in unison. Wheelsets are often mounted in a bogie ("truck" in North America) – a pivoted frame assembly holding at least two wheelsets – at each end of the vehicle. Most modern Railroad car#Freight cars, freight cars and Railroad car#Passenger cars, passenger cars have bogies each with two wheelsets, but three wheelsets (or more) are used in bogies of freight cars that carry heavy loads, and three-wheelset bogies are under some passenger cars. Four-wheeled goods wagons that were once near-universal in Europe and Great Britain and their colonies have only two wheelsets; in recent decades such vehicles have become less common as trainloads have become heavier.


Conical wheel-tread

Most train wheels have a cone (mathematics), conical taper of about 1 in 20 to enable the wheelset to follow Civil engineering#Surveying, curves with less chance of the wheel flanges coming in contact with the rail sides, and to reduce Curve resistance (railroad), curve resistance. The rails generally slant inwards at 1 in 40, a lesser angle than the wheel Tire uniformity#Conicity, cone. Without the conical shape, a wheel would tend to continue in a straight path due to the inertia of the rail vehicle, causing the wheelset to move towards the outer rail on the curve. The cone increases the effective diameter of the wheel as it moves towards the outer rail, and since the wheels are mounted rigidly on the axle, the outer wheels travel slightly farther, causing the wheelsets to more efficiently follow the curve. Abnormal wear at the wheel–rail interface is thus avoided, along with the loud, piercing, very high-pitched squeal which usually results from it – especially evident on curves in tunnels, stations and elevated track, due to flat surfaces slipping and flanges grinding along the rail. However, if the degree of conicality is inappropriate for the suspension and track, an unpleasant Hunting oscillation, oscillation can occur at high speeds. Recent research is also showing that marginal changes to wheel and rail profiles can improve performance further. Not all railroads have employed conical-tread wheels. The Bay Area Rapid Transit (BART) system in San Francisco, built with cylindrical wheels and flat-topped rails, started to re-profile the wheels in 2016 with conical treads after years of complaints about the train noise, squeal by its passengers. Australia's Queensland Railways used cylindrical wheels and vertical rails until the mid-1980s, when considerably higher train loads made the practice untenable.


Specialised wheelsets

Some rubber-tyred metros feature special wheelsets with rubber tire, tyres outside of deep-flanged steel wheels, which guide the bogie through standard railroad switches and keep the train from derailment, derailing if a tyre deflates. The Rubber-tyred metro#History, system was originally conceived by Michelin for the Paris Métro; the Paris Métro Line 11, first line opened in 1956.


Gallery

File:Denney Axle.jpg, Denney axle File:Rollingstock axle.jpg, Train wheel, Railroad car wheels are rigidly mounted on an axle to rotate in unison File:SBB Cargo Güterwagen Radsätze.jpg, Swiss Federal Railways wheelsets with fitted journals File:Rail_axl_at_Texas_Transportation_museum.JPG, Wheelset from a railroad speeder; the wheels are pressed steel and the flanges are smaller than those of full-sized rail vehicles File:GWR Spoked wagon wheels.jpg, A wheelset from a Great Western Railway wagon, showing a plain bearing end File:Bettendorf truck at Illinois Railway Museum.JPG, A freight bogie of the William P. Bettendorf, Bettendorf pattern, which became standard in North America and elsewhere File:Пам.Энгельса29 КП Метро Штангист в каске.JPG, Wheelset as part of a welded sculpture in Kharkiv File:Heidelberg funicular wheelset.jpg, Wheelset of a two-rail funicular File:Muzeum MHD, dvoukolí vozu petřínské lanovky 1891.jpg, Funicular wheelset with Rack railway#Abt (1882), Abt rack and pinion brake


See also

* List of railroad truck parts#Axlebox, Axle box * Beam axle * Bogie exchange#Axle exchange, Axle exchange * Drop table * Flat spot * Gölsdorf axle * Interference fit#Force, Interference fit * International Heavy Haul Association * List of railroad truck parts#Axlebox, Journal box * List of railroad truck parts * Luttermöller axle * Plain bearing * Rolling-element bearing * Train wheel * Variable gauge, Variable gauge axles * Wheelbase * Axle track#Rail, Wheel gauge


References


Further reading

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External links

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Train wheels
{{Authority control Train wheels, Bogie