A wheelset is the fundamental running unit of a railway vehicle: two wheels mounted on a common axle, rotating with it as a single rigid assembly.
Wheels are pressed onto the axle at controlled interference fits specified in EN 13260, which covers the complete wheelset assembly.
As with other safety-critical rolling stock components, each element carries its own standard: axles are manufactured to EN 13261, covering material, geometry, and non-destructive testing, while wheels are produced to EN 13262, which defines material grades, geometry tolerances, and mechanical properties.
Wheelset composition
Monoblock (one-piece) wheels are standard on new rolling stock. Tyred wheels — a separate steel tyre shrunk onto a wheel centre — remain in service on some tram and heritage fleets.
Brake discs on disc-braked vehicles are pressed or bolted onto the axle body or the wheel disc. Disc material and ventilation must match the wheel material and the braking energy the vehicle has to dissipate, as classified under EN 14535-2 for design and dimensions and EN 14535-3 for type testing of thermal performance.
Wheel profiles and wear
New wheel profiles are defined by EN 13715, which sets coordinates and geometry for the reference profiles — including S1002, itself drawn from International Union of Railways (UIC) leaflet 510-2 — and national variants.
The tapered tread profile generates a self-centring effect on straight track through differential rolling radius: the wheelset shifts laterally until rolling radii equalise. The same taper produces a self-steering effect in curves, turning the wheelset to follow the curve radius.
The taper keeps the wheelset centred without continuous flange contact against the rail. Excessive conicity from wear, however, increases the risk of hunting oscillation at speed.
Wear modes include tread hollowing, flange wear, and out-of-roundness (OOR). OOR generates impact loads at wheel–rail contact at multiples of rotational frequency and can cause noise, fatigue, and accelerated bearing wear.
Maintenance programmes define re-profiling intervals based on flange height, flange thickness, and tread hollow limits.
Maintenance cycle
Wheelsets are re-profiled on computer numerical control (CNC) underfloor or stand-alone wheel lathes. Underfloor lathes re-profile the wheelset without dismounting it and without lifting the vehicle off its wheels.
Re-profiling removes material to restore the specified tread cross-section, progressively reducing wheel diameter until it reaches the minimum service limit defined for the vehicle type — at which point the wheel is replaced.
Ultrasonic axle inspection intervals are set in the vehicle’s maintenance plan, developed under the entity in charge of maintenance (ECM) requirements of Regulation (EU) 2019/779. EN 15313 specifies wheelset maintenance scope and documentation.
Gauge and axle load standards
Standard gauge is 1,435 mm. Iberian gauge (1,668 mm) applies in Spain and Portugal, with variable-gauge axle systems used on cross-border services; 1,520 mm networks cover the Baltic states and the former Soviet area.
TSI LOC&PAS does not itself fix a maximum axle load; axle load is instead treated as a compatibility parameter against the infrastructure under EN 15528, with the railway undertaking responsible for keeping within a given line’s limit per TSI OPE point 4.2.2.5. EN 15528’s line categories set the reference values in practice, with 22.5 tonnes a common ceiling for passenger stock on TSI-conforming lines. Some high-speed platforms operate at lower axle loads by design.
Freight axle loads on standard European infrastructure also reach 22.5 tonnes under the same EN 15528 categories. Higher loads are not primarily a national exception: EN 15528 line categories E and F, at index 5 and 6, cover 25 tonnes, 27.5 tonnes, and above, and specific freight corridors are built or upgraded to these categories.