Wheelsets & wheel discs
A wheelset is the fundamental running unit of a railway vehicle, consisting of two wheels mounted on a common axle and 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. Axles are manufactured to EN 13261, specifying material, geometry, and non-destructive testing requirements. Wheels are produced to EN 13262, which defines material grades, geometry tolerances, and mechanical properties. 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 wheel disc, and must be compatible with the wheel material and thermal performance requirements under EN 13260.
Wheel profiles and wear
New wheel profiles are defined by UIC 860 and national variants. The tapered tread profile generates a self-steering effect in straight track through differential rolling radius — the wheelset shifts laterally until rolling radii equalise. This conicity reduces the energy required to maintain straight-line tracking, but excessive conicity from wear increases hunting oscillation risk 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 CNC underfloor or stand-alone wheel lathes. Underfloor lathes allow re-profiling without bogie removal, reducing maintenance time significantly. Re-profiling removes material to restore the specified tread cross-section; the process reduces wheel diameter progressively until it reaches the minimum service limit defined for the vehicle type, at which point the wheel is replaced.
Ultrasonic axle inspection is mandatory at defined intervals under ECM maintenance requirements; 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. Baltic and CIS networks operate at 1,520 mm. Standard maximum axle load for passenger stock on TSI-conforming lines is 22.5 tonnes per TSI LOC&PAS; some high-speed platforms operate at lower axle loads by design. Freight axle loads reach 22.5 tonnes on standard European infrastructure, with higher limits permitted on specific freight corridors under national infrastructure rules.