UIC 812-1: Wheel Centres for Tyred Wheels (Trailing Stock) – 2026 Technical Guide

A technical analysis of UIC 812-1 regarding the supply of rolled or forged wheel centres. This guide covers the metallurgical specifications, heat treatment protocols, and mechanical testing required to ensure the structural integrity of the “hub” in tyred wheel assemblies, focusing on safety for freight and legacy passenger stock.

UIC 812-1: Wheel Centres for Tyred Wheels (Trailing Stock) – 2026 Technical Guide
October 16, 2023 7:34 pm
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⚙️ Technical Distinction: This standard applies to Wheel Centres (the inner hub) used in Tyred Wheels. It does NOT cover Monobloc wheels (which are one solid piece). The interface between this centre and the tyre (the “Shrink Fit”) is the most critical safety factor.

While high-speed trains rely on monobloc wheels, a vast portion of the global freight and legacy passenger fleet runs on tyred wheels. UIC 812-1 defines the quality requirements for the “Wheel Centre” — the structural backbone that connects the axle to the wearing tyre.

1. Manufacturing: Forged vs. Rolled

The wheel centre must withstand immense vertical loads and braking heat transfer without deformation. UIC 812-1 permits two main manufacturing methods, provided the steel is “killed” (deoxidized) and vacuum degassed:

  • Forged Centres: Formed by hammering or pressing a hot steel ingot. Offers superior grain flow alignment.
  • Rolled Centres: Formed by rotary rolling processes. Common for high-volume production.

Crucial Rule: The finished product must be free from internal flaws (pipes, segregation) that could compromise the interference fit with the tyre.

2. Mechanical Properties & Testing

The steel used for wheel centres is generally softer than the tyre itself (to prevent cracking the tyre during the shrink-fit process). UIC 812-1 categorizes the steel based on Tensile Strength ($R_m$).

PropertyTypical RequirementWhy it Matters?
Tensile Strength ($R_m$)420 – 500 N/mm² (Typical Grades)Must be strong enough to hold the axle, but ductile enough to absorb shocks.
Elongation ($A_5$)Minimum 18% – 22%Ensures the material yields before it snaps (Fail-safe).
Impact Energy (KU)Min 20 Joules (U-Notch)Resistance to brittle fracture at low temperatures.

3. Heat Treatment & Residual Stress

The wheel centre is not just a shape; it’s a “stored energy” device. UIC 812-1 mandates specific heat treatments:

  • Normalizing: The standard treatment to refine the grain structure and ensure homogeneity.
  • Stress Relieving: Essential if extensive machining is done. It ensures that the wheel centre maintains its precise dimensions over time, preventing the tyre from becoming loose.

4. Inspection: The “Static Balance”

Since tyred wheels are multi-part assemblies, balance is critical. UIC 812-1 requires checking the Static Unbalance.

  • Eccentricity: The machined outer diameter (where the tyre sits) must be perfectly concentric with the bore (where the axle goes).
  • Marking: The position of the residual unbalance is often marked so that when the tyre is fitted, its unbalance can be positioned opposite, cancelling each other out.


Engineering Note: When procuring wheel centres, pay special attention to the Surface Finish requirements of the outer rim. This surface determines the friction coefficient for the interference fit with the tyre.
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