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Radial runout (TIR — Total Indicator Reading) is the total variation in distance measured from a shaft surface to a fixed reference point as the shaft rotates one full revolution. It indicates how much the shaft deviates from perfect concentricity. TIR equals twice the eccentricity.

Mount the shaft on V-blocks or between centers, place a dial indicator perpendicular to the shaft surface, zero the indicator, then slowly rotate the shaft one full revolution. The total needle movement (max minus min) is the TIR.

Common causes include:

• Bent shaft from thermal distortion or impact
• Manufacturing eccentricity (turning error)
• Bearing journal wear or damage
• Improper coupling alignment
• Assembly errors (misaligned press-fit components)

If the mass centre of a rotor is displaced by eccentricity e, the equivalent unbalance is U = e × m, where m is rotor mass. Journal runout can displace the mass centre and thus contribute to unbalance. However, not all unbalance comes from runout (mass distribution matters too), and measured TIR can include form error, bend, bearing seating or setup error that does not translate one-to-one into unbalance.

The geometric runout tolerance comes from the shaft drawing or the manufacturer's specification — ISO 21940-11 sets unbalance limits, not runout tolerances. As balance-risk screening values (TIR equivalent to the residual unbalance limit):

• G6.3 / 3000 RPM: TIR ≈ 40 μm
• G1.0 / 6000 RPM: TIR ≈ 3.2 μm
• G6.3 / 1500 RPM: TIR ≈ 80 μm

Always calculate for your specific conditions and check the drawing tolerance.