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Rim Trueness Test

What Is Rim Trueness?

Rim trueness, or rotational accuracy, refers to the lateral and radial trueness of a rim. Untrue wheels are weaker, have more variance in spoke tension, and can wobble at higher speeds. Ensuring our rims are quite flat and round out of the molds means greater roundness and even spoke tension when building the rims into a wheel.

Testing Goal

Rarely can a handmade rim be 100% flat and round, but we need to make sure that the lateral and radial movement for all Light Bicycle rims is as little as possible.

Test Standard

0.4mm (Light Bicycle’s criterium)

Sample Profile

Size Model External Width Depth Weight Rim Condition
700C WR35 32mm 35mm 430+/-15g Newly Produced

Test Machine

We built a test jig to measure the lateral and radial run-out to 0.01mm. The device rotates the rim slowly several times in both directions and the average readings are recorded automatically.

Test Conditions

Rotation Speed 0.3m/s
Accuracy 0.01mm
Rim Position Horizontal
Test Positions Both rim sides
Rim Movement Automatic


  • Step 1:Lay flat and clamp the rim on the rig.
  • Step 2:Tare the digital scale (lateral run-out) and approach the cylindrical tips to the rim edge.
  • Step 3:Press the button “rotate” and the rim revolves at a controlled speed.
  • Step 4:Lateral and radial movements are recorded.
  • Step 5:Turn the rim over and repeat the process.

Test Results

Roundness Flatness
0.26 0.3 0.21 0.26
.04mm Deviation .05mm Deviation

The results are only valid for this tested sample. The deviation is less than 0.4mm so it has passed this check.

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