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 |
Methodology
- 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 | ||
|---|---|---|---|
| MIN | MAX | MIN | MAX |
| 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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