How to Visually Inspect Pinewood Derby Wheels Before Machining or Racing
Before you polish or true your Pinewood Derby wheels, a visual inspection can save you time and money. Derby Dust® technicians examine every wheel for mold flaws, off-center bores, and surface defects that can cause wobble or friction loss during a race.
1. Check the Inner Bore for Center Alignment
The most important step is verifying that the inner bore is centered with respect to the outer tread. Off-center bores cause uneven rotation and result in wobbling at speed. If the bore appears offset or egg-shaped, discard the wheel.
2. Inspect the Bore Surface for Factory Flaws
Only about 20% of factory wheels are completely free of voids or blistering in the bore. Use a magnifier or spin test to identify voids, scratches, or pits. Some voids can act as graphite reservoirs if smooth — others will cause friction.
3. Test for Wobble or Concentricity
Place the wheel on a solid 0.094″ axle and spin it. Observe side-to-side motion at the tread edge. Wobble means the bore axis and wheel diameter are not concentric. Use light lubrication during this test to prevent false friction drag.
4. Understand Why Mold Variations Matter
Derby wheels are injection molded, not machined. Each mold cavity produces slightly different geometry. After millions of cycles, mold wear increases defects like bore tilt, surface ripples, or internal bubbles. Modern molds are better, but wear still occurs over time.
5. Recommended Inspection Tools
- Derby Dust® Wheel Wobble Stand – for checking bore concentricity
- Speed Wheels Collection – pre-inspected, machined wheels
- Speed Axles – paired for smooth rotation
6. Video Demonstration
Watch how we visually inspect and spin-test Pinewood Derby wheels before machining:
Pro Tip: Always inspect at least 12 wheels to find a perfect set of 4. A single bad bore or offset hub can destroy race alignment. Visual inspection is the first step toward a truly race-ready wheel set.
Derby Dust® does not alter bore dimensions beyond legal limits. Always follow your pack’s rules regarding wheel preparation.