I often see trucks (school buses, ambulances, sometimes dump trucks) which have metal chains hanging off the rear axle, on either side of the differential. What are these for?

  • Need to see a picture as both answers given so far can be correct.
    – Solar Mike
    Nov 3, 2018 at 22:08
  • Chains across mudflaps keep them weighted down so they don't fly up in the wind, but we really need a picture.
    – JPhi1618
    Nov 6, 2018 at 16:11

2 Answers 2


Theoretically, they discharge static electricity, so you don't get a shock when opening the doors, etc.

Whether they really work, I'm not so sure.

Vehicles where static electricity is a real issue (for example fuel tankers) use much better-engineered solutions to avoid sparks causing fires and/or explosions.

Ambulances are an interesting case - they have a lot of static-sensitive electrical equipment inside (e.g. EEG monitors) but I don't recall ever seeing an ambulance with anti-static chains in the UK.


I think you may be seeing these automatic snow chains - https://m.youtube.com/watch?v=LxOh8Qav5tY

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