What are those chains that you can see hanging from underneath fire trucks, around the area of the rear axle? Maybe they’re on other trucks, too, but I’ve noticed them on fire trucks.
They look about 8 or 10 inches long and don’t quite touch the ground. Nothing to do with snow chains because we don’t have snow around here.
– Greg, Atlanta
Trucks carrying flammables (actually the trailers) sometimes drag chains to dissipate any static electricity charge. The chains are hung to barely touch the ground.
Just a WAG, but perhaps for static discharge. Gasoline trucks have them too. Maybe all that water running through the truck generates some static electricity.
They are, indeed, self deploying tire chains. There’s a button in the cab that one presses when the truck is moving a low speeds. Works like so:
–Driver sees something up ahead (snow, ice, etc) he would need chains for, presses button to turn the chains on.
–The chains are arranged in a spoke pattern, and are attached to a drive unit in the center of the spoke.
–When the button is pressed, the drive unit spins the chains in relation to the speed the rear wheels are moving at, and lowers itself to the ground.
–The chains are flung to the ground just in front of the rear wheels.
–The rear wheels then drive over the chains.
–The chains then get spun back around (remember they’re moving in a wheel-like motion) and go under the wheel again.
The key to this whole system is that you have to me moving when the system is deployed and retracted, and you can’t stop while the system is being used. We have them on most of our ambulances around here, and (I think) one of our engines has one. Unfortunately, we still have to put real tire chains on the trucks at my station when it snows.
Here’s a link, they’ve got a picture of the unit on the main page: http://www.onspot.com
Jeremy…
I can think of no more stirring symbol of man’s humanity to man than a fire engine - Kurt Vonnegut
Thanks for the link, Jeremy, but those aren’t the ones I see. They look almost like they’re hanging from the axle, but pretty much in the center, not near the wheels. And they’re not at all on a spindle like the auto snow chains. Think more of a bracelet hanging off someone’s wrist (the axle).
But that’s a pretty cool snow chain gizmo.
– Greg, Atlanta
Trucks carrying flammables drag chains on the ground to dissipate static electricity?
Just what they need - an automatic method for generating sparks…
“Static straps” are made of rubber.
If those aren’t what you saw, my next answer would be to call the fire department and ask them. It would be even more helpful if you know what Engine or Ladder it was (Engine 12, for example). I’m sure the dispatcher would be able to get the information for you, or at least hook you up with someone who does know.
Jeremy…
I can think of no more stirring symbol of man’s humanity to man than a fire engine - Kurt Vonnegut
Are both ends of the chain attached to something?
I’ve seen chains from frame to differential to limit suspension travel (preventing the driveshaft yoke from pulling out of the gearbox).
"…Just what they need - an automatic method for generating sparks… "
D’oh!
All the same, I think I saw it done. It was about ten years ago.