[Vwdiesel] mileage

James Hansen jhsg at sasktel.net
Sun Nov 29 19:42:47 PST 2009

> My statement of it being pure kinetic is just because it's relatively
> easy to lock up all the brakes and that is more of fair comparison
> between the different vehicles. It's just a simpler way to test them,
> is all.

Except that is difficult to attain on a fully loaded semi.  In practical
tests (collision avoidance) we have killed 2 tires, and spun 2 rims on the
older trailer with the clamp on style rims.   I have NEVER seen a car able
to break the bead loose from brake application, even on race applications
where there is much more brake and traction.

Wheel hop on a semi occurs because of loading of the suspension during brake
application while the wheel is still turning but breaking.  When the tire
eventually loses traction, the suspension unloads, driving the wheel forward
and down.  It achieves a harmonic frequency almost immediately.  It's nearly
identical to braking wheel hop in a car, but far more dramatic.

I once watched a fully loaded concrete mix truck wheel hop the rear tires
when an air line broke and the maxi's went on. (safety feature when there is
air loss)  This is spring applied by a giant spring in the air brake pot.
He spun some of the lead tandem tires, (they went flat after), and broke a
control arm. I was behind him at a safe following distance.  I used all my
brakes to not hit him.  It stopped fast, remarkably so. The hopping was so
intense, it unloaded all the trinkets that a concrete truck carries, like
hose, troughs, shovels, etc...

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