We started
out nice and easy at the differential spin pit, or split µ as Mumaw
called it. µ (mu) is a Greek letter used to indicate the coefficient
of friction between two surfaces or the ratio of force required to move
your truck forward relative to the truck's weight on a given surface.
The higher the µ the stickier the surface. Too much µ and
your truck isn't going to budge. Too little µ and your truck will
be spinning in place.
To demonstrate
Mumaw flooded a shallow concave surface under the left front and rear
wheels with a sprinkler, while the right front and rear wheels remained
on a dry surface.
Stepping
on the gas in the Silverado there was a split second of wheel spin and
yaw to the left until the locking differential kicked in with a jolt and
then we were quickly out of the pit. In repeated tests the Silverado's
wheels always slipped for an instant before locking and allowing us to
drive away.
In the SuperCrew
with both lockers disengaged, effectively acting as open differentials,
we gave the Ford pickup full throttle. With the wet wheels getting all
the power but no traction we quickly pegged 5,000 rpm on the tach without
moving more than a few inches but spraying water and smoke from the tires
everywhere. Engaging the ELocker and then trying the differential spin
test on the SuperCrew was an entirely different story. No fuss or muss
this time. The SuperCrew neatly climbed out of the pit at full throttle
without even a hint of yaw or locker engagement like the Silverado and
certainly without the sound and fury of the open ELocker.
The next
test, another split µ, added gravity to the equation. We drove to
a 20% grade that featured steel rollers embedded in a portion of the surface,
like the kind you find at the airport to place your luggage on during
the security screening.
Driving up
the ramp with the Silverado we placed the rollers under the left wheels
while leaving the right set on concrete and slowed to a stop. Hitting
full throttle on this type of surface and grade was almost impossible
to overcome with the mechanical diff. There was lots of rubber squealing
and tire smoking as the wheels spun but eventually the locking diff was
able to kick and compensate as it chattered off the rollers and got pavement
under both sets of wheels.
The SuperCrew
without the ELockers engaged was a hopeless story. Pulling the right wheels
onto the rollers stopping and giving it gas quickly redlined the engine
until the rev limiter stepped in and forced us to step on the brakes to
keep from going backwards. Engaging the ELocker again proved to be a dramatic
story. Like some Sybil of traction control, the F-150 suddenly had a new
personality. There was some yaw to the right and a little chatter but
the front and rear ELockers quickly got the pickup off the rollers and
onto a surface both sets of wheels could grip.
Moving off
paved surfaces we made our way over to the twist ditch test. A set of
parallel dirt mounds, the twist ditch was built to repeatedly create situations
where one of a truck's front wheels would hang in the air at the same
time the opposing rear wheel also left the ground. This leaves only two
small patches of rubber to make contact with the slippery earthen surface,
maintain traction and get the pickup into a more manageable position of
control before repeating itself with the opposite wheels.
