Text 5150, 52 rader
Skriven 2005-01-15 13:14:10 av Roy Witt (1:10/22)
   Kommentar till text 5128 av Paul Sanders (3:633/104)
Ärende: Motorcycles
===================
Hello Paul.

15 Jan 05 17:25, you wrote to Robert Bashe:

 RB>> What I still don't understand are these claims that locked wheels
 RB>> _fundamentally_ provide poorer braking than unlocked ones. On a dry,
 RB>> clean road where the braking power depends either on the surface
 RB>> area and contact

 PS> In a perfect world all the roads would be clean & dry, and locking
 PS> your brakes would slow you quicker than unlocked brakes, reality is
 PS> that the roads are rarely clean and / or dry.

It's been explained here several times that locked wheels do not slow a
vehicle faster. In fact the opposite it true.

Lets look at it from a different perspective.

In my youth I was fortunate to drive a Studebaker of the 1940s variety. It
had a feature that allowed the driver to hold the car on a hill after
depressing the clutch and coming to a stop with the brakes. A valve in the
front wheel brake line between the master cylinder and wheels, held the
pressure on the brakes while you waited. When you wanted to go, you just
let out the clutch and you were off, the valve automatically disengaging
upon release of the clutch.

Later on, in the drag racing world, people figured out that a car can be
held at the starting line by the front brakes, while you load the
suspension for launch. They also used a valve in the same manner as I
described above.

Pretty soon, they figured out that they could also hold the car in place
while they heated up the rear (traction wheels) tires and thus the huge
smokey burnouts you may have seen on TV or in person.

What they're demonstrating is just the opposite of what you and Bashe are
saying. The front tires have enough traction on the pavement (0% slip) to
hold the car while the rear tires burn up in a cloud of smoke (100%
slip). They can't go anywhere because they have no traction, just like a
locked wheel during braking.

Meanwhile, the front tire is holding the car back (0% slip) until the
front brakes can't hold it anymore and the front wheel begins to rotate
against the brakes (35% to 8% slip). If the front tire didn't have
traction and began to skid (100% slip), then the car wouldn't go anywhere
until the rear tires gain traction (slip unknown), aka friction with the
track/road surface.



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