On Tue, 28 Oct 2014 11:19:41 +0000, Neil Williams
wrote:

On 2014-10-28 09:20:43 +0000, Roland Perry said:

The concept I've having difficulty with is that braking a wheel causes
that wheel to transmit more power to the road. Let's say it's a long
uphill slippery road with 100HP from the engine; does this braking
activity swap the 100HP from one driven wheel to the other and back as
each one encounters a slipperier side of the road?

Ah, I see. Essentially, yes, that's how it works, using a side-effect
of how a diff functions.

With a normal diff, if one wheel spins all power is lost via that
wheel, none goes to the one with traction (like my water example, all
the power goes the easiest way it can, which is a free-spinning wheel).
Braking therefore allows the power to be passed to the *other* wheel,
with the aim that when the brake is released that wheel might have had
chance to gain some grip and try again.

I *think* it's also the case that maximum traction is gained at the
point *just before* a wheelslip, which stopping the spin to try again
from that point will help, though I admit I find that quite hard to get
my head around. (ABS mainly prevents wheels locking up for another
reason - to allow them to keep their ability to steer).


Yes, so ASC would first brake a spinning wheel to a standstill, then
reduce the brake force until the wheel just starts spinning again,
after which it increases the brake force, and so on. In effect, it
keeps the wheel near the point of maximum adhesion through letting it
turn at the optimum speed by modulating the brakes.

One important point is that this is available at all times (unlike a
lockable diff), and it doesn't stop the car turning (unlike a locked
diff).