DIYbanter - View Single Post - Need help INTERPRETING these test results police cruiser SAE J866a Chase Test

Clare Snyder

On Mon, 15 Jan 2018 14:19:45 -0000 (UTC), Mad Roger
wrote:

On Sun, 14 Jan 2018 17:52:27 -0800 (PST),
wrote:

There are presumably 2nd order differences in pad performance,
but we've no idea what they are. EE versus FF is not it seems
the relevant criterion as long as the car can apply enough force
to lock wheels with the pads.
Whether all modern cars can do that with EE or not I also have
no idea. FWIW certainly all historic ones can't.

I agree with you that the primary role of friction material is their
friction, but as the AMECA engineer told me, the way they outgas alone can
have an effect that is huge, as you are also noting.

It would be nice to figure out what these second-order effects are, such as
outgassing as mentioned by the AMECA engineer, as the police cruiser test
already eliminated any second-order effects from a difference in vehicles
since they tested the different pads on the exact same vehicle.

So we can tentatively state that you are 100% correct that second-order
effects (outgassing) apparently are as big as first-order effects
(friction).

The AMECA engineer said that all materials heat up differently, which, he
said, also effects the performance of the pads.

So I think we have two potentially high second-order effects which are
(shockingly) almost as important as the first-order effect of friction
coefficient:
1) outgassing (outgasing sp?)
2) heating
3) ?

What other potentially very high (as high as friction) second-order effects
could we have, when we've eliminated the difference in vehicles and driver?

Pad vibration - which has an effect on gas venting, counterd by the
effect of reduced pad contact

May not be a HUGE difference, but it is possibly a factor. Also heat
CONDUCTANCE - metallic pads conduct more heat to the caliper than
ceramice - making the boiling point of the fluid more critical (if
running metallic or semi-metalic pads you want to be sure to be
running DOT4, not DOT3, and you want it freash and dry) One reason
Chrysler was using composite pistons for several years in the early
no-asbestos days (until they found the pistons swelled and stuck - - -
)