Re: Brakes--swept area

[Bob Wilkinson <wilk@domain.elided>]

I wasn't the one who alluded to R&T, but I did comment, incorrectly or at
least out of context, on swept area.  I was actually referring to the area
of the pad(s), and their theoretical non-importance in braking.  Swept area
depends on pad area, but is of course the area swept under the pads in one
revolution.  This depends on the pad area (or, more precisely, the length
of the pad along the radius of the rotor) plus the distance from the center
of the rotor to the pad.  Thus larger rotors give more swept area for the
same pad.  There are two advantages of this--neither specifically talked
about in our previous thread.  One is heat dissipation--more "heat sink"
area means cooler brakes.  The second is lever arm--moving the brakes
outboard enhances the (slowing) torque exerted for a given frictional force
at the pad.  This latter factor is less important because the overall
mechanical advantage of the brakes can be adjusted in many other
places--like the diameter of the caliper piston(s).  But having the brakes
farther from the center means that less force (stress) is needed in the
caliper itself--and therefore the caliper deforms less and performs more
ideally.  Anyway, swept area IS important (Bigger brakes are better), but
the reason is primarily cooling and ideal performance, not braking force
per se.

Bob Wilkinson
72 Spider

From: "Ev-Arch1" <mdg36@domain.elided>
Subject: Brakes--swept area

I stand by my earlier comment that all cars that brake well have higher
swept areas in their brake system designs....all the other factors
previously raised, i.e., pads friction co-efficient, hydraulic pressure,
assist, tire to surface co-eff, wheel diameter, yada, yada, yada....
are all governed by a relatively fixed and narrow design criteria-at least
with regard to passenger cars- leaving total swept area as the starting
point for vehicle stopping dynamics.
And swept area to vehicle weight. Kudos to R&T for publishing this data.
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided