Subject: [Tigers] Stopping distance testing

From: Jeff Feit <[email-masked]>
Date: Thu, 20 Jun 2013 06:30:17 -0400

A few things about stopping distances, having been involved with this kind of
testing before.

Certainly the surface used and test conditions can vary a lot, which has a big
effect. The big magazines like to do most of their testing at the same
location when possible-- but they don't always. If they are testing a car at a
remote location, they make do with whatever they can find. My guess is that
Classic Motorsports doesn't have access to a good test surface.

More importantly, there are 2 factors that have a huge impact on the stopping
distance, that have nothing to do with the ultimate deceleration capability--
how the test is run, and how quickly the car can build up deceleration.

Think about this. The 60 mph starting speed is 88 feet/second. What do you
consider the start of the test? Do you use a brake pedal switch (this is what
automakers use, but magazines don't)? Brake pressure switch? What pressure? Do
you signal the driver to start the brake event (adding driver reaction time)?
Trigger at .10g? .50g? The method can easily account for 1/2 second
difference, which is 44ft at 60mph.

Then there is the fact that a car can't instantly go from zero to maximum
decel, and the things that affect this often don't have anything to do with
maximum decel capability. Things like the suspension, shocks, stiffness of the
brake components (calipers, lines, pedal) will effect how fast the decel can
build up-- and at a starting speed of 88ft/s it makes a big difference. The
effect would show more if you trigger off a brake pedal switch than if you
trigger at .50g.

So, while in theory a "better" brake system shouldn't improve stopping
distances with the same tires, in reality it does. As Pirelli likes to say,
"power is nothing without control".
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