Re: Corrado Brakes -- Physics Question: Are they pointless?

[16V JASON <jason@scirocco.org>]

At 10:53 PM 2/4/99 , Riley McDowall wrote:

>Only because the tires, as a variable, aren't controlled.  How else could a
>heavier car outbrake a lighter one, if both have the same brake systems?
>Or is ABS another variable you haven't controlled for...

	There are a lot of reasons-- chassis stiffness, for one.  Suspension
design (are all four tires squarely on the road under suspension
dive/squat?) Weight distribution (the Audi, for one, is nowhere NEAR as
front-heavy as the Rocco, meaning the fronts don't have to do as much, and
the rears can help out more), Tires (as you said), Ventilation (the Audi
has bigger hubs and a 41mm offset), overall drivetrain drag... the list
goes on.  And yes, the Audi has ABS... but ABS is (debatedly, of course),
of minimal value on a well-balanced proportion-valved sports coupe under
controlled, straight line braking... we're talking about 1 or 2 feet
difference, probably, from 60.  The Audi, to answer someone's question,
needed 145 feet to stop from 60, the 16v needs 150.  From 80 (where fade
starts to enter the picture), the Audi takes 248 feet, the Scirocco needs a
full 257.  And remember, this is with stock (i.e. not exactly
fade-resistant) pads.  Because of the lighter weight, though, we would
assume that if fade had indeed become a problem on the 80mph stop, the
Scirocco would stop more quickly than the Audi did, being that the 60mph
figures are so close.  This, of course, isn't the case, leading me to
believe that fade is not, in fact, a factor.  (All figs from Road & Track)

>He's right, there's more to braking systems than initial bite.  And he
>makes a good point WRT CART (and F1 and pretty much every other
>professional series) - by your logic, their brakes are massive overkill
>since they can lock all 4 wheels at any speed they want, without
>difficulty.  The whole point to moving up to the 11" Corrado stuff is their
>ability to absorb heat and continue to work.

	The "ability to absorb heat and continue to work" is just fade resistance
in fancy words, right?  But didn't we agree that the 10.1"s are fade
resistant enough?  Or maybe I just don't drive as hard as you do!  Dunno..

	And Shawn does make some good points, as usual.  However, as usual, I have
to be a pain in the ass and point something out.  :)  Shawn said:


>True, the tires ability to grip can be the limiting factor in the cars
>ability to stop. However a skilled driver will know how to make the
>brakes work to their fullest without locking them up. Need I refer to the
>CART series as an example? Al Unser Jr. was famous for being able to
>outbrake the competition going into a turn. Nuff said, point made. 

	Shawn, that's a great point-- and it's very true.  The Physicists among us
know all that bullshit about the static coefficient of friction being
higher than the dynamic one... which all translates into "You'll get
shorter stopping distances with the tires on the verge of lockup rather
than locked up".  And while it's true that a skilled driver will be better
able to do this, it's not really relevant to our argument-- unless for some
reason the 11"s enable easier modulation... maybe they do... I don't know!
Anyone know?  I can't see why they would-- in fact, I would think the
opposite is true because they're able to create so much more stopping power
than a 2300lb car on 195s (or whatever) needs to lock up...

>You can't 'neglect' the fade factor.  There's no doubt at all that the
>Corrado brakes will resist fade better than 10.1s, no matter what
>fluid/pad/rotor/brake line combination we're talking about.  And Shawn and
>I have first-person evidence that the 11s will give you shorter 70 or 80-0
>stopping times.

	You're right, you can't normally neglect the fade factor... but if you
can't get the 10.1"s to fade, then there's no point in going to 11s, if
that's the only benefit, right?


And to this point, Jason R asked:
>easy to do? And most importantly do you think it's possible to get cross
>drilled brembo's with ferodo's to fade on a rocco 16v without going crazy on
>them?

	I doubt it-- I can't get my Ferodos to fade on my *stock* rotors, and I've
done some pretty nutty shit (8 consecutive threshold stops from 60mph, and
*almost* no fade)... so I'm pretty confident that with cross-drilled
Brembos, you would have to trailer a boat to overheat them.

Then, Jonas asks:
>So are the corrado brakes better?? Well, assuming that they give you more 
>control, you can then make better use of the tires ability to stop your 
>car. That, and their increased resistance to fade, are key factors.

	But can we assume that they give you more control? Not as far as I know...
so we're back to the fade issue, right?

But Jonas adds:
>Technique. The quicker and closer you can get your brakes to the most 
>efficient braking, and keep that friction applied without locking up 
>your brakes, the quicker your car will slow down. 

	This might actually be a benefit to the 11" brakes under full braking.
The increased stopping power of the 11s might stop the wheels, tires, and
driveline from turning more quickly than the 10s do... BUT, these gains are
probably negligable, right?  I mean, how long do you think it takes from
the second you mash your pedal until the wheels lock? (or achieve max SCF?)
Probably less than about 1/4 second, right?  

	I will, of course, be the first to admit that the 11s might give a better
feedback under normal (=not maximum) braking conditions.  The larger swept
area will result in less pedal effort, so with the same effort that it took
to stop you at, say, 0.2g with the 10s, you might be able to stop with
0.3g.  But, as we've pointed out, the 10s have enough strength to lock the
wheels up anyways, so as long as you're capable of giving the pedal 50lb of
pressure, the difference is negated under full braking.

	And, once you convert to the 11s, you are probably also creating a serious
front/rear bias problem.  Under normal braking, the fronts are doing so
much more work than the rears, that who knows... stopping distances might
even be increased?  And you can't mess with the proportioning valve to fix
that-- the valve only limits the *maximum* amount of pressure delivered to
the rears... which means you would have to upgrade the rears, to, say, 10"
rotors to compensate for the added stopping power up front.  And that's not
possible, right?  I believe Danny asked that one...

	So, phew, in one post, I covered everyone's responses thus far to this
thread!
	Thanks for all your responses guys!

			Jason



----------
jason@scirocco.org
1987 Scirocco 16v
57,000 original miles.
http://members.aol.com/rocco16v  

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