Message text written by "Michael D. Porter"
>Suggestions that one might drive the car differently, having more power
available, are irrelevant to the original argument. Such suggests a
change in variables (such as braking from top speeds in excess of the
design limitations of the original brakes, or repeated braking inducing
fade, or suggestions that drum brakes are different in character than
disc brakes, or any other arguments not related to the original
postulation). Those were not part of the original assertion.
All that said, would I, putting a 350 hp engine in a car normally
equipped with a 110 hp engine think that better brakes, given natural
human tendencies to excess, be a good idea? Yes, perhaps. Nevertheless,
that immediately begs new calculations based on behavior, rather than on
physics.
<
Michael:
First of all our condolences on the loss of your friend, our prayers for
your mother and happy bithday to your daughter.
I think that a distinction needs to be made here as for the intended use of
the car. If one were racing the car on a closed circuit then the
accumulative effects of repeated braking will generate more heat with the
larger engine due to the higher speeds achievable with the larger engine in
the limited spaces available.
But this is not a race oriented list. Most listers are operating their
cars on the public streets and their speed is limited by traffic and the
constabulary. Sure the occasional blast to 130 MPH on an open freeway
followed by a brisk brake back to within acceptable limits will occur but
this is well within the capabilities of the stock TR6 brakes. Don't forget
that the TR6 was recognized for its excelent brakes in its day. Also, the
bigger engine gives one the option of greater compression braking if one
were to down shift to take advantage.
Back to a: your statement about a (acceleration) -a (deceleratio) not
being of equal magnitude is indeed true. a will always be of a lower
magnitude than -a, even with a larger engine because -a is only limited by
the friction present between the tires and road surface. a, on the other
hand is limited to either the torque available or the friction, whichever
is less. And since only two wheels provide force for acceleration* and all
four do so for deceleration, the the force available for braking will
always be greater. Up sizing brakes does nothing to alter this priciple of
physics. Upgraded brakes have a better capability of absorbing and/or
disipating the heat generated and this is the issue that comes into play on
the racing circuit. The occasional stop from any given speed is no problem
for stock TR6 brakes.
>Argue at your peril. <big smile>
I would never argue with you. I like to think that I am smart enough to
know better than that. I am only trying to fill in around the edges.
Cheers, Michael
Dave Massey
* I know, I know, with a non-posi rearend all the torque could be
distributed to one wheel and the force would be limited that wheel's
friction. But even with posi you are still left with two wheels unless you
put in a four wheel drive conversion. But then, come on!
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