Brake Question

Given the expertise of some of the participants in this group I have a
question.

Approaching a stop sign at 60 mph is it better for the brakes if I

A) Slow at a steady rate over a period of say 15 seconds
or
B) Brake at a higher rate of deceleration so that I come to a stop in
say 4 seconds?

Any opinions would be appreciated as I have had this discussion and
there seems to be no "right" answer.

 

My primary thought is that if you stop slow and steady, it gives the heat
more time to dissipate. That will help protect your rotors and drums.
This method (at least on level ground or uphill) will also allow drag to
slow the vehicle a little, saving fuel and brake wear (although probably
not much).

 

I agree with that. As for wear, it takes a given amount of friction to stop
the moving mass. The brakes will generate approximately the same amount of
heat, but the curve in temperature rise will be considerably different. The
fast heating is more likely to induce rotor warp.

The smart thing to do to minimize brake wear and possible rotor warp is to
coast down a bit and then drop back a gear.

An even smarter thing would be to drive closer to the speed limit in the
first place.

 

That comment is certainly reasonable with the given example...... I don't
know of many stop signs in 60 mph zones. Of course, if you were approaching
a red traffic light at 65 mph, that would change everything.

 

The smart thing to do to minimize brake wear and possible rotor warp
is to
coast down a bit and then drop back a gear.

I would rather replace pads and rotors than clutches or add stress to an
automatic.

An even smarter thing would be to drive closer to the speed limit in the
first place.

Exiting the freeway (speed limit 70) there is a short ramp (angled down)
approaching a T, light controlled intersection. With traffic on my
bumper I don't have the option to slow down prior to getting off. Well
I do, I suppose, but then I would be one of those people that I
occasionally talk about slowing down on the freeway .

My point of inquiry was whether a slow application of friction/build up
of heat was better than a quicker one. Rather than the dissipation of
heat it is a question of a slow or rapid build up of heat, if one method
produces more heat than another and whether the slow process wears the
pads more than a more rapid approach.

I suspect that it is really a moot point as one way uses the pads longer
as opposed to using the pads harder. Unless, of course the pads are
worn quicker with one application or another.

 

I would rather replace pads and rotors than clutches or add stress to
an automatic.

Exiting the freeway (speed limit 70) there is a short ramp (angled
down) approaching a T,
light controlled intersection. With traffic on my bumper I don't have
the option to slow
down prior to getting off. Well I do, I suppose, but then I would be
one of those people
that I occasionally talk about slowing down on the freeway .

My point of inquiry was whether a slow application of friction/build up
of heat was better
than a quicker one. Rather than the dissipation of heat it is a
question of a slow or rapid
build up of heat, if one method produces more heat than another and
whether the slow process
wears the pads more than a more rapid approach.

I think you are right about the lower curve of heat build up.

Thanks for the responses.

 

FWIW, I've driven on some rural highways with high speed limits that
actually have traffic lights every few miles. IIRC, they were in
Delaware and the Carolinas.

 

Around here there are lots of stop signs in 55mph zones - not so far from
the 60mph the OP referenced.

 

Here's the deal. Except for nearly negligible wind drag/rolling resistance
losses, you're generating the same amount of heat either way. Brakes are
nearly 100% efficient in their conversion of your vehicle's kinetic energy
to heat energy. The more quickly you add heat, the higher the rotor
temperature will become, because it dissipates the heat at a slower rate
than it is absorbed when braking. In fact, the heat dissipation is indeed
the important factor for this reason.

 

It depends somewhat on how you define better, but if I assume that by
better you mean less wear and lower brake peak temperatures and less
thermal strain to the brake components, then a long and gradual stop is
better than a rapid stop.

Matt

 

Around here, we have a sense of humor about such comments. When I was 17 or
so, it was not uncommon to see how fast I could go and still make the stop
sign on the corner. And I could not understand why the insurance company
would charge me more than some 30 year old.

 

Damn that sense of humor thing. It's so easy to miss sometimes...