Terrible Fuel-Efficiency - 2003 Accord

1. all brakes heat on application. that's fundamental fact. if you're
dissipating /all/ your forward energy through the brakes and are not
using engine braking because you are in neutral, the brakes will heat
more!!! that's fact!!!

2. you can easily have constant application of brakes. you're never
going to have road conditions that just happen to suit you!

3. brake lines deteriorate with age! fact.

4. brake fluid absorbs water from the air. it starts to degrade the
moment you open the bottle. fact.

that's stupid.

you don't know what you're talking about. any brake fades as a function
of temperature. temperature is a function of the speed you want to turn
into kinetic energy. any form of stop start driving, regardless of
hills, heats brakes. period.

dude, apart from the fact that coasting is illegal, you're also
indicating you don't have the vehicle under proper control.

eh? what has synchromesh got to do with it? that's utterly irrelevant.

but engine braking does!!! that's why automatics down-shift - for
engine braking and safety.

only if the brakes can supply sufficient friction. if they're toast,
you can have the best tires in the world, but they won't mean a damned
thing to stop you running into that kid that's just kicked their ball
into the road.

what planet are you on??? look up engine braking on google. truck
manufacturers invest millions in engine braking technology because its
so effective AND SAFE BECAUSE IT DOESN'T OVERHEAT BRAKES.

be my guest. geeze. i can maybe understand ignorance as an excuse if
the engineering is not understood, but using it as an excuse against the
law??? buddy, you take the prize!

 

Hahaha..! Agreed.

 

No; the *fact* is, braking will generate more heat. If that heat is
dissipated in some other, controlled manner, the brakes will not be any
hotter.

I don't know what flobert is talking about here either.

The kinetic energy is the car in motion. The conversion desired is from
kinetic energy to heat energy. I think you know this, but that's not
how your paragraph read. Any form of braking heats brakes, period. The
point made was that the incline adds to kinetic energy being overcome by
the brakes. This is entirely correct, but your note indicates that
gravity is irrelevant as a contributor. Again, I think you know this,
but your paragraph doesn't indicate it.

Even if you are in a place where the local populace has enacted some
statute, your blanket statement is wrong. For it to be correct in the
United States, it would have to be a federal statute. It is not. To
me, it sounds like the old canard we heard when we were kids, that it
was illegal to drive your car barefoot.

It what respect is the vehicle not under proper control? Granting that
if it's moving, it *may* not be under proper control, I don't see that
coasting automatically means it is not.

I agree. I don't understand this at all.

Apples and oranges here, Jim. The truck has a great deal more weight
(and therefore kinetic energy) to overcome at any given time, and the
typical over-the-road truck is driven anywhere from 5 to 20 times as
many miles over its lifetime.

I don't get this either.

Please tell me what law you're speaking of, and what jurisdiction you're
referring to. There is no such reference in the US Code (federal law).

Although I've found one place that indicates that there is such a law in
British Columbia, that forum points out that each province makes its own
laws. I found a reference to a California law and a Texas law as well,
so wherever this guy is (looks like Florida), he may be covered, he may
not. In either event, simply saying coasting is illegal generally is
incorrect.

RFT!!!
Dave Kelsen

 

I'm not arguing that the brakes will generate more heat. I did not at
any time say that. however, brake fading is only an issue in modern
brakes if the temperature goes over a certain temperature. The amount
of fade, and the temperature at which it occurs is variable depending
on the brake type/composition. For instance, brakes in a Formula 1 car
INCREASE in braking abaility as they get hotter, until they actually
burn. there is virtually no fade. They get hot, they get better, they
get too hot, they burn, they dissapear, but it takes a GREAT deal of
heat to burn the,.

I saw some test figures from the development of the Lotus Elise some
10 years ago. They tested the vehicle on an extreme downhill section
of the Alps, at racing constions, and found less than 1% fade. Those
are two clear examples that countradict your blanket assertions.
Modern brakes do not decrease in retardation ability in direct
relationship to their temperature, and haven't for many years.

So, i can't pick when i'm going to coast? My gearbox has a life of its
own?

What it seems you fail to distinguish here is the difference between
coasting on ALL slopes, regardless of grade, and only doing so where
needed. I will give you two examples from here in Georgia - thers a
series of hills on US19 betwen thomaston and zebulan, they're not
steep gradients, and quite long, i will often coast down them. no
brakes needed, except for the occasioanl momentary check-brake as my
speed rises too high (the southmost slope is by the county line, and
often deputies will hide there checking for speeders). The second
example is a hill much further north - Barnes Mill Road, in Marietta
(just off the 120 loop by exit 265 of I75) a much steeper slope, of
about 1 mile in length, where not only do you keep it in gear, but
have to use your brakes over aout 40% of it. Gradent of the second is
about double that of the first. no-one is suggesting its an 'all or
nothing', and i for one certainly haven't. its you that suggesting
that in all situations, in all circumstances, you're risking life and
limb

Certainly, and if a brake line was to go, it'd be more likely under
the greater heat and pressure of a high speed emergency deceleration,
than under a gentle coasting, where the brakes may or may not be used
at all, see above.

I don't know about you, but i would call brake fluid with heavy water
contamination to be 'under spec'

Whats stupid? The forces and energies invloved in any high speed
sudden deceleration are much more severe on a vehicle's braking
system, than, as you're suggesting, lightly riding them for a mile or
two.

fraid not. go look up some test results, there is no direct
corrolation between fade and temperature on modern brakes. no straight
line graph that starts with retardation ability being at max when the
temperature is some 'cold point' that we should take to be air ambent
temp, with retardation ability dropping in direct response to
temperature increase. There is instead a gradual decrease from the
brak systems optimal temperature (whichis NOT air ambient) to the 'max
operating' and then a more rapid decrease.

I asked a friend (a deputy in the next county) and he's never heard of
any such law here. Another fact in error/

prior to the synchromesh, when changing gear, entering a gear etc. -
it was neccesary to adjust the engine speed to match, to select the
gear, and so on. with a synchromesh, its easy to put the car in any
gear suitable for the speed of the vehicle. That was the basis of the
original 'loss of control' arguments - you had no near-immediate
ability to recouple the engine to the wheels.

how does engine braking work to increase safety?

ok, so let me get your argument straight. engine braking is required
because its unsafe to coast. Its unsafe to coast because everyone that
does so, does so with badly adjusted and maintained brakes, and
insists on riding those brakes to the point of failure whilst
coasting. thus when there is an emergency, the small engine
retardation effect is then VITAL to stop the car.

I did some tests this adrernoon, using two automatic vehicles, using
an old airstrip here. I weighted things in your favour, by using older
vehicles (which would have brakes more liekly to fade, and have worn
brake systems - a 87 caravan, and an 88 civic. one big car, one little
car. Unfortunatly, both are automatics, but on the upside, they have
drum brakes with cable-operated handbrakes.

I used a speed of 50mph, and attempted a stoping manouver with ONLY
engine braking, so as to measure the braking distance, which can then
be compaired to a standaised figure, such as ohh, the UK DOT standard
braking distances (http://www.highwaycode.gov.uk/09.htm at the bottom)

the civic with its 4speed autom box, with me manually downshifting
managed to slow to 8mph in 450ft, and wouldn't slow any further. on
the second run, engaging the handbrake at 20mph reduced the vehicle to
8mph in 420ft and to a stop in 460.
The caravan, with a 3lv6, and 3sp auto, slowed to 9mph in 390ft, and
stopped in 430ft with the handbrake application. (well, foot activated
parking brake)

by constrast, the UK figures show the braking distance to be a total
of 120ft, INCLUDING THINKING DISTANCE - not a factor since it was a
pre-planned stop point. so, 125ft is the actual stopping distance. so
its more than 3x as bad. It gets worse though, since the vehicle used
in the uk govt. figures is a 1964 ford Anglia - a car not noted for
its agility, and which had a braking system marginally better than a
foot operated wooden block pressed to each wheel. Modern cars and SUVs
achieve braking distances almost half that. Both vehicles managed a
standard braking distance of around 100ft (repeated many times - both
with and withouth being in gear)

whats 'eh' about it. The only way the addition of engine power can
assist in any incident is if you are in a spin, or in a situation
where you would be required to go faster. In any other case, the car
being in gear would no be of any consequence, or positive benefit.

Ignorance of engineering is, apprantly, your forte. As is indeed
ignorance of the law. If it was so illegal, why did Saab in the 70s
sell vehicles that were despigned to freewheel down hills without
having to take the car out of gear, you only had to pull a lever i
think it was. It was discontinued mainly because most drivers didn't
use it, and felt uncomfortable when they did, mainly due to the
commonly held misconception you share.

This, like any long term myth, is one that clearly won't go away after
having being delt with in common sense. In short, you say that if you
coast down any hill, you must coast down all (can't pick your
situation, as you call it) and you must ride your brakes at al times.
Oh, and you have an old brake system, that's been poorly maintained,
so they would fade to nothing (despite the fact it would fail at the
50mph braking test above, due to the greater heat generation vs
dissipation, on your straight-line temp-retardation graph) and that in
an emergency, a braking system that has no effect on actual
deceleration under proper braking, and which has very poor
deceleration figures when used on its own is not only usefull, but
legally required to be used. Would you care to attempt to refute these
facts, maybe do some measurements of your own with your own vehicles.
Maybe even employ some simple logic.

 

When you admit you have ceased to speed on a regular basis, then you might
be worth listening to when it comes to safety issues.

Quit freaking out over casual coasting. If you must whine, whine out riding
the brakes.

 

those are carbon fiber brakes. they're banned for road use and for
motorcycle track use. different materials behave different. the
materials we're discussing here, cast iron brake disks and carbon/aramid
fiber/ceramic/metal pad composites do not exhibit those characteristics.
they progressively fade as temperature rises. certain formulations
used on racing/performance cars fade less at high temperatures, and oem
honda pads are better than many after-market ones, but they all still
fade. citing an illegal unobtainable exotic is clutching at straws.

dude, i used to live in san francisco. and i still work there. have
you ever driven down filbert st hill from broadway to lombard, stopping
at every stop sign? using a crappy set of aftermarket brake pads that
fade like mfsob's? i have. don't talk to me about brake fade being a
thing of the past.

not legally, no. how many times do you need to be told? if you have an
accident and the cops investigate, they'll throw the book at you.
assuming you don't run into me of course, in which case the cops would
be the least of your concerns.

1. so you waste gas because your fuel injected car /is/ injecting gas
while you're idling not engine braking

2. you don't have the vehicle under full control /and/

3. you're using brakes where you needn't?

wow, how did nasa ever miss the opportunity of hiring you?

but dude, you're using the brakes /more/ when coasting in neutral!!!

water absorbtion means lowers boiling point. excess brake use
approaches the boiling point of a contaminated system more quickly!!!

eh? of course! but the energy you can absorb by braking is a function
of the available temperature delta. if the initial temperature is
already high because you've been riding the brakes, the available delta
is less. it that hard to understand?

dude, you're turning speed into heat. if the brakes fade more as the
temperature rises, and they do, you want the initial temperature to me
minimized.

so what is "optimal" for a normal car braking system??? and there's no
physical way brake temperature can decrease if you're dumping kinetic
energy into them.

california vehicle code #21710.

"Coasting Prohibited. The driver of a motor vehicle when traveling on
down grade upon any highway shall not coast with the gears of such
vehicle in neutral."

rubbish. if you can't get the vehicle into gear, whether it's automatic
or stick, synchro or not [i've driven non-synchro transmissions and
there's no reason you can't shift if you double-clutch] then either
you're not competent or the vehicle is defective and shouldn't be on the
road. again, synchro is irrelevant.

because, as mentioned so many times before, it takes a substantial load
off the brakes!!! it also allows you to instantly re-power the vehicle
if required.

no, it's necessary to keep the brakes cool for maximum stopping power.
remember the temperature delta thing???

dude, the engine does not /stop/ the car [unless you turn off the
ignition]. but it does offer braking in proportion to engine speed
[which is why you downshift when engine braking] and yet again, this
reduces the thermal load on the brakes. that's why cars with automatic
transmissions, like honda, detect when the car is braking and down-shift
to increase engine braking. i guess you'd never notice that if you
habitually coast in neutral, but it's fact nevertheless.

so these situations never occur? you should know that it does rain
occasionally...

well, funky cv transmissioned daf's & volvos had a button that
/increased/ engine braking for downhill situations. one of these
situations does not compute.

you're the guy riding brakes. i use the engine.

no. you're using twisted logic to put utterly incorrect words in my
mouth. the physics are very simple: a brake turns kinetic energy into
heat. as the temperature rises, the ability to continue turning k.e.
into heat falls. let me know if you can grasp that concept, then we can
continue this discussion.

 

One of those was an 'exotic', but the brakes on an elise is fully road
legal - hell, they were designed and developed in the US, in
California actually - I'll dig out the manufacturers name if you want.
I could go and retrofit a set onto my civic or caravan any time I
wanted.

I'd love if you could cite me a make, and manufacturer of a brake
system that had its optimal braking temperature at room temp. Any type
of vehicle will do, as long as its a powered braking system (no
bicycles)

Its been about 5 years since i was in san fransisco last (i used to
work on contract for a company, having to drive to, from, around SF
all day long, as well as oakland, sausalito, and yerba buena/treasure
island. i think i only drove over the hill once, usually i take the
tunnel, california street was it? all i remember is driving from the
bay bridge to the GG bridge, i drove past the strip clubs, througha
tunnel, and then joined up with lombard about 3 streets over. First
time i ever drove in America, back then, and the first time i'd ever
driven an automatic on the roads.

From what i remmeber, though, the hills weren't that bad. I id much
heavier testing and laoding of my brakes, i had no fade problems. It
sounds like you need to take better care of your brake system. Use
adequately rated parts, not any old crap you can find.

You ahve strange definitions of whats legal and whats not. You believe
that if its illegal in californai, it is everywhere. Its not, as far
as i, and the law enforcment personnel i have questioned, illegal
here, where i am, therefore they would NOT throw the book at me. nor
was it, or is it illegal in the UK - its not reccomended there, but
then neither is crossing your arms on the wheel - the action is not
'citeable'. No action can be taken. In other words, it is legal. Do it
during your driving test, and you will get a minor error, not even an
immediate failing error.

but i then save it due to the increased momentum when i come to the
next incline - i need to accelerate later. See later for actual
figures.

still not sold me on this 'full control' thing. I've given two
situations, the ONLY two me and the deputy mentioned further down
could think of.

when am i doing that. repeatedly told you, i don't ride the brakes as
part of coasting. I allow the vehicles momentum to increase - thats
half the point. whats the point of concerving the energy of memntum by
not dumping it in the engine, if you're gong to dump it into the
brakes instead?

by me not having applied. Friends already work there, and i've heard
too many bad stories about what moral,a nd the structure and work
situation is like.

not really. depends on the hill, the situation, my speed, the speed of
the vehicles around me, and a few other facts under my control. As i
noted previously, on the hills i coasted down (LEGALLY) yesterday, the
brakes were not used at all, and the engine was not put back into gear
until a mile after the last hill, when my speed 'boost' from coasting
had diminished.

yes, and a contaminated system is one which has obviously not been
taken care of. Such fluid would boil, and thus make the car fail under
any severe braking condition. It is thus underspecification, and
dangerous. Any brake fluid this highly contaminated with water should
already ahve been changed.

again, you have this assumption, this ERONOIUS assumption, that
1) you are not using the engine to check the speed thus
2) you MUST be using the brakes to perform the same action.

the problem, that you seem to have trouble accepting is that *shock
horror* 2 does not follow from 1. performing action number 1 does NOT
require action number 2 to be followed. Instead of riding my brakes,
checking my speed, I LET MY SPEED INCREASE. the amount is usually
5-9mph, but it is momentum which keeps me going on the flat at a speed
and for a distance that would require me to re-engage the
transmission, and power my engine, meaning it runs on fuel, a time
earlier. can i quantify those fuel consumptiopn figures, no, i can't.

Hows about this way. on those same hills on US19, that i have
previously described, there is a small hill in between two of the
largest. if i go down that hill, in gear, at a starting speed of
55mph, i have to use about 40% throttle half way up that minor hill in
between, in order to stay above 45mph. If I coast down the first hill,
in neutral, at a starting speed of 55mph, i am up and over the small
hill, and 20% or so up the next big hlil before my speed drops to
45mph.Which uses more fuel? 90 seconds at idle, or 30 seconds at 40%
throttle.

of cours,e you say its rubbish, so it must be so. no proof, no
research, one single word. modern brakes are not as simple nowadays as
the brake systems of the 60s and earlier. you do know what 'direct
corrolation' means, don't you? it means there is a very simple,
linearr (no quadratics, or logarythmic functions) equation, of the
form y = kx where k is some constant. charting retardation ability
against temperature.

yes, i notice your phrasing, "*IF* the brakes fade more as the
temperature rises" they do, but its not a straight line graph. You
don't have maximum retardation at 20C, and complete failure at say
300c, and at 150C they're only at 50% strength.

Lets use the tank analagy. Its one often used to illustrate energy
changes. You have a water tank, and you have a tap, or hose, that puts
water into that tank. the water is the amount of thermal energy. if
the tank has a number of perforatiosn in it, to allow the water to
leave the tank, is there any way the hose can be running, and yet the
level in the tank decrease? yes, simply, the amount of water leaving
the tank via the holes, can be greater than the amount brought in by
the hose. its a fitting analagy, since the greater the water level,
the higher the pressure, and the faster the water leaves, same as the
radiative and conductive levels of a body to its surroundings
increases as the thermal difference between the two increases - a fact
easily verifyable with a cup of boiling water, a thermometer, and a
watch - just measure the temperature every minute.

great, thats california, and they have, from experiance, some of the
stupidest, and most politically minded laws there. For isntance, i had
an event out in Long Beach in 99 - mainly gasolene and electricaly
powered vehicles, and the possibility of ONE alcohol powered one.
Because of that possibility, HALF our fire extinguishers had to be
water, and not CO2, because that was state regs. The additive
requirement has already been argued elsewhere on this group in the
last day or two, now they're thinking about (last i heard) certifying
hybrids like the pruis as suitable for carpooling, even with single
occupancy, on the highways. I've already stated elsewhere how modern
diesel vehicles (available in europe, but not the US) get much better
consumption figures than any hybrid can, or does, and yet despite this
easily available, vastly documented fact, the laws are still
considered. One states regulatiosn banning a practice does not hold
for all states. No moreso than, say, west virginia's ban on radar
detectors doesn't make them illegal in the rest of the country.

irrelevent, you've just proved my point. without it, youll have to
double-clutch, taking time, and some thought, meaning att he critical
time, you're not placing full concentration on avoidance, as you're
attempting to match engine RPMs. nor can you, as you have called a
requirement and the whole reason its so illegal, slap it into the
lowest gear possible and let the clutch take a heavier load, dumping
it to rob the vehicle of more speed as the energy is transfered to
rotating the engine fast enough to match the wheel speed, throught he
transmission. In an emergency, as you claim this whole thing is the
reason for, this method slows the vehicle substantially quicker than
double clutching, can, or allowing the automatic gearbox to kickdown
on its own. .

what substantial laod off the brakes? I think my actual experimental
figures show that at best, they'll work as quarter as well as brakes.
however, they make no difference to the braked stopping distance. In
fact, since the braking is so much quickre than the engine-braked
time, the brakes are actually having to dissipate the inertia of the
engine and flywheel AS WELL.

You can't have a connected system slowing down at different speeds.
the engine wants to slow you from 50mph in about 450ft. the brakes
want to slow you from 50mph in 100ft. therefore the brakes must
dissipate 4x the energy of the engine, and so, for each watt of energy
the engine dissipates, the brakes has to dissipate 3 for the engine.

really. then why is it, after 6 heavy braking runs, one after another
(to test distance repeatedly for neutral and in gear) could i still do
a 4 wheel lockup on demand. 6 times I'd dumped excessive amounts of
heat, with little ventalation cooling into the brakes (6 stops from
50mph to 0mph, with the resulting lack of airflow over the brakes that
comes with motion) and they hadn't faded. This was both vehicles. No
standard pads, both vehicles at their standard weights, a bit over if
anything, what with the car seats, vcr, tools+fluids in the van, and
200lb of batteries in the back of the civic (lots of lovely hawker
SBS30's- never know when they'll come in handy). They were hot, yes,
faded, no. Both vehicles had standard pads, regular ones from
autozone, civic's changed in december (all 4, plus master cylinder)
and the caravans in march (front only, plus master cyl). Lovely and
humid here too, so when i check the fluid levels, you can be sure they
get some moisture from the air. Brake lines are original, but don't
appear to have any cracks. Heavy loads, lots of heat, possibly wet
brake fluid, not-new pads, still NO FADE. perhaps you ought to rethink
your theory somewhat. I could even probably work out for you the
approximate brake temps after the first run, if you really wanted. I'm
sure that would be 'hot enough' for you.

well, lets see. i did listen to the engine. under the heavy braking, i
didnt hear it shift once, not in D, or D3 in my civic. Something i
will check tomorow, when its light, is which gears have engine braking
on them. Its something that just poccured to me. The onyl automatic my
father had, was a 1979 ford granada, 2.8 ghia. It had no engine
braking on its 3rd speed.

Oh, i know rain very well, being a brit. i know if a lot better than
you do in Sf. The only time you use or need piower still, is to drive
a car out of a rear-wheel slide, and even then only REQUIRED if its
over a certain angle, 30-45deg, depending on car balance. OR to go
faster. In any other situation, excess of power will not help. dynamic
friction (when a wheel is spinning in comparison to the ground, aka a
skid)) is less than static (the normal driving method) and so an
excess of power would not help, except to provide some form of force
tangental to the slide to correct, or for acceration. I think i've
said these two reasons, these ONLY two reasons enough times, in enough
ways for even you to understand.

i HAD one of theem. A 1986 'rubber band' volvo 340. it wasn't so much
a button that incrased engine braking, it was just one that locked the
transmission ratio to a fixed number. was mainly used for towing, and
hill climbing. I still ahve a 340 in fact, but a 89 manual tranmission
one. Its my work vehicle when i'm in thre UK - love them.

i'm not now, nor have i ever ridden brakes. show me where i said i
have. You're the only one that can't seem to understand that the only
way to coast is to then ride your brakes. Who can't understand that
you can instead let your vehicles momentum incrase, just as if you
were using your accelerator slightly down the hill.

Oh, i understand the concept just fine. Lets see if you can grasp the
more basic one. coasting, does not require riding the brakes. if the
hills incluide is such that you must ride the brakes, you don't coast.
its a judgement thing, Clearly you have no judgement.

Here's another thought to ponder. By your definition, push-starting a
vehicle, is not only illegal, but impossible. illegal because push
starting is, at its basis, coasting, and then putting the car into
gear. This is clearly illegal all over the world, since theres a law
about it in California. Secondly, its impossible because, whilst
caoating, you have your foot on the brake, riding it. You ride your
brakes when people are giving youa push, and they'll wake your ass up
in a hurry.

When you can get THAT concept, that coasting does not require riding
the brakes, that continuance of a limited speed is not the aim, rather
the utlisation of the concervation of momentum, , then by all means
post back. If you still haven't grasped that, then don't bother.

 

To him, it seems the two are one and the same. If you're in neutral
down a hill, you MUST be riding the brakes. Your brakes must also be
in poor condition, have parts replaced with below spec cheap and/or
unsuitable parts, or be from 40+ years ago.

Hes got no clue.

 

In what juristiction are they banned?

Do you have a citation for this?

 

Yup. But the guy's not stupid. His ego is preventing him from admiting a
post-o.

He likes to lecture about safety, then admits he speeds or rides his bicycle

Among other things already mentioned, like a _very_ long, steep, grade is
needed to raise the likelihood of a brake malfunction to something
meaningful.

You're wrong on this one, Jim.

 

Ok, i just spent the last half hour or so getting some figures to
match to my facts.

The difference in values for the figures for a fast emergency stop to
zero, and for riding the brakes was even greater than i thought. and
to vastly simplify the maths (so i comfortably got the entire set of
calculations on s single sheet of paper, i even made many assumptions
in your favour. Lets see them brakes burn!.

I'm using for the vehicle, my 88 honda civic DX - partly since its
relevent, this being a honda group, but also because i had the figures
for it to hand, unlike the caravan, and its been so much longer since
its brake service (which plays to you)

Mass, approximatly 1000KG (2200lb) Its about right, and makes a nice
easy figure for calculations. for the rapid braking, i'll use the
50mph distance from yesterday, but attribute itt o a speed of 55mph -
eases to your argument, since its more energy dumped into the brakes,
and saves me calculating too many values. For the 'coasting and riding
your brakes' which i'll call 'coasting' now, I used the model of the
hill on US19 that i've previously mentioend. cresting the hill at
55mph, in gear the engine braking keeps the speed at 55mph, or
thereabouts, unchecked it gets to about 65mph, in the distances of
about 1 mile. Thus, i'll call the difference in KE between 55mph and
65mph (now see why i picked 55mph as the speed for the braking
distance above) as the amount dumped into the brakes, or engine going
down a hill.

Kinetic energy: (1/2 Mv^2)
brake - 0.5 x 1000 x 24.5872^2 (using meters/sec)
= 302,265.2 J
coast - 0.5x 1000 x 29.6576^2 - 302265.2
= 422172.05 - 302265.2
= 119,906.85 J

Hmm, the coast energy is only just over 1/3 the brake energy. Oh dear,
not looking good for your argument...

Lets see about how much energy per second is put into the brakes per
second. I'm assuming, of course, that the vehicle only has front
brakes. Again, simplifies for me, and is biased towards your claims.

assuming a linear speed decrease - it isn''t, i know, but as its a
quadratic decrease, divide it by your straight line assertation of
brake performance decrease with temp,a nd it comes to a near linear
line

55-0 mph in 100ft is a time of 2.47sec. 55mph to cover 1 mile is 65.44
seconds.
joules per second works out as
brake - 302265.2 / 2.47 = 122374.57 J/s
coast - 119906.85 / 65.4 = 1832.3174

Hang on, notice something there? in one second, the emergency stop has
absorbed more energy than over the entire run of the coast. Odd...

Now, i mentioned temperature just before. how hot will it get? Again,
for simplicity, all the energy is going into heating the brake discs
only. There is NO cooling effect allowed for. This HEAVILY favours
your arguments, and this is where you win through, clearly. The weight
of each brake disc for a honda civic is 10lb, or 4.54Kg. The specific
heat capacity of cast iron is 460J/Kg/K - or, in other words, for
every 460J of energy put into it, 1Kg of cast iron will be raised 1
Kelvin (or 1 Centrigrade) in temperature. Lets dump those energies in,
shall we? Remember, 2 discs, (or rotors if you will) so 9.08kg

lets see then
brake - (302265.2 / 9.08) / 460 = 72.36K rise.
coast - (119906.85 / 9.08) / 460 = 28.70K rise.

Lets say the ambient temperature here in georgia was 90F, or 32.2C. We
add those figures, and what do we get?

brake - 104.2C - 219F
coast - 60.9C - 141F

look att hat, If we used water as our brake fluid, assuming it was run
right onto the disc, it would have boiled.

What are the boiling points for brake fluid?
acording to govt. specs, the WET boiling point of DOT3 brake fluid
(3.7% h2O by vol) is 284F - significantly higher than the maximum
possible temperature of any braking componant in these tests.

in short, your claims and assertations are utter bullshit. I've given
the amth, worked it through. Where i've had to approximate, i've done
so heavily biased in your direction (front brakes only, no cooling,
all temperature udmped into one comonant only) and even then they were
a ways away from failure point. As I said, only very badly maintained
brakes would fail the way you claim happens, and only then if you
heavily ride the brakes as you coast, and if that were to happen,
you'd be a lot more fucked if you had to do any kind of emergency
stop. Just as an aside, any ideas what sort of speed that coast energy
figure represents? just 35mph. So, a car that has the braking from
35mph spread over a mile and still has brake failure - sounds like
you've got a lot of problems there.

thats the brake failure utterly annihilated, even for your claims that
you have to be riding the brakes. AS for 'full control' - the only two
manouvers, as i've said before now, is aceleration (which was what you
were trying to counter with your engine braking anyway) and to correct
rear wheel skids. anything else you do NOt want the application of
power, and thus having the engine connected to the wheels is
meaningless.

hope i've enlightened you with how things actually, numerically work
in the real world, or even in heavily biased 'jim beam world'. If you
can prove any factual, or numerical problems with my figures, then go
ahead, if not, why not act like a man for onec, and actual admit you
were wrong.

 

flobert wrote:
<snip>

dude

if i've been short tempered or even rude, i apologize. i'm really not
interested in personalizing any disagreement, so in future, let's just
try and stick to the tech stuff. and i'm pushed for time right now, so
i'm not in a positon to do a point-by-point review of your posts, but i
hope to get back to you later in the week. meanwhile, other than to say
that your "filling tank" analogy is absolutely on-target and that i
disagree with a lot of your other stuff, check out the following:

http://encyclopedia.laborlawtalk.com/disc_brake
http://www.whnet.com/4x4/brakepads.html
http://www-personal.engin.umich.edu/~jbarber/animation.html
http://www.e-z.net/~ts/ts/Brakfade.htm

 

Whats more to say, the maths is there. Its broken down simply. Its
heavily biased towards your degrees, and it STILL doesn't come close
to your predictions of doom.

Taken a car, made it stop from a faster speed, using front brakes
only, eliminated cooling, eliminated heat dissipation, eliminated heat
spread, and its still only equating a 35mph stop.

you're talking shit. If you can disprove the maths, do so. You can't
get more 'tech stuff' than simple mathematics and physics. You know,
energy calculations. I'm Kinda busy at work myself too - you know, got
car designs to work on, funnily enough, i start work ona braking
system on thursday. The maths though i purposefully kept simple, just
so you could follow it - took me less than half an hour, start to
finish, and that included getting references. Any website you care to
try and use, as a reference will actually detract from your argument.
theyll point out heat dissipation, ablation energy disipation, thermal
transference, ventilation and all those other things which DROP the
temperature of the brakes from the peak temp.

None of this matters though, as you still claim that riding your
brakes as a check speed causes excessive heat buildup and failure. As
i more than amply demonstrated, all things being equal, the braking
energy required to keep a vehicle at a speed when it would normally go
faster is insignificant in reference to any form of sudden stop. in
short you say that putting 1832J of energy into a braking ssytem per
second leads to failure - equivilent to a stop of 2mph.

You'd best get back to work though, must be time for you to change all
the oil at the McD's you work at. You sure as hell don't work in any
technologically related field.

 

Oh, i checked out your links too

Factually incorrect in many areas. A good example was the MMC piece,
which is WAY off the mark. The MMc brakes didn't require a high
temperatureand ran cooler, due to the differing method of ablation
used. The manufacturer is still very much in operator (and theres not
just one, there's many) the reason for the change was for reasons of
cost. The first few thousand were done 'cheap' but after the initally
licensed 2000 sets, the full costs were passed onto lotus. Hence after
chassis number 3700-ish, they switched perminantly back to cast iron
discs. Oh yeah, there was also some question of wet operational
ability.
http://www.elises.co.uk/components/s1/brakes/ is a better link on that
detail, for instance.

A sales page about a new 'type of brakepad' - basically one that has
an integrated anti-squeal shim, whoopie.

This is the only one of any relevence. It does show a disc getting to
the point of DOt3 wet boil after appoximatly 36 seconds. i have sent
an email to Prof barber (and as a fellow brit, he'll help me out
(especially as i believe i have a friend who was studying mechanical
engineering at cambridge at the same time as him) and i'm sure we'll
find that he was putting excessive braking loads throguh a single
disc. I wouldn't be surprised if he was simulating at least twice the
load that i calculated. I'm sure he'll drop an email back to me in the
next day or so.

Drum brakes, utterly irrelevent. Thermal masses and mass ratios, plus
heat dissipation figures are massivly different to those of disc
brakes. Also, unless i'm very much mistaken, drum brakes haven't
provided more than about 40% of braking ability in any vehicle made in
the last 30 years.

in short, what little research you have done has turned up one usefull
page, which is basically a thermal buildup animation, with no
accompanying data. Thus whilst it is contributory, and shows how the
heat builds up, it doesn't explain under what conditions this buildup
of heat over time occurs. Persoanlly, i'm betting its a static jig, as
in no ventilation. Again, we'll wait and see.

 

flobert wrote:

"getting"? you didn't do them yourself?

first, for this to be a safe vehicle, you have to assume max gross
vehicle weight [mgvw]. that's ~3000lbs or 1363kg. the brakes are no
good if they can't stop the vehicle when fully loaded.

that's KE = 0.5 x 1363 x 24.5872^2
i.e. 412,180J from your 55mph velocity.

to clarify & grossly simplify, "coast" is the _additional_ energy that
needs to be dissipated by the brakes if it's not being dissipated by
engine braking.

using mgvw, KE = (0.5 x 1363 x 29.6576^2) - 412,180
i.e. 599,429 - 412,180 = 187,249J is dissipated by engine braking.

not sure you understand the concept, but let's continue...

ok, let's just get back to mgvw, so we have:
412,180J / 2.47 = 166,874W

this is way off. the "coast" is the energy difference. you're not
trying to calculate the energy dissipated by just drifting along, you're
trying to calculate how much difference engine braking makes to brake
temperature.

per the above, if the engine is not braking the car, you need to
dissipate an additional 187,249J / 2.47 = 75,809W. this is a GROSS
simplification ignoring wind, friction, etc., but it'll do for first order.

the running surface of the disk, the bit that gets hot, is less than
that because the 10lbs includes the hub part, not just the rotor. that
does not heat significantly for this first order calc, but hey...

so, with mgvw, that's 412,180J / (9.08lbs x 460) = 99K rise.

with mgvw, that's 187,249J / (9.08lbs x 460) = 45K rise.

that gets /added/ to the rise in disk temp if you're coasting because no
energy is being dissipated by the engine.

make that:
131C for normal braking, and
176C without additional engine braking
but neither are anything too serious given that we're talking single
application.

that's true, for one single stop, from cold. here's where we get to the
point, and where your water tank analogy comes in: you don't just
operate a brake once. for example, like my descent of filbert st,
coming to a halt at each stop sign. each time you brake, you "fill the
tank". particularly if you're at mgvw. now we need to figure out how
quickly is the heat "leaving the tank"? in other words, to what already
existing disk temp are you now adding your delta T? you want to take a
shot at the heat dissipation rate? [hint: it's /less/ than the heating
rate.]

ok, let's get to the links i posted.

if you'd bothered to scroll to the bottom of this page:
http://www.whnet.com/4x4/brakepads.html
you'd see this:
http://www.whnet.com/4x4/pix/hot_brake.jpg

that looks remarkably like a disk that's exceeded 176C to me. how could
that possibly be? [rhetorical]. easy, multiple brake applications that
"fill the tank", just like the one i described to you for filbert st.

and let's look at this:
http://www.e-z.net/~ts/ts/Brakfade.htm
that graphic shows brake fade. you try to assert it's "irrelevant"
because it happens to mention drums, not disks. that's an
extraordinarily incorrect statement considering that the friction
material and the drum material in both systems is identical and their
friction characteristics are temperature dependent in exactly the same way.

disks don't get hot? from:
http://encyclopedia.laborlawtalk.com/disc_brake
we have:
http://encyclopedia.laborlawtalk.com/Image:1901.jpg
now, that's a stretch because it's a racing car driven to the limit, but
the disks still look warm to me. [i initially included the article for
the carbon disk discussion, since you raised them.]

finally, from:
http://www-personal.engin.umich.edu/~jbarber/animation.html
we have the animated disk warming measurement where delta T is shown
settling at 236C after peaking at 242C. this exceeds your worse case
scenario, and still does not approach the temperatures seen in the links
i've just posted. did you notice hot the temp rise starts at 98C?
that's only possible if the time for heat dissipation to ambient is
somewhat slower than the period to brake re-application, i.e. real world
usage.

now, to be fair, i acknowledge that your opinion may be colored by your
never having experienced brake fade, particularly if you live in
flatlands that surround airfields and drive a well-braked car like a
lotus elise, but to say fade does not happen is simply incorrect.

let's just re-state some facts for the record:

1. fade can and does happen.

2. brake heating is exacerbated by not taking advantage of engine braking.

3. fade is partly dependent on brake materials.

4. fade is partly dependent on the rate at which a brake component can
be cooled.

i have personally seen brakes on a normal family sedan glow red after
repeated emergency braking tests. i can personally attest to these hot
brakes exhibiting significant fade. i have cited links that evidence
both fade and highly elevated brake temperatures. if you've never seen,
experienced or don't care to believe, hey, good luck to you.

 

Oh, naturally, i 'get them' in the sense that i ut them on a piece of
paper, and work them out.

as long as the vehicle weights are the same for both calculations,
they cancel out. using MGVW for coasting, and for braking, the 1/2MV^2
for both has the same M, and thus is equivilent. I didn't actually do
the tests at mgvw either, so the braking distances, and so on are not
empyrically correct. If you want to increase the value of m by 30%,
you are free to do that, although it becomes experimentally incorrect,
and will just raise all figures by 30%.

Yes, exactly. At the bottom of the hill, after a coast, i would be
travveling at 65mph. that is what the first of the 3 lines above
calculates. The secondline removes the initial starting energy (ie
that of the car at 55) o give the figure of the third line, or the
energy gain through free coasting.

the 'concept' is that quite simple one. in short, cancelling out 0.5M
we get
55^2 = k (65^2 - 55^2) where k is some constant. this is the raw
difference in energy values. this is the crux of the argument.
3025= k (4225 - 3025)
3025 = 1200k
2.52 = k
the coast energy is 2.52x SMALLER than the emergency stop energy.

no, Lets reiterate what goes on, shall we? going down a hill of 1 mile
length with a starting speed of 55mph. if the engine is left in gear,
the vehicle stays at 55mph. if it is taken out of gear, it reaches
65mph at the bottom. Thus, the energy difference between 55mph and
65mph is dissipated by the engine over that 1 mile. In one second of
braking from 55mph, the amount of energy transfered to the braking
system is greater than the ENTIRE rise in energy due to coasting over
64 secondsLater on, i even calculate for you that the change in
vehicluar energy due to the coast is equivilent to a stop from 35mph.
thats if you want to incease the figures by 30% for 'mgvw' or not,
since mass is purely a linear variable in all the calculations.

an additional amount? wheres this come from? you seem to have just
gone ahead and generated some additional energy value and added it to
the emergency stop value, something to do with engine braking. Is this
the added enegery value required to stop the rotational inertia of the
engine in an emergency stop?

over the 3 seconds of the emergency stop, no it wouldn't. Over the
60-seconds or so of the coast, sure it would. thats more than enough
time to transfer heat.

see, this is the bit i don't get. You've taken the value for a 2.5
second emergency stop, and THEN you've added the 55mph emergency stop
figure. What i'm guessing is that you're assuming someone coasts to
the bottom of the hill riding their brakes, and THEN makes an
emergency stop.thats something completely different, but ok.

and we're talking front brakes only, AND we're discounting the huge
amount of cooling flow you actually get of the brakes during that 60+
second coast, dissipating all that heat in the discs.

So, let me try and understand what you're trying to say. If you go
down a steep hill, in neutral, riding your brakes, and then make an
emergency stop, then accelerate up to a fair speed, and repeat, after
a couple of occasions, your brakes are toast? In that convoluted
situation, then yes, they would be. Is that how you drive down filbert
street, or how you expect i drive down filbert street? as in
[D] 35mph [N] brakes on, ride those brakes, and STOP!
[D] 35mph [N] brakes on, ride those brakes, and STOP!
[D] 35mph [N] brakes on, ride those brakes, and STOP!
[D] 35mph [N] brakes on, ride those brakes, and STOP argh i can't stop
what out people in lombard!!!!!
Don't be a fucking idiot.

filbert street, no. Nurenburgring, silverstone, any race track
application, yes. Normal road use, no. through coasting downa hill,
don't be stupid. Iron gets to around that temperature at around 750C
(1382F) maybe he was coasting down Everest

WEll, i hated to point this out before but ok...
you say just before

176c is 348F. looking at that graph, for quality linings, it seems
that thats in the OPTIMUM retardation range, for a decent quality
shoe. however...

Which this graph CLEARLY disproves. It might be true for cheap low
quality pads+shoes, such as the ones you buy (which you stated
earlier) but *shem*
i /do/ however care if [your] willful ignorance affects /my/ safety on
the road. if [you] careens out of control onto /my/ side of the
freeway and hits /my/ car because [you've bought cheap useless
brakepads] and has lost control because his brakes are toasted, he'd
better make sure he can run faster than me, because i /will/ be upset.

Sorry, just had to change your statement from ealier to reflect my
attitudes, and yours. You buy cardboard brakepads, and then drive like
a bat out of hell down filbert, i will make you regret it.

And what you didn't realise, it seems, is thats those rbakes
functioning at their ideal temperature. Go watch any high end
motorsport, and you'll see that. Cars at LeMans will do that all day
long, and have no problems. These are not running the same braking
systems as you and me on the roads

www.canadiandriver.com/articles/tw/brembo.htm
"Many racing brake systems use discs of carbon composite material
(often misnamed "ceramic") which offer long life, light weight and
exceptional braking efficiency, among various benefits. In race-car
applications, these brakes can glow red-hot under hard use. So far,
only a limited number of exotic sports models offer carbon discs, but
I wouldn't be surprised to see their use widen over the next few
years."

I have yet to get a reply back from the Professor, but bet you that
the disc was completely stationary, and the applied brakepads were
rotated agaisnt it. This makes experimental sense, since that way, the
wires for the temperature sensors don't end up being all twisted, and
you ahve more control over the frictional energies, plus don't require
arotation rig for the disc, and a compression rig for the pads,

Thus there is zero coling due to airflow, which is how modern brakes
are cooled. Again, i point out that it shows vastly increased heat
buildup than even your emergency stop AFTER riding the brakes can
show. at 36 seconds its still a ways hotter than after 66 seconds by
your worst calculation. I think the best way we could give a
qualitative aspect to that is a prelude at mgvw going down filbert
street, with only the front right brake from an 88 civic working.

however, lets not lose sight of what that annimation tells us, and
ONLY what it tells us. under an unspecified (but very large) braking
force, with unspecified componants, non-uniform heat buildup occured
across the face of the disc. thats ALL that says, nothing more,
nothing less. No indication of the materials used, no conditions
listed, Thus inferrence to everyday use is useless, and unwise, since
the relevence to everyday conditions is unknown. In fact, considering
he was testing the pattern of heat buildup, i wouldn't be surprised if
he took all possible efforts to reduce as far as possible the ability
of the disc to cool.

First time i've ever heard of northern/central georgia as flatland.
Nor are 88 civic, or 87 caravan (the two vehicles i did the brake,a nd
engine-braked stops with) elises. In fact, an elise would have
favoured you, since that cars engine is so much bigger in relation to
the vehicles overall weight, on the same hill that engine braking
keeps me at 55 in my two US vehicles, it would actually slow me down
in the elise. Of course, i don't have an elise, and my friend with one
is back in the UK. I am hankering after an atom2 myself (which, in
case you don't know, is the 3rd fastest street legal vehicle around a
track, as tested by top gear, beaten only by the Ferrari F60, and the
F60 based Masserarti MC12, from a supercharged JDM civic type-R
engine,)
Tell you what though, if you think Filbert street is bad, go south a
little to Portola vally, and try Old Spanish Trail. If your brakes
cooked in SF, you'll not make it a quarter-way down that. my friends
who live there (and with whom i sometimes stay when i work in SF)
would surely crash into a ditch, if they drove in the apprantly
reckless and careless way you do. just part of the road (vista verde,
from old spanish trail, or ramona road) is a 1 in 6.8 gradient (worse
than filbert, and its not even half way down). overall its 4.2 miles
from the interstate, averaging 1 in 19

Can happen yes. Does happen, no. not in all but extreme circumstances,
or on badly maintained vehicles.

If the 1800W (the amount engine braking dissipates) in the real-life
coast example, would make such a big difference to your vehicles
braking system, you really need to get it into a shop, and have it
overhauled by professionals. 122KW to stop from 55mph, averaged, and
engine braking is 1.8KW. Its almost 1%.

Persoanlly, i'd ahve lumped these together - 'fade is dependant mainly
on temeprature, energy dissipation, and the frictional materials
used.'

My word, you must ahve a long neck, in order to see the brakes glow
red, AND feel them fade. You ahve just disproved, though, the whole
argument above, and in all other posts. REgular car brakes that glow
red hot have significant fade. Not 'gotten so hot they faiiled, which
is your entire argument about riding the brakes, but 'significant
fade'. Any ideas how hot said brakes were? I'll give you a hint - Cast
iron glows red at about 750-800C (as any machinists handbook will tell
you). That is SO far above the experimental values we have both
calculated above, its not funy, and still, they only had 'significant
fade' They didn't fail, as you claimed coasting would do. Lets see,
using our 'test' vehicle of a civic with only 2 front brakes, no
dissipation to air, 1000K (you might do your brake tests with a couple
of porkers next to you, but i don't) and we're raising 9.08KG of cast
iron from 32C to 750C, lets round off again, and call it 720C (or
Kelvin), and if you think that sort of temperature only builds up on
the surface, you're dreaming - the expansion would shatter the disc.
420j/kg/k for iron...

720*9.08*420 = 2,748,537,792 - thats a LOT of energy.
Its EQUIVILENCE is an emergency stop from well...
KE = 0.5mv^2
(KE/500)^1/2 =
5497075.584^0.5 = 2344.58m/s

about 5244.67miles/hour.Hmm, lets see about 10 runs, eh

549707.5584^0.5=741.42m/s
or 741.44miles an hour.
*thinks* Your sedan wasn't testing thrust SSC's engines was it?

100 runs is 234m/s or 523.44mph.

Either your vehicle was using carbon-based brakes, or you're talking
out of your arse. Considering all your other claims, i'm going with
the latter.

I've experianced fade. I've studied brake systems in length. If yoursa
are failing on you going down filbert street (which isn't that bad a
hill
http://maps.google.com/maps?q=marietta,ga&ll=33.969666,-84.507480&spn=0.008791,0.015819&t=h&hl=en

there's a hill your vehicle will thus fail on. The hills highest point
it at the top right, just at that bend, and it goes downhlil to the
juntion of merrit road, distance is approx 0.58 mile, peak elivation
is 1261ft, 980ft at the bottom, A 1 in 16 slope, compaired to
filbart's 1 in 7.5 slope, its not very steep, but it IS long. and that
is the average grade. and Barnes mill road is overall more than 50%
greater drop. As everyone knows, potential energy is MGh. for the same
car, m and g both cancel, the 50% greater hight drop means 50% more
energy. its also a 40mph road, whilst filbart is a 10 or 15mph road,
if memory serves me. Lets go easy on you and say 20, which is half the
speed, or one quarter the energy.

In short, your maths doesn't add up, your theories show little to no
scientific basis, or enginering basis. You quibble over a weight,
increasing it wholesale by 30%, just to fit your 'worst case' then
suggest that the brakes should be ridden, then an emergency stop, AND
the enegy from riding the brakes applied again (because there was no
engine braking, you say). All this, you claim, is evidence of fade and
failure, and THEN you contradict yourself by saying you've driven a
sedan till its brakes glowed red, and then there was quite a it of
fade. thats after erm, about 688 runs stopping from 200mph, with ZERO
cooling to ambient air, or, by your argument, riding the brakes for a
mile or two down a hill at 55mph.Gee, these figures are not mathcing
up.

Don't give up your day job - good fry chefs are hard to find in SF.

 

Wow .. you guys are writing some long replies in this thread!

I'd like to point out two facts, which may be contrary to an extent to what
each of you are saying:

1) Modern cars do suffer from brake fade (I had a Civic as my last car and
when I drove it like I stole it, there came a point after a few *really*
heavy stops from high speed where the pedal would disappear to the floor
virtually with the pressure before doing anything much - get out of the car
and smell the wonderful baking smell of toasted brake pads!). However, with
a normal person driving it legally, there are very few situations in the
world where it's going to be a worry. OK - some of us live in the Alps and
drive for 15 mins as fast as we can down a hill ... worry! The rest of us
rarely see a hill more than 1km long!

I now have a ATR - no matter what I've done to it so far, it's coped fine.
But then it's got whopping great vented discs that are built to take a
constant heat input and dissipate it as quickly as possible and keep all of
the braking materials at an operational temperature.


2) Driving out of gear is rightly illegal in many places. This is because
you are less in control and less able to respond to any given situation.
The engine breaking is a bonus for those of us who aren't so goddam tight
that we'll do anything to save £1 a year on fuel costs. Many situations
occur where you need to take evasive action and drive out of trouble. A car
is also more stable and "drivable" in gear. If you're coasting around in
neutral, you're doing two things - concentrating less than you should on the
road because you're worrying about keeping your toboggan going fast enough
for your lazy arse not to get back into gear again and perhaps taking risks
by going faster than you should in places to keep up that precious momentum;
and two, you're probably annoying the living hell out of the driver behind
you by driving in an unexpected and erratic manner (too slow at times,
correct or too fast at others), thus increasing the likelihood of a crash
out of frustration from other road users.



Please, guys - life is too short!! There is a reason why coasting is
frowned upon - you don't know better than most driving standards across the
civilised worlds. Also, car brakes are more than able to cool themselves
adequately under normal driving conditions.





al

 

flobert wrote:

but dude, that energy is otherwise dissipated by engine braking. if
it's /not/ being dissipated by engine braking, it's being dissipated by
the brakes.

again, you're mission the point. you still seem having difficulty
grasping the concept that /less/ engine braking means /more/ service
braking, which means higher operating temperatures. you can't just
gloss over it with a dismissive "it's equivalent to coasting 64
seconds". same for mass - clutching at "linearity" is either a
deliberate red herring or conceptual myopia.

ok, this is where i quit arguing with you. if the engine is disengaged,
the energy that would otherwise be lost to engine braking is added to
the energy that needs to be dissipated in the braking system. this is
the 3rd time in a single response that you've fudged this point. the
math is grade school. the science is grade school. if you won't or
can't grasp that concept, sorry, i have no more time for you. have a
nice day.

 

flobert was totally wrong on the rear fog light thing, too. I checked. It
seems the rear fog light in the UK is the sole exception to the "all lights
must work" general rule. The driver's side is the ONLY one that has to work
if two rear fog lights are fitted.

It further seems that there are many MoT testers who are not fully familiar
with their own rules. It is common for testers to fail cars based on their
own personal pseudo-knowledge, and not the actual law, especially when it
comes to older vehicles.

I'm damn glad Ontario has no MoT.

 

ONLY IF THE BRAKES ARE APPLIED INSTEAD.

If/when you coast, you generally don't ride the brakes. If the hill is
steep enough to ride the brakes, then generally you don't coast. Very
simple, point it out like 50 posts back. (after you claimed that you
can't pick the situatiosn you coast in)

The science is grade school eh. Its very grade school. Energy
dissipated by a d15b2 (the one in my civic, which we've been using for
caculations) is 1800W. Doesn't matter how much mass you put in a car,
its 1800W, if you're stopping the car in, or out of gear, those 1800W
don't matter. in fact, if you're stopping it in gear, you end up
loading the brakes MORE since you've also got to stop the rotational
energy of said engine. It can't dissipate any more, or any less. It
dissipates by operating, the energy is used to have the engine
continue to operateat that speed. It takes 1800W to keep the engine at
that speed. If the vehicle speed is producing a load on the engine of
1800W (as the downhill segment does) then the engine dissipates that,
and keeps it at a steady speed, If you then try and suddenly reduce
the engine speed, the engine, which has this great inertia (just try
leaving it idling in netrual, then jam is straight into gear, and see
how much inertia there is transfered to vehicular momentum.

you can't ahve it both ways, you see. the engine braking you attribute
to 'saving the brakes' is loading the brakes up similarly in an
emergency stop when you're not coasting. wheels, transmission, engine,
all connected. when you try and stop, you see, the wheels have an
inertia, the transmission has an inertia, the engine has an inertia
(hell, thats the point of the damned flywheel) In gear, that has to go
somewhere. When engine braking, the momentum of the car is used to
move that, This is what engine braking is. Under REALy braking, its
stoping those same moving parts.

It all comes down to one thing, we've established that you believe
that if you've taken the car out of gear, you must automatically apply
the brakes to do the same job - fundamentally untrue, but it is the
basis of your argument. We then proved, mathematically, under a worst
case scenario, that even riding the brakes at 55mph for a mile, then
an emergency stop, does NOT casuse significant heat rise, that the
riding of the brakes doesn't impart more than a comparitively
minescule amount of energy. If you want to think about it this way,
that coast down the hill, and the sudden stop from 55, is the EXACT
same thing, using our calculation parameters, as a single stop from
the 'free' speed (or the speed of the vehicle had the brakes not been
ridden, nor the car in gear). After all, in the simplistic model we're
using, the instant before the brakes are applied, its KE is equal to
the initial KE and the Pe at the start. Work backwards through your
own figures. In practice, the airflow through the brakes wilst going
down the hill dissipates the heat over the free speed stop.

You stated it was bad, because it was illegal, but could only site the
most knee-jerk of the US states, where laws are made with more regard
to the spin, and the perception, than the actualfacts. (single
occupancy hybrids counting as carpool, the fuel additives are two
examples)

In short, and in conclusion, coasting, and then stopping, the brakes
will recieve the same amount of braking energy. Go down the hill in
gear, the engine will contribute in its momentum what it took from the
vehicles speed, minus a small amount for friction. The higher speed of
the free, will cause greater wind resistance (its a square increase,
like KE) the greater the speed, the greater the air ressitance. so
energy is lost there. increased brake wear, loss of control, you never
did respond with any manouvers or measures in which the engine being
connected was required, except the two i listed. One, the speed up,
runs counter to your argument of being unsafe because you're going
faster, and the other (power application to correct oversteer) can be
avoided by better driving practice.

I will prove this one way or another. This weekend, i will get some
more sensitive measurement devices, some friends, and we'll go and
actually measure the forces, temperatures, etc. I'm willing to put the
theories, both of ours, to the test. We will see then which one is
accurate. I will put my money where my mouth is, will you?