good comparison! but here's the difference: i don't care if he wastes his money on excessive oil changes. really. i /do/ however care if his willful ignorance affects /my/ safety on the road. if he careens out of control onto /my/ side of the freeway and hits /my/ car because he's been coasting in neutral 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.
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.
eh?
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.
On 8/20/2005 2:34 PM jim beam spake these words of knowledge:
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
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."jim beam" wrote
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.
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?
rubbish.
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.
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 in heavy traffic. Go figure .
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.
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
On Thu, 25 Aug 2005 22:35:35 GMT, "al" wrote:
Yeah, i tend to get a bit frothy at the mouth when i see sloppy thinking touted as fact. Comes from my nature i guess. and my father, who as a rally driver, and mechanical engineer, often tried and forced me into arguments just be sure i know my stuff. He was a hard bastard, but he really drummed into me how to make a complete and concise argument, which should bend to your opoonants view as much as is reasonable, in order to prove how silly it is. This is something i do a lot of. Since part of my job involves prototyping vehicles, for various uses, safety systems are where my priority lies, mainly in overestimating them - Half the time, i'm the one inside (if i won't ride it, its not safe enough)
not at any kind of grade, no. one of the worst of that length that i do quite regularly, is the 0.85mile one 9about what, 1.2km) which averages a 1in16, just north of atlanta. We've both given examples of a steeper one, but much shorter (some 0.3km only). You are someone who's had real wold practical experiance with heavy braking, hills and fade, or lackthereof.
Yep, brakes dissipate lots of heat when the vehicle is in motion - something we deliberately removed from the calculations, primarally because i have no way to measure, but also because it leans to Jim's side (see above)
Here i'm not too sure. We agree that about the only use being in gear has, is accelerating, or 'driving out' of a situation. Avalanches, yes, not situations you'll see on either cost of the US though, where we are. If it were really that important to accelerate, I'd be changine gears anyway, for a lower one, for better acceleration, if a tornado is comming (a more common risk over here at least, 4rth or 3rd would be a better gear to aceclerate in, than the 5th gear i'd be in for the cruise down the hill.
i wouldn't say its unpredictable, or 'less concentrating' though. When keeping the momentum up, you end up glacing at the speedo, yes, (but isn't that the point of all those speed cameras, to make you watch your speedo!) but putting it into gear from neutral is no more involved than just changing gear, after all, in a manual car, part of changing gear is 'coasting'. Eratic speeds don't match either, since i will put it into gear to keep my speed to a point i set myself at. i'll aim to keep that speed above that minimum regardless. downhill you'll be going faster, not slower, so you'll be leaving those brake riders, or engine brakers behind. (assuming of course, they don't either coast, or accelerate down the hill themselves).
I've fuond that only a few palces actually BAN coasting, or at least make it a ticketable offence. Many others frown on it, the same way corsing your hands on the wheel, or changing gear ina corner is fornw upon. Of course, there is something i've been longing to say, but have avoided it hoping someone else would. Automatic hgearboxes, in the main, do not offer any form of engine braking at hgiher speeds, in higher gears. Lock them into 2, or ! and they will, but regular D, nope. "Many automatic transmissions use overrunning or one-way mechanical clutches to transmit power through the transmission. These devices make upshifts smooth because only one clutch has to apply during a shift instead of one applying and another releasing (the overrunning clutch releases automatically). The disadvantage of overrunning clutches is that they can only transfer torque one way so they provide no engine braking." (source
Just for the record, I have an '03 Toyota Corolla that was bothering me for some time until I finally realised that it downshifts from overdrive when the brakes are applied (fairly hard) going downhill. I haven't determined exactly why it does it (that, the parameters of when it happens), but it definately does downshift.
Hello, I just wanted to let people know that plan to coast their vehicles down hill that it causes more WEAR on the transmissions. It also causes more WEAR on the clutch. In other words, if you two people have the same type of cars, the person that coasts down the hills is more likely to have to have the transmission or clutch repaired or replaced than the other person that did NOT coast down hills. Jason
You said this early as well, and then, as now, you gave nothing to back it up.
Murphy's Law and common sense. The more that a transmission or clutch is used, the more likely it is to develop problems. That's one of reasons that most people trade in or sell their cars after they are three or four years old. They know that those older cars will have more problems than a new cars will have.
Hmm ... I still think you understate the usefullness of being in gear. A car looses certain handling characteristics when out of gear too - hard to explain, but from trying both, it certainly feels less surefooted without drive.
When you change gear, you really don't coast - you momentarily interrupt drive. If you stay out of gear, it takes time to react, grab the knob, get it in gear (you'll probably miss if you panic) and drive away. Much better to be in gear in the first place. Sometimes just a small bit of throttle is needed to minimise risk - not quite the live/die evasive action scenario you refer to.
I get what you're saying, and you're defending against an opinion that goes too far the other way, but I still don't think you should coast - it's kinda lazy driving. That in conjunction to the points above to me means you could be slightly (not a lot, but a little) more likely to suffer misfortune than if you didn't.
So to sum up, I agree and disagree with you both, on separate points ;p
a
While that is literally true, I'm not so sure it's particularly relevant. In the scheme of things, clutches take a lot of wear. How many times you change isn't nearly as important as how often you pull away in 1st/2nd and how badly you change gear!
Also, new cars have problems because they're new and unproven, which can often equal the problems of older cars - particularly on reliable models.
a
Hello, Those cars don't develop problems due to WEAR. They develop problems due to other problems. New cars are covered by warranties. The issue in this case is the extra WEAR that is caused by over use of the clutch and transmissions. If people want to do it--just don't be shocked when you have to spend several thousand dollars replacing the clutch or transmission. Jason
Dont it for years, in mainly older cars. Only in one have i had to replace transmissions/clutches - my 89 mg metro twin turbo, snapped clutch cable, and once i also overfilled the engine with oil a bit - those engines are real finicky, as the oil is also shared with the gearbox. it seeped out and into the clutch itself. took about an hour or twos work, to clean the oil off the plates, a few hundred miles of driving,a nd it was good as new.
i think you minsunderstand just whats going on. In coasting, the cluthc is used to disengage the transmission, as it would be in changing gear. it is then left out of gear, meaning that the wheel side is going at the road wheel speed, as is ormal, so no difference in wear there, and the engine side is going at the engine speed, which is lower, thus LESS wear there. Struggling to see how this increases wear myself...
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