Heavy or Light Braking
Heavy or Light Braking
(OP)
Will you get more brake and tire wear if you quickly apply the brakes or "drag" them coming to a stop say from a set speed of 50 mph??
Obviously - the slower method allows aero and engine braking to help out longer but all things considered - does it make any difference? The theoretical work is the same - so would not the wear be the same??
Just a dumb old Structurual here that likes fooling around with old cars.
Obviously - the slower method allows aero and engine braking to help out longer but all things considered - does it make any difference? The theoretical work is the same - so would not the wear be the same??
Just a dumb old Structurual here that likes fooling around with old cars.





RE: Heavy or Light Braking
From a real-world standpoint? Pretty much irrelevant, particularly since brakes are cheap to replace (compared to engine wear, clutch wear, etc.)
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Heavy or Light Braking
I always get very long life out of brake pads and rotors on my cars.
RE: Heavy or Light Braking
MS
RE: Heavy or Light Braking
Temperature and shear force within the friction material are of greater interest than work. Temperature variation within the material (hot spots) are also important.
RE: Heavy or Light Braking
I am sure it is very dependant on circumstances as to how it nets out at the end of a trip, but late hard braking does save time but costs fuel, tyres and brake components.
Regards
Pat
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RE: Heavy or Light Braking
Yesterday I was talking to a UPS driver and commenting on the fact that every time he sat in his seat he buckled his seat belt. In this instance he was simply backing his truck up to make it possible for me to leave...in his truck for no more than a minute...
Me---"Safety first, eh"?...his reply---"The company has harassed me for taking those extra seconds to buckle up when they thought it not necessary. Time is money"! Fancy that...comes as no surprise, though.
Rod
RE: Heavy or Light Braking
Because 1 the engine is in high revs so no fuel is going in the engine. So more engine braking
2 Aero does more job at high speed.
3 And shorter pressure on brakesputs less heat on them. even though applied harder.
PGP
PGP
RE: Heavy or Light Braking
RE: Heavy or Light Braking
RE: Heavy or Light Braking
RE: Heavy or Light Braking
If there is no traffic and you are on a winding country road, late braking and quick acceleration between curves definitely saves time BUT costs in almost every other variable cost.
A lot also depends on speed limits and compliance to them vs cornering speed. ie If there are frequent large changes in speed you can save a lot of time. If they are infrequent and small, the time becomes insignificant, but the cost also becomes insigifican by about the same factor.
Regards
Pat
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RE: Heavy or Light Braking
The measure of a good driver is not only the number of accidents one has, but also the number of accidents one causes. The societal costs of all those accidents that the late braker leaves in his or her wake adds to the indirect cost of operating a vehicle.
In a completely just world, the costs of accidents that one triggers through selfish driving habits would be in some manner charged directly to that person. As it is, all we can do is remind people that absolutely nothing is done in isolation.
RE: Heavy or Light Braking
Pat: do you actually have orange lights in your area or are you making a funny?
RE: Heavy or Light Braking
There you go. Fixed.
Also, in a no traffic situation how does late braking cause others to have an accident. Even in a heavy traffic situation, it is the responsibility of the following driver to maintain a safe distance as you never know when a emergency stop that has nothing to do with late braking practices might be required by the car in front, like a kid on a skateboard shooting out onto the road or a large animal running onto the road.
Regards
Pat
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RE: Heavy or Light Braking
So, if you see a bullet coming at you, you wouldn't duck? Yes, they hit have hit you anyway, but why wouldn't try to avoid the incident if you can?
TTFN
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RE: Heavy or Light Braking
Heavy braking often goes with heavy acceleration, so that kinetic energy is wasted. No relevance to wear, but bad for fuel economy.
But if the vehicle really needs to stop, why put the brake discs through more of a thermal/stress cycle than they need?
- Steve
RE: Heavy or Light Braking
Norm
RE: Heavy or Light Braking
Wonder if they use a G force sensor to put a shaped f=ma breaking force on the passenger to keep their comfort level at optimum?
I know Lexus LS460's have this laser system, I'd expect all the high end cars do too.
RE: Heavy or Light Braking
Of course the obligation to avoid rear-ending a hard braking vehicle belongs with the car following.
The point is that unless no other cars are allowed to use the road at the same time, driving is not a solitary pursuit; it is a cooperative endeavor.
Any driving style that fails to recognize the neccessity of the cooperative part of the endeavor is selfish. Whether that is using up people's available reaction time in hard non-emergency braking, not being smart enough to figure out the turn signal lever, meandering along below the speed limit, or just in general acting as if no other vehicles exist all come down to selfishness.
Traffic engineering has long recognized that vehicle flow resembles shock waves near critcal velocity; one person stabs the brakes, and each of the following vehicles has to stop progressively harder as the reaction time cushion is used up, until some poor sap, ten vehicles behind, and who was following at a reasonable distance is presented with a total speed change that is cumulatively impossible to handle.
Talking about the mechanical engineering aspects of hard braking in a race environment is one thing, but talking about the mechanical engineering aspects of non-emergency habitual hard braking on public roadways without simultaneously talking about the traffic and human factors engineering aspects seems irreponsible.
I'm sorry if that view offends anyone, but as Engineers, aren't we trained to look at the whole picture?
RE: Heavy or Light Braking
Elsewhere in another thread, I posted that at one time I lost a LR wheel on my MG-TD and stopped to pick up all the brake shoes and parts to reassemble the LR wheel/drum. Well, there is always a bit more to the story...This instance happened just over the crest of a road bridge over a RR track...four lanes. While I was quickly putting it all back together I could hear (over the crest of the bridge) a series of screeching brakes and loud collisions. Several. I'm pretty sure they never knew what caused the stoppage.
Now, today, as a result of this and many other such cases, I always keep an eye on the mirror. It's a religion born from many years as a race car driver, in part. As a driver of the Socal freeway system, to boot.
In racing, I have a reputation of going into a corner deeper than my competition...Perhaps it's true, dunno. I do know that I am NOT a proponent of very late, heavy braking, race track or street. It creates handling problems on the track and excessive wear and tear on the street...In addition to the increased possibility of being rear ended!
Rod
RE: Heavy or Light Braking
The law, in California anyway, allows assignment to the car in front, if its deemed that the front car's actions or inactions directly caused the accident.
TTFN
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RE: Heavy or Light Braking
You must travel at a safe distance. If you rear end someone who was not travelling backwards, you where clearly not travelling at a safe distance.
I also use the mirrors a lot. In fact I found the most enduring unsettling aspect of driving a LHD (being used to RHD) car was not seemingly instinctively knowing exactly what was going on behind me as the subconscious mirror glances found no mirrors.
My point is that driving styles that save time also often increase other operating costs and the drivers and possibly other occupants time is a significant cost.
Of course consideration of others (if they are present) should be taken into account even if it has no impact on the costs, which is what this thread is about.
Regards
Pat
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RE: Heavy or Light Braking
It's just not the most sensible method to consistently get from point A to point B without the emotional impact.
I'm not a saint. I learned the hard way and I'm just pointing out that after a 52 year racing career and somewhat longer driving career, I learned a couple things. Not trying to be preachy...lord knows I have little room for that. Just "fore warned is fore armed" kinda thing.
Rod
RE: Heavy or Light Braking
I think it's all a matter of degree and on the time and place and how much time might be saved and how much it costs.
Regards
Pat
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RE: Heavy or Light Braking
I love my racing. I love the competition. I love being twenty something even if it's only for a half hour. I really dislike the long tow to the races...but...I think I dislike riding while someone else is driving even more.
Oh well.
Rod
RE: Heavy or Light Braking
Possibly, but I'd argue that most of these are invariably mitigated by planning and allocating sufficient time. I won't deny that I'm sometimes guilty of procrastination and insufficient planning, but I've decided that these risks just aren't worth it. In most cases, we're talking about a few minutes difference, and that allowing for sufficient time and contingencies makes for a more serene and less hectic trip.
It seems that too many people thrive on the adrenaline high of being late and having to rush. But cutting corners is bad in business and bad in your personal life.
TTFN
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RE: Heavy or Light Braking
Time is money is part of that equation.
How much time is saved at what cost is the point. I am not saying how that nets out, in fact I think I said something like I don't know how it nets out and it will vary with circumstance, but it is an economic argument that should be considered in a purely financial analysis. What constitutes a good driver or a comfortable or safe trip is not part of the financial analysis.
Regards
Pat
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RE: Heavy or Light Braking
- Steve
RE: Heavy or Light Braking
What happened to the exchange on motorcycle "stoppies" etc.?
Was that this thread? Where did the replies go? Did I hallucinate the whole thing?
RE: Heavy or Light Braking
The basis for this claim is false. There is no such thing as a person, following at a safe distance, being presented with a speed change that is "cumulatively" impossible to handle, because the speed change is not cumulative. If you are following somebody, they may need to come to a full stop at any point in time (the aforementioned kid in the street, or wild animal, or otherwise). You need to leave space for your reaction time coupled with the maximum rate at which they could decelerate. If you do this, no occurrence in front of you will cause an accident.
Furthermore, Pat (and others) was not recommending (I do not think) that people practice late braking in the form of full-on, traction limited, ABS-active braking for every light, stop sign, and curve. Rather, he was (presumably) advocating simply braking somewhat later and somewhat harder than average, still leaving a significant margin for increased braking if/when necessary. This is a far cry from your "example" of somebody pounding the brakes and causing a pileup.
There is really no reason for the high horse regarding driving style.
RE: Heavy or Light Braking
It depends on your definition of "safe driving distance". Is it defined as enough distance to come to a complete stop should the person ahead of you slam on the brakes, or is it defined as enough distance to come to a complete stop if something were to suddenly appear in front of you?
Two situations:
1) You're at distance 'X' from car ahead of you. They slam on the brakes and skid (or slow down) over some distance 'Y'. You waste a bit of reaction time before hitting your own brakes, but you come to a stop without hitting them. Distance 'X' is a safe distance. Distance 'X' had enough buffer space in it to take care of your reaction time.
2) Same distance 'X' between you and the person ahead of you. A concrete pipe rolls into the road. The car ahead hits it and basically stops dead in its tracks. You hit your brakes after the same reaction time, but this time you slam into the back of them.
In case #2, I would call that being "presented with a total speed change that is cumulatively impossible to handle."
Just a thought...
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Heavy or Light Braking
The scariest situations I've experienced involve a sudden drop in visibility on freeways due to rain burst or brush fire. You should slow down immediately, but you know that if you do, someone will rear end you.
RE: Heavy or Light Braking
Two urgent decisions.
1) Where the *&^% is the road ahead vs where is the rock face and where is the ravine.
2) Where can I SAFELY park this thing within coasting range as all engine power went with the lights.
Turned out the battery cable had gone open circuit between the wire and the battery terminal fitting.
It all turned out alright so maybe we sometimes have more safety factor than we think. Also sometime a bit of luck helps.
Regards
Pat
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RE: Heavy or Light Braking
This is also known to Morris Mini drivers as the "Mr. Lucas - Prince of Darkness" effect.
RE: Heavy or Light Braking
Rod
RE: Heavy or Light Braking
So, if you stab the brakes for a short enough time without generating the heat necessary to cause wear, then would that not be easier on the friction surfaces then lightly holding the pedal long enough to cause heat buildup?
Late braking is up to the driver, unless you're not being considerate. ie, coming up hard on someone at a light, or a pedestrian at a crosswalk. This can be very stressful because they're not sure if you're going to stop or not.
As far as someone behind you; its completely the responsibility of that driver to maintain distance. If they can't see what's going on and that you're intending to brake late, they're not paying attention, watching your bumper and not the road, or tailgating a higher performance vehicle beyond their vehicles capacity, as in motorcycle. Either way, the onus is on the following vehicle..
Don't tailgate!
RE: Heavy or Light Braking
I doubt that bikes are inherently better-braking machines, given similarly grippy tires (and rider skill with respect to managing/avoiding stoppies). More that the sort of person who rides a bike in the first place tends to drive in a shall we say more enthusiastic manner, and that it is more difficult when following one to tell just how rapidly it is shedding speed. A bike simply doesn't get as "wide" visually as you approach it as anything else you're ever likely to be behind in traffic.
Norm
RE: Heavy or Light Braking
RE: Heavy or Light Braking
The kinetic energy is converted to heat at the interface between the moving and the stationary friction surfaces; that heat then soaks into the bulk of the lining and rotor materials.
Because all materials have a thermal time constant, the bulk of those materials can't instantly be at thermal equilibrium with the interface surfaces. From this, it seems that the higher the rate of heat input into the interface surfaces, the higher the temperature of the thin layer of lining or rotor material closest to the heat input, and consequently more ablation.
Yes; total heat input into the lining and rotor is based on change in kinetic energy, regardless of rate of change. Average temperature of the materials some time after braking action has ceased is probably likewise independent of rate of speed change.
The instantaneous temperature of the infitesimal layer of friction materials making up the interface, and consequently wear, is likely strongly dependent upon rate of heat input.
RE: Heavy or Light Braking
Obviously, many other factors enter into the equation, not the least of which is "engine braking". Cars driven gently will usually outlast ones that are driven aggressively.
Exceptions to the 'rule'? You bet, especially considering the desperate build quality of some aftermarket parts.
Rod
RE: Heavy or Light Braking
Regards
Pat
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RE: Heavy or Light Braking
I make a point to get the brakes nice and hot about once a week. I never have rotor rust issues.
RE: Heavy or Light Braking
RE: Heavy or Light Braking
Norm
RE: Heavy or Light Braking
Slightly off the subject - the early model VN Commodores have noticeably shorter brake pad life than comparable cars due to the lack of engine braking caused by the overdrive top gear in the automatic gearbox.
RE: Heavy or Light Braking
But my VW pads certainly get hot now and then
Fe
RE: Heavy or Light Braking
Fe
RE: Heavy or Light Braking
RE: Heavy or Light Braking
Dan - Owner

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RE: Heavy or Light Braking
It is usually not linear, from my understanding. As we heat the material the rate of removal of particles also increases.
So say the MMR in braking from 50mph to 0 in 5 seconds is 12mg/min, the MMR for braking from 50mph to 0 in 20 seconds may be 8g/min.
This is my understanding of this.
Fe
RE: Heavy or Light Braking
Second, The difference in the 'braking per unit time' concept mentioned above is heat. Heat is usually the enemy of most everything. I think I remember that the wear rate of brake material goes up significantly as material temperatures increase.
If you are asking this question because you have drum brakes, the cooler you keep the drums, the longer you have brakes. If they are Disc's, then the preceding doesn't hold true.
If you have an older vehicle and you haven't changed the brake fluid in your lines and calipers (or cylinders) heat can boil the moisture that your brake fluid absorbs and then you have no brakes whatsoever. I've had that fun at least twice in my life at the most inopportune times, usually on some mountain pass with a vicious name like Wolf Creek Pass or one of his sisters. Terrifying.
Funny how the thread changed from technical to philosophical a while back.
rmw
RE: Heavy or Light Braking
Funny, though...your first paragraph sounds like me in the late 50's talking to my 50 something year old dad!!! I was into sports car racing where brakes were much better than production cars of the era. Now, all I drive are antiques in which I always "gear down"...Full circle...bet he's smiling.
Rod
RE: Heavy or Light Braking
You have become your Dad.
rmw