Why Do Cars Have Brakes?

http://www.devjoy.com/2013/02/why-do-cars-have-brakes/

by galaktor • 13 years ago

50 97 13 years ago

brudgers• 13 years ago

The analogy between automobiles and software testing can be extended to consider the racing line - the combination of velocity and distance through a corner which results in the fastest time.

http://en.wikipedia.org/wiki/Racing_line

makira• 13 years ago

Which brings me to the point that the steering wheel is much more important than brakes. Being able to go faster because of brakes is not very useful if you are heading into a wall.

ygra• 13 years ago

Well, you can still stop before hitting that wall. Steering might be of little use if you're going fast and approaching a dead end with walls on either side.

ynniv5• 13 years ago

We're on the verge of realizing trail braking and heel toe in software development!

digitalWestie• 13 years ago

If people knew how to drive efficiently they'd use gears to do this and only use brakes to stop. Just sayin'

__alexs• 13 years ago

I'd like to see a gearbox that can get you from 120 mph to 0 in less than 3 seconds.

cuu508• 13 years ago

Well, that's not driving efficiently!

k00pa4• 13 years ago

So, everytime you slow down you need to go from 120mph to 0 under 3 secs? On that situation brakes are useful.

When you need to go from 50mph to 30mph you dont need brakes at all.

Toucan5• 13 years ago

How would that be efficient?

Engine braking wears transmission components which are considerably more fragile and expensive than replacing brakes. Engine braking only stops you using the driven wheels, brake discs apply to all wheels.

mpyne3• 13 years ago

Engine braking allows you to save fuel (by using stored energy of the drivetrain to handle compression of the air that normally would require work from combustion).

And, as long as the car remains in gear there's not much extra wear on the transmission itself (certainly not compared to the torque from the acceleration the preceded it, at least).

ferongr• 13 years ago

>Engine braking wears transmission components

No it doesn't. Synchronized, rev-matched downshifts put negligible load on the drivetrain. Coasting to a stop with the gear already selected, putting it in neutral just before stall does that even less. The stresses produced by acceleration are ballpark estimate around an order of magnitude greater. This can be inferred by the fact that usually the rate of deceleration by engine braking is smaller than the rate of acceleration for a given gear ratio, ergo, the drivetrain is strained less.

jamesjguthrie8• 13 years ago

Using gears to slow your car uses more fuel vs just braking.

Just saying / rant over / other clichéd sign off.

k00pa4• 13 years ago

Fuel usage is 0 when you slow down without brakes... When you use brakes your engine needs fuel to idle. (Assuming you are using manual transmission, and on automatic you can force down the gear to do the same.)

jamesjguthrie8• 13 years ago

Note: perfectly matching revs while downshifting isn't using your gears to slow; it's just slowing.

X-Istence13• 13 years ago

Has the art of using the engine to slow down become so unknown that it is no longer considered a way to slow down a vehicle?

monochromatic3• 13 years ago

It's not nearly as effective as braking.

k00pa4• 13 years ago

I can drive without using brakes at all... And I do slow down.

Brakes are when I need to slow down fast.

X-Istence13• 13 years ago

In most cases though if you pay attention to the road and the conditions around you, engine braking can be used quite effectively, and it is not as jarring as braking using the brakes. This helps when you've got friends/family that easily get car sick, mainly due to the jerky motions from people hitting the gas too hard, and slamming on their brakes.

I use my engine to brake about as much as I use my brakes. It provides for a smoother ride overall.

That being said, engine braking tends to only work really well with stick shifts...

roel_v6• 13 years ago

Only works on stick shifts.

mpyne3• 13 years ago

It also works on automatics that can be command-shifted, which are becoming somewhat more common.

TorKlingberg• 13 years ago

Some automatic transmissions allow the driver to force a lower gear to engine break. It is not used as often, but can be useful in long slopes to avoid overheating the breaks and reduce wear.

monochromatic3• 13 years ago

Every automatic I've ever seen allows you to shift to a lower gear.

AUmrysh2• 13 years ago

My auto Mazda 3 has 'manumatic' shifting, and you can downshift to slow down in it. I guess it's not really the same though as the computer does a lot of shifting and timing for you even in manumatic mode.

sageikosa• 13 years ago

Ford Freestyle with continuously variable transmission. Revs the engine way up on downhills.

X-Istence13• 13 years ago

And every single last automatic. Besides D there is always a couple others, like 1, 2, 3 that are used for getting out of sticky situation or when you need a lot of torque... those also apply for engine braking.

Do I suggest engine braking in an automatic in the general case? No, generally because the torque converter isn't too happy unless it was specifically designed for it. However if you are going down a steep mountain you better downshift even in an automatic and use the engine, or when you get to the bottom your rotors will be glowing red, your brake pads will be disintegrated, your brake fluid will be boiling and your car will be smelled from miles away.

Yes, I have seen people brake all the way down the I-70 coming over the vail pass in Colorado, and it isn't pretty... if it doesn't break everything your rotors are going to be warped completely...

hackmiester2• 13 years ago

If this was written by an American, yes. I don't know many people who know what "engine braking" is. A very slightly higher number of people I know are capable of driving a standard shift vehicle. Most people know what a manual transmission is, but not everyone.

ry0ohki• 13 years ago

This was my first thought too. People use their brakes way too much (and usually because they drive automatic transmissions)

Isamu• 13 years ago

The US is a big place. Those who live in mountain states certainly know to downshift rather than burn out their brakes.

eitland2• 13 years ago

We hardly have automatic transmissions in Scandinavia, in fact I had to explain it to my wife just the other day when she were using a rental car.

Also you have to use manual in driving schools including at the exam or you will get a second class license that only counts for automatic cars.

jamesjguthrie8• 13 years ago

It was completely frowned upon in my driving education (around 7 years ago) - and my driving school was/is the most popular in the UK.

I always do a combination of down-shifting and braking as this saves fuel vs purely engine braking and I'm using my brakes what they were designed for; and you don't ever want to try emergency braking with cold brakes.

k00pa4• 13 years ago

Something wrong with your driving education then...

TylerE2• 13 years ago

You're more or less totally wrong, in a modern car.

Under overrun conditions (e.g. engine braking - driveshaft turning the engine, essentially), a modern engine totally shuts off fueling completely, so engine braking alone is always a MPG win, as zero fuel consumption is less than idle fuel consumption with the clutch in.

Also, brakes these days are so good that you really NEED anti-lock. The limiting factor in stopping is the grip of the tire.

georgefox3• 13 years ago

> I always do a combination of down-shifting and braking as this saves fuel vs purely engine braking...

Assuming your car is reasonably recent, engine braking doesn't use significant fuel. See http://en.wikipedia.org/wiki/Engine_braking#Legal_implicatio....

lutusp• 13 years ago

> Has the art of using the engine to slow down become so unknown that it is no longer considered a way to slow down a vehicle?

Most cars now have automatic transmissions, and in many such cars the habit of slowing down by downshifting will destroy the transmission's bands and wear down the rear differential, neither of which is designed for the stress caused by downshifting.

I'm not speaking hypothetically -- I mostly drive manual transmissions and I'm accustomed to downshifting to slow down. I then acquired a car with an automatic transmission, but didn't change my behavior. Within 20,000 miles I had destroyed the transmission and the rear differential.

monochromatic3• 13 years ago

I drove a motor scooter as a kid that had broken brakes. He's right--it wasn't much fun, because I knew I couldn't go fast.

barrkel• 13 years ago

And by extension, my scooter has ABS brakes, which means I can go faster in the wet.

adam-a• 13 years ago

The premise is surely nonsense! The full logic ought to go: Why do we have cars? To go faster. Why do cars have brakes? In order to slow down again.

If all we were concerned about was going fast then why ever slow down? Cars need to regulate their speed in order to provide safety, and also so they are usable, if I can't stop then I can't get out at my destination. Many elements of a car help in it's overall function, which is to go fast, but you may as well say the purpose of a fan belt is to go fast. Brakes are a part of a car and saying that their purpose is the same as the whole car is useless and confusing. They have a specific purpose within the machine.

From the linked article: "[the] answer feels paradoxical which usually means there's a deep truth". Indeed. The simpler explanation is that it's pure twaddle.

alexkus• 13 years ago

It's just one possible result of applying "two whys" and then not stating the answer to the first why.

michaelt• 13 years ago

  if I can't stop then I can't get out at my destination.

Different people seem to have different interpretations of this question. My interpretation was: Why have brakes instead of coasting to a stop? Coasting to a stop is popular with drivers who are 'Hypermiling' [1] - and bicycles used in velodromes don't have brakes [2].

While this isn't consistent with Richard Dalton's blog post (if you coast to a halt, you wouldn't need to throw your children out of a moving vehicle) but it isn't inconsistent with Jon Jagger's blog post, which Dalton credited as his inspiration.

[1] http://en.wikipedia.org/wiki/Energy-efficient_driving#Accele... [2] http://en.wikipedia.org/wiki/Velodrome#Bicycles_and_track_de...

rdtsc• 13 years ago

To really add breaks where you can stop while running without blowing completely up you need to add fault isolation and tolerance in your system. You need to use actors and messages (you might get parallel execution as well depending on your algorithm as a bonus).

The alternative is to prove that your program won't crash. So you need to write in a very restrictive style. This is more like you need to be able to compute a path your car will take ahead of time given all the other obstacles that could get in its way. That works too but it is highly impractical.

atc• 13 years ago

What a load of shit.

robotic• 13 years ago

analogies gone wrong -- terribly wrong

codeulike• 13 years ago

Why dont the lightcycles in Tron have brakes would be a better question.

ynniv5• 13 years ago

Wow, a silly brain teaser AND a strained metaphor. I'll never hear the end of this one!

bazzargh• 13 years ago

Overextending the analogy, there's no brakes on track bikes but they go fast too. They don't need them, the fixed gear means applying counter pressure on the pedals stops the bike.

The clunky software analogy would be to do with lightweight simplicity.

ilcavero• 13 years ago

I wonder if car technicians go around making weak analogies with software development to justify their industry practices. Something like: "Why do software developers have compilers? blah blah blah, and that's why we need to keep your tools organized"

wikwocket• 13 years ago

Why do computers have virus scanners? They only serve to slow down the computer and to block some programs from running. This is contrary to the goal of a computer, which is to run programs! But by blocking evil programs, the good ones can run faster, with less disruption.

...and that is why we change our motor oil.

eitland2• 13 years ago

My expeerience is they mostly wants to know as little as possible about computers. Computers are necessary evils to most craftsmen I can think of. And I kind of understand them.

abraininavat• 13 years ago

This is ridiculous. The typical "stoner effect" -- a phrase that sounds in some way deep or metaphysical causing susceptible people's neurons to flare, producing only the word: "Woah..." I know this is probably controversial, but in my opinion it's the same effect that causes people to find deep meaning in a Jackson Pollock painting.

As others have pointed out, lots of fast things don't have brakes, because they don't need to stop. As I don't think others have pointed out, slow things have brakes too, such as the space shuttle transporter.

SatvikBeri• 13 years ago

You're certainly right in that there are logical flaws in the article. But the stoner effect is useful (and dangerous) because it's much better at creating changes in beliefs/behavior than rational argument. It's a pattern worth understanding because you can use your understanding to defend yourself, or use parts of the effect to communicate your ideas and convince others.

The book Switch[1] goes into more detail about what actually works when you're trying to get people to change. I highly recommend it if you're interested in Psychology or Marketing.

[1] http://www.amazon.com/Switch-Change-Things-When-Hard/dp/0385...

lazyant• 13 years ago

Even my parody "Ten Reasons Why Building a Startup is Like Riding a Motorcycle" has more meat than this :-) http://lazyant.com/post/37406994081/ten-reasons-why-building...

AUmrysh2• 13 years ago

When I was on my company's R&D team, we were looking at possibly designing a car. One of our ideas was regenerative braking (nothing new, I admit). Basically, you can use several types of pump or motor as a generator when run in reverse. This allows you to collect that energy back into the system instead of wasting it all as heat. It also has the added benefit of turning the rotational kinetic energy into stored potential energy, thereby slowing down the vehicle. Our design still included disc brakes for safety, but would have used the regenerative braking most of the time.

Why Do Cars Have Brakes?

Related Stories