so what destroys brakes...
12-11-2003, 04:17 PM
#2
Copy & Paste Moderator
This is a hard question to answer. You'll probably get answers that say one or the other is worse. Auto magazines get this question occasionally too. Basically, full-on hard stops wear breaks faster. Now, during regular breaking, shorter versus longer stops aren't better or worse. Simply using your breaks wears them out and eventually they will need to be replaced (I bet you know that already 
). Harder stops are harder on the rotors (ex: warping), and longer stops are harder on the pads (more pad wear).
--VIP1
). Harder stops are harder on the rotors (ex: warping), and longer stops are harder on the pads (more pad wear).--VIP1
12-11-2003, 06:07 PM
#4
Friction generates heat. The longer you generate heat, the worse it is on brakes.
Pressure plays a very small part of the equation.
10 seconds @ X amount of pressure generates a given amount of heat
5 seconds @ 2X amount of pressure generates less heat because of duration.
Pressure plays a very small part of the equation.
10 seconds @ X amount of pressure generates a given amount of heat
5 seconds @ 2X amount of pressure generates less heat because of duration.
12-11-2003, 09:12 PM
#6
Yes .. that has been my experience.
Another example ... a clutch disc.
Which lasts longer ....
A clutch where you very slowly let out the clutch, slipping it for several seconds or letting out the clutch pedal rapidly (not dumping it, mind you)?
Another example ... a clutch disc.
Which lasts longer ....
A clutch where you very slowly let out the clutch, slipping it for several seconds or letting out the clutch pedal rapidly (not dumping it, mind you)?
12-11-2003, 09:45 PM
#7
TECH Resident
Join Date: Dec 2001
Location: Mehlingen, Germany
Posts: 937
Likes: 0
Received 0 Likes
on
0 Posts
just plain *** over heating the brakes is the destroyer of pads and rotors. Normal braking methods you will have no problems , this vs. that for normal braking and you will not see any difference. This has been a big debate for big rigs going down mtn grades for ages. And ther is diffent opinions . Do iuse the brakes constantly going down the hill to check my speed with light pressure , or do I Apply firm pressure and release to check my speed. Bottom line gotta beable to dissipate the heat , or trouble is brewing ahead.
Trending Topics
12-12-2003, 09:08 AM
#8
On The Tree
Join Date: Jun 2002
Location: Doniphan, MO
Posts: 155
Likes: 0
Received 0 Likes
on
0 Posts
Try this if possible. Find a long, relatively steep hill, like the last 10 miles of the "Grapeline" going north as you drop into the cenrtal valley of CA.
Start down the hill @ 70 mph, put the car in neutral and 'ride the brakes', using them to keep your speed constant @ 55mph for a couple of miles if possible. (Hard to do on the grapevine, the trucker's will run over you )
Repete the experiment, only this time, slow to 55 then take your foot off the brake, when you get back up to 65, slow again to 55, etc. over the exact same distance and tell us how much brake you have left at the end!
My educated guess is you'll have more in the second case.
Start down the hill @ 70 mph, put the car in neutral and 'ride the brakes', using them to keep your speed constant @ 55mph for a couple of miles if possible. (Hard to do on the grapevine, the trucker's will run over you
)Repete the experiment, only this time, slow to 55 then take your foot off the brake, when you get back up to 65, slow again to 55, etc. over the exact same distance and tell us how much brake you have left at the end!
My educated guess is you'll have more in the second case.
12-12-2003, 10:08 AM
#9
Originally Posted by mitchntx
Friction generates heat. The longer you generate heat, the worse it is on brakes.
Pressure plays a very small part of the equation.
10 seconds @ X amount of pressure generates a given amount of heat
5 seconds @ 2X amount of pressure generates less heat because of duration.
Pressure plays a very small part of the equation.
10 seconds @ X amount of pressure generates a given amount of heat
5 seconds @ 2X amount of pressure generates less heat because of duration.
Hmmm....I'm not so sure about this one (of course, Mitch and I can never seem to agree...
). The hotter a brake pad gets, the more it wears. Meaning, a fast, hard stop will build a higher peak temperature. I say this because brakes are in the heat dissapation business. They are designed by nature to radiate heat to the air for cooling. During a stop, the brakes are radiating some of that heat as it is being added to the rotors. Meaning, a long "easy" stop (like lightly dragging the brakes on a slight hill) may add less heat than the brakes can dissapate and therefore cause very little temperature rise in the system as a whole. However, running down that same hill and making a "panic" stop from the 90 mph that you may be doing will add a lot of heat to the rotors quickly, this can shock the rotors and cause surface checking (small cracks) as well as heating the pads to a temp where they will be more prone to wear more quickly. However, it all depends on the severity of the stop and the thermal capacity of the brake system in question. Meaning, it is a very individual, situation specific, judgement call. In my opinion anyway....
As always, just my thoughts (I could be wrong....
)
12-12-2003, 03:10 PM
#11
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
The total heat energy generated in the brakes is the
kinetic energy of the car, that you have to scrub off
to stop. From a given speed, that energy is constant.
The faster you stop, the faster you put heat into the
rotor and pads. Heat is also extracted by air cooling and
some conduction to the wheel (more air cooling, but
further away and some heat mass to soak up transient
thermal input). Heat removal goes mainly with temp
and cooling airflow (see brake ducts, etc.). It does
not care how fast you are adding heat, except as the
temperature rises you shed more.
Brake component temperature is going to be higher with
faster braking than slow braking because the heat added
increases faster than the heat removal rate does.
Energy to be dumped goes as speed squared. Hauling
down from 100 to 60 dumps over 2X more heat
than 80 to 60.
The clutch analogy is not really very close. With the
clutch, you very rarely would run the engine full open
and sand the clutch until zero slip at redline. You would
let it grab once you are onto the power band. The
brakes, however, you don't ever lock up (unless you
took out ABS; then, your brakes would see zero heat
and your tires would take it instead, and maybe the
undercarriage as you traverse the ditch....
kinetic energy of the car, that you have to scrub off
to stop. From a given speed, that energy is constant.
The faster you stop, the faster you put heat into the
rotor and pads. Heat is also extracted by air cooling and
some conduction to the wheel (more air cooling, but
further away and some heat mass to soak up transient
thermal input). Heat removal goes mainly with temp
and cooling airflow (see brake ducts, etc.). It does
not care how fast you are adding heat, except as the
temperature rises you shed more.
Brake component temperature is going to be higher with
faster braking than slow braking because the heat added
increases faster than the heat removal rate does.
Energy to be dumped goes as speed squared. Hauling
down from 100 to 60 dumps over 2X more heat
than 80 to 60.
The clutch analogy is not really very close. With the
clutch, you very rarely would run the engine full open
and sand the clutch until zero slip at redline. You would
let it grab once you are onto the power band. The
brakes, however, you don't ever lock up (unless you
took out ABS; then, your brakes would see zero heat
and your tires would take it instead, and maybe the
undercarriage as you traverse the ditch....
12-12-2003, 03:25 PM
#12
As mentioned, a 3600 lb car at 60 mph has a measureable amount of kinetic energy. It will always be the same amount of energy. So, if I have to absorb "X" amount of heat, the faster I try to absorb it, the more the temp will rise. This is again based on the consideration that brakes will dissapate some heat during the stop (if you stop from 60-0 in 800 feet, you will not put much heat into the brakes, but do it in 100 feet and temps will be much higher). Also, the longer you take to stop, the more engine braking will occur as well as speed being absorbed by tires and friction (air drag and such as well). Now, with all that said, we are down to splitting hairs at this point. I doubt you are going to make many 800 foot stops from 60 mph, so it is only applicable as an engineering example. I also doubt that you will "do 90 mph to the traffic light and hammer the brakes at full ABS engagement". So, I guess you should just drive it and let the brakes dust where they may....
I'd think that moderate braking would be easier on parts than panic stops, but who makes every stop a full ABS event? So, I think we are overanaylizing this problem to the point of losing focus on the actual point. You must stop the car and you won't save enough money in brake pad wear to justify all the concern over the wear rate, so I'd not be too worried about it.
My thoughts....
I'd think that moderate braking would be easier on parts than panic stops, but who makes every stop a full ABS event? So, I think we are overanaylizing this problem to the point of losing focus on the actual point. You must stop the car and you won't save enough money in brake pad wear to justify all the concern over the wear rate, so I'd not be too worried about it.
My thoughts....
12-12-2003, 11:17 PM
#13
Id Also Say The Pad Compsistion Has Alot To Do With Which Method Is Better Id Bet (not Being A Break Expert) That All Pads Have A Sweet Spot And A Reccomended Temp Range Exceeding That Is Probally Exxessive Wear So.... Id Think Its Situational But Whit Stock Stuff Id Go For Moderate Stopping Force With Not Long Times Of Holding While With Good Aftermarket Stuff Id Go Fast N Hard...just A Guess
12-13-2003, 10:04 PM
#14
TECH Apprentice
iTrader: (1)
Join Date: Jan 2003
Location: Charlotte, NC
Posts: 355
Likes: 0
Received 0 Likes
on
0 Posts
Roy, I glad that we have our brakes b/c we don't really have to worry about it too much. i beat the hell out of my brakes and they still work just like the first time i put them on my car.