Brake Question
Brake Question
Hotshot
Joined: Jul 2005
Posts: 11,931
Likes: 180
to slow the vehicle down from lets say 60 MPH takes a given amount of energy. if you stop fast, all the energy goes thru the brakes. if you stop slow, the vehicle will loose some of the energy thru rolling resistance and motor deceleration. take your foot off the gas at 60 mph and coast for 30 seconds---- if you dropped lets say 10 mph, that is energy that did not go into the brakes.
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Senior User
Joined: Dec 2005
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Steve, That wasn't the question. I personaly drive like I'm in a 18 wheeler, I start coasting way before I come to a red light. I can't even remember the last time I had to come to a complete stop at a light. The question is, which generates more heat, or rather which is harder on the rotors. I wish I had one of those laser type temp guns to check it.
Mike, or to build up heat.
Someone needs to check this out for us.
Mike, or to build up heat.
Someone needs to check this out for us.
Senior User
Joined: Dec 2005
Posts: 159
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If you were to graph it I'm guessing there would be a cross over were temp at the rotors is equal. No idea where that is, but in general the harder you apply the brakes the more friction is produced between the pads and the rotors and friction generates heat. On the flip side the longer the brakes are applied the more friction and heat will be generated. For what it's worth, I think longer braking is a better idea. The rotors will be able to dissapate the heat more easily and there will be less dramatic effects on the rotors. Heating and cooling the rotors rapidly will be more likely to cause them to warp given that they will expand and contract just as rapidly.
Hotshot
Joined: Jan 2004
Posts: 19,760
Likes: 1,079
From: St Louis
If the brakes were doing ALL of the work in slowing the vehicle, there is no difference in the the heat generated by slow/easy vs. fast/hard. You are still converting the exact same amount of kinetic energy into thermal energy.
The dissipation of this waste heat, on the other hand is a different matter.
Over a slow/easy stop's time span, the heat will have a better chance to dissipate and will likely result in a lower peak rotor temperature than would a fast/hard stop.
Steve
The dissipation of this waste heat, on the other hand is a different matter.
Over a slow/easy stop's time span, the heat will have a better chance to dissipate and will likely result in a lower peak rotor temperature than would a fast/hard stop.
Steve
Postmaster
Joined: Sep 2002
Posts: 3,077
Likes: 1
From: None of your business
Originally Posted by projectSHO89
If the brakes were doing ALL of the work in slowing the vehicle, there is no difference in the the heat generated by slow/easy vs. fast/hard. You are still converting the exact same amount of kinetic energy into thermal energy.
The dissipation of this waste heat, on the other hand is a different matter.
Over a slow/easy stop's time span, the heat will have a better chance to dissipate and will likely result in a lower peak rotor temperature than would a fast/hard stop.
Steve
The dissipation of this waste heat, on the other hand is a different matter.
Over a slow/easy stop's time span, the heat will have a better chance to dissipate and will likely result in a lower peak rotor temperature than would a fast/hard stop.
Steve
Basicly you don't have a sharp, rapid temperature swing.
Mike
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Hotshot
Joined: Jun 2003
Posts: 12,334
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From: SW VA
Rub your hands together real fast for a long period of time with light pressure. Now, push you hands together with force, and rub them together real fast.
That will give you an idea...
That will give you an idea...
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Senior User
Joined: Dec 2005
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From: Piney Point Shores, Md
More than you wanted to know
WORK = FORCE X DISTANCE = Force thru a Distance
Usually measured in Horse Power which is -
550 lbs per Ft Per Second or 33,000 Ft lbs per min
However In the question as stated:
Work = Work done on the rotor to slow it down which is converted to "BTU'S of Heat energy"
While it does not solve for a specified problem because many variables are not known such as inirtia, velocity, mass, surface area, heat transfer coefficients to name only a few;
The elementry application would indicated Fast & Hard i.e. (Max Force X (thru) distance ) would yeild Max Btu/Sec developing the greatest differential Temperature (Deta T) across the rotor or Maximum Temperature.
More useless trivia...
1 HP ~43 BTU's
1BTU Will increase 1 lb of water 1 Deg F
<TABLE cellSpacing=2 cellPadding=5 border=0><TBODY><TR><TD align=right>IF you really need to calculate it, (LOL) the formula below is a starter<TD><TR><TD><TD><TR><TD>
<TD></TD></TR></TBODY></TABLE>
(Sorry, it's what 10 years of teaching in a vocational school will do to you)
Usually measured in Horse Power which is -
550 lbs per Ft Per Second or 33,000 Ft lbs per min
However In the question as stated:
Work = Work done on the rotor to slow it down which is converted to "BTU'S of Heat energy"
While it does not solve for a specified problem because many variables are not known such as inirtia, velocity, mass, surface area, heat transfer coefficients to name only a few;
The elementry application would indicated Fast & Hard i.e. (Max Force X (thru) distance ) would yeild Max Btu/Sec developing the greatest differential Temperature (Deta T) across the rotor or Maximum Temperature.
More useless trivia...
1 HP ~43 BTU's
1BTU Will increase 1 lb of water 1 Deg F
<TABLE cellSpacing=2 cellPadding=5 border=0><TBODY><TR><TD align=right>IF you really need to calculate it, (LOL) the formula below is a starter<TD><TR><TD><TD><TR><TD>
<TD></TD></TR></TBODY></TABLE>(Sorry, it's what 10 years of teaching in a vocational school will do to you)
Last edited by smecomark1; Feb 1, 2006 at 02:20 AM.
Posting Guru
Joined: Jan 2000
Posts: 1,899
Likes: 1
From: Cullman Alabama
Originally Posted by smecomark1
WORK = FORCE X DISTANCE = Force thru a Distance
IF you really need to calculate it, (LOL) the formula below is a starter<TD><TR><TD><TD><TR><TD> <TD></TD></TR></TBODY></TABLE>
(Sorry, it's what 10 years of teaching in a vocational school will do to you)
IF you really need to calculate it, (LOL) the formula below is a starter<TD><TR><TD><TD><TR><TD>
<TD></TD></TR></TBODY></TABLE>(Sorry, it's what 10 years of teaching in a vocational school will do to you)
She probably knows by now that it's better not to ask you any questions. She wont understand the answers anyway.
I saw some stone carvings on a cave wall once. They looked a lot like that formulae.
Tuned
Joined: Mar 2003
Posts: 498
Likes: 18
From: Santa Fe
Other benefits with "slow" braking would be the pads should last longer with less brake force, and fuel saving while the foot isn't applied to the gas pedal. As well as it's safer to drive that way, minimize the chance for collison if "fast" brake is applied, thus lowering the insurance premiums. 