Racing Brake Pad / Brake system discussion/questions
07-17-2014, 12:36 AM
#181
Rennlist Member
Thread Starter
what are the thoughts on a 2 piece rotor that is somewhat thermally isolated to the hat, and thus the hubs and bolted on wheels. ( a lot of mass there) is there a drawback in cooling if you have everything stock, where the rotor is a huge heat sink, vs just the rotor skinny track, taking and trying to dissipate all the heat. has anyone gone to a 2 piece rotor and had thermal issues?
I got to get that variable temp paint. we have a lot of testing to do here, i can tell!
I got to get that variable temp paint. we have a lot of testing to do here, i can tell!
07-17-2014, 09:27 AM
#182
The purpose of two piece rotors is to allow the friction surface to expand and contract without being bound to the hat. In a one piece rotor, when the friction surface heats up from use, it expands, but it is constrained by the rigid attachment to the hat and this can make it warp. An added bonus, is the the hat can be made of aluminum and the two piece rotor can be lighter than the one piece.
Also, thermal mass is the wrong way to think about this. You don't need thermal mass, you need efficient transfer of heat away from the brakes. Thermal mass will only help with short and relatively rare heat loads. Track loads are not like that. All added thermal mass does is delay the inevitable if there is insufficient heat transfer to shed the energy away from the brakes.
Indeed, a key difference between pedestrian street brakes and "racing brakes" is this ability to shed heat. Take just about any bone stock grocery getter and do a panic stop with it. In that first stop, the brakes will perform *very* well - on par with a lot of high performance track cars. The difference is the track brakes can do it over and over and over again while the stock brakes will decrease in performance and perhaps overheat.
BTW, I really do think you are over thinking this. The concepts are simple:
-Mike
Also, thermal mass is the wrong way to think about this. You don't need thermal mass, you need efficient transfer of heat away from the brakes. Thermal mass will only help with short and relatively rare heat loads. Track loads are not like that. All added thermal mass does is delay the inevitable if there is insufficient heat transfer to shed the energy away from the brakes.
Indeed, a key difference between pedestrian street brakes and "racing brakes" is this ability to shed heat. Take just about any bone stock grocery getter and do a panic stop with it. In that first stop, the brakes will perform *very* well - on par with a lot of high performance track cars. The difference is the track brakes can do it over and over and over again while the stock brakes will decrease in performance and perhaps overheat.
BTW, I really do think you are over thinking this. The concepts are simple:
- Lighten the car as much as possible.
- Use rotors as large as possible.
- Lose any brake dust shields (doubt if you have those)
- Get air to the backside of the rotor at the hub where the rotor vanes can draw it in.
- Profit.
-Mike
07-17-2014, 09:41 AM
#183
Rennlist Member
Mark, I think you would argue that war is good and orgasms are bad, just to argue & hear yourself speak.
Believe what you want to believe. Pontificate as you see fit to salve yoru own ego. Ignore all of the REAL WORLD experience from all the folks here, who have been there/done that, as well as from subject matter experts like Mr Walker. Extract that tiny tidbit that you believe justifies your comical arguments while ignoring and deriding all the body of actual evidence to the contrary.
Have fun in T2 of Laguna, son.
Believe what you want to believe. Pontificate as you see fit to salve yoru own ego. Ignore all of the REAL WORLD experience from all the folks here, who have been there/done that, as well as from subject matter experts like Mr Walker. Extract that tiny tidbit that you believe justifies your comical arguments while ignoring and deriding all the body of actual evidence to the contrary.
Have fun in T2 of Laguna, son.
07-17-2014, 10:18 AM
#184
Mr. Excitement
Rennlist Member
Rennlist Member
The purpose of two piece rotors is to allow the friction surface to expand and contract without being bound to the hat. In a one piece rotor, when the friction surface heats up from use, it expands, but it is constrained by the rigid attachment to the hat and this can make it warp. An added bonus, is the the hat can be made of aluminum and the two piece rotor can be lighter than the one piece.
Also, thermal mass is the wrong way to think about this. You don't need thermal mass, you need efficient transfer of heat away from the brakes. Thermal mass will only help with short and relatively rare heat loads. Track loads are not like that. All added thermal mass does is delay the inevitable if there is insufficient heat transfer to shed the energy away from the brakes.Indeed, a key difference between pedestrian street brakes and "racing brakes" is this ability to shed heat. Take just about any bone stock grocery getter and do a panic stop with it. In that first stop, the brakes will perform *very* well - on par with a lot of high performance track cars. The difference is the track brakes can do it over and over and over again while the stock brakes will decrease in performance and perhaps overheat.
BTW, I really do think you are over thinking this. The concepts are simple:
-Mike
Also, thermal mass is the wrong way to think about this. You don't need thermal mass, you need efficient transfer of heat away from the brakes. Thermal mass will only help with short and relatively rare heat loads. Track loads are not like that. All added thermal mass does is delay the inevitable if there is insufficient heat transfer to shed the energy away from the brakes.Indeed, a key difference between pedestrian street brakes and "racing brakes" is this ability to shed heat. Take just about any bone stock grocery getter and do a panic stop with it. In that first stop, the brakes will perform *very* well - on par with a lot of high performance track cars. The difference is the track brakes can do it over and over and over again while the stock brakes will decrease in performance and perhaps overheat.
BTW, I really do think you are over thinking this. The concepts are simple:
- Lighten the car as much as possible.
- Use rotors as large as possible.
- Lose any brake dust shields (doubt if you have those)
- Get air to the backside of the rotor at the hub where the rotor vanes can draw it in.
- Profit.
-Mike
Mark. Add cooling and check / fix as needed the bias were offered up as answers to your original question. Do you think cooling and bias are likely issues with your car?
You seem to like to ask a question or present an idea then argue with those that bother to spend their time to offer up answers or rebuttals. Not just this thread but many that you are a large part of.
KB MO. One size fits all.
Ask question or post idea.
Accuse those that spend the time to offer up answers/insights that MK is not looking for as our need to boost our egos, then retreat into back and forth on some unimportant little detail. (KV, heat paint and the like)
Skip over or argue with any information counter to your pet idea/answer. an example for this this thread would be about all the cars with higher KV than yours that are not having brake issues under even harsher conditions that you present.
Focus on your own often mostly hap-hazard data gathering as proven givens to be used to dismiss the offered info from others. An example is "I did 2 laps with no brakes and it still did it so it is not a cooling issue"
Don't take any steps recommended and check back with results. Just argue round and round about some footnote. The good of your threads is mixed into the head scratching, double facepalm rendering go-round and arounds are some good info and links, offered up by others.
Not an ego boost just an observation. Please carry on.
07-17-2014, 10:42 AM
#185
Ironman 140.6
Rennlist Member
Rennlist Member
A tedious thread that's almost Ghettoracer worthy.
If one only wants to endlessly pontificate it should be done in the proper forum.....
https://rennlist.com/forums/hey-wait...ing-forum-146/
If one only wants to endlessly pontificate it should be done in the proper forum.....
https://rennlist.com/forums/hey-wait...ing-forum-146/
07-17-2014, 11:33 AM
#186
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Mark, I think you would argue that war is good and orgasms are bad, just to argue & hear yourself speak. Believe what you want to believe. Pontificate as you see fit to salve yoru own ego. Ignore all of the REAL WORLD experience from all the folks here, who have been there/done that, as well as from subject matter experts like Mr Walker. Extract that tiny tidbit that you believe justifies your comical arguments while ignoring and deriding all the body of actual evidence to the contrary. Have fun in T2 of Laguna, son.
07-17-2014, 02:06 PM
#187
Rennlist Member
Thread Starter
The purpose of two piece rotors is to allow the friction surface to expand and contract without being bound to the hat. In a one piece rotor, when the friction surface heats up from use, it expands, but it is constrained by the rigid attachment to the hat and this can make it warp. An added bonus, is the the hat can be made of aluminum and the two piece rotor can be lighter than the one piece.
Also, thermal mass is the wrong way to think about this. You don't need thermal mass, you need efficient transfer of heat away from the brakes. Thermal mass will only help with short and relatively rare heat loads. Track loads are not like that. All added thermal mass does is delay the inevitable if there is insufficient heat transfer to shed the energy away from the brakes.
Indeed, a key difference between pedestrian street brakes and "racing brakes" is this ability to shed heat. Take just about any bone stock grocery getter and do a panic stop with it. In that first stop, the brakes will perform *very* well - on par with a lot of high performance track cars. The difference is the track brakes can do it over and over and over again while the stock brakes will decrease in performance and perhaps overheat.
BTW, I really do think you are over thinking this. The concepts are simple:
-Mike
Also, thermal mass is the wrong way to think about this. You don't need thermal mass, you need efficient transfer of heat away from the brakes. Thermal mass will only help with short and relatively rare heat loads. Track loads are not like that. All added thermal mass does is delay the inevitable if there is insufficient heat transfer to shed the energy away from the brakes.
Indeed, a key difference between pedestrian street brakes and "racing brakes" is this ability to shed heat. Take just about any bone stock grocery getter and do a panic stop with it. In that first stop, the brakes will perform *very* well - on par with a lot of high performance track cars. The difference is the track brakes can do it over and over and over again while the stock brakes will decrease in performance and perhaps overheat.
BTW, I really do think you are over thinking this. The concepts are simple:
- Lighten the car as much as possible.
- Use rotors as large as possible.
- Lose any brake dust shields (doubt if you have those)
- Get air to the backside of the rotor at the hub where the rotor vanes can draw it in.
- Profit.
-Mike
so, warping not an issue.
sure, always great to have less weight, but to your point. if that one spot on the track is where the heat problem is, and i have that much more thermal mass, do you think if i had a two piece rotor, (all other things being equal), ill make the problem worse? im trying to absorb your last paragraph. my brakes work great at all the other tracks.. even racing at laguna in a 50min race. they dont get worse, the pedall doesnt get long. no issues, except, turn 2 turn in point. I get that fade, and if i go to a two piece, will that part get worse? maybe to your point, all that heat soaks into the center portion...... it doesnt efficiently dissipate due to it being steel and already being heated. (although i did have that one test where i started out very cool), and this prevents the heat build up at the turn 2 turn-in point to dissipate and we get fade.
you say, the stock rotors are good at sheding heat, the very first time. welll, they are doing the job based on how i use them and the crude cooling i do have, but the problem is one narrow point of the track, and ive tested going into that segment cool , or during a 30min race..... the problem is still there and doesnt change by starting temp levels.
I dont think im over thinking it. i have a fade in a very narrow point of the track, and from the performance window. no problem at all at sears, or other tracks, just laguna, turn 2. a factor of why i think this is, is the KE im asking to dissipate is just plain larger. the fastest we get at sears is 120mph down to the same turn in speeds. the problem doesnt show, because the change in KE is much lower. 120 to 60 vs 130 to 60mph at laguna. alll other points in the track , (laguna) there are no issues at all. brakes are firm and slowing is done at the limit of the tires, even slicks!
to your last points:
I have no dust shields. very open. mounted to light wheels as welll, so i have a HUGE heat sink, but no direct ducting, only reflective.
lightening the car , i believe (see next post) wont help and unless you can fight the physics there, i dont think lightening will help with the issue, but surely will lower the lap times, which is great. BUT, its a side bar discussion, as i cant go any lighter. (well, changing out the brake rotors will help with 10lbs a side, so thats 20lbs and that would be nice too) I also dont want to save 20lbs, witih a two piece, if i make my particular problem worse.
1. getting some ducting installed. (dont think that will do much because the problem is in such a narrow performance area, but will try.)
2. getting double the bias installed as well to the rear. (also dont think that wiill help much, due to the total performance potential of the rear brakes for a car decelllng at 1.5 to 2g.
3. I believe the performance of a 12.6" rotor has found the limit here. I think going larger would help a lot and most here would agree. more surface area, less pedal pressure, more torque for same pedal pressure, all in direct proportions. would solve the grooving problem for sure for the ST41s.
07-17-2014, 02:18 PM
#188
Rennlist Member
Thread Starter
A tedious thread that's almost Ghettoracer worthy.
If one only wants to endlessly pontificate it should be done in the proper forum.....
https://rennlist.com/forums/hey-wait...ing-forum-146/
If one only wants to endlessly pontificate it should be done in the proper forum.....
https://rennlist.com/forums/hey-wait...ing-forum-146/
thank you
Mark, I think you would argue that war is good and orgasms are bad, just to argue & hear yourself speak.
Believe what you want to believe. Pontificate as you see fit to salve yoru own ego. Ignore all of the REAL WORLD experience from all the folks here, who have been there/done that, as well as from subject matter experts like Mr Walker. Extract that tiny tidbit that you believe justifies your comical arguments while ignoring and deriding all the body of actual evidence to the contrary.
Have fun in T2 of Laguna, son.
Believe what you want to believe. Pontificate as you see fit to salve yoru own ego. Ignore all of the REAL WORLD experience from all the folks here, who have been there/done that, as well as from subject matter experts like Mr Walker. Extract that tiny tidbit that you believe justifies your comical arguments while ignoring and deriding all the body of actual evidence to the contrary.
Have fun in T2 of Laguna, son.
This. But this was discussed on the first page and too simple and math free to be the answer. IIRC mark posted some images of his front brake setup with stock shields in place and little to no added brake cooling other than some A arm type scoops.
Mark. Add cooling and check / fix as needed the bias were offered up as answers to your original question. Do you think cooling and bias are likely issues with your car?
You seem to like to ask a question or present an idea then argue with those that bother to spend their time to offer up answers or rebuttals. Not just this thread but many that you are a large part of.
KB MO. One size fits all.
Ask question or post idea.
Accuse those that spend the time to offer up answers/insights that MK is not looking for as our need to boost our egos, then retreat into back and forth on some unimportant little detail. (KV, heat paint and the like)
Skip over or argue with any information counter to your pet idea/answer. an example for this this thread would be about all the cars with higher KV than yours that are not having brake issues under even harsher conditions that you present.
Focus on your own often mostly hap-hazard data gathering as proven givens to be used to dismiss the offered info from others. An example is "I did 2 laps with no brakes and it still did it so it is not a cooling issue"
Don't take any steps recommended and check back with results. Just argue round and round about some footnote. The good of your threads is mixed into the head scratching, double facepalm rendering go-round and arounds are some good info and links, offered up by others.
Not an ego boost just an observation. Please carry on.
Mark. Add cooling and check / fix as needed the bias were offered up as answers to your original question. Do you think cooling and bias are likely issues with your car?
You seem to like to ask a question or present an idea then argue with those that bother to spend their time to offer up answers or rebuttals. Not just this thread but many that you are a large part of.
KB MO. One size fits all.
Ask question or post idea.
Accuse those that spend the time to offer up answers/insights that MK is not looking for as our need to boost our egos, then retreat into back and forth on some unimportant little detail. (KV, heat paint and the like)
Skip over or argue with any information counter to your pet idea/answer. an example for this this thread would be about all the cars with higher KV than yours that are not having brake issues under even harsher conditions that you present.
Focus on your own often mostly hap-hazard data gathering as proven givens to be used to dismiss the offered info from others. An example is "I did 2 laps with no brakes and it still did it so it is not a cooling issue"
Don't take any steps recommended and check back with results. Just argue round and round about some footnote. The good of your threads is mixed into the head scratching, double facepalm rendering go-round and arounds are some good info and links, offered up by others.
Not an ego boost just an observation. Please carry on.
so, yes, i will be cleaning up the duct work, and ive said, i dont think it will work due to the amount of heat at the end of the straight, and yes, going into it cold, doesnt help, so its a heat issue in a 2 second range. sounds like more power than air flow can help, but thats a feeling, not fact. its why im bringing it up for discussion.
thanks for the post.
07-17-2014, 02:25 PM
#189
Rennlist Member
Thread Starter
Mark, I think you would argue that war is good and orgasms are bad, just to argue & hear yourself speak.
Believe what you want to believe. Pontificate as you see fit to salve yoru own ego. Ignore all of the REAL WORLD experience from all the folks here, who have been there/done that, as well as from subject matter experts like Mr Walker. Extract that tiny tidbit that you believe justifies your comical arguments while ignoring and deriding all the body of actual evidence to the contrary.
Have fun in T2 of Laguna, son.
Believe what you want to believe. Pontificate as you see fit to salve yoru own ego. Ignore all of the REAL WORLD experience from all the folks here, who have been there/done that, as well as from subject matter experts like Mr Walker. Extract that tiny tidbit that you believe justifies your comical arguments while ignoring and deriding all the body of actual evidence to the contrary.
Have fun in T2 of Laguna, son.
why didnt you bother to quote the second sentence in your "Friends" article? its telling of your motivation here. you dont want to help, you want to self promote.
read the article again and let me know if Mr Walker would condone your interpretation of his article or mine. for those playing at home... Mr walker said basically, (paraphrasing), heat is due to the mass of the vehicle, and a factor of 4x due to speed if the speed is doubled. (just after he quotes the KE equation). I found nothing in contraction to my claim that going lighter is not a solution for solving a heat problem in your brakes. (unless of course, you want to run the same lap times, or brake at the same points with the same force and duration) This is borderline common sense. Your a smart guy.. you should know better!
https://rennlist.com/forums/11513120-post180.html
and OH GOD Dave, he even says, "more importantly" when he starts to talk about speed (velocity) relative to the heat issue. "He", your friend, your article, says that speed is more important..... DUH!! its a squared function Dave. wake up!!
http://www.stoptech.com/docs/media-c...raking-systems
07-17-2014, 02:51 PM
#190
Mr. Excitement
Rennlist Member
Rennlist Member
please, go away if you have nothing to contribute here.
thank you
your the only one that can have your OWN information tossed back to you and you still fall back to your "army" of exeprts and friends information that you clearly have misinterpreted. you maybe a really good instructor for teaching the art of car control, but you have no clear of how and why things work, based on your last comment and this subject. I challenge you to really take my next response to any knowledgeable entity, and contradict anything i have said. Its coming next. if you can prove im wrong I will end this thread now never to bring it up again, until ive made the changes the list has provided here.
Kurt, yes, I willl admit is easy to get derailed here to fight the ego maniacs. stilll puzzeled over their motivation. but not to digress. I get your point. I understand that this is a cooling issue. whether this is directing more air to cool the brakes, or using them less with more rear bias, OR, they might just be being asked to do more than they can do. Thats why i asked. instead, i get nonsensical testimonials of others running faster laps. we as racers know how almost unrealted this is to my problem. what i need is the same KE lost by the brakes, of similar size. if someone else is doing it, im good. to hear of a 2000lb 360rwhp car, running the lap times that anderson is runnning there (poc champ, 1:31 lap time), doesnt do me any good, even if he is running 322mm rotors, becuase there are more differences to the forces on that lap, than similarities to my issue. KE down that main straight comes to mine first!!
so, yes, i will be cleaning up the duct work, and ive said, i dont think it will work due to the amount of heat at the end of the straight, and yes, going into it cold, doesnt help, so its a heat issue in a 2 second range. sounds like more power than air flow can help, but thats a feeling, not fact. its why im bringing it up for discussion.
thanks for the post.
thank you
your the only one that can have your OWN information tossed back to you and you still fall back to your "army" of exeprts and friends information that you clearly have misinterpreted. you maybe a really good instructor for teaching the art of car control, but you have no clear of how and why things work, based on your last comment and this subject. I challenge you to really take my next response to any knowledgeable entity, and contradict anything i have said. Its coming next. if you can prove im wrong I will end this thread now never to bring it up again, until ive made the changes the list has provided here.
Kurt, yes, I willl admit is easy to get derailed here to fight the ego maniacs. stilll puzzeled over their motivation. but not to digress. I get your point. I understand that this is a cooling issue. whether this is directing more air to cool the brakes, or using them less with more rear bias, OR, they might just be being asked to do more than they can do. Thats why i asked. instead, i get nonsensical testimonials of others running faster laps. we as racers know how almost unrealted this is to my problem. what i need is the same KE lost by the brakes, of similar size. if someone else is doing it, im good. to hear of a 2000lb 360rwhp car, running the lap times that anderson is runnning there (poc champ, 1:31 lap time), doesnt do me any good, even if he is running 322mm rotors, becuase there are more differences to the forces on that lap, than similarities to my issue. KE down that main straight comes to mine first!!
so, yes, i will be cleaning up the duct work, and ive said, i dont think it will work due to the amount of heat at the end of the straight, and yes, going into it cold, doesnt help, so its a heat issue in a 2 second range. sounds like more power than air flow can help, but thats a feeling, not fact. its why im bringing it up for discussion.
thanks for the post.
07-17-2014, 03:12 PM
#191
Rennlist Member
Thread Starter
Braking Physics Discussion - Does going lighter help with over heating brakes?
This is for VR (Dave), Mike and a few others that have questioned the presentation of the physics behind the conclusion that lightening a car will not help an overheating of the brakes situation.
If you look at the numbers and the logic presented and you find any flaws, please bring them up. I think , most use intuition and experience in making conclusions and decisions in racing. sometimes changes have little or nothing to do with the outcome, because the environments in racing are so dynamic.
Too many examples to list. However, let me frame a picture of what happens at the end of the straight into a braking zone. the entire braking zone and no more.
Conditions: 120mph top speed before brakes applied and speed brought down to 60mph before turn in.
Example: two exact same cars, one with 200lbs removed . (3000lbs and 2800lbs)
Units of measure: Im keeping with "LBS" and "MPH", rather than KG and Meters/sec for mass and velocity. Lets call my new units of measure, "VR"s in the spirit of the discussion. (1) VR is equal to 19.8 J. (Joules).
A Joule is a measure of energy. the numbers are a little bigger, but i think the familarity for the speeds in MPH vs m/s and weight in lbs vs KG is better.
both cars reach a common braking point , call it the #4 marker. they apply brakes to the limit of the tires.
Assumptions: the 7% lighter car reaches a 4% higher speed. (sounds fair right?) so, the 3000lbs car gets to 120mph and the 2800lb car gets to 125mph.
both cars brake down to 60mph from their top speed and turn in.
How much KE was released by the brake. Stoptech says 80% of the energy is released by the braking system to slow the. lets still with 100% for sake of simplcity.
KE=1/2mass x velocity^2
3000lb car at 120mph is 21,600,000 VRs
2800lb car at 125mph is 21,875,000 VRs
(NOTE: if the 2800lb car wanted to sand bag and go the same speed, even though lighter, it would have 7% less KE and that would solve heating issues in most cases)
the 2800lbs car has 1.2% more KE (just as a note here)
Now, if they both slow to 60mph and turn it whats the KE at 60mph for both cars? :
3000lb car at 60mph is 5,400,000
2800lb car at 60mph is 5,040,000
see , again same speed , the difference in 7% mass determines the 7% difference in KE. but hold on.
for both cars to decel to the 60mph, the KE the brakes have to absorb and shed is the difference. Using 2nd grade math, we get:
KE released by decelling from 120 to 60mph 3000lb car:
16,200,000VRs
KE released by decelling from 125 to 60mph 2800lb car:
16,835,000VRs
This proves that the l7% lighter car that brakes to the same speed before turn in, has to deal with 3% more KE. its worse for the brakes! not better by going lighter! AGAIN, if both cars , at their respective weight did this drill from the same speed 120mph to 60, the lighter car would have 7% KE savings. who cares... we know if you go lighter , you will go faster, and faster generates more KE than weight. (see James article). so, this begs the next observation that "well, if the car is lighter, it will not have to slow as much! ". GREAT question, right.....??
So, lets say the 7% lighter car turns in at 4% faster speed. (keeping the effects of acceleration in a straight line, consistent with lateral acceleration. sounds fair right? . So , now the lighter car turns in at 62.5mph.
what happens now?
the lighter car's change in KE to go from 125 to 62.5mph is 16,318,400VRs This is STILL 1% greater than the lighter car.
So, the conclusion:
you lighten the car by 7% its reasonable to expect a 4% greater terminal velocity, and a 4% faster turn in speed. (you can play with the numbers a little and not much will change)
removing weight, in no way , will help your brake cooling or heat release issues you are dealing with the same change in KE with slowing a lighter but faster car vs a heavier slower car. this is usually the way things in physics work. you don't need to dig into thermodynamics Mike, to see the obvious here. Now, are there things you can do to rid heat? sure. ducting, bias, all the things mentioned can change these results to benefit a lighter car for a multitude of problems. The specific problem I'm trying to solve is a heat at the end of a straight, where starting cool or hot doesn't seem to matter. it points to a limit of the components, an no one has offered someone with the same KE issues for a 12.6 rotor. not to mention the smaller caliper size.
this is a sidebar discussion.
if you truly believe that lightening your car willl help with a braking overheating problem, find a flaw in the above presentation. talk to someone that knows physics, racing or just institutional. It seems pretty straight forward to me. But, we all can be wrong or misinterpret the information.
Ive seen it man times before. remember guys that put on a 5 lb lighter rim and see 10hp gain? Just because you see the results, it doesnt mean its due to the mod. so many factors as i said. In the dyno situation, you can actually calibrate the dyno knowing rates of change of acceleration, weight and diameter of wheels. if you know the effects of the wheel lightening is 1hp, and you see 10hp..... its due to something else. you cant fool Mr Watt or newton!
If you look at the numbers and the logic presented and you find any flaws, please bring them up. I think , most use intuition and experience in making conclusions and decisions in racing. sometimes changes have little or nothing to do with the outcome, because the environments in racing are so dynamic.
Too many examples to list. However, let me frame a picture of what happens at the end of the straight into a braking zone. the entire braking zone and no more.
Conditions: 120mph top speed before brakes applied and speed brought down to 60mph before turn in.
Example: two exact same cars, one with 200lbs removed . (3000lbs and 2800lbs)
Units of measure: Im keeping with "LBS" and "MPH", rather than KG and Meters/sec for mass and velocity. Lets call my new units of measure, "VR"s in the spirit of the discussion. (1) VR is equal to 19.8 J. (Joules).
A Joule is a measure of energy. the numbers are a little bigger, but i think the familarity for the speeds in MPH vs m/s and weight in lbs vs KG is better.
both cars reach a common braking point , call it the #4 marker. they apply brakes to the limit of the tires.
Assumptions: the 7% lighter car reaches a 4% higher speed. (sounds fair right?) so, the 3000lbs car gets to 120mph and the 2800lb car gets to 125mph.
both cars brake down to 60mph from their top speed and turn in.
How much KE was released by the brake. Stoptech says 80% of the energy is released by the braking system to slow the. lets still with 100% for sake of simplcity.
KE=1/2mass x velocity^2
3000lb car at 120mph is 21,600,000 VRs
2800lb car at 125mph is 21,875,000 VRs
(NOTE: if the 2800lb car wanted to sand bag and go the same speed, even though lighter, it would have 7% less KE and that would solve heating issues in most cases)
the 2800lbs car has 1.2% more KE (just as a note here)
Now, if they both slow to 60mph and turn it whats the KE at 60mph for both cars? :
3000lb car at 60mph is 5,400,000
2800lb car at 60mph is 5,040,000
see , again same speed , the difference in 7% mass determines the 7% difference in KE. but hold on.
for both cars to decel to the 60mph, the KE the brakes have to absorb and shed is the difference. Using 2nd grade math, we get:
KE released by decelling from 120 to 60mph 3000lb car:
16,200,000VRs
KE released by decelling from 125 to 60mph 2800lb car:
16,835,000VRs
This proves that the l7% lighter car that brakes to the same speed before turn in, has to deal with 3% more KE. its worse for the brakes! not better by going lighter! AGAIN, if both cars , at their respective weight did this drill from the same speed 120mph to 60, the lighter car would have 7% KE savings. who cares... we know if you go lighter , you will go faster, and faster generates more KE than weight. (see James article). so, this begs the next observation that "well, if the car is lighter, it will not have to slow as much! ". GREAT question, right.....??
So, lets say the 7% lighter car turns in at 4% faster speed. (keeping the effects of acceleration in a straight line, consistent with lateral acceleration. sounds fair right? . So , now the lighter car turns in at 62.5mph.
what happens now?
the lighter car's change in KE to go from 125 to 62.5mph is 16,318,400VRs This is STILL 1% greater than the lighter car.
So, the conclusion:
you lighten the car by 7% its reasonable to expect a 4% greater terminal velocity, and a 4% faster turn in speed. (you can play with the numbers a little and not much will change)
removing weight, in no way , will help your brake cooling or heat release issues you are dealing with the same change in KE with slowing a lighter but faster car vs a heavier slower car. this is usually the way things in physics work. you don't need to dig into thermodynamics Mike, to see the obvious here. Now, are there things you can do to rid heat? sure. ducting, bias, all the things mentioned can change these results to benefit a lighter car for a multitude of problems. The specific problem I'm trying to solve is a heat at the end of a straight, where starting cool or hot doesn't seem to matter. it points to a limit of the components, an no one has offered someone with the same KE issues for a 12.6 rotor. not to mention the smaller caliper size.
this is a sidebar discussion.
if you truly believe that lightening your car willl help with a braking overheating problem, find a flaw in the above presentation. talk to someone that knows physics, racing or just institutional. It seems pretty straight forward to me. But, we all can be wrong or misinterpret the information.
Ive seen it man times before. remember guys that put on a 5 lb lighter rim and see 10hp gain? Just because you see the results, it doesnt mean its due to the mod. so many factors as i said. In the dyno situation, you can actually calibrate the dyno knowing rates of change of acceleration, weight and diameter of wheels. if you know the effects of the wheel lightening is 1hp, and you see 10hp..... its due to something else. you cant fool Mr Watt or newton!
07-17-2014, 03:18 PM
#192
Ironman 140.6
Rennlist Member
Rennlist Member
07-17-2014, 03:26 PM
#193
Rennlist Member
Dave, you bring up an example, and read half a paragraph that suits your argument. You dont have any more knowlege and acesss to smart people than I do.
why didnt you bother to quote the second sentence in your "Friends" article? its telling of your motivation here. you dont want to help, you want to self promote.
read the article again and let me know if Mr Walker would condone your interpretation of his article or mine. for those playing at home... Mr walker said basically, (paraphrasing), heat is due to the mass of the vehicle, and a factor of 4x due to speed if the speed is doubled. (just after he quotes the KE equation). I found nothing in contraction to my claim that going lighter is not a solution for solving a heat problem in your brakes. (unless of course, you want to run the same lap times, or brake at the same points with the same force and duration) This is borderline common sense. Your a smart guy.. you should know better!
https://rennlist.com/forums/11513120-post180.html
and OH GOD Dave, he even says, "more importantly" when he starts to talk about speed (velocity) relative to the heat issue. "He", your friend, your article, says that speed is more important..... DUH!! its a squared function Dave. wake up!!
http://www.stoptech.com/docs/media-c...raking-systems
why didnt you bother to quote the second sentence in your "Friends" article? its telling of your motivation here. you dont want to help, you want to self promote.
read the article again and let me know if Mr Walker would condone your interpretation of his article or mine. for those playing at home... Mr walker said basically, (paraphrasing), heat is due to the mass of the vehicle, and a factor of 4x due to speed if the speed is doubled. (just after he quotes the KE equation). I found nothing in contraction to my claim that going lighter is not a solution for solving a heat problem in your brakes. (unless of course, you want to run the same lap times, or brake at the same points with the same force and duration) This is borderline common sense. Your a smart guy.. you should know better!
https://rennlist.com/forums/11513120-post180.html
and OH GOD Dave, he even says, "more importantly" when he starts to talk about speed (velocity) relative to the heat issue. "He", your friend, your article, says that speed is more important..... DUH!! its a squared function Dave. wake up!!
http://www.stoptech.com/docs/media-c...raking-systems
WHOOSH !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
07-17-2014, 03:49 PM
#195
Drifting
