Let's talk track brakes...
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From: Tejas
We call it 'gettin' all horned up' here in Texas...
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From: Tempe AZ
I would agree with Matt also. Unless the weight or the speed of the car is changed the net amount of energy to slow it would be the same.
The use of the friction material is but one aspect of the braking systems way to convert this energy. The others being piston area (how hard it clamps) and rotor diameter (the leverage point of the clamping). The pad CF is only the abrasive (or Mu) of the three parts.
A more abrasive pad while providing more "bite" provides the same amount of total rotor torque (assuming same 12" rotor) but does not require the same amount of clamping pressure. Conversely adding a 14" rotor adds more leverage to the torque value thus negating the needs for either high clamp load or high pad Cf.
As I often point out; max deceleration is of course a skid. How you achieve this peak tq value is up to what parts you are using to do so.
**BTW; tell me if she's "incapable of getting the job done" and maybe I'll hire her!
The use of the friction material is but one aspect of the braking systems way to convert this energy. The others being piston area (how hard it clamps) and rotor diameter (the leverage point of the clamping). The pad CF is only the abrasive (or Mu) of the three parts.
A more abrasive pad while providing more "bite" provides the same amount of total rotor torque (assuming same 12" rotor) but does not require the same amount of clamping pressure. Conversely adding a 14" rotor adds more leverage to the torque value thus negating the needs for either high clamp load or high pad Cf.
As I often point out; max deceleration is of course a skid. How you achieve this peak tq value is up to what parts you are using to do so.
**BTW; tell me if she's "incapable of getting the job done" and maybe I'll hire her!
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6th Gear
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From: NJerz
Okay, maybe I do have something to say: This picture just symbolizes the awesomeness of this thread. We've got novices like me posting experience, we've got experienced people posting experiences, we've got vendors adding helpfully, we've got scientists testing brake dust in particle accelerators, and we've got her. Let's just call her "her."
mb
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Question....
This is a great thread. Mike Jr. the Brake guy here with Autoxcooper.com.
Dr. O, could you brake that formula down for me? I'm not a physicist but I have a pretty good idea of the factors involved and the physics of stopping a car, and I have never seen this formula, and there is no way I would remeber it from Physics in 1991! I try to learn something new every day. Thanks for the help.
There has been a good deal of info on this thread, I can't really see or address anything that hasn't already been taken care of by Dustin. If anyone has any questions, feel free to PM me.
BTW- I had a great time at Mini's on the Dragon in May, thanks to all who came and visited us at the tent and thank you to the guys who participated at the autocross event on Saturday.
Mike Jr.
Dr. O, could you brake that formula down for me? I'm not a physicist but I have a pretty good idea of the factors involved and the physics of stopping a car, and I have never seen this formula, and there is no way I would remeber it from Physics in 1991! I try to learn something new every day. Thanks for the help.
There has been a good deal of info on this thread, I can't really see or address anything that hasn't already been taken care of by Dustin. If anyone has any questions, feel free to PM me.
BTW- I had a great time at Mini's on the Dragon in May, thanks to all who came and visited us at the tent and thank you to the guys who participated at the autocross event on Saturday.
Mike Jr.
Last edited by MikeJr@AutoXCooper.com; Sep 19, 2008 at 06:52 AM.
It is a great thread, one of the best we've had in a long time. Jan gets tingly all over with physics equations, but I get all tingly over new brake sales reps...Please invite her to post at will and without restraint in this thread!
But what would make this thread even better is someone would come up with a brake duct kit that: 1. utilizes the foglight 2. directs air to the hub.
Looks like we can get 1 or 2, but not 1 AND 2....
But what would make this thread even better is someone would come up with a brake duct kit that: 1. utilizes the foglight 2. directs air to the hub.
Looks like we can get 1 or 2, but not 1 AND 2....
Mike,
1/2*mass*velocity^squared is the formula for kinetic energy. You probably learned about it the same time you learned potential energy (gravity) = mass*gravity*height. Kinetic energy must be conserved, so basically you can compare the energy it takes to stop two vehicles. A car that's 2000 lbs going 60mph will have twice as much kinetic energy as a car that's 1000 lbs going 60mph, but the first car will have four times as much energy as a 2000 lbs car going 30mph. The formula is the first derivative of momentum, mass*velocity (if you know calculus).
(Ok, engineer-speak done.)
Dustin, can you put her on the phone next time I call? No offense, but I'm much more interested in her brake pads.
Also, re: the gas released during bedding, does that mean that I should only bed the pads once? If I switch from street pads to track pads and back again, should I bed the street pads a second time?
Also, Todd, to be specific, max car deceleration is right before a skid, because for the interface between tires and pavement the coefficient of static friction (not sliding) is higher than the coefficient of kinetic friction (sliding). Think of moving a desk across carpet - it's always hardest to start it moving, but once it starts sliding it's easier. That's why brake modulation is important - you want to slow the car down as fast as possible at the threshold of static and kinetic friction. That threshold changes due to variation in the normal force caused by the car's weight shifting, bumps in the pavement, and steering input. Modulating the braking force allows you to adjust that stopping force and stay as close to the threshold as possible, which is where max car deceleration is.
As you stated, max wheel deceleration is locking up the brakes, which creates static friction between the pads and rotors. And that's when your instructor gets nervous. =)
1/2*mass*velocity^squared is the formula for kinetic energy. You probably learned about it the same time you learned potential energy (gravity) = mass*gravity*height. Kinetic energy must be conserved, so basically you can compare the energy it takes to stop two vehicles. A car that's 2000 lbs going 60mph will have twice as much kinetic energy as a car that's 1000 lbs going 60mph, but the first car will have four times as much energy as a 2000 lbs car going 30mph. The formula is the first derivative of momentum, mass*velocity (if you know calculus).
(Ok, engineer-speak done.)
Dustin, can you put her on the phone next time I call? No offense, but I'm much more interested in her brake pads.
Also, re: the gas released during bedding, does that mean that I should only bed the pads once? If I switch from street pads to track pads and back again, should I bed the street pads a second time?
Also, Todd, to be specific, max car deceleration is right before a skid, because for the interface between tires and pavement the coefficient of static friction (not sliding) is higher than the coefficient of kinetic friction (sliding). Think of moving a desk across carpet - it's always hardest to start it moving, but once it starts sliding it's easier. That's why brake modulation is important - you want to slow the car down as fast as possible at the threshold of static and kinetic friction. That threshold changes due to variation in the normal force caused by the car's weight shifting, bumps in the pavement, and steering input. Modulating the braking force allows you to adjust that stopping force and stay as close to the threshold as possible, which is where max car deceleration is.
As you stated, max wheel deceleration is locking up the brakes, which creates static friction between the pads and rotors. And that's when your instructor gets nervous. =)
Former Vendor
Joined: Mar 2004
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From: Tempe AZ
Yes, understood. You're correct on the tire.
I only mention "skid" as I often point people to the brake bias page where one can pick a max rotor tq value and consider that the point of lock up.
http://www.tceperformanceproducts.co...alculator.html
By default the value shown is 82,868 and you can then plug and play various options of piston size, rotor size, pad Cf and leg input pressure knowing that regardless of what values you put in...anything exceeding the 82k range is pointless.
For example; you could use a 20" rotor and see what leg change is needed to get to 82k. Or you can put a massive six pot caliper on there with 2" pistons (3x) and note that the leg is going to be very low. Or you can put a 6" rotor on it and push with all the passengers to get enough leg effort in order to get back to 82k.
For the sake of this conversation, it doesn't matter 'how' you get there. Max is max.
I only mention "skid" as I often point people to the brake bias page where one can pick a max rotor tq value and consider that the point of lock up.
http://www.tceperformanceproducts.co...alculator.html
By default the value shown is 82,868 and you can then plug and play various options of piston size, rotor size, pad Cf and leg input pressure knowing that regardless of what values you put in...anything exceeding the 82k range is pointless.
For example; you could use a 20" rotor and see what leg change is needed to get to 82k. Or you can put a massive six pot caliper on there with 2" pistons (3x) and note that the leg is going to be very low. Or you can put a 6" rotor on it and push with all the passengers to get enough leg effort in order to get back to 82k.
For the sake of this conversation, it doesn't matter 'how' you get there. Max is max.
Bedding only needs to happen the first time. However, when swapping back and forth there may be some "schmutz" on the rotor from pad transfer. That might take an application or two of the brakes to get cleaned off the rotor.
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From: Car Nut Since 1987, Owner Since Fall 2005, Vendor Since Fall 2007
Dustin, can you put her on the phone next time I call? No offense, but I'm much more interested in her brake pads.
Also, re: the gas released during bedding, does that mean that I should only bed the pads once? If I switch from street pads to track pads and back again, should I bed the street pads a second time? =)
Also, re: the gas released during bedding, does that mean that I should only bed the pads once? If I switch from street pads to track pads and back again, should I bed the street pads a second time? =)
Like Nate said, bed in once and good to go. If running CT track pads, then street and back again, not to worry they play well together like all of us on this thread
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6th Gear
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From: NJerz
.mb
Me things you've been inhaling too much brake dust...
Brakes, pretty women and a Yiddish lesson in one thread. What more could ya want!!
Schmutz (also shmuts, (shmŭtz or shmootz) is a Yiddish word of direct German derivation. It can be a noun, a verb, or an adjective.
As in the original German, its use in Yiddish as a noun can designate a range of types of unpleasant substances from any kind of soil such as mud or dust to thick or ground-in dirt such as soot or grass stains. More strongly, and less accurately, it's used to indicate a particularly foul or repulsive matter such as animal waste or the fuzzy stuff found growing in the jar way at the back of the fridge. A Jewish comic once raised schmutz to the exalted status of “dirt that moves.”
As a verb, it can be used literally to describe an action as in, “Five minutes into the party and she schmutzes on herself already,” or it can move into a figurative indication of messing up things in general as in, “I don’t need you to come in here and schmutz things up for me.”
Its adjectival form is schmutzic (also shmutsik) and means dirty or soiled as in, “He dropped his blintz and got his shirt all schmutzic.”
Schmutz is in no way related to or interchangeable with either weiner schmaltz or schmuck. Nor is it any kind of dreck which should be reserved for garbage in the sense of being poorly made, worthless, or simply crap. It is also not chazeray which is junk in disarray.
As in the original German, its use in Yiddish as a noun can designate a range of types of unpleasant substances from any kind of soil such as mud or dust to thick or ground-in dirt such as soot or grass stains. More strongly, and less accurately, it's used to indicate a particularly foul or repulsive matter such as animal waste or the fuzzy stuff found growing in the jar way at the back of the fridge. A Jewish comic once raised schmutz to the exalted status of “dirt that moves.”
As a verb, it can be used literally to describe an action as in, “Five minutes into the party and she schmutzes on herself already,” or it can move into a figurative indication of messing up things in general as in, “I don’t need you to come in here and schmutz things up for me.”
Its adjectival form is schmutzic (also shmutsik) and means dirty or soiled as in, “He dropped his blintz and got his shirt all schmutzic.”
Schmutz is in no way related to or interchangeable with either weiner schmaltz or schmuck. Nor is it any kind of dreck which should be reserved for garbage in the sense of being poorly made, worthless, or simply crap. It is also not chazeray which is junk in disarray.
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Schmutz!
That is an old term, My grandparents and my father used it (Dad still does). I learned the definition of it today, another good day, learned 2 new things!
Doc, thanks for the explanation, that makes perfect sense, I have a new formula to look even smarter with now (LOL!). I still don't remember learning it though. I agree with your Max braking explanation, it's right on the money. There is less friction when the tires are sliding. Brake late, hard and don't lock up, that is the fast way around the track. Think of grass vs. wet grass, I have actually accelerated in wet grass when going on off-track excursions!
Brake modulation is the most important part of threshold braking. That comes with experience, you have to "feel it". Knowing how hard you can brake in changing conditions, temps, tire pressures, tire temps and type of tire all affect and change your threshold braking. An AIM data acquisition system can tell you all of that Data, but it is an entirely different thing to actually be able to do it. Part of the compound selection process for the track is the type of tire that an individual is using.
This has to be one of the most informative threads I have ever read or been a part of. Thanks to all.
Doc, thanks for the explanation, that makes perfect sense, I have a new formula to look even smarter with now (LOL!). I still don't remember learning it though. I agree with your Max braking explanation, it's right on the money. There is less friction when the tires are sliding. Brake late, hard and don't lock up, that is the fast way around the track. Think of grass vs. wet grass, I have actually accelerated in wet grass when going on off-track excursions!
Brake modulation is the most important part of threshold braking. That comes with experience, you have to "feel it". Knowing how hard you can brake in changing conditions, temps, tire pressures, tire temps and type of tire all affect and change your threshold braking. An AIM data acquisition system can tell you all of that Data, but it is an entirely different thing to actually be able to do it. Part of the compound selection process for the track is the type of tire that an individual is using.
This has to be one of the most informative threads I have ever read or been a part of. Thanks to all.
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Former Vendor
Joined: Jun 2008
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I just wanted to express my appreciation for the newest BBK on my '02 MCS: a TSW BDM. With the industry standard 11.75x1.25" rotor and "Dynalite" caliper, rotors and pads are not only cheap to replace but easy to get. The billet-aluminum caliper mounts and billet rotor hats are beautifully machined, and the hard-anodized coating is excellent.
I got a chance to give these brakes a real workout this weekend during an SVT Mustang Cobra Club sponsored track-weekend at Gingerman Raceway. 3.5 hours of track time later [in 30 minute sessions], the brakes held up to my Hoosier-tire-assisted abuse. I use Wilwood BP-10 pads on the street, but Raybestos ST-43 on the track. I've used many pads over the years, and the ST-43 are quite good. They offer good modulation, quick release, and appear not only easy on the rotors and themselves, but have minimal brake dust too [LOL!]. While the TSW BBK doesn't have the most torque out there, that's not a bad thing. The Wilwood 12.2" Race kit I had lacked the cooling or caliper stiffness to stay on the car, and the DT kit, while being the king of stopping power, is simply too powerful for my stripped out 2290# MINI, not to mention too big to fit under my 16" bridge spokes. The TSW kit fit my bill perfectly, and didn't disappoint. The only improvement I can think of is having more tire grip in the front to stop even quicker! Props to TSW for putting together a professionally made kit that gets the job done with no excuses.
Cheers,
Ryan
I got a chance to give these brakes a real workout this weekend during an SVT Mustang Cobra Club sponsored track-weekend at Gingerman Raceway. 3.5 hours of track time later [in 30 minute sessions], the brakes held up to my Hoosier-tire-assisted abuse. I use Wilwood BP-10 pads on the street, but Raybestos ST-43 on the track. I've used many pads over the years, and the ST-43 are quite good. They offer good modulation, quick release, and appear not only easy on the rotors and themselves, but have minimal brake dust too [LOL!]. While the TSW BBK doesn't have the most torque out there, that's not a bad thing. The Wilwood 12.2" Race kit I had lacked the cooling or caliper stiffness to stay on the car, and the DT kit, while being the king of stopping power, is simply too powerful for my stripped out 2290# MINI, not to mention too big to fit under my 16" bridge spokes. The TSW kit fit my bill perfectly, and didn't disappoint. The only improvement I can think of is having more tire grip in the front to stop even quicker! Props to TSW for putting together a professionally made kit that gets the job done with no excuses.
Cheers,
Ryan
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From: Tejas
I just wanted to express my appreciation for the newest BBK on my '02 MCS: a TSW BDM. With the industry standard 11.75x1.25" rotor and "Dynalite" caliper, rotors and pads are not only cheap to replace but easy to get. The billet-aluminum caliper mounts and billet rotor hats are beautifully machined, and the hard-anodized coating is excellent.
I got a chance to give these brakes a real workout this weekend during an SVT Mustang Cobra Club sponsored track-weekend at Gingerman Raceway. 3.5 hours of track time later [in 30 minute sessions], the brakes held up to my Hoosier-tire-assisted abuse. I use Wilwood BP-10 pads on the street, but Raybestos ST-43 on the track. I've used many pads over the years, and the ST-43 are quite good. They offer good modulation, quick release, and appear not only easy on the rotors and themselves, but have minimal brake dust too [LOL!]. While the TSW BBK doesn't have the most torque out there, that's not a bad thing. The Wilwood 12.2" Race kit I had lacked the cooling or caliper stiffness to stay on the car, and the DT kit, while being the king of stopping power, is simply too powerful for my stripped out 2290# MINI, not to mention too big to fit under my 16" bridge spokes. The TSW kit fit my bill perfectly, and didn't disappoint. The only improvement I can think of is having more tire grip in the front to stop even quicker! Props to TSW for putting together a professionally made kit that gets the job done with no excuses.
Cheers,
Ryan
I got a chance to give these brakes a real workout this weekend during an SVT Mustang Cobra Club sponsored track-weekend at Gingerman Raceway. 3.5 hours of track time later [in 30 minute sessions], the brakes held up to my Hoosier-tire-assisted abuse. I use Wilwood BP-10 pads on the street, but Raybestos ST-43 on the track. I've used many pads over the years, and the ST-43 are quite good. They offer good modulation, quick release, and appear not only easy on the rotors and themselves, but have minimal brake dust too [LOL!]. While the TSW BBK doesn't have the most torque out there, that's not a bad thing. The Wilwood 12.2" Race kit I had lacked the cooling or caliper stiffness to stay on the car, and the DT kit, while being the king of stopping power, is simply too powerful for my stripped out 2290# MINI, not to mention too big to fit under my 16" bridge spokes. The TSW kit fit my bill perfectly, and didn't disappoint. The only improvement I can think of is having more tire grip in the front to stop even quicker! Props to TSW for putting together a professionally made kit that gets the job done with no excuses.
Cheers,
Ryan
Killed my rotors (again) a couple of weekends ago at road america. Total of three track days, a total of 9 thirty minute sessions at Road America, and 5 20 minutes sessions at autobahn two weeks prior (and I didn't run very hard at Autobahn, was really taking it easy, not so at Road America), and they're cracked. They're in good enough shape to get through the winter, but they'll need to be replaced before any more track days.
So I've got all winter to decide: go the BDM route, or switch to carbotech pads on the dynapro caliper and add ducts.
Is there a list of 15 inch wheels that'll fit over the BDM? I know the TD 1's will, but are there any other (thankfully I have a set of TD's, but you can't get them anymore, and I'd need two sets of rims).
I'm not complaining about the dynapro kit--Todd warned me I might hit the limits of them sooner rather than later on the small kit, and I should have listened a bit better--I did a bunch of track days this year, and I'm driving the car faster and braking harder than I'd ever anticipated. Not a bad thing, but I've come to limits of what I can do with my current setup, and I really want to stay on 15 inch wheels; I think Mark's in the same boat (actually he's probably further along on the learning curve than I am).
So I've got all winter to decide: go the BDM route, or switch to carbotech pads on the dynapro caliper and add ducts.
Is there a list of 15 inch wheels that'll fit over the BDM? I know the TD 1's will, but are there any other (thankfully I have a set of TD's, but you can't get them anymore, and I'd need two sets of rims).
I'm not complaining about the dynapro kit--Todd warned me I might hit the limits of them sooner rather than later on the small kit, and I should have listened a bit better--I did a bunch of track days this year, and I'm driving the car faster and braking harder than I'd ever anticipated. Not a bad thing, but I've come to limits of what I can do with my current setup, and I really want to stay on 15 inch wheels; I think Mark's in the same boat (actually he's probably further along on the learning curve than I am).
Former Vendor
Joined: Mar 2004
Posts: 1,851
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From: Tempe AZ
I don't think 9- 30min sessions there and the other time is all bad for what you could expect from the 11.75-.810 rotor really. It does however lead you to the gut check time of exactly what way to move from here for next year....
There are a few options that I can see. First is to plan on changing out those rotors at a predetermined time line and factor that into the budget. Figure about $250 per change. Next would be a custom rotor for that kit where we can "push" it to about .900 to fatten the rotor walls some. Here you'd pretty much max the options with this caliper. Cost; about the same. Adding good ducting will help in the long term as well.
From there you're looking a more "hard parts" replacement via one of the options for a wide rotor, small diameter kit. Clearly there are pros and cons to both so spend some time looking over the costs of such changes vs replacements as well as all the reasons for or against all the options.
Another thing to consider is moving away from the 15" wheel. Moving to 16s and larger 12.2 (maybe wider also) rotor nets you about 6% more swept area. Going to 17s and 13" rotor boosts that to a full 13% more swept area. What that means is that the overall efficiency of the system is up and the duty cycle is lower. Net gains; longer life with less wear. And depending upon the package perhaps lower operational costs by way of longer pad life, and often a lesser need for pad aggression due to the design.
No matter how you slice it, smaller kits will always be working harder to produce the same net result. That's not to say one is right and the other wrong, only that like anything in racing it's a balance in trade offs.
There are a few options that I can see. First is to plan on changing out those rotors at a predetermined time line and factor that into the budget. Figure about $250 per change. Next would be a custom rotor for that kit where we can "push" it to about .900 to fatten the rotor walls some. Here you'd pretty much max the options with this caliper. Cost; about the same. Adding good ducting will help in the long term as well.
From there you're looking a more "hard parts" replacement via one of the options for a wide rotor, small diameter kit. Clearly there are pros and cons to both so spend some time looking over the costs of such changes vs replacements as well as all the reasons for or against all the options.
Another thing to consider is moving away from the 15" wheel. Moving to 16s and larger 12.2 (maybe wider also) rotor nets you about 6% more swept area. Going to 17s and 13" rotor boosts that to a full 13% more swept area. What that means is that the overall efficiency of the system is up and the duty cycle is lower. Net gains; longer life with less wear. And depending upon the package perhaps lower operational costs by way of longer pad life, and often a lesser need for pad aggression due to the design.
No matter how you slice it, smaller kits will always be working harder to produce the same net result. That's not to say one is right and the other wrong, only that like anything in racing it's a balance in trade offs.