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Motorsports & Track Forum
From Auto-X to Trackday to Racing and Professional Motorsports this is the place to discuss making BMWs fast

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Old 08-24-2005, 09:43 PM   #61
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gbn,

Did you bed the pads?
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Old 08-24-2005, 10:51 PM   #62
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Quote:
Originally Posted by gbn
With the non-slotted cryo rotors it seems that I have to apply noticably more force to engage the ABS. I think that's a good thing.
Why would that be better?
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Old 08-25-2005, 02:13 PM   #63
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Quote:
Originally Posted by Mahjik
Bigger brakes don't offer more force. You aren't changing the proportion of the braking force from the brake master cylinder. The same force is just spread over a wider pad, but it's the same force.
This statement is not totally correct. The total FORCE that the pad applies to the rotor is the same (assuming similar sized pads) but it is the torque generated from this frictional force that stops the car from moving. Force x distance = torque. So if the distance from the pad to the center of the wheel is larger (like with bigger brakes) you will be able to apply more braking torque to the wheels. If the tires don't lose traction this will slow the car quicker.

BBK's can generate more braking power, so if the tires can handle it they will stop the car faster.
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Last edited by Renaud; 08-25-2005 at 02:34 PM.
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Old 08-25-2005, 02:15 PM   #64
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Quote:
Originally Posted by Renaud
BBK's can generate more breaking power
Why would I want more breaking power?
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Old 08-25-2005, 02:25 PM   #65
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Quote:
Originally Posted by vaio76109
Why would I want more breaking power?
Hmmmmm, maybe to stop the car faster

I assume your post was meant to be sarcastic. It seems pretty obvious why you would want to be able to stop faster
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Old 08-25-2005, 02:29 PM   #66
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Yes it was sarcastic. Its spelled braking, not breaking.
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Old 08-25-2005, 02:34 PM   #67
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Quote:
Originally Posted by vaio76109
Yes it was sarcastic. Its spelled braking, not breaking.
I am so smart. I read over that about ten times after you posted to see if I made a mistake and still didn't notice it
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Old 08-25-2005, 04:01 PM   #68
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Quote:
Originally Posted by gbn
With the non-slotted cryo rotors it seems that I have to apply noticably more force to engage the ABS. I think that's a good thing. I'm not convinced I like the Metal Masters. Anybody try them and have something else to compare them to? Compared to OEM they have less dust, less high speed fade, more noise (squeeky), and a little less stopping power at low speed, initial bite.
I don't think the cyro rotors really help in anything related to braking performance except the longivity of the rotors themselves. I had them and I sold them. I am sure it's good to be used in Rolex series or Grand AM or Speed World Challenge. If you don't mind me saying, that money was down the drain for me.
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Old 08-25-2005, 04:08 PM   #69
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Great post, Renaud.

Also, tractive force and braking force are functions of slip angle (or as they say, tires stop the car). If you have BBK, and 1000 hp under the hood, don't go cheap on tires.

Quote:
Originally Posted by Renaud
This statement is not totally correct. The total FORCE that the pad applies to the rotor is the same (assuming similar sized pads) but it is the torque generated from this frictional force that stops the car from moving. Force x distance = torque. So if the distance from the pad to the center of the wheel is larger (like with bigger brakes) you will be able to apply more braking torque to the wheels. If the tires don't lose traction this will slow the car quicker.

BBK's can generate more braking power, so if the tires can handle it they will stop the car faster.
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Old 08-26-2005, 08:34 AM   #70
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Quote:
Originally Posted by Renaud
This statement is not totally correct. The total FORCE that the pad applies to the rotor is the same (assuming similar sized pads) but it is the torque generated from this frictional force that stops the car from moving. Force x distance = torque. So if the distance from the pad to the center of the wheel is larger (like with bigger brakes) you will be able to apply more braking torque to the wheels. If the tires don't lose traction this will slow the car quicker.
All that does is allow you to reach the braking threshold sooner. Doesn't necessarily make you stop any quicker given the same tires (i.e. keeping the tires from locking up is the key). Bottom line, if someone wants to stop quicker, get better tires.
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Old 08-26-2005, 08:53 AM   #71
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Quote:
Originally Posted by Mahjik
All that does is allow you to reach the braking threshold sooner. Doesn't necessarily make you stop any quicker given the same tires (i.e. keeping the tires from locking up is the key). Bottom line, if someone wants to stop quicker, get better tires.
Exactly, that's why I said "if the tires don't lose traction." Big brakes are better than small, I'm not sure what we are really debating here
Obviously if you have bad tires it doesn't matter, but bigger brakes WILL stop you quicker with adequate tires PERIOD. There is alot more to the physics of it, but the fact is that a larger disc will be able to apply more torque and also dissipate heat better.
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Old 08-26-2005, 12:08 PM   #72
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Renaud:
Exactly. Better tires will hold/grip longer before exceeding their coefficent of friction. Larger rotors equal greater torque and better heat dissapation. Good tires and larger brakes will slow the car quicker and more times that stock brakes will. This is only really noticable on the track, however, when bringing a car down from say 100-150 mph. Stock brakes simply cannot handle, nor are they designed to, slow the car from those speeds repeatedly. For street driving, OEM is fine. For some really good information, some may want to visit www.stoptech.com Follow the links to the tech page and FAQ page. They make excellent brakes for BMWs and they give a lot of real world tangible inforamtion. The whole thing is not being able to lock the wheels to stop; any brake system will do that. It's about maintain traction and control at higher thresholds over a greater period of time (multiple stops/slows).

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Old 08-26-2005, 06:02 PM   #73
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Quote:
Originally Posted by Renaud
Exactly, that's why I said "if the tires don't lose traction." Big brakes are better than small, I'm not sure what we are really debating here
Obviously if you have bad tires it doesn't matter, but bigger brakes WILL stop you quicker with adequate tires PERIOD. There is alot more to the physics of it, but the fact is that a larger disc will be able to apply more torque and also dissipate heat better.
You were commenting on my comment about the force. And we do agree that the force doesn't change from the brake master cylinder and that moving the pad further outside on the rotor increases torque (not force).

However, torque increase doesn't mean the car will stop quicker. You are still limited by the ABS threshold (and tires) regardless how quick you reach it.

For a good technical read on BBK's check this thread:
http://www.rx7club.com/showthread.ph...5&page=3&pp=15
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Old 08-26-2005, 06:08 PM   #74
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Quote:
Originally Posted by Mahjik
However, torque increase doesn't mean the car will stop quicker. You are still limited by the ABS threshold (and tires) regardless how quick you reach it.
Thats what most of us are saying, including renauld.
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Old 08-26-2005, 06:12 PM   #75
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Quote:
Originally Posted by vaio76109
Thats what most of us are saying, including renauld.
Not quite:

Quote:
Originally Posted by Renaud
So if the distance from the pad to the center of the wheel is larger (like with bigger brakes) you will be able to apply more braking torque to the wheels. If the tires don't lose traction this will slow the car quicker.
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Old 08-27-2005, 07:56 AM   #76
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Quote:
Originally Posted by Mahjik
Not quite:
How is the quote from me any different than what you are saying? You say torque increase can stop the car quicker up to the ABS threshold, and what sets the ABS threshold.....The tires do (assuming the same car and suspension setup), and thats what I am saying.

I stick to my orginal statement that bigger brakes WILL stop the car quicker as long as the tires can handle it. The OEM brakes work quite well, and until you get better tires and increase the speed the biggest gain you will see is decreased fade. OEM brakes are good, but you can't argue with the physics that a larger rotor can generate more torque to stop the wheels. Again, the tires will usually be the limiting factor for a street car.
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Old 08-27-2005, 08:10 AM   #77
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Quote:
Originally Posted by Renaud
I stick to my orginal statement that bigger brakes WILL stop the car quicker as long as the tires can handle it.
Moving the pad further out (to increase torque) or a pad with a higher coefficient of friction (on stock calipers) will allow the car to stop quicker ONLY if the tires are also upgraded.

Quote:
Originally Posted by Renaud
but you can't argue with the physics that a larger rotor can generate more torque to stop the wheels
The larger rotor doesn't make more torque on the brakes, moving the pad further out does. (Racing) People have done this for years as a cheap way to modify their stock brakes before there were caliper alternatives for their cars.

But that doesn't stop the car any quicker given the same tires. You just reach the ABS threshold sooner which doesn't make the car stop any quicker without a change to the tires.

Quote:
Originally Posted by Renaud
Again, the tires will usually be the limiting factor for a street car.
With the same tires, the stopping distance always limited regardless if it's a BBK or not. BBK's do NOTHING for stopping distance without a change to the tires. You are basically saying the same thing so I'm not sure why you just don't come out and say it that way. Using all the "if this and if that", just state it as it is that tires are the first limiting factor of braking.
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Old 08-27-2005, 08:55 AM   #78
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Quote:
Originally Posted by Mahjik
Moving the pad further out (to increase torque) or a pad with a higher coefficient of friction (on stock calipers) will allow the car to stop quicker ONLY if the tires are also upgraded.
"will be able to apply more braking torque to the wheels. If the tires don't lose traction this will slow the car quicker."

The larger rotor doesn't make more torque on the brakes, moving the pad further out does. (Racing) People have done this for years as a cheap way to modify their stock brakes before there were caliper alternatives for their cars.
"but you can't argue with the physics that a larger rotor can generate more torque to stop the wheels. " With a larger rotor it is assumed the caliper is moved out further
Yall are saying the same thing! And Renauld agrees! Whats the argument here?

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Old 08-27-2005, 08:57 AM   #79
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double post, oops!
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Old 08-27-2005, 11:27 AM   #80
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Quote:
Originally Posted by vaio76109
With a larger rotor it is assumed the caliper is moved out further
Not necessarily. Simply saying "larger rotors" doesn't assume or imply anything. If someone who doesn't understand braking systems reads that, they'll think they can go out and get "larger rotors" for improved braking and nothing else. For all we know, that may have been exactly what he meant. Since you aren't "him", you don't know.

You have to realize that there are more than just "people who understand braking systems" reading these forums. Providing correct and complete information is the key. Never assume or imply.
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