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      01-19-2012, 11:24 AM   #1
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one piece vs 2 pieces rotors / 4 pistons vs 6 pistons

Hi Guys,

I want to put a BBK on the front of my car to get more brakes. So, I've been looking at BBKs and I have a few questions:

I know that 2 pieces rotors are better than one piece but why? Is it just a better design for heat dissipation?

How much difference do you get from a 6 pistons BBK from a 4 pistons BBK?

Thanks
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      01-19-2012, 02:37 PM   #2
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i went with the 6pot fronts 4 pot rears, 2 piece floating rotors...... they are prodcued by AP racing as is the kit and are literally breath taking, never have i experienced better braking... awesome stuff, the only issue i can see is the parts are really expensive....

brake feel, retardation, heat management, pad choice, pad changes, pedal feel,... the pro's are night and day....
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      01-19-2012, 03:56 PM   #3
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2 piece rotors are always lighter, and have the option of replacing just the disk section of it
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      01-19-2012, 04:01 PM   #4
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So, is the Brembo BBK with one piece rotors just a waste of money?
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      01-19-2012, 04:06 PM   #5
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I wouldn't say its a waste of money, but it better be cheaper than 2 piece rotor kits. The bigger brakes you get, the bigger the caliper will be, and you can't run a big brake pad with just one piston pushing it in the middle. Thats why you have kits with 4 or 6 pistons-- so that the force is spread out more evenly upon contact. Keep in mind that the actual total volume of those 4 or 6 pistons will (SHOULD) still equal the volume of your stock single piston. At least thats my current understanding...
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      01-19-2012, 05:04 PM   #6
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That makes sense

Quote:
Originally Posted by Roffle Waffle View Post
I wouldn't say its a waste of money, but it better be cheaper than 2 piece rotor kits. The bigger brakes you get, the bigger the caliper will be, and you can't run a big brake pad with just one piston pushing it in the middle. Thats why you have kits with 4 or 6 pistons-- so that the force is spread out more evenly upon contact. Keep in mind that the actual total volume of those 4 or 6 pistons will (SHOULD) still equal the volume of your stock single piston. At least thats my current understanding...
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      01-19-2012, 05:05 PM   #7
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What Roffle is trying to say is what four or six pot calipers have is 'Clamping Force'. Clamping force is the single largest factor for braking performance.

On smaller single piston units, the pad can skew and is not contacting the rotor absolutely 'true' so you loose some of that clamping force (braking power). The larger (cross section wise) the single piston is, the better (more linear) the clamping force is across the face of the rotor and the better braking power. Rotor size only contributes a small percentage to the overall braking power. What a large rotor adds is the ability to hold more heat until you get to a cool down cycle.

One drawback to going to a aftermarket four or six pot brake system is they weight more than stock. Sometimes a lot more. This can be offset with lighter wheels.
Also, a two piece rotor allows the rotor surface to heat up and expand in a uniform manner (not constrained my the rotor hat) so rotor warping is reduced. The reverse is true when the rotor cools down.

What Raffle also touched on is the 'hydraulic bias' or 'brake bias' that the brake system is designed with. If you get a kit not designed for the car, then the brake bias can be upset resulting in difficult braking.
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      01-19-2012, 05:27 PM   #8
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^ shipkiller offers a good detailed summary.

in plain speaking terms big brake upgrades offer a more positive brake feel, delay fade, and better appearance. if the first two are an issue on the street - stop driving like that. if you just want big assed rotors and calipers for appearance - than have at it. so if you don't track your car (and i don't mean autocross) than mostly bbk is an appearance / vanity item relative to your tires in terms of stopping power.
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      01-19-2012, 06:06 PM   #9
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Ok, now I'm starting to understand the problems there

I'm thinking of getting a front StopTech BBK with 4 pistons as it's pretty affordable. I have a choice of 328mm x 28mm rotors vs 332mm x 32mm rotors. The calipers, pads and pistons are the same so I'm thinking going with the 328mm as it will be lighter. What do you think?

Quote:
Originally Posted by Shipkiller View Post
What Roffle is trying to say is what four or six pot calipers have is 'Clamping Force'. Clamping force is the single largest factor for braking performance.

On smaller single piston units, the pad can skew and is not contacting the rotor absolutely 'true' so you loose some of that clamping force (braking power). The larger (cross section wise) the single piston is, the better (more linear) the clamping force is across the face of the rotor and the better braking power. Rotor size only contributes a small percentage to the overall braking power. What a large rotor adds is the ability to hold more heat until you get to a cool down cycle.

One drawback to going to a aftermarket four or six pot brake system is they weight more than stock. Sometimes a lot more. This can be offset with lighter wheels.
Also, a two piece rotor allows the rotor surface to heat up and expand in a uniform manner (not constrained my the rotor hat) so rotor warping is reduced. The reverse is true when the rotor cools down.

What Raffle also touched on is the 'hydraulic bias' or 'brake bias' that the brake system is designed with. If you get a kit not designed for the car, then the brake bias can be upset resulting in difficult braking.
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      01-19-2012, 06:20 PM   #10
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I want the brakes to be in sync with the car power (I'm supercharged). Also, I'm planning to get on the track as soon as I solve my current tires problem. Also, it looks good

Quote:
Originally Posted by aftercorbu View Post
^ shipkiller offers a good detailed summary.

in plain speaking terms big brake upgrades offer a more positive brake feel, delay fade, and better appearance. if the first two are an issue on the street - stop driving like that. if you just want big assed rotors and calipers for appearance - than have at it. so if you don't track your car (and i don't mean autocross) than mostly bbk is an appearance / vanity item relative to your tires in terms of stopping power.
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      01-19-2012, 06:42 PM   #11
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      01-19-2012, 06:45 PM   #12
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Is Stoptech a dirty word?

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Originally Posted by Shipkiller View Post
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      01-19-2012, 06:58 PM   #13
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No. Stoptech makes great braking systems. My comment would have angered some on the forum.
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      01-19-2012, 07:11 PM   #14
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In any case, thank you very much for your advise. I now understand a lot more about brakes.

Quote:
Originally Posted by Shipkiller View Post
No. Stoptech makes great braking systems. My comment would have angered some on the forum.
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      01-20-2012, 03:29 AM   #15
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op just wanted to point out in terms or my ///M car the complete braking system was lighter than the stock items!! pretty impressive when you see the size of the rotors and particularly front calipers!!

chris also weighted in the stoptech stuff and it was also lighter as well :-) im unsure i this is true with the smaller non-m stuff!!!
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      01-20-2012, 12:30 PM   #16
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Brembo's two peice rotors are great, their floating rotors which they developed for the McLaren F1 and they really perform, under heavy breaking a one peice rotor can cone as it heats up differently as the thickness is different from rotor hat to disc, the two peice
rotor can exspand and not become distorted and move freely.

and yes the aluminum hat reduced unsprung weight.

here is some good information.

http://www.zeckhausen.com/Brembo/Rotor_Replacement.htm

http://www.rallylights.com/images/Br...log%5B1%5D.pdf

Last edited by -c-; 01-21-2012 at 10:03 PM..
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      01-20-2012, 12:39 PM   #17
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I'm expecting the difference in weight to be even bigger for a non-M. You guys already have pretty nice brakes.

Quote:
Originally Posted by Beedub View Post
op just wanted to point out in terms or my ///M car the complete braking system was lighter than the stock items!! pretty impressive when you see the size of the rotors and particularly front calipers!!

chris also weighted in the stoptech stuff and it was also lighter as well :-) im unsure i this is true with the smaller non-m stuff!!!
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      01-20-2012, 01:33 PM   #18
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ontop of everything else, they look awesome tooo!! lol!! this really shouldnt matter but, its nice to get alittle cosmetic boost as well..... simply cant explain the beating ive thrown at these brakes!! ive had the rotors glowing.....

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      01-20-2012, 02:12 PM   #19
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Thanks a lot for those links

Quote:
Originally Posted by -c- View Post
Brembo's two peice rotors are great, their floating rotors which they developed for the McLaren F1 and they really perform, under heavy breaking a one peice rotor can cone as it heats up differently as the thickness is different from rotor hat to disc, the two peice
rotor can exspand and not become distorted and move freely.

and yes the aluminum hat reduced unsprung weight.

here is some good information.

http://www.zeckhausen.com/Brembo/Rotor_Replacement.htm

http://www.rallylights.com/images/Br...log%5B1%5D.pdf


http://www.racepads.co.uk/mwg-intern...?id=RF5FjZv48w
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      01-21-2012, 11:33 AM   #20
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The benefit to a multi-piston FIXED caliper system is not the clamping force, since a properly engineered system SHOULD have roughly the same piston area as a stock system, otherwise your brake pedal would be all f**ked up. If the aftermarket system has a larger overall piston area than stock, the brake pedal would be soft/mushy feelie. If the aftermarket system has LESS piston area, the pedal would be ROCK HARD to press.

The benefit to a multi-piston caliper is two-fold. First, the same piston area is spread out onto multiple surfaces, thus allowing the engineers to build a system that spread out the forces applied evenly to prevent flex or twist in the brake pad. Second, a rigid, fixed caliper design has less flex. Both of which contribute to a more precise brake control and modulation compared to stock sliding caliper design. However, the pads must be longer in shape to accommodate the spread-out piston pattern, leading to a smaller sweep area.

Another "benefit" to a fixed style caliper is that since the mount is fixed and rigid, the caliper bodies can be constructed out of aluminum to save weight. Typical 4 or 6 pot calipers can weigh a few lbs lighter than the stock iron caliper since the bracketry required to mount a fixed caliper is much lighter and smaller.

Since brake rotors discs can only be made of iron or exotic material like ceramic composite for their heat dissipation properties and strength, a single piece rotor will weigh more than compound rotors. Compound or 2 piece rotors can have the hub area be constructed of a lighter material, typically aluminum, and saving quite a few lbs. especially custom constructed kits that uses a multi-piston fixed calipers, where the sweeping area is drastically reduced from the stock sliding caliper design, so the rotor rings can be constructed to be much shorter and the hub area increased to further reduce weight.

In addition, 2 piece rotors can be designed to separate the rotor disc away from the rotor hub. There are multiple benefits to this as well, a hub separated from the heat sink that is the iron rotor will prevent heat from being transferred directly to the wheel bearing, prolonging the life of the bearing in a race application. Additionally, separating the hub and the heat sink allows the rotor to expand and contract independently from heat to prevent stress cracks and warpage. Lastly, the physical separation of the disc and hub allows for an open area where the internal cooling vanes of a vented rotor to draw in more ambient air thus allowing for a more efficient cooling. The only drawback to 2 piece floating rotors is that they're very expensive to make.
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      01-21-2012, 08:38 PM   #21
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To resume (including what I got from everyone):

2 pieces rotors are lighter, are better ventilated, have less heat is transmitted from the wheel bearings, wrap and crack less as they can expand in a uniform manner.

Multi piston calipers are lighter, more rigid and spread the clamping force in a more uniform manner over the pads reducing pad skew.

Clamping for should be exactly the same as stock.

Is the total pad contact surface area larger in a BBK even if the sweep area is smaller?

Quote:
Originally Posted by The HACK View Post
The benefit to a multi-piston FIXED caliper system is not the clamping force, since a properly engineered system SHOULD have roughly the same piston area as a stock system, otherwise your brake pedal would be all f**ked up. If the aftermarket system has a larger overall piston area than stock, the brake pedal would be soft/mushy feelie. If the aftermarket system has LESS piston area, the pedal would be ROCK HARD to press.

The benefit to a multi-piston caliper is two-fold. First, the same piston area is spread out onto multiple surfaces, thus allowing the engineers to build a system that spread out the forces applied evenly to prevent flex or twist in the brake pad. Second, a rigid, fixed caliper design has less flex. Both of which contribute to a more precise brake control and modulation compared to stock sliding caliper design. However, the pads must be longer in shape to accommodate the spread-out piston pattern, leading to a smaller sweep area.

Another "benefit" to a fixed style caliper is that since the mount is fixed and rigid, the caliper bodies can be constructed out of aluminum to save weight. Typical 4 or 6 pot calipers can weigh a few lbs lighter than the stock iron caliper since the bracketry required to mount a fixed caliper is much lighter and smaller.

Since brake rotors discs can only be made of iron or exotic material like ceramic composite for their heat dissipation properties and strength, a single piece rotor will weigh more than compound rotors. Compound or 2 piece rotors can have the hub area be constructed of a lighter material, typically aluminum, and saving quite a few lbs. especially custom constructed kits that uses a multi-piston fixed calipers, where the sweeping area is drastically reduced from the stock sliding caliper design, so the rotor rings can be constructed to be much shorter and the hub area increased to further reduce weight.

In addition, 2 piece rotors can be designed to separate the rotor disc away from the rotor hub. There are multiple benefits to this as well, a hub separated from the heat sink that is the iron rotor will prevent heat from being transferred directly to the wheel bearing, prolonging the life of the bearing in a race application. Additionally, separating the hub and the heat sink allows the rotor to expand and contract independently from heat to prevent stress cracks and warpage. Lastly, the physical separation of the disc and hub allows for an open area where the internal cooling vanes of a vented rotor to draw in more ambient air thus allowing for a more efficient cooling. The only drawback to 2 piece floating rotors is that they're very expensive to make.

Last edited by philippelyp; 01-21-2012 at 08:59 PM..
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      01-21-2012, 08:38 PM   #22
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I nearly forgot

Quote:
Originally Posted by The HACK View Post
The benefit to a multi-piston FIXED caliper system is not the clamping force, since a properly engineered system SHOULD have roughly the same piston area as a stock system, otherwise your brake pedal would be all f**ked up. If the aftermarket system has a larger overall piston area than stock, the brake pedal would be soft/mushy feelie. If the aftermarket system has LESS piston area, the pedal would be ROCK HARD to press.

The benefit to a multi-piston caliper is two-fold. First, the same piston area is spread out onto multiple surfaces, thus allowing the engineers to build a system that spread out the forces applied evenly to prevent flex or twist in the brake pad. Second, a rigid, fixed caliper design has less flex. Both of which contribute to a more precise brake control and modulation compared to stock sliding caliper design. However, the pads must be longer in shape to accommodate the spread-out piston pattern, leading to a smaller sweep area.

Another "benefit" to a fixed style caliper is that since the mount is fixed and rigid, the caliper bodies can be constructed out of aluminum to save weight. Typical 4 or 6 pot calipers can weigh a few lbs lighter than the stock iron caliper since the bracketry required to mount a fixed caliper is much lighter and smaller.

Since brake rotors discs can only be made of iron or exotic material like ceramic composite for their heat dissipation properties and strength, a single piece rotor will weigh more than compound rotors. Compound or 2 piece rotors can have the hub area be constructed of a lighter material, typically aluminum, and saving quite a few lbs. especially custom constructed kits that uses a multi-piston fixed calipers, where the sweeping area is drastically reduced from the stock sliding caliper design, so the rotor rings can be constructed to be much shorter and the hub area increased to further reduce weight.

In addition, 2 piece rotors can be designed to separate the rotor disc away from the rotor hub. There are multiple benefits to this as well, a hub separated from the heat sink that is the iron rotor will prevent heat from being transferred directly to the wheel bearing, prolonging the life of the bearing in a race application. Additionally, separating the hub and the heat sink allows the rotor to expand and contract independently from heat to prevent stress cracks and warpage. Lastly, the physical separation of the disc and hub allows for an open area where the internal cooling vanes of a vented rotor to draw in more ambient air thus allowing for a more efficient cooling. The only drawback to 2 piece floating rotors is that they're very expensive to make.
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