Big Brake Kits - Real Numbers

Here are a few comparison figures I have generated for our common big brake kits. All calculations are based on some assumptions and come with some caveats:

1. Pads sit in 0.5mm from the edge of the disc.

2. The same pad compound is used for every comparison

3. All kits are listed as "improvement" or "reduction" with a percentage based on their comparison to the UK spec setup ("improvement" means it is more powerful than UK spec)

4. Front to rear bias change is calculated relative to the UK spec setup

5. UK spec front pad depth = 58mm - could somebody verify this please?

6. UK spec rear pad depth = 49mm

7. Use at your own risk - I worked these out for my own benefit when looking into buying a BBK off the shelf

8. I am sharing the numbers here for interest's sake - not to start any arguments or for anyone to go away and build their own kit based on my calculations

9. If you have any piston diameters or pad depths for the applications where I have gaps in the data then please let me know.

10. Please let me know if you think there are any mistakes or contradictions.

11. This data relates to actual braking capability based on the dimensions of the disc, pad and caliper. There is no accounting for temperature, heat capacity, feel and pad knock back, rotating mass, unsprung mass, caliper stiffness, pad choice etc. Some of these are subjective whereas others can be quantified (another post coming on that soon).

I'll add more to this list and fill in the gaps as I get the time and extra info (e.g. Brembo's "C" non-monoblock rear caliper that they sell to go with the 14" monoblock front kit). Rear caliper info is generally very hard to come by!

Brembo

Brembo 6 Piston Monoblock - 14" (51.75mm pad depth) with a UK rear setup

Braking torque: 4.6% reduction

Front/rear bias: 1.5% extra to rear

Brembo 6 Piston Monoblock - 14" (48.7mm pad depth) with a UK rear setup

Braking torque: 3.9% reduction

Front/rear bias: 1.3% extra to rear

Brembo 6 Piston Monoblock - 14" (51.75mm pad depth) with Brembo 13.58" rear and Brembo "C" caliper

Braking torque: ??% reduction

Front/rear bias: ...(need rear caliper info)

Brembo 6 Piston Monoblock - 14" (48.7mm pad depth) with Brembo 13.58" rear and Brembo "C" caliper

Braking torque: ??% reduction

Front/rear bias: ...(need rear caliper info)

AP

AP Road Kit CP5555 6 Piston caliper - 356mm (54mm pad depth) with a UK rear setup

Braking torque: 0.5% reduction

Front/rear bias: 0.1% extra to rear

AP Road Kit CP5555 6 piston caliper - 356mm (54mm pad depth) with an AP 330mm rear (44.1mm pad depth)

Braking torque: 2.7% reduction

Front/rear bias: 1.4% extra to front

AP Race Kit Pro5000+ 6 piston caliper - 362mm disc (54mm pad depth) with a UK rear setup

Braking torque: 0.9% improvement

Front/rear bias: 0.3% extra to front

AP Race Kit Pro5000+ 6 piston caliper - 362mm disc (54mm pad depth) with an AP 343mm rear

Braking torque: ??% improvement

Front/rear bias: ...(need rear caliper info)

KAD

KAD 17" Wheel Kit - 6 Piston G caliper on UK front disc (46mm pad depth) with a UK rear setup

Braking torque: 7.8% reduction

Front/rear bias: 2.7% extra to rear

KAD 18" Wheel Kit - 6 Piston H caliper - 356mm disc (46mm pad depth) with a UK rear setup

Braking torque: 0.6% reduction

Front/rear bias: 0.2% extra to rear

KAD 18" Wheel Kit - 6 Piston H caliper - 356mm disc (46mm pad depth) with a UK rear disc and KAD rear caliper (49mm pad depth - can someone confirm this please?)

Braking torque: 5.1% improvement

Front/rear bias: 3.9% extra to rear

KAD 19" Wheel Kit - 6 Piston H caliper - 378mm disc (46mm pad depth) with a UK rear setup

Braking torque: 4.3% improvement

Front/rear bias: 1.3% extra to front

KAD 19" Wheel Kit - 6 Piston H caliper - 378mm disc (46mm pad depth) with a UK rear disc and KAD caliper (49mm pad depth - can someone confirm this please?)

Braking torque: 9.9% improvement

Front/rear bias: 2.3% extra to rear

Rotora

Stoptech

K-Sport

K-Sport 8 Piston caliper - 356mm (54mm pad depth) with a UK rear setup

Braking torque: 0.5% reduction

Front/rear bias: 0.1% extra to rear

K-Sport 8 Piston caliper - 356mm disc (54mm pad depth) with K-Sport 4 Piston rear caliper on 356mm disc

Braking torque: ??% reduction

Front/rear bias: ...(need rear caliper info)

K-Sport 8 Piston caliper - 380mm disc (54mm pad depth) with a UK rear setup

Braking torque: 5.0% improvement

Front/rear bias: 1.5% extra to front

K-Sport 8 Piston caliper - 380mm disc (54mm pad depth) with K-Sport 4 Piston rear caliper on 380mm disc

Braking torque: ??% improvement

Front/rear bias: ...(need rear caliper info)

997 Turbo

Brembo 6 Piston caliper - 350mm (66mm pad depth) with 350mm rear 4 Piston monoblock caliper (60mm pad depth)

Braking torque: 14.6% improvement

Front/rear bias: 9.6% extra to rear

996 Turbo

Brembo 4 Piston caliper - 330mm (60mm pad depth) with 330mm rear 4 Piston caliper (61mm pad depth)

Braking torque: 6.6% reduction

Front/rear bias: 2.6% extra to rear

SL55 AMG

AMG 8 Piston - 360mm (65mm average pad pad depth) with a 330mm rear 4 Piston caliper (45mm pad depth)

Braking torque: 7.7% improvement

Front/rear bias: 0.2% extra to front

Paul Mac - I know the front pads are extremely deep at something like 80mm with the extra material around the mounting lugs. Would you say the 65mm "average" pad depth seems accurate?

Edit: (I just changed the rear pad depth to 45mm - thanks)

Alcon

Alcon 6 Piston Monoblock - 365mm (54mm pad depth) with a UK rear setup

Braking torque: 10.9% improvement

Front/rear bias: 3.1% extra to front

Only seen this kit in one place - Autralia!! http://www.tweakit.net/shop/product_info.php?cPath=57_228_229_243&products_id=1506

Others

Alcon 6 Piston Monoblock - 323mm (54mm pad depth) with a UK rear setup

Braking torque: 0.3% improvement

Front/rear bias: 0.1% extra to front

Alcon 6 Piston Monoblock - 325mm (54mm pad depth) with a UK rear setup

Braking torque: 0.8% improvement

Front/rear bias: 0.3% extra to front

Alcon 6 Piston Monoblock - 330mm (54mm pad depth) with a UK rear setup

Braking torque: 2.1% improvement

Front/rear bias: 0.6% extra to front

Alcon 6 Piston Monoblock - 343mm (54mm pad depth) with a UK rear setup

Braking torque: 5.4% improvement

Front/rear bias: 1.6% extra to front

Alcon 6 Piston Monoblock - 355mm (54mm pad depth) with a UK rear setup

Braking torque: 8.4% improvement

Front/rear bias: 2.4% extra to front

Great info

Could you add the Alcon on a smaller stock sized disc?

Great stuff, interesting and very informative:thumbs:

Edit, also should have added very surprising in some cases.

Cheers chaps - just making a few changes to make it more understandable.

Originally I had the improvements/reductions based on the front calipers and used the bias to tell the rest of the story. The more I thought abut it the more unfair this seemed as, for example, the 997 turbo makes use of immensely powerful rear brakes...somehow.

The percentages for improvements/reductions are now based on both front and rear totals compared to the UK's front and rear totals. That is why some of the data has disappeared where I have no rear caliper info.

A couple of questions to anyone looking...

1. Does anyone have a Rotora or Stoptech kit they could take some measurements off?

2. Could any of the Brembo users tell me the rear caliper piston size please?

3. Could any of the AP users tell me the rear caliper piston size please and ideally the part number of the caliper too?

Great info

 

Could you add the Alcon on a smaller stock sized disc?

Done - jigged a few things around so post 9 has it in.

Done - jigged a few things around so post 9 has it in.

Top stuff, how about with 325, 330, 343 and 355 disc sizes, I wonder what I could squeeze under my 17" wheels

Top stuff, how about with 325, 330, 343 and 355 disc sizes, I wonder what I could squeeze under my 17" wheels

Done.

Done.

Top stuff

How does pad area come into play in this or are you just comparing the force applied between pad and disc?

The reason I ask is that Alcon have various 4 pot calipers where in fact the pad area is greater than the 6 pots.

4 pot B-type http://www.alcon.co.uk/Catalog/9.pdf

32mm disc

300-330 disc diam

133cm2 pad area

pad thickness 16

4 pot K-type http://www.alcon.co.uk/Catalog/10.pdf

32mm disc

295-355 disc diam

152cm2 pad area

pad thickness 20

6 pot http://www.alcon.co.uk/Catalog/11.pdf

32mm disc

242-380 disc diam

74cm2 pad area

pad thickness 18

The area doesn't play a direct role. The clamping force is generated in the hydraulic system and acts over the piston area(s). This force is applied direct to the back of the pad and then that exact same force is applied to the disc face (no force is "lost" going through the pad).

Pads of different areas can still only transmit the force they get applied to them from the piston(s). None of that force is lost and the pad can't generate any more force on its own - it all comes from the pistons. The contact pressure between the pad and disc will change as pad size changes...more area = less contact pressure but the applied force doing the braking is still the same. There are other effects of contact pressure changes (and pad size and material - not least pad and disc wear) but I wasn't going to get into any of those here as they don't affect the maths for the brake torque (similar to heat and caliper stiffness).

Now if the pad depth (or height depending on how you want to think of it) changes then that does have to be taken into account. The force acting on the disc has to be applied at a certain radius in order to get the brake torque. This radius is usually referred to as the effective radius and that is the disc radius minus half the pad depth.

So a 360mm disc with a 60mm deep pad will have an effective radius of 150mm. The same disc with a 46mm deep pad will have an effective radius of 157mm meaning that the clamping force is applied closer to the edge of the disc. This will increase the braking torque.

A good example to make you think about this is the AP CP5555 vs Brembo Monoblock. The AP's pad depth is pretty big at 54mm compared to the Brembo's 49mm and yet the AP still generates more torque on the same size disc....reason being the AP has more piston area. If you put a 49mm deep pad in the AP caliper it would generate a tiny bit more brake torque than the UK spec whereas the Brembo is approx 4% shy of the UK spec.

So basically ... pad depth plays a direct role. If the disc face design and pad retention mechanism will allow it, the brake torque and bias can be adjusted by altering the pad depths. This isn't ideal as the discs are designed to work with a particular depth pad in order to stabilize the disc temperature variations but it can be done...and people do it.

So is it correct to assume that a larger pad area would be better at dissipating heat therefore more fade resistant but offers less pad to disc contact pressure if the same braking force is applied?

The pad thickness's I listed are much lower than the ones you had, how does this change things?

Somewhat flawed,in a perspective point of view:

it's pascals principle in use, the force gained ( multiplied)is from the difference in piston sizes between the input piston ( brake pedal cylinder if you like, and the output piston size ( caliper piston area) , the work difference being the distance of the pistons moved,and the force being the brake pedal pressure multiplied.

Given the master cylinder is the same in all cases .

Let's say 10 lb pressure is applied and multiplied 1000 times so output force is 10000

now let's use 1/2 the output piston area ,(a lot smaller piston indeed) the result is only 5000 ,lots less eh! , but to get the same force as the much bigger first case , then all we have to do is push the brake pedal twice as hard!

But we only applied 10 lb,not the end of the world to simply apply 20 lbs to get the same brake force , despite only half the caliper piston size!!

Now factor that against the different brake piston areas and make a guess at how much pedal pressure we make!!

Then also factor the difference in pad areas compared to piston areas to get the force / area

it's not that hard to add foot pressure to the brake pedal and lots cheaper

good stuff , informative and usefull

I googled it .

Typical ratios for master cylinder are around 30 to 1

too much can be as bad as too little.

And of course the ABS will kick in way before you approach any maximum pedal pressure.

Someone could I guess google how much % pedal force it typically kicks in at , but for sure you will have a lot more leg force left than the system could use , and any excess brake force is pointless as the wheels are locked up

I think maybe you need to clarify about the pad thickness or depth, as on my first read i took it to mean the actual thickness of the pad, IE pad material between the backing metal and disc, maybe me being too literal, or thick:innocent:

But i do think others who do not have a technical grasp on things may misconstrue the info because of this.

Also there is a big variable, IE force applied to the peddle, how do you quantify that?

Somewhat flawed,in a perspective point of view:

 

it's pascals principle in use, the force gained ( multiplied)is from the difference in piston sizes between the input piston ( brake pedal cylinder if you like, and the output piston size ( caliper piston area) , the work difference being the distance of the pistons moved,and the force being the brake pedal pressure multiplied.

Given the master cylinder is the same in all cases .

Let's say 10 lb pressure is applied and multiplied 1000 times so output force is 10000

now let's use 1/2 the output piston area ,(a lot smaller piston indeed) the result is only 5000 ,lots less eh! , but to get the same force as the much bigger first case , then all we have to do is push the brake pedal twice as hard!

But we only applied 10 lb,not the end of the world to simply apply 20 lbs to get the same brake force , despite only half the caliper piston size!!

Now factor that against the different brake piston areas and make a guess at how much pedal pressure we make!!

Then also factor the difference in pad areas compared to piston areas to get the force / area

it's not that hard to add foot pressure to the brake pedal and lots cheaper

I like your thinking - stamp harder, save the cash!

I'd like to make it clear that I am not a "big brake kit seller" or anything like that - I only posted the numbers up as people have been talking about comparing calipers and kits and how good the UK parts are so I thought I'd share the numbers.

I think maybe you need to clarify about the pad thickness or depth, as on my first read i took it to mean the actual thickness of the pad, IE pad material between the backing metal and disc, maybe me being too literal, or thick:innocent:

 

But i do think others who do not have a technical grasp on things may misconstrue the info because of this.

 

Also there is a big variable, IE force applied to the peddle, how do you quantify that?

Good point.... The pad thickness doesn't play any role at all, it is the depth as shown by the blue arrow here. I should have posted that earlier to make it clear.

Hydraulic pressure is directly linked to the braking torque and is completely linear..... double the pressure = double the torque. However it is almost impossible to throw that into the mix to show up anything useful. This comparison was only to compare one brake setup to another for a given set of inputs (same pad compound, same pedal effort, same master cylinder etc).

As Jagman said - stamping on the pedal will increase the hydraulic pressure and increase the braking torque, that is a fact. However, it has to be kept constant in order to make any meaningful comparison between setups or else you could quite rightly say that the brake system off a Fiesta is as good as that on a Supra as long as it's balanced, you can stamp hard enough on the pedal, the seals can handle the pressure and the whole lot can cope with the heat.

I noticed the pad depth when reading a caliper guide earlier, as in its not the pad thickness as I originally thought

Some great info in here and I think it would make a great sticky for the tech section once its been trimmed down.