Porsche Caliper 996.351.425/426

[ShaneMitchinson]

Hi there, basically I have standard brakes on my 2012 Seat Leon FR+ Supercopa CR170 and I sometimes feel as if they fade very quickly and the pedal starts to have little movement before they are on, during a fast road drive. I'm looking into the 996.351.425/426 conversion with 330 x 28 discs. From what I understand my standard caliper has a single 54mm piston, the 996 caliper has 40/36mm pistons. I have been using this calculator to work out the braking power. http://brakepower.com/help_abc_27_PAC_t.htm it says to times the standard caliper power outputs by 2 which would give me an output of 4578.12 mm squared. Putting the Porsche caliper specs into that calculator gives me 9093.44 mm squared.. so effectively the standard calipers have more power? Or am I not understanding this correctly? Any help will be appreciated as I don't want to spend however much and have brakes that are no better.

Thanks, Shane.

 

[ShaneMitchinson]

Anyone?

 

[Deleted member 98167]

Shane, you are right. The standard calipers have more clamping force (if that is what you mean with “power”). But the difference is only 0.7%, so therefore unnoticeable.

Total caliper piston area per front axle: 9093.44 mm² (996 Porsche) and 9156.24 mm² (your Seat). Clamping force is the product of hydraulic system pressure and total piston area. But what we “feel” is something you could call “brake torque”. Clamping force is only one part of that. Another is the effective radius of the rotor. The larger this radius, the higher the torque.

But it seems that your problem is temperature related, rather than “power” related.

In order to address your fade problem, you could look at three possible ways to improve the current situation:

1) Increase the maximum operating temperature of the brake pads (increase resistance against fading).
2) Increase cooling capacity of the system (with cooling ducts that force air into the rotor centers).
3) Increase heat sink capacity of the system.

Step one and two are easy and relatively affordable.
Step three is the one where some people get in trouble... let me explain.

To increase heat sink of the pads, you have to use larger ones, which means bigger calipers (not bigger pistons!). And to increase heat sink of the rotors, you will have to get heavier ones, which usually also means bigger in diameter. This introduces you to the “big brake bias game” where you could end up with front brakes that require less force on the brake pedal to lock up the front wheels, resulting in less hydraulic system pressure in your rear brakes as well... Now your rear brakes are doing less than in the previous situation under threshold braking, resulting in ..... longer brake distance! In other words, you made your brake system less effective, or put differently, you decreased the maximum deceleration capacity of your vehicle.

To counter the increase in brake torque of the larger rotors, you will have to decrease the total piston area of the new calipers that go with the larger rotors, in order to maintain the proper brake bias.

Another thing to keep in mind is that bigger brakes usually increase the un-sprung weight, which is not beneficial for the “bond” between tire and road under threshold braking... just a thought.

I hope this helped to answer some of the questions you had (but it may have raised some other ones).

Good luck!
Arne

 

[ShaneMitchinson]

Shane, you are right. The standard calipers have more clamping force (if that is what you mean with “power”). But the difference is only 0.7%, so therefore unnoticeable.

Total caliper piston area per front axle: 9093.44 mm² (996 Porsche) and 9156.24 mm² (your Seat). Clamping force is the product of hydraulic system pressure and total piston area. But what we “feel” is something you could call “brake torque”. Clamping force is only one part of that. Another is the effective radius of the rotor. The larger this radius, the higher the torque.

But it seems that your problem is temperature related, rather than “power” related.

In order to address your fade problem, you could look at three possible ways to improve the current situation:

1) Increase the maximum operating temperature of the brake pads (increase resistance against fading).
2) Increase cooling capacity of the system (with cooling ducts that force air into the rotor centers).
3) Increase heat sink capacity of the system.

Step one and two are easy and relatively affordable.
Step three is the one where some people get in trouble... let me explain.

To increase heat sink of the pads, you have to use larger ones, which means bigger calipers (not bigger pistons!). And to increase heat sink of the rotors, you will have to get heavier ones, which usually also means bigger in diameter. This introduces you to the “big brake bias game” where you could end up with front brakes that require less force on the brake pedal to lock up the front wheels, resulting in less hydraulic system pressure in your rear brakes as well... Now your rear brakes are doing less than in the previous situation under threshold braking, resulting in ..... longer brake distance! In other words, you made your brake system less effective, or put differently, you decreased the maximum deceleration capacity of your vehicle.

To counter the increase in brake torque of the larger rotors, you will have to decrease the total piston area of the new calipers that go with the larger rotors, in order to maintain the proper brake bias.

Another thing to keep in mind is that bigger brakes usually increase the un-sprung weight, which is not beneficial for the “bond” between tire and road under threshold braking... just a thought.

I hope this helped to answer some of the questions you had (but it may have raised some other ones).

Good luck!
Arne

Wow! So basically going for the bigger calliper sand rotors will make a difference for the better, but to benefit that I should also upgrade the rear brakes to something bigger with 4 pots? I was going to look at the rears in future which would be the Cayenne 955 calliper with larger rear and vented rotor. So doing this should make a big difference? Also do you think the pedal would feel reasonably okay with a full set of 4 pot calipers? The only problem with these rear calipers is the handbrake. Creation make a mount which allows you to fit the standard calipers on also to act as a handbrake, but I was wondering if I can get a mechanically engaged hydro brake cylinder to make the rear brakes lock like that. But I understand a hydro rear brake will fail an MOT, but I never read anything about a mechanically engaged hydro? Sorry for all the questions! Thanks for the help.

Shane

 

[Deleted member 98167]

Shane, please don’t read too much between the lines

I will respond to the several questions you asked by quoting them first:

“Wow! So basically going for the bigger calliper sand rotors will make a difference for the better, but to benefit that I should also upgrade the rear brakes to something bigger with 4 pots?”

I don’t think so. But first things first: what is the diameter of your current front rotors? I tried to find it online, but am not sure whether it is 312mm, 345mm, or even an entirely different size. Can you help me out there? If you decide on the 330x28 mm rotors I would not worry too much about the difference in diameter. A couple of hard stops on clean/dry tarmac or concrete with the ABS fuse pulled (in a safe environment!) should tell you whether the front or rears are locking up first. Let someone outside of the car observe if you can’t feel it.

If the rears are locking up before the front ones do, pads with a slightly lower friction coefficient in the rear brakes might be all you need to get bias in the ball park. If the front brakes lock up first, but just slightly, because a LITTLE more force on the pedal locks up the rears as well, than brake bias is close to perfect. If the fronts lock up and it takes a lot more pedal effort to lock the rears too, then your brake bias is way off and you will need either front calipers with less piston area, or rear calipers with more piston area, or/and rear rotors with a larger diameter.

“I was going to look at the rears in future which would be the Cayenne 955 calliper with larger rear and vented rotor. So doing this should make a big difference?”

That depends on the effective radius of the rotors (the distance from rotor-center to halfway the swept area of the rotor) and the total piston area of the calipers.

“Also do you think the pedal would feel reasonably okay with a full set of 4 pot calipers?”

4 pot calipers don’t necessarily have more total piston area than single piston floating calipers. Remember your front calipers: single piston 54 mm calipers have the same total piston area as the 4-pot calipers from the 996 Porsche (2x40mm and 2x36mm). This means that fluid displacement is comparable as well, and therefore pedal travel.

Regarding your question about the hand brake and the MOT, I don’t think anything hydraulic in the e-brake circuit will fly, but that’s just a guess. Here in the U.S. annual technical inspections are a lot less intimidating and several states don’t have any kind of annual inspection.

Arne

 

[ShaneMitchinson]

Shane, please don’t read too much between the lines

I will respond to the several questions you asked by quoting them first:

“Wow! So basically going for the bigger calliper sand rotors will make a difference for the better, but to benefit that I should also upgrade the rear brakes to something bigger with 4 pots?”

I don’t think so. But first things first: what is the diameter of your current front rotors? I tried to find it online, but am not sure whether it is 312mm, 345mm, or even an entirely different size. Can you help me out there? If you decide on the 330x28 mm rotors I would not worry too much about the difference in diameter. A couple of hard stops on clean/dry tarmac or concrete with the ABS fuse pulled (in a safe environment!) should tell you whether the front or rears are locking up first. Let someone outside of the car observe if you can’t feel it.

If the rears are locking up before the front ones do, pads with a slightly lower friction coefficient in the rear brakes might be all you need to get bias in the ball park. If the front brakes lock up first, but just slightly, because a LITTLE more force on the pedal locks up the rears as well, than brake bias is close to perfect. If the fronts lock up and it takes a lot more pedal effort to lock the rears too, then your brake bias is way off and you will need either front calipers with less piston area, or rear calipers with more piston area, or/and rear rotors with a larger diameter.

“I was going to look at the rears in future which would be the Cayenne 955 calliper with larger rear and vented rotor. So doing this should make a big difference?”

That depends on the effective radius of the rotors (the distance from rotor-center to halfway the swept area of the rotor) and the total piston area of the calipers.

“Also do you think the pedal would feel reasonably okay with a full set of 4 pot calipers?”

4 pot calipers don’t necessarily have more total piston area than single piston floating calipers. Remember your front calipers: single piston 54 mm calipers have the same total piston area as the 4-pot calipers from the 996 Porsche (2x40mm and 2x36mm). This means that fluid displacement is comparable as well, and therefore pedal travel.

Regarding your question about the hand brake and the MOT, I don’t think anything hydraulic in the e-brake circuit will fly, but that’s just a guess. Here in the U.S. annual technical inspections are a lot less intimidating and several states don’t have any kind of annual inspection.

Arne

I'll give the ABS thing a shot once it's dry!
The front brakes if upgraded would be 36/40mm pistons with this rotor kit http://www.creationsmotorsport.com/product-detail.php?pid=538

And the rear would be this kit http://www.creationsmotorsport.com/product-detail.php?pid=666

My current rotors are 312mm I believe. The rears are much smaller and non vented. These are the rear calipers I'd like to use but I'm unsure of the piston sizes on them.. http://www.porschepartsused.co.uk/114-brakes/278-rear-brembo-calipers.html
Just don't want to spend silly money and not have better brakes!

 

[Deleted member 98167]

Shane, nice kits, but if you ask me, the rear kit seems too much for the front kit. Keep in mind that the Porsche Cayenne has a more even weight distribution front vs. rear than your Leon (that has most of the weight on the front wheels).

So here are the numbers: The Cayenne 4-pot rear calipers have 2x28 mm + 2x30 mm pistons and your Leon has standard a 1x38 mm floating caliper. Do the math in the calculator on BrakePower.com as you mentioned in your first post of this thread and you will see that total piston area on the rear axle of your Leon is 4534 mm², opposed to 5288 mm² for the Cayenne. That is 17% more. Add to that the fact that your OEM rear rotor is 255 mm diameter (or 286? anyways, a lot smaller), verses 310 mm for the R32 rear rotor from the kit, and you can see why I expect the rear brakes to become way too much in combination with the front brakes, no matter whether that will be the OEM or the Porsche 996 brakes.

So based on your information, I think that the front kit would be a good investment. The rear kit (again, based on your information) not so much.

Maybe there is someone out there that has experimented with these kits, that can join our conversation. I just give you my opinion based on general brake knowledge.

 

[ShaneMitchinson]

Shane, nice kits, but if you ask me, the rear kit seems too much for the front kit. Keep in mind that the Porsche Cayenne has a more even weight distribution front vs. rear than your Leon (that has most of the weight on the front wheels).

So here are the numbers: The Cayenne 4-pot rear calipers have 2x28 mm + 2x30 mm pistons and your Leon has standard a 1x38 mm floating caliper. Do the math in the calculator on BrakePower.com as you mentioned in your first post of this thread and you will see that total piston area on the rear axle of your Leon is 4534 mm², opposed to 5288 mm² for the Cayenne. That is 17% more. Add to that the fact that your OEM rear rotor is 255 mm diameter (or 286? anyways, a lot smaller), verses 310 mm for the R32 rear rotor from the kit, and you can see why I expect the rear brakes to become way too much in combination with the front brakes, no matter whether that will be the OEM or the Porsche 996 brakes.

So based on your information, I think that the front kit would be a good investment. The rear kit (again, based on your information) not so much.

Maybe there is someone out there that has experimented with these kits, that can join our conversation. I just give you my opinion based on general brake knowledge.

So something with slightly smaller pistons on the rear to balance it out? Or maybe go for the 996.351.429/430 calipers? Even though it would probably be massive overkill but I'm hoping in the future to take the leon to around 300bhp area!

 

[Deleted member 98167]

If you have your mind set on the 310 mm rear rotors, the matching calipers should have less piston area than the Leon rear calipers that go with the smaller OEM rotors. A calculation would be the proper way to come to a number, but that would require a lot of data we currently don't have. Therefore a wild guess: 4200 - 4400 mm².

Otherwise a dual master cylinder with balance bar would solve your problem, and than the 310 mm rear rotors can very well go with the Cayenne rear calipers (just use a large M/C in the rear circuit). It is the way to go for dedicated track cars (calculation of M/C sizes required). Big operation though, and this would eliminate your ABS and boost function (built in your ABS pump). I'm not sure if this is MOT legal ...