GP4 MS , Brake disc size.

Hyuk Jang

New member
안녕하세요.
gp4 ms 구매를 준비하고 있습니다. 다만 ms 피스톤이 30파이라서 330mm 디스크 사이즈로 가는게 맞는지 궁금합니다.
제 개인적인 생각으로는 320mm를 쓰는게 맞나요?
피스톤이 30파이라서 마스터실린더도 17rcs 코르사를 쓸 예정입니다.

현재 hypermotard gp4 rx+19rcs corsa를 사용하고 있습니다.
 

BMW Alpina

FOUNDING Member & Administrator
Staff member
Hello Hyuk Jang,
Please use Google Translate so you can post it in English and here is the weblink: https://translate.google.com/

For this first time, I will translate your post above on behalf of you:
hello.
Preparing to purchase gp4 ms. However, since the ms piston is 30 pie, I wonder if it is correct to go with a 330mm disc size.
Is it correct to use 320mm in my personal opinion?
Since the piston is 30 phi, I plan to use the 17rcs corsa as the master cylinder.

Currently using hypermotard gp4 rx+19rcs corsa.


My answer:
For Panigale V4, the stock Stylema caliper also have 30mm pistons exactly like the GP4-MS and it use 330mm disc size.
So if you are using the GP4-MS on a Panigale V4, it is best to use 330mm disc size, however you can also use 320mm disc size. If you are using 320mm disc size, you just need to take out the spacer between the caliper and the forks caliper bracket.
17 RCS Corsa Corta is the correct master cylinder for the GP4-MS

Now, if you are using the GP4-MS on a hypermotard, then you just need to use whatever diameter the Hypermotard disc brake came from and it should be ok.
 

Hyuk Jang

New member
Hello Hyuk Jang,
Please use Google Translate so you can post it in English and here is the weblink: https://translate.google.com/

For this first time, I will translate your post above on behalf of you:
hello.
Preparing to purchase gp4 ms. However, since the ms piston is 30 pie, I wonder if it is correct to go with a 330mm disc size.
Is it correct to use 320mm in my personal opinion?
Since the piston is 30 phi, I plan to use the 17rcs corsa as the master cylinder.

Currently using hypermotard gp4 rx+19rcs corsa.


My answer:
For Panigale V4, the stock Stylema caliper also have 30mm pistons exactly like the GP4-MS and it use 330mm disc size.
So if you are using the GP4-MS on a Panigale V4, it is best to use 330mm disc size, however you can also use 320mm disc size. If you are using 320mm disc size, you just need to take out the spacer between the caliper and the forks caliper bracket.
17 RCS Corsa Corta is the correct master cylinder for the GP4-MS

Now, if you are using the GP4-MS on a hypermotard, then you just need to use whatever diameter the Hypermotard disc brake came from and it should be ok.






Sorry for posting in Korean.

If so, don't you adjust the presence or absence of 330mm, 320mm disc size according to the normal piston pie?? Would there be any difference in braking even with 330mm?
 

BMW Alpina

FOUNDING Member & Administrator
Staff member
Sorry for posting in Korean.

If so, don't you adjust the presence or absence of 330mm, 320mm disc size according to the normal piston pie?? Would there be any difference in braking even with 330mm?
Hello, the 330mm should provide a bit more "leverage" due to the larger diameter resulting in slightly more powerful braking force. The cooling surface area will also increased and the heat capacity (due to more weight) should also increase.
I think your GP4-RX have larger piston diameter so it should have more clamping power (in relation to your hand press input), compare to the GP4-MS. So the 330mm should be better for the GP4-MS.
Either way, I am quite sure you will not feel too much differences in (locking the wheel) braking power.

The main different will be the consistency and less fade prone of the higher quality GP4-MS caliper and the larger heat capacity of the 330mm.
So, if I were you, I will definitely use the 330mm.
 

Hyuk Jang

New member
Hello, the 330mm should provide a bit more "leverage" due to the larger diameter resulting in slightly more powerful braking force. The cooling surface area will also increased and the heat capacity (due to more weight) should also increase.
I think your GP4-RX have larger piston diameter so it should have more clamping power (in relation to your hand press input), compare to the GP4-MS. So the 330mm should be better for the GP4-MS.
Either way, I am quite sure you will not feel too much differences in (locking the wheel) braking power.

The main different will be the consistency and less fade prone of the higher quality GP4-MS caliper and the larger heat capacity of the 330mm.
So, if I were you, I will definitely use the 330mm.



Thank you for the really good advice.
But according to my common sense, isn't the bigger the Piston Pi the better the braking? For RX, it is 32 Pi. Stylema or ms is 30 pie, but is the smaller 30 piston pie better for braking?
 

BMW Alpina

FOUNDING Member & Administrator
Staff member
Thank you for the really good advice.
But according to my common sense, isn't the bigger the Piston Pi the better the braking? For RX, it is 32 Pi. Stylema or ms is 30 pie, but is the smaller 30 piston pie better for braking?
So the RX with 32mm piston should be able to push more pressure (more clamping power), but it will also require more power from your finger to pull the larger RCS19 master cylinder.
However, the GP4-RX was an older 2 pieces design, while the GP4-MS is a one-piece monoblock.
So the GP4-MS is more rigid and will provide a better feel than the GP4-RX (at least in theory).
The GP4-MS smaller piston also should provide a better "feel."
The GP4-MS is also a bit heavier, allowing for more mass to absorb the heat (heat capacity).

This website provides good comparison between GP4-RX and GP4-MS: This is a summary of the different types of Brembo calipers for motorcycles and the differences between them. [Latest 2021].
 

Hyuk Jang

New member
So the RX with 32mm piston should be able to push more pressure (more clamping power), but it will also require more power from your finger to pull the larger RCS19 master cylinder.
However, the GP4-RX was an older 2 pieces design, while the GP4-MS is a one-piece monoblock.
So the GP4-MS is more rigid and will provide a better feel than the GP4-RX (at least in theory).
The GP4-MS smaller piston also should provide a better "feel."
The GP4-MS is also a bit heavier, allowing for more mass to absorb the heat (heat capacity).

This website provides good comparison between GP4-RX and GP4-MS: This is a summary of the different types of Brembo calipers for motorcycles and the differences between them. [Latest 2021].


Big caliper pistons aren't good!
I thought that if the piston was small, the braking force would be weak.
Because the master cylinder also has to use 17 pie.
There was a lot of discussion because of this.

Lastly, what do you think is the big difference between a 2pc caliper and a monoblock?
 

BMW Alpina

FOUNDING Member & Administrator
Staff member
Big caliper pistons aren't good!
I thought that if the piston was small, the braking force would be weak.
Because the master cylinder also has to use 17 pie.
There was a lot of discussion because of this.


Lastly, what do you think is the big difference between a 2pc caliper and a monoblock?
The reason why you need to use master cylinder 17 for the smaller piston GP4-MS is because if you use the 19 master cylinder then the brake lever will have very short travel and it will feel very hard (less brake feel).
Because the 19 mm diameter will be able to push more brake fluid at less stroke then the 17mm.
Big caliper piston can be good for application where you need more clamping power like in racing use, that is why the more race oriented caliper such as the GP4-RR and GP4-LM has larger diameter piston compare to the GP4-MS.
But for street use, the GP4-MS, will have a better feel.

The 2 piece caliper will NOT be as rigid as a monoblock, and a more rigid a caliper, the more flex it is allowing it to transfer more clamping power to the rotor surface, thus more precision and better feel too.

HOwever, the monoblock caliper is also harder to produce thus more expensive cost of GP4-MS compare to the 2 piece GP4-RX.
 

Hyuk Jang

New member
The reason why you need to use master cylinder 17 for the smaller piston GP4-MS is because if you use the 19 master cylinder then the brake lever will have very short travel and it will feel very hard (less brake feel).
Because the 19 mm diameter will be able to push more brake fluid at less stroke then the 17mm.
Big caliper piston can be good for application where you need more clamping power like in racing use, that is why the more race oriented caliper such as the GP4-RR and GP4-LM has larger diameter piston compare to the GP4-MS.
But for street use, the GP4-MS, will have a better feel.

The 2 piece caliper will NOT be as rigid as a monoblock, and a more rigid a caliper, the more flex it is allowing it to transfer more clamping power to the rotor surface, thus more precision and better feel too.

HOwever, the monoblock caliper is also harder to produce thus more expensive cost of GP4-MS compare to the 2 piece GP4-RX.



It was the answer I really wanted and wanted to know. Thank you very much sir!
I will use it for both competitions and public roads, but if I use it only for the race, is the GP4 RR the right answer then?

If it's going to be used on general roads, MS is the answer, right?
 

BMW Alpina

FOUNDING Member & Administrator
Staff member
It was the answer I really wanted and wanted to know. Thank you very much sir!
I will use it for both competitions and public roads, but if I use it only for the race, is the GP4 RR the right answer then?

If it's going to be used on general roads, MS is the answer, right?
Well, since you already bought the GP4-MS, you might want to try it at the race track, and you might find the GP4-MS has enough braking power that you need. Please note that it is useless to have a more powerful brake unless your tire also has a higher grip (like a slick / race compound tire).
However, if you need even more braking power, plus you want more heat resistant, then the GP4-RR might be the better choice because GP4-RR is equipped with Titanium Pistons while the GP4-MS is equipped with aluminum pistons.
 

Hyuk Jang

New member
Well, since you already bought the GP4-MS, you might want to try it at the race track, and you might find the GP4-MS has enough braking power that you need. Please note that it is useless to have a more powerful brake unless your tire also has a higher grip (like a slick / race compound tire).
However, if you need even more braking power, plus you want more heat resistant, then the GP4-RR might be the better choice because GP4-RR is equipped with Titanium Pistons while the GP4-MS is equipped with aluminum pistons.




MS will also change to titanium pistons. Since I always use only slick tires on the circuit, I will listen to your advice and use it because it is a course that requires extreme brake clamping. Because RR is expensive to use on frequent cleaning and public roads.

Thank you very much for the good advice. It really helped me a lot.
 
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