I would take 19x18 or 19x17 for those calipers. GP4-RX have 32/34 pistons. Have you checked this website Master cylinder fit calculation DOUBLE│GALE SPEED ?

 

I would take 19x18 or 19x17 for those calipers. GP4-RX have 32/34 pistons. Have you checked this website Master cylinder fit calculation DOUBLE│GALE SPEED ?

Thanks for your answer !
GPR-RX have 32/32 pistons not 32/34 .
i will check, thanks.
if it is for calculating the good MC piston size , based on the brake calipers pistons total surface , to get the right ratio i have done the calculation but it doesn't help to choose between 19x18 and 19x20 but only to choose rhe right piston size on the MC to get the good ratio.

 

An important issue is the ratio of the total caliper piston area to that of the MC. You can calculate that if you know the various diameters. The general rule is 30 or more is soft, 27 is sweet spot, 23 if firm, and 20 or less is wooden. This is just the hydraulic ratio and doesn't account for the lever ratio. The difference between x20 and x18 is 23%.

JK750 got in while I was composing. That's interesting stuff.

 

GP4RX - 4x 32mm pistons per caliper
19x20 - streetable
19x18 - soft touch, more modulation

Like you said, the manager recommends the 19x20 (eventhough the 19x18 is recommended for race/track) based on feedbacks from riders.

It depends on the preference of the rider, is he a 1~2 finger rider and prefers the modulation of the 19x18, or a 3~4 finger rider that prefers the feel of the 19x20?

 

Thanks for your answer as well !
unfortunately i don't know the pilots who told him this setup ( 19x20 brake MC being more adapted to the GP4-RX brake calipers , than the 19x18 brake MC ) is the best setup to choose for track use for those GP4-RX calipers ( in their experience and opinion ) .
From what i read , in the absolute 19x20 give less bite in the braking , making the braking less immediate ( less ON/OFF effect ) than a 19x18 but gives more precision / control , more dosing margin, having to pull the lever on a slightly longer distance to get the same braking power .
That team manager told me that for some M4 calipers , he would have recommended to buy the 19x18 brake MC but for the GP4-RX the return of experience he got from some pilots makes him advise me the 19x20 .

 

@Killing Floor - I suppose so, some riders prefer stiffer brake lever (19x20) over a softer feel (19x18).

The little circles and triangles, are from the page shared by @-JK750- (Master cylinder fit calculation DOUBLE│GALE SPEED)

From the tables, the second numbers determines the 'total ratio', including lever ratio to master pump to caliper. This number determines the circles and triangles.

For GP4RX, the feeling between 19x20 to 19x18 is different. You can try with the 19RCS that can change between 19x20 and 19x18.
The terms 'middle hard touch' and 'hard touch' is subjective. The rider must decide what suits best.

I think 19x20 is more suitable for street use, in case emergency braking and the bike tips forward (endo).

M4 with 19x18 or 19x20, GP4RX with 19x18 or 19x20 - All the combination will work. The rider decides his preferred combination.

 

@Killing Floor - I suppose so, some riders prefer stiffer brake lever (19x20) over a softer feel (19x18).

The little circles and triangles, are from the page shared by @-JK750- (Master cylinder fit calculation DOUBLE│GALE SPEED)

View attachment 585292

From the tables, the second numbers determines the 'total ratio', including lever ratio to master pump to caliper. This number determines the circles and triangles.

For GP4RX, the feeling between 19x20 to 19x18 is different. You can try with the 19RCS that can change between 19x20 and 19x18.
The terms 'middle hard touch' and 'hard touch' is subjective. The rider must decide what suits best.
View attachment 585293


I think 19x20 is more suitable for street use, in case emergency braking and the bike tips forward (endo).
View attachment 585294

M4 with 19x18 or 19x20, GP4RX with 19x18 or 19x20 - All the combination will work. The rider decides his preferred combination.

Thanks very much for your help and explanations , it's really nice from you !

Are the two pictures above the picture of the bike on the front wheel , showing the distance / travel of the lever between the lever position at rest and the lever position pulled at the max when braking ?

If it that is the case , the 19x20 Seems to have less distance between the rest position and the full braking position !

What i had read about the entraxe ( the second number in 19x18 or 19x20 , the first number being the size of the MC's piston ) is that it affects the bite of the brake, in a way that , the smaller the entraxe , the less effort it takes to pull the lever to apply a given force to the piston.
On the other hand , a larger entraxe will give less bite , will make you have to pull the lever harder for the same type of braking but will give a more precise braking.
So i would have thought that there would be more distance / travel , between the lever at rest position and the lever at full braking position .

About the PR19 RCS and PR 19 RCS Corsa Corta , the team manager who advised me to but a 19x20 brake MC , to use with the GP4-RX calipers on track , told me that those two MCs are really well suited for road / street use but much less for track use , the Billet or the forged Brembo 19x18 and 19x20 , being much better for track use ( i am not sure i remember correctly what he had told me and the reason why he told me they are more suited for road/ Street use but iif i remember correctly what he told me , i think he said the RCS and RCS Corsa Corta don't bare the heat of the heavy use on track , as well as the forged and billet versions of the PR 19 , or something like that ) .

I suppose that if the RCS and RCS Corsa Corta settings were working really well on tracks, they would have included those setting on the very expensive Brembo MCs made for Moto GP and Superbike but Brembo didn't include them , whereas they cost about 2500 to 3000 €

 

@Killing Floor
Are the two pictures above the picture of the bike on the front wheel , showing the distance / travel of the lever between the lever position at rest and the lever position pulled at the max when braking ?

• No, the levers are at rest.
• 19x20 the distance between the fulcrum to the piston = 20mm
• 19x20 the distance between the fulcrum to the piston = 18mm

 

@Killing Floor
What i had read about the entraxe ( the second number in 19x18 or 19x20 , the first number being the size of the MC's piston ) is that it affects the bite of the brake, in a way that , the smaller the entraxe , the less effort it takes to pull the lever to apply a given force to the piston.
On the other hand , a larger entraxe will give less bite , will make you have to pull the lever harder for the same type of braking but will give a more precise braking.
So i would have thought that there would be more distance / travel , between the lever at rest position and the lever at full braking position .

entraxe = distance
in this case, it's the 'lever ratio'

You are correct about the applied lever force vs the braking power (bite)
'Precise braking' is another matter - this depends on the rider, and I personally thinks it depends on the following:

• bite point (see remote adjusters)
• modulation - I'm using CNC 19x18 with Tokico 30mm calipers for street riding. To some riders, the range of lever movement on the 18mm is too big, and they prefer the range of 20mm.

Also, the RCS are suitable for ABS, but the Billet/CNC are not recommended.

 

@Killing Floor
What i had read about the entraxe ( the second number in 19x18 or 19x20 , the first number being the size of the MC's piston ) is that it affects the bite of the brake, in a way that , the smaller the entraxe , the less effort it takes to pull the lever to apply a given force to the piston.
On the other hand , a larger entraxe will give less bite , will make you have to pull the lever harder for the same type of braking but will give a more precise braking.
So i would have thought that there would be more distance / travel , between the lever at rest position and the lever at full braking position .

entraxe = distance
in this case, it's the 'lever ratio'

You are correct about the applied lever force vs the braking power (bite)
'Precise braking' is another matter - this depends on the rider, and I personally thinks it depends on the following:

• bite point (see remote adjusters)
• modulation - I'm using CNC 19x18 with Tokico 30mm calipers for street riding. To some riders, the range of lever movement on the 18mm is too big, and they prefer the range of 20mm.

Also, the RCS are suitable for ABS, but the Billet/CNC are not recommended.

When you say " To some riders, the range of lever movement on the 18mm is too big, and they prefer the range of 20mm."
Do you mean there is more travel distance between the rest position of the brake lever and the maximum distance you can pull it towards the handle bar grip, with a 19x18 compared to a 19x20 ?

i thought it was the opposite , explaning why some say the 19x20 gives more precise control on the braking ( and is more adapted for road use than the 19x18 ,which is recommended more for track use ) than the 19x18 which has more bite ( is more ON/OFF ) !

i had never heard about the remote adjuster , so i looked on the net to see what it is but i don't think on my level, i would need that type of part on my braking system as i won't participte to championship races ( at least for some time, if ever i do it one day ).
i may be wrong but i suppose with some GP4-RX , a good brake master cylinder and correct rotor discs ( and good brake fluid ) , i should not have too much brake fade .

I won't use any ABS system on track .
i don't have any on my 2015 750 and 1000 and if later i use my 2018 1000 R on track , i will remove the ABS system , as unlike on the 206-2020 ZX10R where you can deactivate the ABS ( front , rear or both ) without being obliged to remove the whole ABS system ( although it must be better to remove it if the bike is dedicated to track use ) , i believe on the 2017-2021 GSX-R 1000 R , it is not possible to deactivate the ABS the same way as on the ZX10R , although it is possible to remove the whole ABS system and put a part ( like the I2M ABS Emulator ) which prevents the ABS indicator on the dashboard to signal a problem .

 

I have no experience dealing with brake fade, but I think it has more to do with calipers (M4, M50, GP4's), or the pads, or the brake fluid, much more than MC. I feel the heat from the braking wouldn't travel as far up to the MC. Maybe I'm wrong.

 

I am still looking for some informations to buy my MCs for track use and i wonder what size are the stock / OEM radial master cylinders on the 2012-2016 GSX-R 1000 , 2017 and on GSX-R 1000/1000 R and 2011 and later GSX-R 750 ?

In another topic on the forum , someone was saying that the 2017 and later GSX-R 1000 / 1000 R have a master cylinder with 19mm pistons , is that true and if it is , is it the case as well on the two other GSX-R i spoke about ( 2011 and later GSX-R 750 and 2012-2016 GSX-R 1000 ) ?

If they all 3 have 19mm pistons , then what is the size of the entraxe , are they 19x18 , 19x20 or 19x?? ( i looked on the stock Nissin MCs but couldn't find anything like that written on them) ?

Maybe , to have a point of comparison . Would help me to know what size to choose between 19x18 and 19x20 !

Knowing it is an expensive purchase ( especialy if i buy some billet MC ) and that feeling confident / confortable with the control of my braking setup on track is quite important, i wouldn't like to choose the wrong one ( at least , one i don't feel confortable with ) !

 

If there's anything to add, that would be the riders chose 19x20 on the GP4RX because they moved from older, lesser calipers. Both are not wrong. If you are not at the level to need remote adjusters, then, I'd say you will be fine with 19x20, but better on the 19x18.

There are worse combinations of MC-calipers out there, and here we are beating on a 11% problem.

 

As a matter of fact , i have no idea if i am or not on the level of using a remote adjuster , as i have not yet riden those bikes on track , so i don't know if i would need to adjust my brake system with a remote adjuster, after some time riding them during some sessions on track .
Maybe i would , maybe not but i prefer to say i am not as i don't want to brag having more competences / riding skills than i have before knowing about something !
Before the remote adjuster , i prefer to look for the right MC and see after that if i need a remote adjuster or not , knowing all the important things i have / have had already to buy to upgrade my bikes for track use ( good suspensions , better calipers, track fairings, full exhaust racing system, a small truck or van to take the bikes to the tracks as the bikes won't be allowed to ride on the road anymore once transformed for track use ...etc )

 

Fron what i found as infos about the stock OEM Nissin front brake MCs , it seems the 2011 and later GSX-R 750 and 2012-2016 GSX-R 1000 , have a 17,5 mm piston on their stock OEM Nissin front brake MC .
As a matter of fact ,it is written 11/16 on both MC ( which seem to be the same on both bike ) and from what i read on a GSXS1000 forum ,someone ( who seemed to know what he was speaking about ) was saying that Nissin only makes two sizes of Radial front brake MCs , 17,5mm and 19mm ( and that is what i saw as well on the Nissin website ) and that both have a 18mm entraxe.
Obviously ,that doesn't mean Nissin cannot make some specific parts for different Japanese brands of motorcycles , like Brembo does ( like the M4 type Radial front brake calipers Brembo makes for Suzuki and which is used on 2011 and later GSX-R 750 , 2012 and later GSX-R 1000 , as well as on the 2017 and on 1000 R , which is a 32/32 M4 whereas Brembo aftermarket M4 is a 34/34 ) but it is really written 11/16 on the Nissin MCs for the 17,5 ones ( and 3/4 on the 19mm ones it seems ) , so that what should be on those GSX-Rs although i am not 100% sure it is a 18 mm entraxe but that's possible .

I guess it must make quite a difference with a 19x18 or 19x20 which must brake quite harder than the 17,5 one.

On the GaleSpeed link :

Master cylinder fit calculation DOUBLE│GALE SPEED

that JK750 had posted on the post where he was answering me at the begining of the topic , if i understood it correctly - with some 32/32 brake calipers ( unlike what JK750 was saying the GP4-RX are not 32/34 but 32/32 ) ,Galespeed seems to say that some 17,5x17 and 17,5x18 are appropriate for street use , as well as some 19x16 and 19x17 but that 19x18 , 19x19 and 19x20 , are not adapted/ appropriate for street use !

That said , i am looking for some MCs for track use, so that would have been interesting to see what that type of app would recommend for track use but i am not sure Galespeed has it available for track use as well on their website ( i will check ).

 

@Killing Floor yes, that's lever ratio