I hate to tell you this, but a larger bore generates less pressure for any given amount of pedal or lever force, not more. It will firm up the feel because it takes more force to generate any given level of stopping force.
Mark
Thanks for the correction.
Just expressing the experience i have had with a required modification on a popular car that worked for me, as such perhaps a bigger mc is available to give the same level of increased braking performance for the GS that i experienced with my porsche. Although pedal effort is higher( increased pedal pressure i should have said is needed ), it provides less pedal travel and eliminates the spongy feeling of the original lines.
I pasted this following article ( using car braking systems as example but some principles may apply to bikes) which goes into detail explaining the pros and cons of bigger bore mc's. Ultimately it's a matter of what you are looking to achieve from your ride, that determines what size mc is best to use.
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Technical Corner
With regard to braking it’s always helpful to refresh the basic rules of brake systems. If you fit larger discs you will increase the braking mechanical advantage. This will reduce pedal effort. If you find this results in brakes that are too sensitive for track use you can increase pedal effort by changing the master cylinder or removing the brake servo. A larger master cylinder bore size will increase pedal effort but reduce pedal travel. Master cylinders are usually available in inch sizes, pedal effort in lbs per sq inch and piston sizes in mm (great!).
Some formulas will demonstrate what you might end up with:
If you increase disc size from 284mm to 300mm you would end up with a 5% decrease in the pedal force required to get the same braking force. Therefore a 100lb force required before would become 95lb
New pedal force = Pedal force x (Old brake disc radius/New brake disc radius)
The rolling radius of the tyre has the opposite effect - increase the diameter of the tyre/wheel combination and you increase the pedal force required.
New pedal force = Pedal force x (Old tyre radius/New tyre radius)
In this case if you went from a 14” Wheel with 195/60 up to a 16” wheel with 205/55 you would increase the pedal effort required by 10%.
When looking at master cylinders the formula is as follows:
New pedal force = Pedal force x (new master cylinder bore diameter?/ old master cylinder bore diameter)?
Because of the square in the above formula the effect of a change is more pronounced. E.g a move from a 1” master cylinder to a 1.25” master cylinder will change the pedal force required from 100lbs to 156lbs.
Next thing to remember is bigger pistons in the calipers mean more force and, therefore, less pedal effort. Bigger pistons in the calipers mean more pedal movement. For comparing one brake to another on the same car, you can simply multiply the total caliper piston area times the effective radius. If you have a sliding calliper although it has piston(s) on one side the area should be doubled. A single piston sliding calliper with the same piston size as a twin fixed calliper will have the same clamping force.
When planning your braking modifications it is a good idea to consider these factors. Naturally bigger brakes often require bigger wheels so the two cancel each other out to a degree."
(only briefly, as I'd ease lever pressure). It had the older (no hole) disks.
