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-   -   Classic brakes - sharper MC? (https://www.biker.ie/forum/showthread.php?t=247160)

ascalon 5th January 2019 11:56 AM

Classic brakes - sharper MC?
 
My VF1000 is very, eh, classic in the braking department.

It has 2 piston sliding calipers on 296mm discs, so never marvellous, and even worse hauling up a kerb weight of some 258kg.

It has braided hoses, freshly cleaned and greased calipers and Goldfren carbon ceramic HH pads running on Brembo discs, but it seems to take a long time for the lever pressure to build into braking effect.

Would moving from the OEM 5/8" (15.875mm) master cylinder to a 14mm one give me more pressure for better performance?

Would a radial master cylinder work with this set up?

All the radial cylinders seem to be quite large bore, do they work differently to the axial ones?

Cheers,
A

sharpbikes 5th January 2019 11:51 PM

Re: Classic brakes - sharper MC?
 
you can bolt on any master cylinder that fits the clip on and it will make a difference, a 14mm would be a step down from a 15.875 i would say, it would give more travel at the lever which in turn offers more feel.

i assume you need to be able to pump more fluid down and get a quicker take up on the brakes so id recommend a 16mm radial brembo from a r1/r6 of newer years, its radial and offers better feel due to this but also a tiny bit more pressure, the other options include brembo radial master cylinders or accossato, a 19x18 radial would be best i would say for your setup, 19x20 would be overkill as it would make the brakes like an on off switch.

a radial master cylinder works better than an axial master cylinder by allowing the rider to pull directly against the piston and thus give us more feel and the ability to moderate the lever better in any given situation including giving us better leverage on the piston. a axial master cylinder has its piston parallel to the bar usually and this requires a turning force to apply the lever pull to the piston rather than acting on the piston directly.

ascalon 6th January 2019 09:52 AM

Re: Classic brakes - sharper MC?
 
[quote=sharpbikes;3561227]you can bolt on any master cylinder that fits the clip on and it will make a difference, a 14mm would be a step down from a 15.875 i would say, it would give more travel at the lever which in turn offers more feel.

i assume you need to be able to pump more fluid down and get a quicker take up on the brakes so id recommend a 16mm radial brembo from a r1/r6 of newer years, its radial and offers better feel due to this but also a tiny bit more pressure, the other options include brembo radial master cylinders or accossato, a 19x18 radial would be best i would say for your setup, 19x20 would be overkill as it would make the brakes like an on off switch.

a radial master cylinder works better than an axial master cylinder by allowing the rider to pull directly against the piston and thus give us more feel and the ability to moderate the lever better in any given situation including giving us better leverage on the piston. a axial master cylinder has its piston parallel to the bar usually and this requires a turning force to apply the lever pull to the piston rather than acting on the piston directly.[/quote]

Thanks for that.

I see what you mean on the smaller MC bore size and lever travel, but is a smaller bore size not the way to go to increase system pressure? (Pressure = (force/area))

I had thought that system pressure is what would achieve greater braking force, over moving a greater volume of fluid?

sharpbikes 6th January 2019 12:32 PM

Re: Classic brakes - sharper MC?
 
the bigger the piston the more fluid is pushed down to the calipers and thus moves the pistons faster and applies more pressure to the pads. forcing more fluid through the lines to the calipers is going to give more pressure.

going down in master cylinder size could cause you to be double pumping the lever to get system pressure.

corkgsxr 6th January 2019 05:44 PM

Re: Classic brakes - sharper MC?
 
Try a brembo rcs19. Buying a fixed ratio is near as dear. I always thought they were Abit much until I used one and there majorly better than any master I've used before

Gixxer 6th January 2019 08:21 PM

Re: Classic brakes - sharper MC?
 
[quote=sharpbikes;3561244]the bigger the piston the more fluid is pushed down to the calipers and thus moves the pistons faster and applies more pressure to the pads. forcing more fluid through the lines to the calipers is going to give more pressure.

going down in master cylinder size could cause you to be double pumping the lever to get system pressure.[/quote]

That's 100% arse about face. A smaller diameter piston will give more pressure.

faz1 6th January 2019 09:07 PM

Re: Classic brakes - sharper MC?
 
[quote=Gixxer;3561260]That's 100% arse about face. A smaller diameter piston will give more pressure.[/quote]

Larger piston diameter results in greater force exerted actually, generally expressed as:
Resultant Force equals (Pressure on surface of piston x (Pi x radius of piston squared))
it's all here if you are bored stiff.........

[url]https://www.globalspec.com/learnmore/fluid_power_components/hydraulic_equipment_components/hydraulic_cylinders[/url]

Gixxer 6th January 2019 09:14 PM

Re: Classic brakes - sharper MC?
 
[quote=faz1;3561264]Larger piston diameter results in greater force exerted actually, generally expressed as:
Resultant Force equals (Pressure on surface of piston x (Pi x radius of piston squared))
it's all here if you are bored stiff.........

[url]https://www.globalspec.com/learnmore/fluid_power_components/hydraulic_equipment_components/hydraulic_cylinders[/url][/quote]

Thanks for the link, but you're wrong :thumbsup2:

sharpbikes 7th January 2019 12:21 AM

Re: Classic brakes - sharper MC?
 
[quote=Gixxer;3561260]That's 100% arse about face. A smaller diameter piston will give more pressure.[/quote]

im no expert so id be interested to hear how it does work, ive always thought bigger piston gives more pressure assuming the stroke remains the same? in my experience the bigger diameter the piston in the master the more pressure ive had unless im confused between pressure and something else.

vifferman 7th January 2019 12:39 AM

Re: Classic brakes - sharper MC?
 
[quote=sharpbikes;3561277]im no expert so id be interested to hear how it does work, ive always thought bigger piston gives more pressure assuming the stroke remains the same? in my experience the bigger diameter the piston in the master the more pressure ive had unless im confused between pressure and something else.[/quote]

Bigger piston gives more pressure at the caliper for a given movement at the master cylinder. The down side is that you need more pressure at the master cylinder to achieve that movement, so the lever will feel harder and less feel for what's happening at the wheel.

Aidanm 7th January 2019 05:54 AM

Re: Classic brakes - sharper MC?
 
Assuming all stays the same with calipers, greater pressure means greater breaking force.
Force=pressure x area
pressure in the system = force (of your fingers) divided by area of your master cylinder piston.
This means for a given amount of finger force the smaller the piston the more pressure will be generated in the system.
The downside is that less VOLUME of fluid will shift meaning longer lever travel, but more "feel"...

The other factor at play is the distances between the lever pivot and the m/c piston contact and your finger grip. This is also an important leverage factor, and modern radial m/c's are better designed in this regard.

Gixxer 7th January 2019 04:38 PM

Re: Classic brakes - sharper MC?
 
[quote=sharpbikes;3561277]im no expert so id be interested to hear how it does work, ive always thought bigger piston gives more pressure assuming the stroke remains the same? in my experience the bigger diameter the piston in the master the more pressure ive had unless im confused between pressure and something else.[/quote]

It works exactly the same as the gearing on your bike. It's all about multipliers. Small front sprocket + big back sprocket = more force at the wheel. Hydraulic pistons work exactly the same way.

Let's assume a hypothetical 10 lb force applied to the brake lever, with a 10:1 multiplier from the lever to the piston. Friction losses aside, if the master cylinder and slave cylinder have the same area piston, the slave cylinder piston would travel the same distance as the master cylinder piston, and the same 100 lb of pressure would be output from the slave cylinder. If the master cylinder piston has 1/2 the surface area of the slave cylinder, and assuming the same travel of the brake lever, only half the volume of oil will move from the master to the slave, so the slave cylinder piston would travel half the distance of the master cylinder piston but at twice the pressure.

sharpbikes 7th January 2019 05:47 PM

Re: Classic brakes - sharper MC?
 
[quote=Gixxer;3561322]It works exactly the same as the gearing on your bike. It's all about multipliers. Small front sprocket + big back sprocket = more force at the wheel. Hydraulic pistons work exactly the same way.

Let's assume a hypothetical 10 lb force applied to the brake lever, with a 10:1 multiplier from the lever to the piston. Friction losses aside, if the master cylinder and slave cylinder have the same area piston, the slave cylinder piston would travel the same distance as the master cylinder piston, and the same 100 lb of pressure would be output from the slave cylinder. If the master cylinder piston has 1/2 the surface area of the slave cylinder, and assuming the same travel of the brake lever, only half the volume of oil will move from the master to the slave, so the slave cylinder piston would travel half the distance of the master cylinder piston but at twice the pressure.[/quote]

makes sense, cheers for that :thumbsup2:

Gixxer 7th January 2019 06:53 PM

Re: Classic brakes - sharper MC?
 
This explains hydraulic multiplication pretty simply.

[IMG]https://c1.staticflickr.com/5/4885/31709704947_0151a5dbf8_o.jpg[/IMG]

To determine the multiplication factor in the figure above, start by looking at the size of the pistons. Assume that the piston on the left is 2 inches (5.08 cm) in diameter (1-inch / 2.54 cm radius), while the piston on the right is 6 inches (15.24 cm) in diameter (3-inch / 7.62 cm radius). The area of the two pistons is Pi * r2. The area of the left piston is therefore 3.14, while the area of the piston on the right is 28.26. The piston on the right is nine times larger than the piston on the left. This means that any force applied to the left-hand piston will come out nine times greater on the right-hand piston. So, if you apply a 100-pound downward force to the left piston, a 900-pound upward force will appear on the right. The only catch is that you will have to depress the left piston 9 inches (22.86 cm) to raise the right piston 1 inch (2.54 cm).

faz1 7th January 2019 08:20 PM

Re: Classic brakes - sharper MC?
 
[quote=Gixxer;3561337]This explains hydraulic multiplication pretty simply.

[IMG]https://c1.staticflickr.com/5/4885/31709704947_0151a5dbf8_o.jpg[/IMG]

To determine the multiplication factor in the figure above, start by looking at the size of the pistons. Assume that the piston on the left is 2 inches (5.08 cm) in diameter (1-inch / 2.54 cm radius), while the piston on the right is 6 inches (15.24 cm) in diameter (3-inch / 7.62 cm radius). The area of the two pistons is Pi * r2. The area of the left piston is therefore 3.14, while the area of the piston on the right is 28.26. The piston on the right is nine times larger than the piston on the left. This means that any force applied to the left-hand piston will come out nine times greater on the right-hand piston. So, if you apply a 100-pound downward force to the left piston, a 900-pound upward force will appear on the right. The only catch is that you will have to depress the left piston 9 inches (22.86 cm) to raise the right piston 1 inch (2.54 cm).[/quote]

Not wrong I don't think - cross purposes - I was referring to caliper piston, same formula applies...

Gixxer 7th January 2019 08:31 PM

Re: Classic brakes - sharper MC?
 
[quote=faz1;3561344]Not wrong I don't think - cross purposes - I was referring to caliper piston, same formula applies...[/quote]

But we were talking about master cylinders :thumbsup2:

corkgsxr 7th January 2019 09:27 PM

Re: Classic brakes - sharper MC?
 
Yes smaller piston is more pressure but limited pressure.

So you need a bigger piston to increase that limit.

So way it feels is smaller piston more feel. Bigger piston firmer lever but better results.

But go rcs19 and you can choose your ratio depending on how you like it.

faz1 7th January 2019 11:17 PM

Re: Classic brakes - sharper MC?
 
[quote=Gixxer;3561346]But we were talking about master cylinders :thumbsup2:[/quote]

I do apologise profusely nice linky diagrams you got there though.

vifferman 7th January 2019 11:29 PM

Re: Classic brakes - sharper MC?
 
[quote=corkgsxr;3561351]Yes smaller piston is more pressure but limited pressure.

So you need a bigger piston to increase that limit.

So way it feels is smaller piston more feel. Bigger piston firmer lever but better results.

But go rcs19 and you can choose your ratio depending on how you like it.[/quote]

How can you choose the ratio. You can't change the ratio of the master cyl piston to caliper piston. Is the lever adjustable to give different lever pressure vs piston travel?

corkgsxr 8th January 2019 03:19 PM

Re: Classic brakes - sharper MC?
 
With a small flat screwdriver you turn a ecentric piece by 180 and it moves the piston pin closer to pivot.


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