Hydraulic Disc Brake Argument...

[Revolver]

You could make a dual magura for the rear brake.

If you had a lever piston with twice the cylinder volume, and hooked it up to four cylinders on the rear. Well, no-one would be complaining about a slipping brake, haha. You could even use two different pairs of pads.

[psycholist]

If you doubled the master cylinder volume by making the diameter bigger you'd be back to the same power as a single Magura as you'd half the pressure in the fluid. If the volume was doubled by increasing the master piston travel you'd have to change the leverage ratio at the lever (To reduce the fluid pressure) to allow a normal sized hand to actuate it, again bringing it back towards to stock setup.

[sstein]

You could make a dual magura for the rear brake.

If you had a lever piston with twice the cylinder volume, and hooked it up to four cylinders on the rear. Well, no-one would be complaining about a slipping brake, haha. You could even use two different pairs of pads.

I wouldn't say the new shimano saint would slip very much and you would save a lot of weight and a lot of time.

and servo wave technology would mean that the pads could be further out.

Edited August 21, 2009 by sstein

[Revolver]

If you doubled the master cylinder volume by making the diameter bigger you'd be back to the same power as a single Magura as you'd half the pressure in the fluid. If the volume was doubled by increasing the master piston travel you'd have to change the leverage ratio at the lever (To reduce the fluid pressure) to allow a normal sized hand to actuate it, again bringing it back towards to stock setup.

What if you had two separate cylinders? Joined by one lever.

[psycholist]

If both pistons feed the same line that goes to both brakes then you've doubled the piston area and will have the problems attendant with that (More power loads of lever travel and sponginess). If each piston actuates a single brake then there's no power increase as the force you apply to the lever is split between two brakes (And setting both brakes to bite at the same time would be awkward and need a linkage in the lever at the very least), so the lever will feel more wooden but the braking power will be about the same as for a single brake.

If you set the brake up with both pistons on one side of the rim and fixed brake blocks on the other side of the rim you'd double the power though...

Edited August 21, 2009 by psycholist

[JT!]

Now to cause more trouble - While opposed piston designs are the most common setup (Done to reduce brake drag and allow the pads to adjust themselves automatically for pad wear without relying on a floating caliper), a 2 pot brake with opposed pistons will be a lot less powerful (Half as powerful assuming each piston acts on the same pad area and the fixed pads are the same as those acted on by the pistons) than a two pot brake with the same diameter pistons where both pistons are on one side and there's a fixed pad on the other. How does this work?

On opposed piston brakes while each piston creates a force based on the pressure in the fluid and its area, the force each piston applies is balanced out by the opposing piston. In the case of both pistons on one side of the caliper, each piston exerts the same force, but the forces are in the same direction and are opposed by the fixed pad on the opposite side of the caliper rather than each other, so effectively there's twice the force squeezing the pads into the disk.

Have a look at the Magura Gustav (Probably the most powerful brake I've ever used) for an existing design that proves this principle...

Holey shit! That's interesting! So why do people design breaks with opposing piston designs at all?!

No one is doubting anymore that two hope mono trials connected to one leaver is going to be twice as powerful in theory. What i'm asking is if it was done physically, would the auto pad adjustment mean that actually, the system would adjust it's self so the leaver pulls like it would when it was connected to one, meaning it would end up being as powerful as just one.

[Greetings]

Holey shit! That's interesting! So why do people design breaks with opposing piston designs at all?!

More mechanically sound? But yeah, that is quite an interesting point.

And I double that Gustav M's are one of the most powerful brakes ever. They're absolutely insane, especially the early ones with full disc rotors.

[sstein]

Now to cause more trouble - While opposed piston designs are the most common setup (Done to reduce brake drag and allow the pads to adjust themselves automatically for pad wear without relying on a floating caliper), a 2 pot brake with opposed pistons will be a lot less powerful (Half as powerful assuming each piston acts on the same pad area and the fixed pads are the same as those acted on by the pistons) than a two pot brake with the same diameter pistons where both pistons are on one side and there's a fixed pad on the other. How does this work?

On opposed piston brakes while each piston creates a force based on the pressure in the fluid and its area, the force each piston applies is balanced out by the opposing piston. In the case of both pistons on one side of the caliper, each piston exerts the same force, but the forces are in the same direction and are opposed by the fixed pad on the opposite side of the caliper rather than each other, so effectively there's twice the force squeezing the pads into the disk.

Have a look at the Magura Gustav (Probably the most powerful brake I've ever used) for an existing design that proves this principle...

I suppose the this could be down to the fact that on opposed piston designs the two pistons create a force on the rotor that is equal on each side as each piston pushes with the same force. On one sided calipers the two pistons create a larger force in one direction which must be counteracted by an equal force on the other side. This force would be created by the stiffness of the caliper, so it is in effect as powerful as an opposing 4 piston design!

Edited August 21, 2009 by sstein

[JT!]

I suppose the this could be down to the fact that on opposed piston designs the two pistons create a force on the rotor that is equal on each side as each piston pushes with the same force. On one sided calipers the two pistons create a larger force in one direction which must be counteracted by an equal force on the other side. This force would be created by the stiffness of the caliper, so it is in effect as powerful as an opposing 4 piston design!

Yeah but the stiffness and rigidity of the other side isn't pushing back in the opposite direction.

[sstein]

Yeah but the stiffness and rigidity of the other side isn't pushing back in the opposite direction.

yes it is!

if the pistons push this way: ----->

then the backing is pushing this way: <-------

[JT!]

yes it is!

if the pistons push this way: ----->

then the backing is pushing this way: <-------

But the backing isn't physically been pushed by the same leaver that is pushing the other pad.

It's hard to get your head around. After thinking about it for a while, i don't think it's right, i don't think two pads been forced in opposing directions is going to make it weaker.

Edited August 21, 2009 by JT!

[sstein]

The back must creat an equal an yet opposite reaction other wise the caliper would snap so if you had two pistons on one side it would be twice as powerful as having two pistons on opposite sides.

[ScottTrials]

Thats exactly what i said. Half the power to each one, meaning half the heat to each rotor?

just wondering, isn't the heat built up by the pads rubbing on the disc. So wouldn't it be the same amount as heat as a normal set-up. Just on two rotors. :/

[JT!]

The back must creat an equal an yet opposite reaction other wise the caliper would snap so if you had two pistons on one side it would be twice as powerful as having two pistons on opposite sides.

Well yeah, which makes me believe the guy who was going on about opposing forces is wrong. I still don't see why 'opposing forces' would reduce the power of a brake.

just wondering, isn't the heat built up by the pads rubbing on the disc. So wouldn't it be the same amount as heat as a normal set-up. Just on two rotors. :/

Heat = friction, friction = heat.

[psycholist]

Friction is not equal to heat. Friction is a force that always acts against the direction of movement (Friction between surfaces and air friction being two of the most common examples). Since energy cannot be created or destroyed (except in converting mass to energy and back), the kinetic energy that friction takes from a system must be converted to another form of energy, usually heat (Energy taken by friction also gets converted to sound energy as evidenced by squeaky brakes, but heat is a far bigger percentage of this energy).

Since brakes start to fade and boil once their temperature passes a certain point and the temperature rise will be proportional to the volume of material the heat is added to, adding a second rotor will also reduce fade (Provided both rotors can lose heat at the same rate as a single rotor).

[Jon_lee9900]

you press the lever and each caliper would move half as much, so you would have so little travel on the pads, but if that travel was enough the pads would have the same force on the disc, just double the braking area, therefore would produce more brakeing, but only from the frictional area not actually the hydraulic power

[Shaun H]

Hooooolllllyyyyyyyyy crap.

I'm gunna hit the maths revision then if I've got time I'm gunna knock up some bad ass paint diagrams to see if I can explain properly/add to the mass of confusion.

[Clawz114]

you press the lever and each caliper would move half as much, so you would have so little travel on the pads, but if that travel was enough the pads would have the same force on the disc, just double the braking area, therefore would produce more brakeing, but only from the frictional area not actually the hydraulic power

Check page 1/2.

Just because theres more pad area, doesnt mean that theres more friction or it will slow the rotor down faster. Theres a few examples on pages 1 and 2 and here... http://www.physlink.com/education/askexperts/ae140.cfm

[JT!]

Check page 1/2.

Just because theres more pad area, doesnt mean that theres more friction or it will slow the rotor down faster. Theres a few examples on pages 1 and 2 and here... http://www.physlink.com/education/askexperts/ae140.cfm

That's a really useful paragraph, i can never put it into words, the obvious thought is the bigger the pads the better the brake and it's really difficult to put down into words why that isn't true.

No one seems to know the answer to my question about what would happen if one leaver was attached to two hope mono trials, so i'm going to ask an engineer / trials rider when i see him some time over the weekend, he'll definitely know.

[Muel]

Been thinking and I've changed my mind to Yes.

It's all about leverage ratios. Adding another caliper would have the same effect as halfing the lever piston area. This would move less fluid, but say the ratio was 2:1, it's now 4:1, so the leverage ratio would be doubled.

The pad area has no real effect, because if you halved the lever piston area it would double the pressure on the pads, but beause instead you've added another caliper the pressure on each pad is the same, but becase there are 4 pads, theres double the overall pad surface pressure.

I think.

[Mark W]

That's a really useful paragraph, i can never put it into words, the obvious thought is the bigger the pads the better the brake and it's really difficult to put down into words why that isn't true.

Because you're making the surface area larger, you're basically reducing the pressure (or force or whatever the right word is) you're putting onto the rotor or rim, so it won't hold/stop you as well?

[psycholist]

No one seems to know the answer to my question about what would happen if one leaver was attached to two hope mono trials, so i'm going to ask an engineer / trials rider when i see him some time over the weekend, he'll definitely know.

I thought the whole thread was devoted to answering this question. The lever would feel spongier and need more travel before it bites but you'd get twice the braking power. The results of the poll mostly show that people don't think about their answers before selecting them... Strangely while many people voted in the poll for the brake not being twice as powerful, nobody is defending this view.

[Matt Vandart]

Use a lever from a four pot brake set up like those hope M4.

Which made me think, what do you think the effect of using an M4 lever for a monotrial rear caliper?

Matt

[N.Wood]

Use a lever from a four pot brake set up like those hope M4.

Which made me think, what do you think the effect of using an M4 lever for a monotrial rear caliper?

Matt

f**k all, they all use the same levers.

[Muel]

Yeh same lever, and roughly the same piston area, but they just use smaller pistons spread over the pad. I believe this is to make the pad toe in and give you more modulation.