Hydraulic Disc Brake Argument...

[Redneck]

the way i look at it is ; does one magura caliper work better than two? the same idea, 2 calipers with a cross over of some sort. more fluid in the line. does each magura caliper get less fluid because there are 2 of them? no. that would make the brake feel very spongy or not work at all.

IMO, yes, you would get a significant advantage because of the greater surface area and less heat (the concept the gatling gun uses, more barrels less heat on each) on each caliper.

id love to see this tried and tested.

[JT!]

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?

Yeah but the bigger pad has more surface area contact so they equal each other out, i know how it works i just couldn't ever find the right words to describe it.

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.

Well this is as far as we've got, at first people thought it'd be the same until a few people explained about it would techncally increase the pistons sise, however the leaver would be moving about twice as much.

My question is if you connected two hope mono trials to one leaver, how would the auto adjustment work, i feel that the auto adjustment would mean that the leaver would pull the same as if it was connected to one, ulmiately meaning that the answer to the OP's question would be that it would be the same power as one. It all hinges on what the auto adjustment would do.

[Shaun H]

Well this is as far as we've got, at first people thought it'd be the same until a few people explained about it would techncally increase the pistons sise, however the leaver would be moving about twice as much.

My question is if you connected two hope mono trials to one leaver, how would the auto adjustment work, i feel that the auto adjustment would mean that the leaver would pull the same as if it was connected to one, ulmiately meaning that the answer to the OP's question would be that it would be the same power as one. It all hinges on what the auto adjustment would do.

The automatic adjustment just comes from the piston/bore interfaces having equal resistance. Hence if one of the pistons gets scratched/dirty then it will tend to stick.

In other words it should have no effect whatsoever on the power of the brake system.

[Muel]

The lever will travel twice as far, because it's actually the piston seals that dictate how far the piston moves.

The slot the seal site in is this sort of shape |_/ so when you pull the lever, the piston moves in and the seal flexes over onto the slanted edge, if the pads need adjusting closer to the rotor, the seal flexes over and the pistons then slide in the seal, then when it returns the seal flexes back but the pistons stays in the new position in the seal. The lever has a valve which opens as you release the lever and sucks more oil into the system. (I think).

Basically the lever will travel twice as far towards the bar, so it would be pretty useless.

[Shaun H]

The lever has a valve which opens as you release the lever and sucks more oil into the system. (I think).

The resevoir you top up during bleeds feeds into the lever bore through an open port which is blocked as the lever piston travels. As the lever piston travels back and a pressure differential is caused by the caliper pistons' resistance to retracting more fluid is induced from the resevoir. The rubber diaphragm you put in place before the cap expands to take up the space of the induced oil, hence it being very important not to get air in!

Edited August 25, 2009 by Shaun H

[JT!]

The automatic adjustment just comes from the piston/bore interfaces having equal resistance. Hence if one of the pistons gets scratched/dirty then it will tend to stick.

In other words it should have no effect whatsoever on the power of the brake system.

It would if that piston / bore interface has an effect on the movement of the leaver....

The lever will travel twice as far, because it's actually the piston seals that dictate how far the piston moves.

The slot the seal site in is this sort of shape |_/ so when you pull the lever, the piston moves in and the seal flexes over onto the slanted edge, if the pads need adjusting closer to the rotor, the seal flexes over and the pistons then slide in the seal, then when it returns the seal flexes back but the pistons stays in the new position in the seal. The lever has a valve which opens as you release the lever and sucks more oil into the system. (I think).

Basically the lever will travel twice as far towards the bar, so it would be pretty useless.

The resevoir you top up during bleeds feeds into the lever bore through an open port which is blocked as the lever piston travels. As the lever piston travels back and a pressure differential is caused by the caliper pistons' resistance to retracting more fluid is induced from the resevoir. The rubber diaphragm you put in place before the cap expands to take up the space of the induced oil, hence it being very important not to get air in!

... if it's a system in the leaver that dictates how close the pads are to the to the disc, then wouldn't that mean the leaver wouldn't actually be moving twice as far because it would put all 4 pistons much closer to the disc?

[Shaun H]

It would if that piston / bore interface has an effect on the movement of the leaver....

... if it's a system in the leaver that dictates how close the pads are to the to the disc, then wouldn't that mean the leaver wouldn't actually be moving twice as far because it would put all 4 pistons much closer to the disc?

The reservoir system on the lever does not dictate how close the pads are, it simply allows the extra oil into the brake system to occupy the extra space where the pistons move in during normal wear/initial adjustment.

The pistons would not be closer to the disc since as I mentioned before, and Muel furthered with the seal diagram, it's the bore/piston resistance that produces an autoadjust effect. Therefore the lever piston has to move twice as far since it needs to displace twice as much fluid. Further to this there would be more "sponge" in the system since there would be more leverage on both caliper bodies.

EDIT: If you were carrying out this for real you would try to get the pistons to sit closer to the disc to reduce lever travel. The manufacturers will have already designed the system to place them as close as is practically possible anyway so this would be extremely hard/costly to achieve.

Edited August 25, 2009 by Shaun H

[Tomm]

Doubling the surface area of piston / pad would make a more powerful brake, with everything else being equal. Like many people have said though, this would make it a LOT spongier at the lever - probably unbearably so.

Manufacturers could double the power of their brakes by using a small diameter master (lever) piston giving exactly the same effect, but they don't because no one likes a brake that squishes to the bar. Does anyone remember the RB magura lever? It was more powerful because it had a smaller piston (13mm compared with 14mm on the normal HS33 lever). They were OK, but the feel of the lever certainly took some getting used to. And that's only a small difference in piston area.

The main advantage of a dual disc design would be in heat dissipation, which isn't really a concern for trials.

[JT!]

I understand all that, but i'm just not 100% clear on what Shaun is refering to, i'm not trying to argue anything i just really don't understand.

The reservoir system on the lever does not dictate how close the pads are, it simply allows the extra oil into the brake system to occupy the extra space where the pistons move in during normal wear/initial adjustment.

The pistons would not be closer to the disc since as I mentioned before, and Muel furthered with the seal diagram, it's the bore/piston resistance that produces an autoadjust effect. Therefore the lever piston has to move twice as far since it needs to displace twice as much fluid. Further to this there would be more "sponge" in the system since there would be more leverage on both caliper bodies.

EDIT: If you were carrying out this for real you would try to get the pistons to sit closer to the disc to reduce lever travel. The manufacturers will have already designed the system to place them as close as is practically possible anyway so this would be extremely hard/costly to achieve.

So where is the device located that corrects for wear on the pads and the initial adjustment, in the leaver, on at the actual brake?

[Muel]

The caliper seals dictate where the pads sit in relation to the disc, the lever port just lets more oil into the brake to allow for the pads wearing and the pistons slowly moving furhter in.

Edited August 26, 2009 by Muel

[JT!]

The caliper seals dictate where the pads sit in relation to the disc, the lever port just lets more oil into the brake to allow for the pads wearing and the pistons slowly moving furhter in.

Ah ok then. That's my theory out the window.

Twice as powerful it is!