What

[Sean Badenhorst]

I don't know the science of braking, but must say that after having ridden many, many MTBs across all price ranges over the past 19 years, hydraulic disc brakes definitely require less perceived effort to slow the bike down and offer a feeling of greater control. Cable discs have improved markedly over the past couple of years, but are not quite as plush as hydraulic. Having said that, my own hardtail has V-brakes, which definitely need new pads (one's skills can only take one so far). When I've saved up enough cash to buy a new MTB, I will make sure it has hydraulic disc brakes.

 

 

 

 

 

[Sean Badenhorst]

 

True but the people in white coats say that if you brake at the right place at the right time with the right brakes (which will be disks) you should be much faster !

 

What people in white coats think is the right place to brake and what I think is the right place to brake will surely differ by a few metres. Life is so much more interesting for late brakers...

 

 

 

 

 

 

[TheLegend]

I have the same feeling as Sean - perceived effort to slow bike down is definitely lower with hydraulic disk brakes than with v-brakes (the good xtr's). especially when it's wet and muddy the discs have a biger advantage because they collect less dirt, grit, water (and so less abrasion on the braking surfaces) ... than the rim surface so close to the tyre and the dirt action. 

[GoLefty!!]

Internal Geared bikes are on the way. I was chatting to a Mr Karl-Heinz Nicolai a few weeks back re an internal geared marathon bike weighing in at 11kg.

He was super keen on the idea and asked me to get back to him early next year. They have been developing it for 4 years already. For them it has to be perfect forst time out or people just won't buy it.

Now back to brakes; I'm with the Bornman fellow in this one.

None of my MTB's can take V's. But even comparing my Girlfriends Argon with V's to my Scalpel with XT Servo Wave Discs there is no difference in effort from my part to stop the bike. Disc's do not exert more mechanical advantage from finger to contact patch. Both types of brake will put you over the bar with ease if you are not careful. Good V-brakes are perfect for entry level bikes and even mid level bikes.

I have used a bike with Magura HS-33 hydraulic rim brakes. Those brakes exert enough clamping force to crush the rim. Granted you need to be a total D**S to achieve this but it's possible. They are the best brakes I have ever used on a mtb. Pity that they just never gained favour due to their weight. The best V-brakes will stop a mtb with rider just as quickly as disc brakes costing x6 more.

 

[SwissVan]

I don't know the science of braking' date=' but must say that after having ridden many, many MTBs across all price ranges over the past 19 years, hydraulic disc brakes definitely require less perceived effort to slow the bike down and offer a feeling of greater control. Cable discs have improved markedly over the past couple of years, but are not quite as plush as hydraulic. Having said that, my own hardtail has V-brakes, which definitely need new pads (one's skills can only take one so far). When I've saved up enough cash to buy a new MTB, I will make sure it has hydraulic disc brakes.




[/quote']

 

Herein lies the problem... never ride a mtb with disks  and you wont know the difference... Ride with good disks and its like a virus...

 

My wiff was complaining the other day how sore here hands and forearms were after a 4 km downhill (Discs on her mtb) and moi with V's kein probleem... Ok so maybe i spent less time braking than she whofears anythingdownhill did...

 

 

 

 

 

 

[GoLefty!!]

comparing bottom end V-brakes to mid to top end disc brakes is unfair.

[SwissVan]

 

 

Not always, my wiffs (again she whohasalltheluck...) bike before the current disc brake bike had Techno something or other V brakes, these things for some reason were much better than my bikes XTR V's in braking performance...

 

 

SwissVan2008-09-30 12:06:46

[Dirtbreath]

For the Rohloff fans. Yeti 575.

 

 

[The Doctor]

JB' date=' surely it is the extra leverage offered by disks that saves the forearm muscles more than gritty cables? Similar to V brakes vs cantilevers. The former have more leverage than the latter. [/quote']

 

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Jules, this is something that I've pondered often, especially when that grit starts to work me up. My experience with clean cables it that it? leaves me less fatigued afterwards. However, I'll admit that this is a subjective statement and you know that I steer away from those. That's why I commented that I'd like to try hydraulic Vs. My perception is that a clean set of cables make me do less forearm work than a bad set.

 

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This is in the context of top end Vs vs top end discs. The stopping force and muscle work required to stop from similar speeds are similar. Poor Vs compare very poorly to even average disks. With poor V-brake pads the brake force required (and hence arm work) is noticeably more.

 

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Speaking of leverage. It is not so much the leverage as the mechanical advantage that makes the difference insofar the force on the discs or rims, with both levers essentially two-finger shorties.

 

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The old cantilevers had a variable mechanical advantage as the straddle cable angle changes in a non-linear fashion with travel on the lever. With Canti's you had the least mechanical advantage at the point where the pads just contact the rims and the best advantage when they're 5mm away from the rim. It was a true braking paradox.

 

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A disc brake can be made with any mechanical advantage and it is up to the manufacturer to decide on the master/slave cyclinder ratios. With too much advantage, the brake become unpredictable. With too little it becomes spongy and you may run out of lever travel before you stop.

 

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I think at the top end, or even serious amateur end of the market disc brakes have more advantages for the rider than Vs and the latter will be the domain of one or two cranks like me or weight weenies.

 

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The average mountain bike needn't have discs and the rider will not suffer for the lack of them. I just lament the youngsters that come through my doors to learn about bike maintenance and the first thing they start asking is where to find cheap discs. They should be asking for training programs, not better components.

 

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There are a number of advantages to disc brakes that cannot be overcome with rim brakes:

 

 

 

A disc can exert a greater mechanical advantage due to two factors.

 

 

 

1) the lateral runout of the disc has tighter tollerances than a rim, allowing the disc to have a very high mechanical advantage without the presence of accidental brake scrub. The greater diameter of the rim and the fact that it is a load bearing structure of the wheel result in lateral forces causing movement. The manufacturers of rim brakes need to keep the mechanical advantage smaller so that the brake blocks retract far enough to allow the lateral movement of the rim. This is not the case in disc brakes.

 

 

 

2) The hydraulic fluid has vitually 0 friction and therefore there is very little loss of force between the lever and the brake caliper. A well maintained cable brake will be similar but will not remain that way, unlike disc brakes which are virtually maintanance free.

 

 

 

Human skeletal muscle fibre unit sizes are recruited in relation to the force needed. If the forces are low, there is recruitment of small muscle fibre units in which a single nerve supplies each muscle fibre. As the force increases, the number of fibres per nerve increases, decreasing the fine motor control.

 

 

 

The result is that under high force situations (panic braking and off road) the ability to modulate the brake is lost with low mechanical advantage systems. Similarly, disc brakes provide greater control during riding in comparison to most cable operated rim brakes.

 

 

 

It is also quite apparent that a lot of the posts on this thread have been made by people who have not ridden a mountainbike in technical terrain with V-brakes and then disc brakes. If they had, they would not ask whcih was better.

 

 

 

Finally, with respect to wet conditions, the rim is simply closer to the ground and therefore picks up a lot more mud and dirt. When it is really muddy and wet, this results in a delay in the application of braking force that does not occur with discs (which remain fairly clean).The Doctor2008-09-30 14:02:35

[Johan Bornman]

There are a number of advantages to disc brakes that cannot be overcome with rim brakes:

A disc can exert a greater mechanical advantage due to two factors.

1) the lateral runout of the disc has tighter tollerances than a rim' date=' allowing the disc to have a very high mechanical advantage without the presence of accidental brake scrub. The greater diameter of the rim and the fact that it is a load bearing structure of the wheel result in lateral forces causing movement. The manufacturers of rim brakes need to keep the mechanical advantage smaller so that the brake blocks retract far enough to allow the lateral movement of the rim. This is not the case in disc brakes.

 

[/quote']

 

Technically, the disc has no say over the mechanical advantage. That is purely a function of the lever or master/slave cyclinder ratios. A V-brake or single pivot calliper brake follows the rim and has a high tolerance for wobbles - denifnitely much more than the spacing in the disc calliper's slot. Discs rub just about all the time, calliper and Vs never need to rub.

 

There is only one force I'm aware of that causes lateral deformation of a rim and that's honking out of saddle up a hill. Even then it doesn't touch the pads of a double-pivot brake calliper which is about 1mm away from the rim at best of times.

 

A single pivot brake has more play, but that's not the issue here.

 

 

2) The hydraulic fluid has vitually 0 friction and therefore there is very little loss of force between the lever and the brake caliper. A well maintained cable brake will be similar but will not remain that way' date=' unlike disc brakes which are virtually maintanance free. [/quote']

 

I agree.

 

Human skeletal muscle fibre unit sizes are recruited in relation to the force needed. If the forces are low' date=' there is recruitment of small muscle fibre units in which a single nerve supplies each muscle fibre. As the force increases, the number of fibres per nerve increases, decreasing the fine motor control.

The result is that under high force situations (panic braking and off road) the ability to modulate the brake is lost with low mechanical advantage systems. Similarly, disc brakes provide greater control during riding in comparison to most cable operated rim brakes.

[/quote']

 

I think this simplifies what happens too much. Panic braking is an out of control situation and will cause lock-up in discs or V-brakes.  I don't agree with your assessment of control, excluding the case of a cable with lots of friction. In this scenario the control is not muscle fibre related by movement of the fork related. As the fork and steering moves, the friction is altered and the brake alters its apparent stable state and does its own thing irrespective of finger position.

It is also quite apparent that a lot of the posts on this thread have been made by people who have not ridden a mountainbike in technical terrain with V-brakes and then disc brakes. If they had' date=' they would not ask whcih was better. [/quote']

 

You allude to a right and wrong answer here. Come right out and tell us.

 

Finally' date=' with respect to wet conditions, the rim is simply closer to the ground and therefore picks up a lot more mud and dirt. When it is really muddy and wet, this results in a delay in the application of braking force that does not occur with discs (which remain fairly clean).[/quote']

 

I hear this argument a lot. Well, my brakes are at the top of the wheel, not in the mud. Before the rim travels from grit to brake, there's lots of opportunity for shake-off. We know this because of the rooster tail of dirty water at the back and the shoot-up from the front wheel into our eyes. Further, in wet conditions, everything is wet. There is no wet and dry patches and the disc doesn't escape the water. It gets wet enough. Wet enough (two molecules thick layer of water) is wet enough. Any wetter makes no difference. A one molecule layer is another matter altogether and ironically improves braking on disc and rim brakes.

 

 

[MintSauce]

 

 

Some people are concerned about reliability. A friend of mine learnt frame building in a custom shop in Germany. 70% of their frames were Rohloff specific.

 

they built touring bikes' date=' hey?

 

[/quote']

 

 

Not sure....you know him