riderseventy7
Likes Dirt
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Braking!:- Lets sort this out.
- Thread starter Minlak
- Start date
marc.r
Likes Dirt
honestly i dont think we should go into how to create the best breaking technique in this thread. there are so many ways you can increase the co-effecient of friction between the ground and your tyre that doesnt really relate to the physics of braking at the caliper/rotor/lever.
technique, weighting, tyres, suspension, soil type, moisture you could go on forever. brakes/discs etc are however relatively simple.
everyone has their own riding ability but 90% of us run one of a handful of caliper sizes/rotor types/sizes and given equal technique this thread should give some real information on the performance you can purchase from chain reaction or similar and the best thing you should be doing to achieve your desired goals be that power, modulation, heat dissipation and cost.
technique, weighting, tyres, suspension, soil type, moisture you could go on forever. brakes/discs etc are however relatively simple.
everyone has their own riding ability but 90% of us run one of a handful of caliper sizes/rotor types/sizes and given equal technique this thread should give some real information on the performance you can purchase from chain reaction or similar and the best thing you should be doing to achieve your desired goals be that power, modulation, heat dissipation and cost.
What is tripping you up?
If the modulation of the brake sucks than even if the traction at the tire is high the brake can still lock up because the rotor and pads lock up causing the tire to lock up breaking traction because the brakes suck not because there is no grip available. My point is, is there a point where the disc has coefficient that actually make the tire traction moot. If you have a light switch brake either fully on or off the traction at the tire would be moot because your brakes suck. Heavy or light rider they will lock up.
A big part of the equation is the tire dictates how well we can brake but the brakes a have their own coefficient with the pads and disc. In some situations what if the bite point of the brake is lower than that tires release point of traction. In that case a heavier rider will not brake as well as a lighter rider. I think it the other thread it was mentioned that both riders will take the same distance to stop.
If there is more traction available to slow down at the tire, but the brake bites before this you have wasted traction/braking potential at the tire, making the extra traction from increase weight pointless.
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riderseventy7
Likes Dirt
You're the one who is being tripped up by the topic, you have the whole cause and effect around the wrong way. The wheel won't lock or skid until the braking force at the pads and rotor has increased to sufficient levels to overcome the grip at the tyre. The level of braking force required to lock up varies depending on the load at the tyre, there is not one magic limit. Basically, unless you have a catastrophic failure of the brake which causes it to seize, it is always the level of grip at the tyre that dictates when a lock up will occur.
Poor modulation just makes it hard to balance your braking force with the amount of grip available at the tyre, in other words it makes it hard not to exceed the force required to lock up. So with good brakes you may be able to smoothly increase the braking force to the point just before it locks, whereas with shit brakes you try and brake the same, smooth way but you get a lock up. No tyre grip is going unused, the shit brakes are just shit brakes and exceed the tyres grip threshold without warning.
If the pads and rotor do have a limit, of any sort, it will be the point at which they are no longer able to overcome the load on the wheel/tyre and won't be able to lock up.
Do this experiment, (it'll be easy, and obvious) lift your back wheel off the ground and spin the wheel, then apply enough pressure to the brake lever to lock the wheel. Repeat this, except this time you will be riding the bike with your weight over the back, the amount of pressure required to lock the wheel will have changed. This will be the same whether you have great brakes or shitty brakes.
The fact you can't understand that, after obviously applying some thought to it going by the length of your somewhat incoherent post, is why I posted the pic.
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pharmaboy
Eats Squid
I think what drifting is saying, is that a light rider on a not very grippy surface doesn't need good brakes - pretty much anything will do the job to the point of lock up of the tyre. Conversely a downhill 95kg rider braking on flat rock needs a more powerful brake.
On bitumen not much matters because slamming on the brakes usually causes an endo.
Call me crazy, but I always think of modulation as what you get when you lack power
( lever to the bar is easy to modulate but sometimes isn't enough)
On bitumen not much matters because slamming on the brakes usually causes an endo.
Call me crazy, but I always think of modulation as what you get when you lack power
( lever to the bar is easy to modulate but sometimes isn't enough)
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riderseventy7
Likes Dirt
Call me crazy, but I always think of modulation as what you get when you lack power
( lever to the bar is easy to modulate but sometimes isn't enough)
Ah, you need to try yourself some Hopes then
The way I read it, and I had to read it a few times, is that he's saying there is a point that the pads will always lock onto the rotor no matter how much *load or grip is on the tyre. His talking about tyre grip being wasted leads me to think that.
*Which is to do with weight and surfaces etc.
Alo661
Likes Bikes and Dirt
Plus one. /thread
Yep. It was also a question less of a statement as I know nothing about the physics of this stuff.
Brakes are going to cover a range but at some point their ability to work is limited. So if you got a heavy enough rider it wouldn't matter how much traction the tire has the brake will lock the disc which will lock the wheel or it wont lock at all (this I guess depends on modulation).. As far as I am aware the discs ability to rotate is dependent on the force and momentum of the wheel/mass. The heavier rider does not give the brake a stronger braking surface as it does the tire. While heavier riders produce more momentum does it actually provide the brake with enough momentum to match the increased traction. (If the rotor is pushed though the pads with an extra 10kg of force, but the tire has an extra 15kg of traction that 5kg of traction is pointless because the rotor will stop and lock the wheel) Ir is the increase momentum equal to the increase in weight and traction at the tire?
So if the added weight does not increase momentum enough at the disc to stop the brake locking than the increased traction that the weight adds at the tire will be useless. As it will lock.
There is equally the other issue that if a brake has not enough power you cant reach the point and slow down enough.
Most arguments I see, seem to jump straight to the tire and its traction but disregard the brakes limits of its effect and how weight effects its function.
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silentbutdeadly
has some good things to say
It strikes me that in most cases the biggest problem with any particular species of bicycle brake is the meat on the lever. Certainly reinterpreting the semantics adds nothing to the truth that 98% of us are really shit at using our brakes efficiently and effectively...no matter which brand we dragon for.
riderseventy7
Likes Dirt
If you keep increasing the weight, or load, on the wheel it would get to a point that it wouldn't lock at all, or work at slowing things up. That is provided the wheel or tyre isn't destroyed under such conditions.
I read that a few times and I couldn't work out what exactly you are trying to say, but,
The Heavier rider will need to squeeze the brakes harder to get the same result as a lighter rider. The brakes strength stays the same, it doesn't change with the *weight of a rider. With a heavier rider the brakes will have to deal with slowing an object with a lot more momentum, at the same time the heavier rider will have more weight on the tyre meaning the grip threshold is greater and the brakes can be squeezed harder before it locks up compared to the smaller guy.
* A bigger rider "may" be able to squeeze a lever harder generating more squeeze on the rotor, but that's not the same thing. The brakes strength is still the same
That's right.
Because it is about the tyres traction.
Beej1
Senior Member
While i agree with some of what you're saying, I'm pretty sure everyone has something in their life that they enjoy nerding-out about. For these guys its the mechanics of braking.
microRobbie
Likes Bikes
This is very interesting but I have to disagree with point (a) that skidding is losing control
I'm not saying skidding is a good thing- it certainly can be bad for the track, and in many instances you can loose speed, but I believe there is such a thing as the "controlled skid"
Nico Vouilloz was the master of this. I cant get the footage but in the the Cairns 1996 DH world championships (which he won), he gives a master class in controlled skidding to get round some of the tight corners.
Its is fascinating to watch as some of the previous riders seem to be tentatively making their way round feathering their brakes, but he just flicks that tail out with a short skid, setting the bike up in the perfect position to accelerate the next section.
I imagine Nico would not have described his skidding as loosing control, he had it way under control and knew exactly what he was doing.
I'm not saying skidding is a good thing- it certainly can be bad for the track, and in many instances you can loose speed, but I believe there is such a thing as the "controlled skid"
Nico Vouilloz was the master of this. I cant get the footage but in the the Cairns 1996 DH world championships (which he won), he gives a master class in controlled skidding to get round some of the tight corners.
Its is fascinating to watch as some of the previous riders seem to be tentatively making their way round feathering their brakes, but he just flicks that tail out with a short skid, setting the bike up in the perfect position to accelerate the next section.
I imagine Nico would not have described his skidding as loosing control, he had it way under control and knew exactly what he was doing.
So the coefficient of the disc braking surface is dictated by the tire coefficient?
That was my question. I was unsure if the increased grip at the tire always provided enough drive at the disc to prevent lock up earlier than the tire can handle.
Ill try to explain what I meant previously.
The pads and disc have their own coefficient.
The wheel and the ground as its coefficient.
My thinking was that when you add weight to the bike you increase the coefficient at the tire. This also increases the drive through he disc brake, more grip equals more force pushing the disc through the pads under braking.
I than was asking, if at any point does the increase in grip at the tire not match the increased drive through the disc and thereby the coefficient at the disc is not increased as much as it is at the tire. Resulting in a brake that will lock up before the tire is ready, thereby locking the wheel before the coefficient is reached at the tire.
That make anymore sense?
After thinking about this more, I realized that this situation would mean that the bike would stop dead in its tracks. As you could effectively lock the brake without breaking traction.
I guess what I was thinking along the lines of initially was actually a situation where the brake would have poor modulation and the bite point would jump up. Say we can only brake in 50lbs increments and the the tire breaks at 630, the 30lbs of traction would be lost as going to 650 would break traction, this however is just a classic case of brakes been more powerful than the tire as the lock up point is still higher than the tire. Its just inefficient braking at 600lbs.
I think most would agree but we are not referring to riding but braking forces. Skidding is not effective for braking and represents a loss of braking control.
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scblack
Leucocholic
But we are talking MTB's here, which ride on dirt. Often the most effective braking action on dirt is to lock up the wheel which then drives the tyre down into the harder substance beneath any loose dirt on the surface. The front wheel would rarely be locked up though (if ever).
Advanced ABS brake systems on cars are intelligent enough to sense this and allow a little locking up when driving on dirt tracks.
Skidding is not effective for braking when you have a good surface for the tyre to grip. Road bikes on asphalt would not need to be skidding at all.
microRobbie
Likes Bikes
Well I'm not sure how people think, I was just going with the definition from the first post.
I think if you told Nico V that his skidding represented a loss of braking control he would be a bit puzzled.
Flow-Rider
Burner
you can wash off lots off speed on loose tracks by skidding and flicking the tyre out as it bites and digs in to the loose rubble.
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I was under the impression we were referring to the action of braking as an isolated action at the moment not specific to any sport or vehicle as of yet. In that case a brake is most effective when it is not locked. Before we dive into specifics of terrain and all the other variables shouldn't we get the basic physic of braking out of the way?
I thought we were still at that point.
Brake control not bike control. I'm with you but as above I was under the assumption this thread was more about the basic understanding of braking before we dive into specific and variations. You can lock up for control, you can also lock up as a abs like style but isnt this putting the cart before the horse right now.
Also nico is a great rider for his time the best of his years but most worldcup riders would destoy him now. Equally back then they had pretty shabby brakes and unreliable parts compared to today so their brakes had much less modulation and control. You are better of comparing current crop of riders and current moto sports. If we look at motox you don't see lots of skidding most of it comes from the undulation and terrain changes as the rider is on the limit of the brakes the tire gains and loses traction so the tire naturally locks and unlocks.
Anyway I still think that is putting things before the horse. shouldn't the thread have a basic run down of braking physics before we address variations in application.
Minlak
custom titis
Controlled Skidding Exists and it is valid but not what we are trying to condense here. Braking techniques themselves is a whole other thread and for this topic Skidding is losing control. What we are trying to finalise here is the constant debate over rotor size and braking effect. Along with modulation and pads. It is more about explaining how they all actually relate to each other to better understand how they work. You pull the lever then what is what I am trying to do.
Very busy day at work I have read all the conversations so far and formulating some more changes to the original post. Keep up the good work.