uraz wrote: ↑
Thu Oct 11, 2018 2:15 am
I think that current road hydraulic disc brakes are lacking power in the name of safety and "good modulation".
Just stop. Excessive braking power <> better performance. There's no difference in user friendly brakes and high performance brakes. There are unfriendly brakes, there are low performing brakes, and high performance brakes are not unfriendly. Locking up a road bike tire is always bad.
I could write an super long post here, but I've only got a few minutes... there may be some edits after I proof read.
I can not resist the impression that most people confuse good modulation with a lack of power. Every time I read that some brake has "good modulation" I just know that it will be weak as hell (aka noob-proof).
As I said earlier - noob proof and world class expert brakes are not on different ends of a sliding scale.
What are good brakes: I'd say good brakes allow the user to reliability slow the bike down the desired amount, allow the use the tire's full traction if desired, provide clear timely feedback to the rider on the amount of friction being applied, and can quickly and consistently respond to the users inputs for the duration of their use. They controls should have a comfortable motion range and resistance.
What are the constraints here: We're talking about disc road bike brakes being used on drop bar bikes for either road/gravel/cx/touring use by a single rider on either flat roads or riding down one mountain. The rider will be anywhere from 35kg and seated very low to 120kg and very high. The bike will not have suspension.
A few facts here:
1) The TIRE is in charge of road grip, not the brake. The brake locks up when the friction in the disc exceeds the tire's ability to grip the road. The tire slows the bike, the brake slows the tire. TWO sources of variable friction you're managing.
2) There is NO PERFORMANCE BENEFIT to locking the tire up. One deformable surfaces (gravel/dirt), having some slip is beneficial. On the road, any noticeable amount of slip is not beneficial- unless you're trail braking the rear tire on a super tight childrens course, grip is ALWAYS better than slip.
3) There is limited lever travel available. People have different size hands. Using all the space is desirable for a few reasons.
4) In a surprise, you want to be able to maximize your braking and stability. Having excess braking power locking up the tires is not desirable.
5) Low sitting, lighter riders and higher seated, heavy riders are going to have a very different relationship with their rear brakes.
6) When you're looking at a braking event, brakes "bite", continuous braking, release/modulation, lock, and unlock behaviors to be concerned with.
7) Determining how much brake to grab is a matter of experience and how much time you have time you have to consult your brake grabbing meter. Your ability to modulate the brakes is dependent on how much information you an gather, how quickly the inputs are taken into account, and how long the braking event is.
You have a braking system, not brakes. Lever, master cylinder, brake fluid, hose, caliper, pistons, pads, disc, wheel, tire, bike frame, rider body, rider senses, rider brain, rider muscles...
The engineer sat down to build a set of consumer brakes. He knows they have to be able to let a fat tall guy ride down a mountain and ensure some starved tall lady doesn't flip over her bars. He knows hes got X amount of lever travel. He knows what friction materials are available. He knows how much grip he's got. He knows he's got a weight target and packaging constraints. He knows what goos/cables and roughly what disc sizes he's got to work with absorb the heat (brakes turn kinetic energy into heat - that will come up a lot. )
He does some math... figures out how much friction he needs for a hard uphill stop with the optimal rider on optimal tire on optimal surface (likely a 40c tire on smooth hard pack dirt). That's the most amount of braking he'd want the system to have.
Then the fat dude standing up going downhill on wet asphalt - he knows that dude needs something between no braking and lock. He needs some lever travel for near 0 traction.
and then light chick doing a cold speed adjustment in a paceline
and then fat dude down a mountain
He's got his window of what the brakes need to do, he knows where the brakes will be physically installed, he know tires and pads will vary. You're on board with all this.
Current generation of road disc brakes have exactly this kind of "good modulation" which is why I don't like them.
The brakes have to modulate under all these conditions within the lever travel he's got available. He'll give up a lot on the fat dude braking uphill to give that guy the ability to use his brakes downhill in the wet or that light chick the ability to make a small speed adjustment in a paceline. He can probably deliver more than one SKU for fat guy and skinny chick if he needs to. Having excess friction available doesn't ever help
Making an argument that you'd like more braking power in the initial movement of the lever is a better argument. Wanting a firmer lever is a better argument. Ok, so why can't you have a firmer lever and more bite? Good question, but the answer is going to be weight and complexity. With a firmer lever, you'd need stronger and more adjustable levers / smaller shift flags, stronger seals, and larger hoses.
There's not necessarily a tradeoff with modulation and ultimate braking power. It may be in feedback and lever travel. Remember that the levers/calipers only supply the force, the pads supply the friction, and there's also leverage. You can greatly modify how much braking power you've got by changing pad compound and disc diameter. Both play an important part in modulation, but a simple leverage or compound change can greatly affect this.
Preventing wheel lockup is not a brake's job. If you don't want to skid just don't squeeze lever so hard or let it go slightly when you feel that tire is on the edge of traction.
The rider's initial action is only one part of the equation. Also, if you've got to be so skidish with the controls that you can't intuitively use them, that's not performance.
1) The amount of grab the brakes have varies GREATLY on pad temp. That cold , one off braking event is going to feel completely different than that 6th repeated action on a crit race. While you're braking the pad is changing friction levels. Here's a graph of automotive racing brake pads, https://wiki.seloc.org/images/4/47/HawkPadChart.jpg
you can see that 10deg can make a HUGE difference in braking power. On higher temp range pads, it is very likely that you'll like a wheel even is steady application of force because the friction level changes aggressively.
2) Along with the temp affecting braking power, the pad will have a different amount of braking power on initial bite, after bite, and release. This relative change will be different depending on temp http://www.apracing.com/Info.aspx?InfoI ... ductID=977
This is a huge problem with race cars. You've probably seen race cars weaving left /right before a race to warm the tires, after they do that they also ride the brake while they hope to god that a pad doesn't bite aggressively.
3) A road bike tire 23-28c with 70+ psi in it mounted on a stiff wheel which is mounted on a rigid frame. The carcass is very pliable, the contact patch basically one dimensional and can't move around much, and the rotating assembly is very light. YOU REALLY DON"T FEEL A REAR TIRE LOSE GRIP OR EVEN LOCK. Losing grip is the absence of feeling. When you're braking, you're transfering weight forward, lifting weight off the rear losing that feeling anyway. The tire is locking because you don't enough weight on it. You feel the bike rise or hop, you feel the Disc/pad contact patch through the cables/fluid, you hear the noise, you feel the loss of traction, you feel the weight transfer rearward as you lose overall braking force, you don't feel the tire do anything on slip or lock.
4) It's senseless to make a braking system user need to be timid of. That's not performance. The flow of the system is regulated by the smallest passage between the lever piston and the caliper piston. I learned this is likely the caliper side hose insert at the end of the hose. If this is too big, even on a modest system, you'd need infinitely soft hands to brake smoothly.
5) Same with brake fluid, viscosity and friction of the brake fluids also dampen lever movement. This is good for initial bite, not modulation though
6) Your system doesn't work for emergency stops. Your brain sends a signal that bypasses your hand control meter.
7) I said road bike rear tires don't give much in the way of feedback under straightline braking, they also don't modulate. There's no weight to them, they are rigid when inflated, they are mounted rigidly - they don't slide, they breakaway abruptly. The traction curve of a road bike tire is a lot closer to the blue line here http://1.bp.blogspot.com/-_zjXCT8lH0U/ ... +Graph.jpg
than we might get on a mountain bike tire on dirt, which would be a flatter line. Just after the peak on that line, you're locked up. The sharper the peak, the less forgiving the tire.
The disc/pad feel is more important than the tire feel. One of the reasons you bed brakes in is to give them some grit, some feel. With some deposits on the disc, you now have rhythmic feel when braking hard.
Ok, so there are a lot of variables with rear tire traction given the riders position, surface, gradient, etc. and the brakes are variable. The brake engineer did the best he could getting the leverage right on the brake lever to caliper force. He gave you a set of pads with good initial cold bite that will work for most riders. He told you to install the brakes with this fluid, use this size disc, and put this connector on the hose. The brakes are mounted on a frame that is stiff enough not to adsorb any feedback you might get. If something is out of spec or you're out of that performance range, you're going to have lockup issues or under performance regardless of your technique.
"How often do you lock up your rear wheel?" - whenever I want to, regardless of a brake type I use.
You can be locking up the rear wheel accidentally even with a newborns touch because you've got the wrong rotor size, the wrong friction material, the wrong fluid, your caliper or disc is not sufficiently mounted, your hose is wrong, your rear tire lacks traction, you're not perceiving the right feedback, the reaction of the brake system is too slow, the force input/outputs are non-liner, the caliper is not rigid, the level is not rigid enough, etc. All these sensitivities, are a factors in your ability to brake at the tires limit. Just because you have a gentle touch and measured inputs doesn't mean you're going to be able to prevent lock ups if there's something off with the hardware calibration.
You want to be ABLE to lock up your rear tire so you know you can use all the tires performance, but you don't ever want to lock up your rear tire. You want to be able to use the brakes within a comfortable movement range and input level. You don't want your brakes to be so sensitive to variables that you can't give them consistent inputs. You want feedback from your brakes to know if there's a change in the inputs:output ratio. You want an inputs change to trigger an output change quickly. You don't want excessive braking power or overly grippy brakes to prevent injury.
There's no difference in user friendly brakes and high performance brakes.