Riders on disc brakes. How often do you lock up your rear wheel?

Discuss light weight issues concerning road bikes & parts.
jfranci3
Posts: 376
Joined: Tue Jul 26, 2016 5:21 pm

by jfranci3

uraz wrote:
Thu Oct 11, 2018 12:00 am
No, why? Fact that I don't have a problem with unwanted wheels locking doesn't make me a troll.
First paragraph was somewhat OK.
Anyone who’s in an engineering related field had their head explode in the 2nd paragraph I’ll type a longer post when I put the kids down later.

You’ve been somewhat coddled by having well spec’d beaking systems under you. You’re right that modulation and ultimate power are different things and in that braking systems are inexperienced user proof. Inexperienced-user proof and pro quality brakes are not opposing goals though. The best braking system I’ve ever used was on a 50cc 2-stroke Kymco scooter. While it had double the power it needed, anyone off the street could easily put both front and rear tires in multiple states of something between slip and grip on the first try. One of the risks of this particular scenario is the users will tend to brake at the absolute limit for every braking event- not a good habit in traffic

uraz
Posts: 98
Joined: Thu Dec 12, 2013 9:48 pm

by uraz

Maybe it would be wise to weaken lower tier brakes to help some people with unexpected rear wheel lockup situation and make da/red/record more powerful for experienced users who can handle them with ease.

by Weenie


superdx
Posts: 516
Joined: Sun Jun 29, 2014 1:27 pm

by superdx

Don't think I've ever locked up my wheel since I started using discs. Rim nearly almost every time I have to panic brake.

jfranci3
Posts: 376
Joined: Tue Jul 26, 2016 5:21 pm

by jfranci3

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.
8) 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...

OK...
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
and then....
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.
8) 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.

uraz
Posts: 98
Joined: Thu Dec 12, 2013 9:48 pm

by uraz

I get your point but let's consider a scale from 0 to 10 where 0 is no braking force and 10 is maximum that a road bike can handle on a clean tarmac just before rear wheel starts to lift up. From your post above I assume that for you ideal brake shoud have maximum force around 8. I like when it's more like 12. Achieveing maximum force require squeezing lever as hard as possible to the point where shift paddle touches the bar. I'm used to braking very hard before a corner so it's fatiguing for me to use brakes that are not "overpowered". I like when rear wheel starts to lift at around 80-90% of maximum force that brake can generate. Also I get more feel and feedback from slightly overpowered brake when tire is on the edge of traction.
superdx wrote:
Thu Oct 11, 2018 2:49 am
Don't think I've ever locked up my wheel since I started using discs. Rim nearly almost every time I have to panic brake.
There is simple explanation of that. Maximum power output of road disc brakes in inferior to for example dura ace mechanical (on clean and dry aluminium rim).

jfranci3
Posts: 376
Joined: Tue Jul 26, 2016 5:21 pm

by jfranci3

uraz wrote:
Thu Oct 11, 2018 2:30 pm
I get your point but let's consider a scale from 0 to 10 where 0 is no braking force and 10 is maximum that a road bike can handle on a clean tarmac just before rear wheel starts to lift up. From your post above I assume that for you ideal brake shoud have maximum force around 8. I like when it's more like 12. Achieveing maximum force require squeezing lever as hard as possible to the point where shift paddle touches the bar. I'm used to braking very hard before a corner so it's fatiguing for me to use brakes that are not "overpowered". I like when rear wheel starts to lift at around 80-90% of maximum force that brake can generate. Also I get more feel and feedback from slightly overpowered brake when tire is on the edge of traction.
superdx wrote:
Thu Oct 11, 2018 2:49 am
Don't think I've ever locked up my wheel since I started using discs. Rim nearly almost every time I have to panic brake.
There is simple explanation of that. Maximum power output of road disc brakes in inferior to for example dura ace mechanical (on clean and dry aluminium rim).
No, the ideal maximum output is 10. Every brake set sold on the market can deliver 12. Your complaint is still about lever travel.

Rim brakes have a thicker pad to wear, more tolerances to deal with, more braking surface materials, less friction material choices/range, different leverage ratio (lever to caliper), a softer pad dampening your inputs , and generally lack the available power of even shitty hydro discs. They need this travel to give maximum braking force when the pad is worn.


Have you tried a Sram hydro setup?

uraz
Posts: 98
Joined: Thu Dec 12, 2013 9:48 pm

by uraz

Yes, I was using Red 22 HRD for past 2 years and I was disappointed. About month ago I've sold disc equipped bike and now I'm back to fully mechanical supersix. I'd like to point out that I'm not an opponent of disc brakes per se but I just don't like current (first) gen of road disc brakes. I'll wait till new etap hrd brake trickles down to a mechanical red/force groupset to give it a second chance.
Last edited by uraz on Thu Oct 11, 2018 5:26 pm, edited 1 time in total.

MoPho
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Location: NorCal/SoCal

by MoPho

uraz wrote:
Thu Oct 11, 2018 5:03 pm
Yes, I was using Red 22 HRD for past 2 years and I was disappointed. About month ago I've sold disc equipped bike and now I'm back to fully mechanical supersix. I'd like to point out that I'm a fan of disc brakes per se but I don't like current (first) gen of road disc brakes

I think there's your issue, the Sram disc is a bit more progressive than Shimano. Shimano disc has more initial 'bite', which sounds like what you are talking about



.

uraz
Posts: 98
Joined: Thu Dec 12, 2013 9:48 pm

by uraz

Lack of initial bite is one thing but also I had couple of situations when maximum power that this particular brake has to offer was not sufficient.

jfranci3
Posts: 376
Joined: Tue Jul 26, 2016 5:21 pm

by jfranci3

That’s just a pad and rotor issue then. You want stupid power, put 180mm on there. Want a firmer feel, that’s not progressive, put bigger hoses on. You’ll have shitty brakes with ultimate power and a broken collar bone.

dvq
Posts: 144
Joined: Mon Sep 25, 2017 1:36 pm

by dvq

uraz wrote:
Thu Oct 11, 2018 5:30 pm
Lack of initial bite is one thing but also I had couple of situations when maximum power that this particular brake has to offer was not sufficient.
Then you've got something wrong with the setup, not bed correctly or bled or piston advanced.

uraz
Posts: 98
Joined: Thu Dec 12, 2013 9:48 pm

by uraz

Or my expectations were too high. I was using them for over 2 seasons so DOT fluid was flushed at least 2 times and I've gone through 2 or 3 sets of pads (OEM organic pads, centerline x rotors). In my opinion they are usable but not as good as they could be. I'll reconsider comeback when they will be on pair with shimano mtb brakes.
Last edited by uraz on Thu Oct 11, 2018 7:36 pm, edited 1 time in total.

bm0p700f
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by bm0p700f

I find it hard to lock up my disc brake bike on the road. In the wet it is possible. When I have IRC RBCC tyres on though I cant.

Locking up wheels means you take longer to stop. How easily you can lock the brake is not a guide to how good the brake is. It is a guide to how much grip you have. not alot if the brake can lock the wheel easily.

uraz
Posts: 98
Joined: Thu Dec 12, 2013 9:48 pm

by uraz

I think that on clean and dry tarmac you would fly over the bar way before moment of locking the front wheel. It's probably good that you can't do it.

by Weenie


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by wheelsONfire

Never, no matter how hard i brake.
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