Do all disc brakes rub?
#101
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Disc brakes, with their ability to let you ride two difference size wheels, is of benefit to anyone living were space and/or money is at a premium. If you've got room for a second set of wheels, combined with a good frame, it's like having a second bike. You can have a commuter setup with sturdy 26" rims and commuter/hi-mileage tires AND you can have a weekend and training speedster by swapping in 700c/29 wheels and 28 mm slicks.
Last edited by cale; 03-28-15 at 01:57 PM. Reason: + clarity
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One is a 'possible' advantage as the word 'may' was used.
The second one is an advantage, I concede.
The third starts as an advantage but then is negated by the words after the comma.
Also, I admit I am nitpicking. I think I have spent too much time in front of the computer this AM.
The second one is an advantage, I concede.
The third starts as an advantage but then is negated by the words after the comma.
Also, I admit I am nitpicking. I think I have spent too much time in front of the computer this AM.
#103
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alright here is the real deal
Cheap rim brakes have more fudge room than cheap disc brakes and since the vast majority of bikes have cheap brakes of one kind or the other people think it is normal for disc brakes to rub. Most people aren't out there riding around on shimano SLX or better hydraulics which rock they are riding around on some low end tektros or any kind of Avids .
Cheap rim brakes have more fudge room than cheap disc brakes and since the vast majority of bikes have cheap brakes of one kind or the other people think it is normal for disc brakes to rub. Most people aren't out there riding around on shimano SLX or better hydraulics which rock they are riding around on some low end tektros or any kind of Avids .
#104
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I have a bike with both disc and rim. I cannot tell the difference between the way that both brakes work. I also own a bike with hydraulic brakes and if you look up the definition of "modulate" (to regulate by or adjust to a certain measure or proportion), they certainly don't fit that definition. They are almost digital in their application, i.e. either being on or off. They certainly don't reduce the possibility of locking the wheel and preventing skidding.
I don't even know anyone, personally, who has blown a tire due to overheating a rim. You would think, living at the base of some pretty fast downhills, it would happen with frightening regularity but it just doesn't.
Disc brakes, with their ability to let you ride two difference size wheels, is of benefit to anyone living were space and/or money is at a premium. If you've got room for a second set of wheels, combined with a good frame, it's like having a second bike. You can have a commuter setup with sturdy 26" rims and commuter/hi-mileage tires AND you can have a weekend and training speedster by swapping in 700c/29 wheels and 28 mm slicks.
Low end Tektro's don't rub if properly setup. The main problem is the use of quick-release wheels and disc brakes. If you don't have the quick release un-godly tight, the wheel shifts under hard braking and then the disc rubs. Quick releases should not be used with disc brakes, ever, thru axles are vastly superior. The high end bikes with SLX/XT/XTR and no rub are all using thru axles. The brakes get a bad name when the real culprit is cheap forks and wheels.
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#105
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Perhaps you missed the news but modulation is THE biggest gain that comes with disc brakes. You get it because the hard disc brakes have to be pressed harder to slow the bike than rubber rim pads (which btw have a higher coefficint of friction). Fortunately, disk calipers can exert a lot of pressure so the combination of having the effort within easy reach and a larger range in which to modulate that friction provides the magic of modulation.
Heat is important even if not in the critical temp region of tire failure. A rim that isn't tasked with heat management can be optimized for other purposes.
Your opinion of the equal viability of different wheels sounds like it's missing "...if you loosen the brake cable to adjust caliper spread for different rim widths, recenter the calipers, and make sure you have the tire/brake clearance..."
Your opinion of thru axles is predictable, and predictably short sighted.
Heat is important even if not in the critical temp region of tire failure. A rim that isn't tasked with heat management can be optimized for other purposes.
Your opinion of the equal viability of different wheels sounds like it's missing "...if you loosen the brake cable to adjust caliper spread for different rim widths, recenter the calipers, and make sure you have the tire/brake clearance..."
Your opinion of thru axles is predictable, and predictably short sighted.
Last edited by cale; 03-28-15 at 07:09 PM.
#106
Constant tinkerer
So the disc is superior how? This supposed "superior" modulation isn't something I've ever experienced with disc brakes. The lever travel is less than most rim brakes are set up to be but that's nothing inherent in a hub mounted disc over a rim brake. Rim brakes can be set so that lever travel is exactly the same.
I have a bike with both disc and rim. I cannot tell the difference between the way that both brakes work. I also own a bike with hydraulic brakes and if you look up the definition of "modulate" (to regulate by or adjust to a certain measure or proportion), they certainly don't fit that definition. They are almost digital in their application, i.e. either being on or off. They certainly don't reduce the possibility of locking the wheel and preventing skidding.
I have a bike with both disc and rim. I cannot tell the difference between the way that both brakes work. I also own a bike with hydraulic brakes and if you look up the definition of "modulate" (to regulate by or adjust to a certain measure or proportion), they certainly don't fit that definition. They are almost digital in their application, i.e. either being on or off. They certainly don't reduce the possibility of locking the wheel and preventing skidding.
Through axles are an unnecessary inconvenience that make wheel removal and installation take longer.
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That's been my experience with hydro discs as well. The lever goes down almost halfway, then they finally start to grab, then you have to apply quite a bit more pressure if you want to lock the wheel. I can get far superior modulation out of rim brakes because the pads are soft rubber and they can be setup to start grabbing with very little lever travel. Once they grab, they have a nice linear ramp-up from gradual braking to full lock. On the emergency stops (true emergencies, not thinking but just grabbing for brake) I've had to do over the past few years I've always noticed I've lifted the rear wheel but never enough to worry about going over the bars. Can't get any better than that.
Wow you're really grasping at straws. Like rim makers were ever concerned with heat management. And what purposes, exactly, could be optimized?
Through axles are an unnecessary inconvenience that make wheel removal and installation take longer.
Wow you're really grasping at straws. Like rim makers were ever concerned with heat management. And what purposes, exactly, could be optimized?
Through axles are an unnecessary inconvenience that make wheel removal and installation take longer.
#108
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As for truing a rotor, I firmly believe truing a rotor is FAR easier than truing a wheel. Grab a wrench and bend it. With a wheel, you have to worry about under/over tension on spokes, mainly proper balance etc. The only reason a rotor ever gets out of true is from crashes or impacts while not riding. The wheel is subject to a whole range of loads and impacts which can screw it up. For mountain biking, you can basically trash a rim and still maintain full braking since wheel trueness does not effect braking.
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I ride year round in all the ice and snow that Madison WI will dish out (woke up to slush this morning), all on cantilever or V-brakes. I've ridden over 2,000 miles since January 1st and never once wished for discs. My rim brakes with Kool Stop pads work just fine in all conditions and never give me reliability issues even with all the salt they use around here. People riding discs here in the winter report corroded/stuck calipers after a few years.
I had BB7s on my cross bike and loved em, so I put one on the front of the 'cog and kept the back an SD-7. That brake has been fine riding summer and winter for the past couple years. Once in a while I replace the cable/housing and the pads, but that's been it. Nowadays, my winter ride is my Ice Cream Truck, set up with hydros. I friggin' love it! Set it and forget it. I no longer need to worry about snow or slush packing up my rims and stealing my braking power.
Another bonus of disc brakes are dealing with clearance issues around tires. I love me some fat tires, and my 'cog can only fit about a 2.35 or so on the back because of the brake. On the front, because it's a disc, I have no issue putting whatever the hell I want on there.
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Most rims die from 'misadventure' long before wearing out, but I assure you it happens to all-weather commuters pretty regularly. I have completely worn through three rear rims and my father in law wore through his first one the year before he died. I inherited all his bike stuff and I realized a few weeks ago that the braking surface on his replacement rims are pretty concave already.
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Perhaps you missed the news but modulation is THE biggest gain that comes with disc brakes. You get it because the hard disc brakes have to be pressed harder to slow the bike than rubber rim pads (which btw have a higher coefficint of friction). Fortunately, disk calipers can exert a lot of pressure so the combination of having the effort within easy reach and a larger range in which to modulate that friction provides the magic of modulation.
Your explaination sounds like a lot of hand waving to me.
If you build or buy wheels with different widths, you might have to adjust the cable tension but that could be done with the adjusters at the bars. You shouldn't need to recenter the calipers any more than you would need to recenter the calipers on a disc brake. In fact, I often find that I need to recenter the calipers of different disc wheels if the hubs are the same make and model.
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#113
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That's been my experience with hydro discs as well. The lever goes down almost halfway, then they finally start to grab, then you have to apply quite a bit more pressure if you want to lock the wheel. I can get far superior modulation out of rim brakes because the pads are soft rubber and they can be setup to start grabbing with very little lever travel. Once they grab, they have a nice linear ramp-up from gradual braking to full lock. On the emergency stops (true emergencies, not thinking but just grabbing for brake) I've had to do over the past few years I've always noticed I've lifted the rear wheel but never enough to worry about going over the bars. Can't get any better than that.
You must have missed all of the research devoted to carbon rims not melting. Aluminum rims, yes nobody cares.
As for truing a rotor, I firmly believe truing a rotor is FAR easier than truing a wheel. Grab a wrench and bend it. With a wheel, you have to worry about under/over tension on spokes, mainly proper balance etc. The only reason a rotor ever gets out of true is from crashes or impacts while not riding. The wheel is subject to a whole range of loads and impacts which can screw it up. For mountain biking, you can basically trash a rim and still maintain full braking since wheel trueness does not effect braking.
As for truing a rotor, I firmly believe truing a rotor is FAR easier than truing a wheel. Grab a wrench and bend it. With a wheel, you have to worry about under/over tension on spokes, mainly proper balance etc. The only reason a rotor ever gets out of true is from crashes or impacts while not riding. The wheel is subject to a whole range of loads and impacts which can screw it up. For mountain biking, you can basically trash a rim and still maintain full braking since wheel trueness does not effect braking.
As to truing a wheel vs truing a rotor, Yes, you can over- or under-tension spokes but only if you are really hamhanded about it. If you do end up over or under tensioning a wheel while trying to true it, you probably have no business truing a wheel. You should either have a professional do it or have a professional watch you so that you don't do damage to the wheel.
I've never found a hub mounted rotor to be sufficiently true out of the box due to the need for very close tolerances of the brake system. A millimeter out of true on a disc rotor is almost beyond repair. 0.1mm is still pretty bad. Given that you have to physically bend the rotor to true it, it's not difficult to bend it too much in the opposite direction and make things worse. I have a rotor guide on my truing stand and find it to be one of the more useless tools I own. I have much better luck using the calipers themselves to true the rotor and even then, it is easy to screw up the truing job...or at least make more work for myself.
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#114
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Nope. Haven't missed the news. It's claimed that modulation is "THE biggest gain" but across several different systems, I've never experienced any "superior" braking from a hub mounted disc. It's equivalent but not superior.
Your explaination sounds like a lot of hand waving to me.
Your explaination sounds like a lot of hand waving to me.
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Remember the second advantage after superior braking. Disc brakes do not scab up your rims. You can run rims that are better designed for strength and aero considerations. In other words IMO disc brakes are an advancement in braking, even if they do require a good mechanic and patience to get them right. You will be rewarded.
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Nope. When setting up rim brakes,the pads must be set for 1) height 2) distance to rim 3) yaw and 4) toe-in. Discs only require the pads be set to distance from the rotor. Disc pads tend to last longer than rim pads,and therefore require less adjusting. Many discs have tool-free pad replacement. Hydros self adjust,and require no cable maintenance. Also,I've never seen a disc brake with loose pads;I've had a couple dozen bikes come into my clinic with rim brake pads that were only finger tight,or loose enough to move out of place.
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#117
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I also think you're experience with warped disc rotors is heavily colored by MTBing. The only time I've ever had an issue with any of my discs has been either from a bike that was shipped,or from playing polo. I've never once had to tweak the rotors on my all-weather commuter,which has north of 10k miles and has been ridden through everything,and locked up all over town.
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#118
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Because bending the rotor is such a back and forth process, it is very difficult to say "you can easily do it in x amount of minutes". How long it will take is going to depend on how much the rotor is bent and how hard you bend it in the direction you need it to go. And how much you have to bend the rotor will somewhat depend on the springiness of the rotor material. You have to bend a steel rotor quite a bit further than you would just to take out a slight wobble. There is far more "art" than science in truing a rotor.
A wheel, on the other hand, depends on how much you tighten or loosen a spoke. With some experience, you know how many turns (or fractions of turns) it takes to move a wheel a certain amount in a certain direction. There's far more science to wheel truing. There's a bit of art as well but not quite as much.
As for damaging spokes, you still have to have a reasonably true wheel hub mounted discs. The wheel also has to be properly tensioned as well. You could ride on a wheel that is horribly out of true but the wheel will eventually fail because it is poorly tensioned. And, yes, you can damage the spokes while truing or tensioning a wheel but that is true for rim brakes as well as disc brakes.
I also think you're experience with warped disc rotors is heavily colored by MTBing. The only time I've ever had an issue with any of my discs has been either from a bike that was shipped,or from playing polo. I've never once had to tweak the rotors on my all-weather commuter,which has north of 10k miles and has been ridden through everything,and locked up all over town.
And that also answers Jarrett2's question. Yes, I have found every disc brake I've owned or installed to rub on installation. They can be made not to rub but it's not as simple as many would have you to believe.
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#119
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I don't know what level you raced at, but if you were just putting the wheel in and cranking down the axle and pinch bolts, you were doing it wrong. As you know, forks twist, even big fat USDs. Tightening the axle and pinch bolts without aligning and eliminating twist is one cause for pad drag.
#120
Calamari Marionette Ph.D
I raced in the CMRA for eight years in a couple of different classes, I've built track bikes, do almost all my own work on my street bikes, I've helped others work on bikes, I've been in many shops and watched mechanics. I know a little about this subject. I would love to be schooled in how to properly install a wheel so the rotor won't rub on the pad. Align and eliminate twist? This is a new one to me. They use thru axles. Hold the wheel up, slide the axle through the fork and wheel, tighten the axle bolt, tighten the pinch bolts, slide the calipers with pads spread over the rotors and bolt them down. Ok so how do you "eliminate twist"? What twist? And how do you do this on the rear wheel so the rear rotor doesn't rub?
It will depend on the type of axle fixing your forks have. A threaded fork end vs nutted, but the principle is the same.
1. Install wheel and axle, but do not tighten axle/axle nut or pinch bolts. Everything should be where it "should be" when tightened, but NOT tight.
2. Install calipers, run the bolts in enough to lightly bottom, but do not tighten.
3. Firmly apply front brake and tightly wrap with a ziptie around the lever or have a team mate hold it.
4. Now tighten the calipers.
5. *Now tighten the pinch bolts.
6. *Now tighten the axle nut enough to hold it in place. If it's a threaded fork end, you are already done. (
7. Remove ziptie
* 5 and 6 seem reversed, I know.
If the piston seals are clean and healthy, after the deformation they experience during brake application, when the brake is released, they should retract the pistons enough to allow the pads to back off of the rotor.
Worked for us.
With regard to the rear end, I've never had a rear rotor drag against the pads. My assumption has always been that the individual sides of the swing arm don't want to twist (rotate) like an individual fork leg does when no wheel is installed. Maybe it was just luck/coincidence.
Last edited by SquidPuppet; 03-30-15 at 09:14 AM.
#121
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Good on ya SquidPuppet
I was a diesel mechanic for 40 years, generally had atleast one m/c and b/c that whole time.
I've done all my bicycle maintenance with the exception of replacing a BB.
In the 5 or 6 bikes with BB5 or BB7, belonging to guys I know, that I have worked on, never had a drag or bent disc issue.
My Trek DS with Shimano hyd discs was a treat, never an issue. It was stolen last year, that was an issue.
None of the above bikes were involved in competition however.
The disc hate is heavy n thick in this thread... get over it. I dislike 11 speed, got over it.
This is what is done by good mechanics working on m/c disc brakes.
At pad replacement time, remove the caliper, remove the pads, gently lift the caliper piston dust boot, pump out the pistons a tad, clean the piston with brake clean on a Qtip, lube the piston with the proper caliper assembly grease, again with a Qtip, reinstall the dust boot, push pistons back, install pads, install caliper, pump up the brakes, ride to bed-in pads.
The same applies to cars, trucks and bicycles.
Now, what retracts the pistons when pressure is released??
The caliper piston seals retract the pistons.
They flex under pressure as to piston moves out, then untwist as pressure is released,
retracting the piston/s.
So, lube the pistons at pad replacement time with the proper caliper assembly grease.. Easy peasy.
BTW, my next bicycle for this old fart will be a Jamis Aurora Elite with TRP HY/RD brakes. Cheers!
I've done all my bicycle maintenance with the exception of replacing a BB.
In the 5 or 6 bikes with BB5 or BB7, belonging to guys I know, that I have worked on, never had a drag or bent disc issue.
My Trek DS with Shimano hyd discs was a treat, never an issue. It was stolen last year, that was an issue.
None of the above bikes were involved in competition however.
The disc hate is heavy n thick in this thread... get over it. I dislike 11 speed, got over it.
This is what is done by good mechanics working on m/c disc brakes.
At pad replacement time, remove the caliper, remove the pads, gently lift the caliper piston dust boot, pump out the pistons a tad, clean the piston with brake clean on a Qtip, lube the piston with the proper caliper assembly grease, again with a Qtip, reinstall the dust boot, push pistons back, install pads, install caliper, pump up the brakes, ride to bed-in pads.
The same applies to cars, trucks and bicycles.
Now, what retracts the pistons when pressure is released??
The caliper piston seals retract the pistons.
They flex under pressure as to piston moves out, then untwist as pressure is released,
retracting the piston/s.
So, lube the pistons at pad replacement time with the proper caliper assembly grease.. Easy peasy.
BTW, my next bicycle for this old fart will be a Jamis Aurora Elite with TRP HY/RD brakes. Cheers!
#122
Calamari Marionette Ph.D
I was a diesel mechanic for 40 years, generally had atleast one m/c and b/c that whole time.
I've done all my bicycle maintenance with the exception of replacing a BB.
In the 5 or 6 bikes with BB5 or BB7, belonging to guys I know, that I have worked on, never had a drag or bent disc issue.
My Trek DS with Shimano hyd discs was a treat, never an issue. It was stolen last year, that was an issue.
None of the above bikes were involved in competition however.
The disc hate is heavy n thick in this thread... get over it. I dislike 11 speed, got over it.
This is what is done by good mechanics working on m/c disc brakes.
At pad replacement time, remove the caliper, remove the pads, gently lift the caliper piston dust boot, pump out the pistons a tad, clean the piston with brake clean on a Qtip, lube the piston with the proper caliper assembly grease, again with a Qtip, reinstall the dust boot, push pistons back, install pads, install caliper, pump up the brakes, ride to bed-in pads.
The same applies to cars, trucks and bicycles.
Now, what retracts the pistons when pressure is released??
The caliper piston seals retract the pistons.
They flex under pressure as to piston moves out, then untwist as pressure is released,
retracting the piston/s.
So, lube the pistons at pad replacement time with the proper caliper assembly grease.. Easy peasy.
BTW, my next bicycle for this old fart will be a Jamis Aurora Elite with TRP HY/RD brakes. Cheers!
I've done all my bicycle maintenance with the exception of replacing a BB.
In the 5 or 6 bikes with BB5 or BB7, belonging to guys I know, that I have worked on, never had a drag or bent disc issue.
My Trek DS with Shimano hyd discs was a treat, never an issue. It was stolen last year, that was an issue.
None of the above bikes were involved in competition however.
The disc hate is heavy n thick in this thread... get over it. I dislike 11 speed, got over it.
This is what is done by good mechanics working on m/c disc brakes.
At pad replacement time, remove the caliper, remove the pads, gently lift the caliper piston dust boot, pump out the pistons a tad, clean the piston with brake clean on a Qtip, lube the piston with the proper caliper assembly grease, again with a Qtip, reinstall the dust boot, push pistons back, install pads, install caliper, pump up the brakes, ride to bed-in pads.
The same applies to cars, trucks and bicycles.
Now, what retracts the pistons when pressure is released??
The caliper piston seals retract the pistons.
They flex under pressure as to piston moves out, then untwist as pressure is released,
retracting the piston/s.
So, lube the pistons at pad replacement time with the proper caliper assembly grease.. Easy peasy.
BTW, my next bicycle for this old fart will be a Jamis Aurora Elite with TRP HY/RD brakes. Cheers!
When the bicycle industry gets the hydraulic volume ratio correct between the master and slave cylinders, disc brakes should work perfectly. On modern top tier motorcycles, the power and modulation capabilities are mindbogglingly good. You can stand a 400lb bike on it's nose at 100mph and balance it there all the way to a full stop. No reason bicycles can't be as precise.
Last edited by SquidPuppet; 03-30-15 at 12:17 PM.
#123
Senior Member
#124
Senior Member
Lots of myths being brought forward here. Anyone use some recent shimano hydro mt brakes, like the deore, slx or xt? Excellent modulation. One or 2 fingers, easy. I'm on the lager side ( 235 lbs) and combined with bike and gear, plenty of weight to slow down. They work great for me, in my conditions. If old school stuff works for you in your conditions , great. The future is now, and has been for 5 years. I love my through axles. A stronger, stiffer interface to attach the wheel is a downside how? My quick release takes 3-4 turns to undo, the through axle maybe 6 or 7. Less fork flex and twist is great when charging though those rock gardens. Road bikes are being equipped with them as well. Some of the old school stuff works fine, for some conditions. Many others have seen the light. Like for mt biking, commuting or touring in adverse conditions. Most bike companies as well. Bad brakes, esp cheap disc ones suck. Try some avid BB7's, set up properly, with good levers and cables and see how good they are. Or good hydros on a mt bike. Come away from the dark side and into the light. Do properly set up canti's and v brakes work well, yup. In snow, slush and mud? YRMV ( your results may vary) It's nice to have choices for your own particular riding area and conditions.
#125
Constant tinkerer
A true quick release system, without lawyer lips, takes zero turns. Flip the lever and remove the wheel. As a bonus the nut is screwed on the right number of turns for wheel re-installation.