cale

If the heat of friction is moved further from the tire, the potential for tire failure due to overheating is greatly reduced. This is a barrier to some alternative materials that could effectively negate the current weight discrepancy that exists between the competing systems.

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.

dwmckee

I agree, though I suspect very few riders actually wear out rims with caliper brakes.

gsa103

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.

cyccommute 

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.

This is rolled out all the time but, honestly, has it ever happened to you? Or even anyone you know? In 35+ years of riding road bikes in mountains, mountain bike riding, riding loaded touring bike in mountains, riding loaded mountain bikes while touring in mountains and tandem riding, I've never even come close to blowing a tire off a rim. I've had some bad tires that blew off the rim around 10 PSI under their recommended pressure but that wasn't heat related.

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.

This may seem like something practical in practice but it's no more practical than having a second set of wheels for any bike. Practically, having the ability to change from 26" to 700c isn't that important.

Thru axles are a PIA! They take all the disadvantages of lawyer lips and make them worse. And they have no effect on how straight a rotor is in the caliper. Rubbing can happen in any rotor system...hub mounted disc or rim...due to an untrue rotor. A rim rotor is a bit easier to straighten if for no other reason then you have 28 to 40 adjusters that can be finely tuned (aka spokes). A hub mounted rotor has no fine adjustment at all, other than how gently you bend the rotor.

cale

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.

FastJake

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.

cale

I think about what could be, you think of what you have... We're different. Get it?

gsa103

You must have missed all of the research devoted to carbon rims not melting. Aluminum rims, yes nobody cares. Carbon rims its a MAJOR issue, and there's a ton of different things to optimize. Reynold's for example, wants you to use a specific brake pad with their rim.

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.

SnowJob

Hm, interesting. I've had issues with both cantis and vbrakes in ice, snow, and slush. Most days, the Avid SD7s on my Monocog were great, but on longer rides through snow and slush I would lose braking power after half an hour or so of riding. I often had to stop often and clear the frozen gunk off my rims. Very annoying. This is something I had encountered quite a lot in my life--brakes that lose a lot of power when the rims get crap all over them.

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.

SnowJob

I see what you did there!

Wilfred Laurier

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.

cyccommute 

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.

Heat doesn't part of the equation for most tire failures. The primary failure mode for bicycle tires is because the tread wears out. I'd put the second most common as road damage...pot holes and road debris. Third is age which is only minimally related to heat. Way, way down on the list...maybe below ELE meteor strikes is failure due to overheating. Again, have you ever had a tire fail due to overheating a rim?

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.

cyccommute 

My experience with hydraulics is different from yours. My levers go from full off to full lock in about 1/4" of travel. They are exteremely touchy. I wonder if your experience was with a system that needed bleeding. No hub mounted disc I've ever used worked well when the lever is set up to half travel before engaging. That kind of set up makes for brakes that are worse than the worst rim brakes.

I have no experience with carbon rim and am not likely to in the future. I will say, however, that carbon fiber and, more specifically, the matrix materials used to hold the fiber together is made of thermoset resins which do not typically "melt". They can thermally decompose at very high temperatures but they don't become liquid and smeer like thermoplastics do.

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.

cale

You're baiting me, I'm done

rydabent

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.

dynaryder

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.

dynaryder

I've own 5 different models of hydros. None were 'digital';all had excellent feel for what was going on down at the caliper. I've also ridden motorcycles with cable and hydro brakes,and cable and hydro clutches. All had better feel with the hydro systems than the cables.

You really need to work on your disc truing technique;I have no probs tweaking a rotor in less than five minutes. I've also never heard of a rotor failing because it was tweaked,I've heard of nipples being damaged when not treated properly.

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.

cyccommute 

I don't need to work on my disc truing technique because there is no disc truing "technique". You bend the rotor where it needs to be bent as much as it needs to be bent. There is no fine adjustment and it's (more or less) a meat clever approach to truing. I suppose you could true wheels the same way...i.e. just apply a pry bar to them and hope for the best...but no one would really like the results.

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.

Yes my experience is colored by MTB use. I don't have hub mounted discs on anything else...mostly because I don't see the need. But, to be honest, I've never damaged a rotor at all. All the rubbing issues and the need to true rotors have been at the installation of new rotors that have never been used. Out of the package, the rotors aren't straight. I've had 4 disc equipped bikes and I've built, roughly, 12 disc wheels and installed about 12 rotors. All of the rotors rubbed upon installation on the wheels and had to be trued. It didn't take hours but it took longer on each rotor than an equivalent wheel would and the process is quite fiddly.

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.

Lazyass

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?

SquidPuppet

As you and I both know, perfect alignment on a production bike (motorcycle) is like a unicorn. I've never built a race bike that didn't need tweaking to get it straight. Even after they "measured" straight, the normal slop that exists even in good tolerances can cause issues. Here is how we dealt with front rotor/pad drag.

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.

pursuance

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!

SquidPuppet

Just position/tighten stuff where it "wants" to be. Makes sense, no?

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.

Leebo

Unless you commute year round in New England.

Leebo

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.

FastJake

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.