Jarrett2

I have a road bike with disc brakes on it and they always seem to rub a little, no matter how I adjust them. This is compared to the caliper and canti brakes on my other bikes.

I've taken the bike to the LBS where I bought it a couple of times to have them look at it and after the second or third time, one of the mechanics sort of exasperatedly said, "All disc brakes rub!"

Is that true? Or just the claim of a bike mechanic having a bad day?

jimc101

What sort of discs? Hydraulic, or mechanical? Hydraulic brakes have a built in auto adjust, and have pistons on both sides, and shouldn't rub if correctly setup.

Most mechanical (TRP Spyre being the exception) only have one side(pad) that moves, normal the left, and the right is fixed; and normally setup close to the rotor, which can although if correctly setup shouldn't rub. Add to this flexy rotors, and you can get rub.

From experience of using Shimano mechanical discs for the last 3 years, correctly setup, there will be no rubbing under normal use. I haven't used Avid BB's, which are the other (more) common brand, so someone else will have to answer if they do rub in use.

FastJake

They don't all rub, but tolerances are extremely tight compared to rim brakes so if the rotor is out of true by a fraction of a millimeter, they'll rub. It's tough to get the rotors perfect enough.

Score one more for rim brakes...

Jarrett2

I've had two sets on the same bike.

Mechanical Avid BB7's

Semi-Hydraulic TRP HY/RD

Same rotors. Both rubbed. Enough that after 40 miles or so, it was a beat down.

cyccommute 

It really doesn't matter if you have mechanicals or hydraulics. Both need to be properly set up and the rotors almost always need some truing at installation. Sometimes they need truing later on as well if they get overheated. Like FastJake says, the tolerances are extremely tight and you don't need much misalignment to get the to rub.

Check to see if your wheel is fully seated as well. Front hubs can also slip under the disc braking load and become misaligned. Keep the front skewers tight...really tight!

SimonSan

Sorry to butt in on an otherwise serious question..

I'm really happy to see this post, I'm totally against the engineering facts regarding disc brakes for bikes especially road bikes.
Motorcycle disc pads touch the rotor (but they have the advantage of up to 200 horsepower to over come the efficiency loss of friction), and for sure given the basic copy design the bike disk pad will touch too, unless there is something to retain the pad to the piston.
Sorry but a steel rotor hydraulically operated pad design for a bicycle is backward engineering, considering the rim is the larger rotor any way.
Also sorry for the segway...

Cyclosaurus

They shouldn't rub, period. However, I know from first-hand experience with disc brakes is that it doesn't take much to throw them out of alignment. And it can be a very frustrating experience trying to nudge things that fraction of a millimeter and maintain full braking power. I think you are seeing that your mechanics aren't quite good enough to make those micro-adjustments and taking their frustration out on you.

nfmisso

+1 not to mention the added weight of disc brakes.

fietsbob

As mechanical, cable type , MTB have a different actuation rate than the Road type .. now if you put a long pull V brake lever on the bars and a Road caliper, at the hub,
a significant gap between the moving pad can be left to be closed with the initial swing of the Lever..


But the fixed pad still has to be close, on the inside, as the moving pad pushes the disc into the fixed pad, flexing the disc sideways..
.Exception, Spyre (& less successful IRD Double banger)


BTW Magura Has made a very nice Hydraulic rim brake for a Long time , recently they reintroduced one for time trial bikes with skinny tires .
but no return of a Master/ road lever .

Opting instead for a cable to hydraulic double master Cylinder..

DiabloScott

Disc brakes can also cause front wheel ejection. I might consider disc brakes on a through-axle frame for a MTB or adventure bike. Looks like the OP's Roubaix has that.

fietsbob

Fitting the Caliper on the front of the Right Fork blade Solves that also.

its the Physics of Torque Centers .. once you apply the brake the pad grabbing the rim becomes the stronger Torque Center/Axis.

Tim_Iowa

No, not true. I'm a mechanic at an LBS and I've never encountered a disc brake that I can't set up properly. However, there is a very tight tolerance, and many times I have to adjust them several times before I get them just right. It's very helpful to get the disc brakes close to your eyes; I flip the bike in the stand to just the right angle.

Some folks hate on disc brakes, and I understand that (I'm a confirmed retrogrouch, look at my bikes). However, in my experience as a rider, disc brakes are tremendously more effective than rim brakes.

Although a rim is a larger rotor (by far), I've never encountered a rim brake that can clamp it as strongly as disc brakes do (Hayes/Magura hydro rim brakes, maybe? Never tried them).

There are many valid reasons to hate on disc brakes, but effectiveness isn't one of them.

You can argue that they are out of place on a road bike, but if the frame is well-designed to take them then I'd consider discs an upgrade. Wet rims = poor braking, wet discs = fine (but noisy) braking.

And like I said, they don't have to drag if they're set up properly.

cale

Lots of space particles and zero sum half-truths floating about this thread...

The bottom line is that disc brakes are no different than any other brakes. They work because of friction. That friction is not significant where contact with the disc is momentary, a fraction of a second or a single mm of contact. The disc material is so hard that it bounces off the steel rotor. In contrast, a rubber brake pad (talk about archaic technology) contacting an aluminum or carbon wheel has a much high coefficient of friction because it is so soft.

Disc pads are so hard that they require much more force to slow the wheel. It means that slight rub you might hear when moving bikes around in the garage will have no impact on your riding enjoyment.

Disclaimer, this post contains a lot of opinion, your mileage may vary.

Jarrett2

A second question, what's the next type of brake with the most stopping power after disc brakes?

SquidPuppet

Not if set up properly.

well biked

No, they shouldn't rub. If they do, either they need to be adjusted or the rotor needs to be trued, or both.....My experience is that cable actuated (including your TPR cable actuated hydraulics) are much more prone to getting out of adjustment and rubbing. I very, very rarely have a problem with full hydraulics rubbing once adjusted properly. Thru axle or not.

SimonSan

Some folks hate on disc brakes, and I understand that (I'm a confirmed retrogrouch, look at my bikes).

I Don't hate on disc brakes..... MY aim i s to get Shimano and Campag to realise they just have to change the rim braking profile, ie carbon rim with metallic braking surface. not alloy rim, metal sintered rim with adapting shoe. lighter nad more effective than a 100 year old concept in disc brake

SimonSan

a brick wall....

I have mentioned this on many posts.... the future is the rim being metalized the caliper being as it is is far enough power for any human. the only issue is wet weather. the carbon rim with poor brake pads is not a great performer in the wet.

Leebo

Nope, not all disk brakes rub. Some rotors do not run true however. On the BB7's both sides move. The 2 piece Shimano ice teks are supposed to be nice. Most of my disc brakes are set and forget. Easy to set up and maintain. Just don't crash and hit a rotor. Never seen a wheel ejected because of a disc brake. No black junk on the rim to clean up after a rainy/muddy/wet ride. For me, and how and where I ride, discs rule. YRMV

SquidPuppet

Your personal attack aside.

On a road racing motorcycle, much attention is paid to wheel position/alignment within the forks during wheel replacement. There is a series of steps in the procedure before the axle pinch bolts receive their final torquing. Also, "Full Floating" rotors are exactly that. Mounted to the carriers with bobbins instead of bolts, they are free to constantly move and self align.

Booger1

They don't rub on paper and in a perfect world....In real life they do at times.

Disk brakes don't have return springs like other setups do.

SimonSan

Owned and raced motorbikes...... Much attention is paid to wheel position? huh? there is NO retention, the pad is free to do what ever it likes, I ran Brembo's and it was the same as my mates Nissin, the caliper floats. same concept as pushbikes... no? Is there a retaining clip on a road bike disc?

SimonSan

Mr SquidPuppet with all due respect, I'm not sure you get my point..... Motorcycles have floating discs to reduce vibration under heavy braking. from say 200mph to 50mph. I can assure you my road motorcycle and my track motorcycle all rub the disc 360 degrees of their rotation, a bicycle does not have the advantage of free horse power so if a bicycle disc rubs (as it is expected to do) it only equals loss of energy to the rider with little gain.

SquidPuppet

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.

Exactly. In a hydraulic system using "FULL floating rotors", not semi floating or fixed, the rotors movement (when at speed) will actually push the pads/pistons back enough to eliminate drag.

That's an unfortunate consequence of improper setup.

What is Full-Floating?

SquidPuppet

That was not the reason full floating mounting was invented. Brembo initially invented it for heat transfer/dissipation reasons. The loss of rub was an unintentional bonus, but very real.