rydabent

What brand of disc brake do you have on your bike? I dont know of any that are not adjustable.

As with most things there is a right way and the "good enough" way. For me since I had to adj machines down to half a thousandth or less, adjusting disc brake calipers is not a problem at all.

I say again-----------------properly adjusted disc brakes DO NOT rub. If you bike mechanic says other wise, find and different mechanic. Sadly the reason this subject comes up often is the fact disc brakes are relatively new, and worse yet some bike techs dont understand the adjustments of various brands, and are not willing to take the time to do the adjustment right.

dabac

Pad travel has everything to to with a more powerful pinch.
If pad travel was the same as lever travel, the cylinders would have to be the same diameter. With the same diameter, the force exerted at the brake would be the same as the force exerted at the lever. No mechanical advantage.
Only way to increase the force is to reduce the travel.
Whether it's a lever and a fulcrum, or two differently sized hydraulic cylinders doesn't matter.
You trade force for travel, or the other way around.

dabac

+1

They CAN be a bit fiddly to set up though.
The standard recommendation of "loosen caliper mounting bolts, engage brake, tighten mounting bolts" has a considerable stroke of wishful thinking in it.
It is IMO quite common for the caliper to creep a little - and thereby destroy the alignment when the bolts are tightened down.
My preferred method is to use the above method as a starting point, but then I leave the bolts loose enough that I can tweak the position of the caliper by hand while eyeballing the alignment before doing the caliper bolts up tight and good.

travbikeman

Ok, this is a bit embarrassing for me to say. But it's also possible to have brake rub if your wheel is not fully or properly on your frame. Found this out the hard way one day with my son's bike after changing it's tire. The disc brake kept rubbing only to later find out that I did not fully install the wheel itself properly.

rmfnla

Ah, I see where we differ.

I was talking about slack in a given system; you are talking about the characteristic differences between mechanical and hydraulic systems.

That's why I used the term "All other things being equal"...

cale

OP, the fact that this is a brand new bike suggests that the wheel, not the disc, may be the source of your problem.

My new bike required both a hub adjustment and tensioning within 100 miles of purchase. Play in the hub, specifically, was responsible for disc rub.

It isn't unusual for a new bike to need adjustment shortly after purchase.

pataspen

Another thing to consider... is the brake mount on your frame properly aligned? Many are not. Even a 1 degreee misalignment will make it difficult to adjust the brake properly. You can tell by checking to see if the pads are parallel to the rotors or if the rotor slightly "tilts" towards one pad.

Park Tool sells a Brake Mount Facing Tool or some fancy name like that. It aligns the brake mount perpendicular to the axle, so the brake pads run parallel to the rotor.

It's not a tool many home mechanics will have, so check around your local bike shops. Not all shops will have it either, so you may have to check a few.

I recently had to do that to a bike of mine. Fixed the rubbing issue.

pataspen

It's called the DT-4, Disc Mount Post Facing Tool

Post Mount Disc Brake Facing with DT-4 - Park Tool

habilis

This is likely the source of many people's problems. On any bike, the wheel must be re-aligned with the frame each time it's installed, or the brakes (especially disc) will certainly rub. With my rim brakes, I visually align the center rib of the tire tread with the brake bolt on the frame. Disc brakes must be a nightmare in this regard.

Automotive hydraulic disc brakes usually have a slight amount of drag because the piston is just "floating" freely in its bore when there is no pressure on the system - there is no retraction device. This is tolerable because the engine has enough horsepower to make this drag inconsequential.

A bicycle is powered by an "engine" that generates only a few watts. Any drag, whether from brakes or bearings, is intolerable. So, if a brake can't be adjusted to be drag-free, it doesn't belong on a bike.

According to some posters, their discs are free of any drag and also stop effectively. Nothing less should be acceptable. I suspect that these brakes do have a retraction device of some kind.

Hydraulic pistons are sometimes defective because of contamination in their bores. This prevents the piston from retracting fully, causing drag. If a brake is adjusted with proper clearance, yet the clearance disappears after the first time the brake is engaged, suspect a faulty piston.

If drag is intermittent when the wheel is spun by hand, the rotor is warped.

Hypno Toad

Very common, this has happened to me more than once, especially when I'm in a hurry.

Jarrett2

I've been waiting to start seeing threads like this since disc brakes have been pushed into the high end road bike realm. I suspect it will be the first of many.

I've had hybrids, MTB's and road bikes with disc brakes. They all rubbed at some point or another. One good bump, some dirt, aggressive riding, whatever is all it takes to cause a tiny change in the tolerances of a disc brake that then causes it to start rubbing slightly during a ride. On a hybrid or MTB, who cares if it is rubbing a little bit, you typically don't push a constant speed for hours on them.

But a road bike, chasing a pack of riders whose brakes are not rubbing at 18+ mph for several hours, one tiny little disc brake rub can start to add up quickly. I've had it happen a number of times. Feels like you're having a bad day on the bike, getting sick, bonking, something. Just enough to make it an off day, then at the end of the ride, you realize the disc brake has been rubbing ever so slightly for miles. I would imagine in racing where every second counts, it would be even worse, costing a racer dearly in placings.

At first I was taking my bike to the LBS every time it happened. After about the third or fourth time, the mechanic barked in frustration, "all disc brakes rub!" At that point, I started learning how to tune them myself. On the mechanical disc brakes, its not that tough to do. Just something I had to do way more often than I wanted to. On hydraulic brakes, I was pretty limited. Since they are "self adjusting" there wasn't much I could do other than meticulously clean and true the rotors to keep the brake spinning friction free.

After a while of doing this, I got sick of it and dumped all of my disc brake road bikes going back to calipers. They may be inferior to disc brakes, but my enjoyment of riding goes way up when the discs go away.

I'm hoping the new crop of road discs solve all of these problems somehow, but I don't see how they really could.

Wilfred Laurier

The exact same thing applies to cable brakes - both disc and rim. The ratio of brake lever travel to brake caliper movement is the ultimate decider of how much power you have for a given force at the lever. Using V brake levers with caliper brakes will give massive clearance at the rim, but not brake worth a *******-***. Using caliper brake levers with V brakes or MTB disc calipers will have virtually no clearance but give massive stopping power (if it all isn't lost in cable housing compression and caliper flex).

habilis

I have no personal experience with disc brakes on bikes. All I can do is think about the concept and apply what I know about automotive braking.

On motor vehicles, disc brakes are far superior to drum - I've experienced it myself. Their greater efficiency means less pressure is needed to achieve maximum braking power, which ultimately means they lock up the wheel more easily. It's not due to any difference in pedal travel; the discs just grip harder than drums can. To prevent loss of control from lockup, some manufacturers added ABS.

Bikes rarely achieve speeds greater than 40 mph. (To go faster on a bike is arguably suicidal.) At high speed, a wheel lockup is even less desirable on a bike, since tire treads are thinner and much more susceptible to blowouts. The frame needs beefing up for disc brakes, or so I've read, so there's bound to be additional weight. Calipers, pistons, fluid-filled reservoirs, rotors - still more weight and complexity. What's next? ABS?

Then there's the added cost as a component of the bike's MSRP.

On a car, disc systems are actually simpler, lighter, and much easier to service than drums. It's all good. On a bike, rim brakes are simpler, lighter, cheaper, easier to maintain, and more than adequate for safe stopping. Okay, maybe discs are better in the rain, but I seldom ride in the rain.

FastJake

Except that they're not

habilis

Haven't discs been proven better at stopping than rim brakes? I mean scientific testing, not "ride impressions." If they aren't, then why use them at all?

FastJake

The rim brakes on my bikes will lock the rear wheel, and can lift the rear wheel by applying the front brake (the front wheel will skid in the rain.) Since it's physically impossible to stop any faster than that, there is no "better" to be achieved with discs. At least for me.

Your car comparison of drums and discs is mostly irrelevant as very very few bicycles use drum brakes. And when they do, it's always noted that stopping power is limited. Rim brakes are already "disc" brakes in that they clamp pads around a huge disc (the rim.)

habilis

I agree with you that if rim brakes can lock a wheel as effectively as discs, then rim brakes are preferable. They have none of the disadvantages of disc brakes that I listed.

I discussed automotive brakes because, in that application, disc brakes are superior to drum brakes. I was making no comparison between drum brakes and bicycle rim brakes, which I recognize as being just another form of caliper brake.

The question is: What added value are disc brakes on a bicycle? What do they offer to outweigh the disadvantages?

Hypno Toad

For me, it's stopping power in wet/dirty conditions. I ride both rim brakes and disc brakes; discs are for the wet, winter, dirt, ... bikes. The pure road bikes have rim brakes since they don't ride wet conditions (for the most part).

Oh and the fatbike has discs - 'cause nobody makes rim brakes for Pugsley.

habilis

This makes perfect sense, since rims are closer to the mud than disc rotors are. For road bikes, where water is the main consideration, do discs work better than alloy rims? Rotors and rims get about equally wet in the rain. Also, do rotors dissipate heat better than rims? Again, only controlled tests are worth considering. Not that I don't value people's impressions, but if you own a particular system, you might be biased in favor of it - or maybe against it!

Hypno Toad

I'll share my opinion, and I know this can vary from rider to rider. Here are my 3 dropbar bikes, the Kona (right) has discs and I use it conditions I won't use the other two (see below). One big difference, tires, the Kona use wider tires than the wider (28 to 35 mm) and the other two use 23 to 25 mm. .... This is an incomplete post, I got interrupted and will come back, just don't want to lose what I started, be back later.

FastJake

You should check this out then! You'd have to have the studs brazed on, but it's apparently possible to run a fat tire with a cantilever brake. Haulin? Some History | Blog | Surly Bikes

Tim_Iowa

Rotors and rims do not get equally wet in the rain. Rims will be wetter/dirtier because of puddles.

Regarding heat dissipation: Even if rotors and rims are equal at dissipating heat, disc brakes have an advantage. Because, the rotor is separate, so heat buildup only endangers braking. Whereas, heat buildup on a rim endangers the braking and may burst your tube.

Discs are a good idea on road bikes with carbon rims. Carbon fiber isn't a great braking surface, and it hates heat. So, carbon rims require either an aluminum brake track glued on, or the use of special (and less effective) brake pads. With disc brakes, the carbon rim doesn't have to include a braking surface. So, modern carbon road rims can be super light and get super aero (for example, Zipp's dimpled carbon rims for disc wheels).

Disc brakes have practical advantages, but they are heavier and require reinforcement of the frame that may negatively affect the ride. They seem like clear winners for MTBs, but road racers are still coming to grips with the compromises.

I've experienced lousy braking with all brakes: disc, rim, coaster.
I've experienced good braking with rim and disc brakes.
I've only experienced superlative braking with hydraulic disc brakes.

Give a disc-brake-equipped bike a test ride sometime, and see if you'd like them on your next bike. I ride vintage steel with rim brakes, and modern carbon with disc brakes.

hueyhoolihan

i've found that that the old-school hard black rubber pads work well with my single front dura-ace 7900 dual-pivot caliper on my generic carbon tubular front rim. it took a few hundred miles before that polyurethane wore off enough to give me a consistent braking surface though.

the disc brake i had on there (XT) was similar to the difference between power brakes on a buick and the manual brakes on the VW bug i learned to drive on. less force necessary to stop was the major difference. the XTs were remarkably smooth too.

fietsbob

OK Heavier yet But My bike with S-A drum brakes has Been undramatically Reliable for several Decades ..

habilis

Back when every kid had a single-speed (mostly Schwinns, I guess), they all had coaster brakes. Never heard of anyone's brakes failing or wearing out. I owned a couple of S-A hubs, but none had coaster brakes.