Lars Halstrom

When ever I stand to climb or put a lot of pressure on my pedals when maneuvering slow, it feels like my brakes are on. I didn't see any wheel rub marks anywhere on chain stays or fork. So I think my wheels are flexing so that I'm getting lateral movement of the rotors in the calipers. One mechanic said you can adjust the calipers to allow for this. The pistons would have to be moved further apart to allow for this wheel flexing or maybe the wheels need adjustment so they don't flex. These are OEM wheels on my hybrid Specialized Sirrus with Tektro Draco hydraulic brakes. The tires are Schwalbe Marathon Plus. The wheels are 32 spokes each. I weigh 210#. Anybody find this happening on their bike?

Bill Kapaun

Since the disc is attached to the HUB..........

DrIsotope

Yeah, I doubt the hubs are flexing, least of all enough to cause the rotors to deflect. I run my calipers with less than 1mm on either side of the pads.

Now when going up a long, steep grade, sometimes it feels like I'm dragging a milk crate full of bricks. My that's just the engine not making enough power. The bike is fine.

Andrew R Stewart 

One of the pluses of rim brakes is there ample rim/pad clearances. Much less so with disk brakes and the same frame, wheel and axle/frame securement. The OP's large mass contributes too. I suspect that a stiffer everything would help, as would a rider who is lighter or spins smoother. Andy (Who really doesn't know the rider but does know how things work).

FBinNY 

As pointed out, the disc is attached to the hub, so wheel flex which involves the rim and spokes is immaterial. OTOH, of there's any play in the bearings, the hub could deflect slightly under load.

But disc rub has a particular chirp, and I strongly doubt you could have rubbing material enough that you'd feel the friction without hearing it also.

I suspect that the bike is fine, and it's all illusory. You're probably feeling the reason you're standing and riding slow in the first place. Sometimes hills are steeper than they look.

well biked

If you're getting brake rub when you're pedaling hard (out of the saddle for example), what's likely happening is the fork is flexing. The ends of the fork are moving enough due to the flexing/twisting of the fork that the caliper is being moved into the brake rotor as you pedal. I've seen this many times, particularly on bikes with a rigid fork equipped with disc brakes.....hybrids with a suspension fork and disc brakes are also prone to this, because the suspension forks that are on hybrids are typically fairly flexy forks.

reddog3

I can't imagine that you'd experience brake rub, on discs especially, without hearing it. How about narrowing it down by making the same climb with the brakes backed off. Unhook the cables and try again.

Oops- they're hydros. Possible you could rotate the calipers off the rotor?

Andrew R Stewart 

Most hydro calipers use the piston seals as the pad retraction spring. So when the brakes are applied the pads extend and the seals are "stretched". When the brakes are released the seals pull the pads back a bit. But dirt and grime can hinder this action. And the pistons can over extend and then the seals might not retract the pads as much as needed. It is possible to have slight pad rub with very little noise, if one pad is rubbing all the time (as in the caliper being positioned off center) then there would be no coming and going of rub or noise.

One of the first things we do to eliminate pad rub with hydros is to move the pads all the way into the caliper. Remove the wheel and use a clean thin device (cone wrench works well) and place it between the pads and pry them apart. The pads will now be farther apart then when in actual use. Reinstall wheel and allpy the brake a couple of times. this will reposition the pads the correct amount apart most every time. now you can check for caliper centering and/or rotor warp. Andy.

cyccommute 

Yup. I'll add that the suspension forks on hybrids aren't the only flexible forks on bicycles. There are a lot of high end suspension forks that have a lot of flex in them. You are depending on a small amount of metal across the wheel to both connect the individual fork blades and to keep them from moving independently.

I'll also add that there are some other factors that could contribute to bending of the rotor during hard effort. Play in the bearings has been mentioned but having a hub that isn't firmly clamped in the forks or a hub that is skewed in the fork tips could also cause rubbing issues. The latter two are common enough that I always check the hub before I do anything else when someone says "my brakes rub".

cale

This is true but I disagree with your conclusion as to which system has the plus on THIS point of fact. The fact that the disc runs so close to the pads is of significant benefit to the cyclist. There is better brake response, as the gap is closed quickly which means that actual braking begins sooner. The rider of a disc-equipped bike will have closed the gap before the rider of the caliper/rim system even reaches the braking surface. This difference makes the disc braking system more responsive in many ways. The pads clear the braking surface of moisture and debris more rapidly which in turn makes braking available sooner.

A caliper/rim solution offers the benefit of more rapidly making high braking forces available. In dry conditions, the immensely higher coefficient of friction, rubber pads compared to dense disc-pads, makes them "grabby". The cyclist quickly adjusts to this "grabbiness" and backs off pressure (or changes posture, etc.) accordingly. The sensation is that of "quick" braking and in some ways it is. But the disc system offers a different sensation and is no less effective in terms of stopping performance.

The OP also mentioned that the effect was noticed during slow maneuvers and standing. Not the circumstances for spinning. As a younger and significantly lighter cyclist, I was able to produce much more flex to my bike than I can now, three decades later. (Which might be due to stiffer frames, etc.) I'm not saying that "mass" isn't real, but there are "factors" as you readily stated. I discount the whole "weight" thing in this scenario in large part because I don't think frame or wheel flex is a likely issue.

FBinNY 

The OP reports feeling drag, but doesn't mention hearing anything.

Brake drag due to flex imparts very little friction because the (normal) force pressing the brake track against the pad is so low. Brake drag of this sort is more annoying because of the noise than any true loss of power.

well biked

True story: I was once riding with a guy who had hydraulic discs on his bike and a cheap suspension fork. This guy is a strong rider, and a big rider. He cut one of the zip ties in half that was holding his hydraulic hose to the fork (fork leg repeatedly hitting the tire), the fork and wheel were flexing so much during hard efforts. He also complained of being "slowed down" because of so much brake rub during out-of-the-saddle climbing. He didn't mention hearing anything until his brake hose was flopping in the spokes. .....Maybe he did hear the brakes, I don't know....FWIW, he later bought a much better suspension fork with 32mm stanchions....problem solved.

Lars Halstrom

All great discussions. One thing I didn't state is that it happens in my lowest gear. I modified my 9 speed drivetrain to an 11-36 cassette instead of the 11-32 and a long cage Shimano Deore rear derailleur instead of the OEM Sora. So when on my 34t chainring and 36t cog, I have a lot of torque climbing. Maybe that is affecting the rear hub bearings, dropout deflection, wheel deflection and chain stay deflection adversely. The 2013 bike has over 4K miles on it. i've test ridden many other bikes with 11-32t cassettes and 50/34t chainrings with hydraulic disc brakes without any issues of drag while climbing. Maybe the best thing to do is take it to my trusted LBS and have him ride it up some hills.

FBinNY 

How about a small experiment.

Loosen the mounting bolts and kick the caliper over a hair so it rubs slightly on one side. Tighten and ride. I'll bet 3 beers to one that you hear it more than you feel it.

Not saying that fork flex can't make a disc brake rub, just that you'd hear it if that were the case.

JonathanGennick 

I'm kind of with FB on this one. But...since the problem manifests while climbing in the lowest gear, why not just take the brakes completely off the bike and ride it up a steep hill. (Just be sure to walk the bike back down the hill). If the symptoms go away with the brakes, then you're on to something. If you still feel resistance, then at least you've eliminated the brakes as its cause. Either outcome puts you closer to a solution.

FastJake

+1 Remove the calipers completely, it's only two bolts per caliper. Bungee them to the frame somehow (toe strap would probably work) and ride up a hill. This will tell you for sure whether it's the brakes or something else.

Just don't ride down the hill without re-installing them! Rim brakes could be released much easier by simply loosening the cable, but unfortunately you have hydro discs.

dabac

Or remove the pass . As opposed to the caliper, pads are made made to be easily replaceable.

FBinNY 

It's a hydraulic brake. I wouldn't remove the pucks, since if the lever is accidentally squeezed it will hyper extend the pistons, and dump more fluid into the lines.

If removing the caliper is difficult, or there's concern about repositioning it correctly (easy enough) I'd remove the rotor (disc). Then I'd put a keeper between the pucks to protect them from my accidentally squeezing the lever.

cale

First off, disc pads don't generate significant friction unless pressed against the disc with lots of force. They aren't grabby. Secondly, I'm not the OP but there's little likelihood that I'd be able to sense "braking" if it was limited to caliper rub.

Now I do think that the tires could be made to rub on the frame. Inadequate skewer tension is not uncommon.

As far as showing frame rub... Got me. Not that big a deal?

cyccommute 

I beg to differ on both counts. Saying that a disc brake won't generate significant drag unless applied with lots of force can be easily tested. Adjust the fixed pad of a mechanical brake so that it rubs on the rotor and spin the wheel in a stand. The wheel will stop quickly. I've worked on a lot of disc brakes and even a little drag will stop the wheel from spinning.

As to disc brakes being "grabby", some are and some aren't. I've got a set of Avid Juicy that are all about being "grabby"...to the point of being digital in their use. They are either on or off and have no middle.

cale

Well, how much force will I apply when tightening the pads? My point was that in the context of a cyclist on the bike and riding as described by the OP. He described a rubbing sensation and I discount the possibility that the pads were rubbing.

It's possible the levers were depressed.