Divtos

I just bought a brand new Cannondale synapse DI2. The disc brakes have been giving me a problem. I rode 50 miles on it before realizing the brakes were constantly rubbing. I had the shop adjust it, with some effect and a mechanic friend further adjust it with better effect but neither front nor back will spin totally freely. The rub is small now but it is still rubbing a little bit. Is this normal for disc brakes??? I can't imagine this is acceptable performance generally. Any advice is appreciated.

rmfnla

47 page installation manual for those:

https://www.google.com/url?sa=t&rct=j...z7v1wfvx23d0GQ

(Yes, I know it includes the shifters...)

OnyxTiger

Pretty normal. Mine rubbed for about 150 miles or so. Did you try speeding up the breaking in time? (Ride around and do some fairly hard stops from 15-20 mph, around 15-20 times.) Now they're functioning really well.

Also, make sure to keep your rotors clean if you start hearing some squealing from the brakes. Spray down with brakleen (or any disc brake cleaner), use nitrile latex gloves to protect your skin, sand down with a light sand paper, and clean down pads with simple dish soap and water, and rub them together to clean and establish a new gritty surface.

Divtos

Thanks!

rydabent

Disc brakes adjusted right do NOT drag. If you cant read up on how to adjust them yourself, find and intelligent bike shop tech that can.

Zef

One way that has worked for me:
(Assuming your caliper mounts to an adapter that mounts on the frame)
1. loosen the bolts that hold the caliper to the adapter mounted to the frame.
2. Take two playing cards and place one on each side between the pad and the rotor
3. Squeeze the brake lever and tighten the caliper bolts
4. Remove the cards
5. check for proper function (e.g. no rubbing)

If your caliper does not mount to an adapter but instead mounts directly to the frame/fork then you will need some really thin washers and play with different combinations on each of the two bolts until you have the caliper situated so that you no longer have any rubbing.


-j

speedy25

First check is to make sure the rotor isnt bent. They are usually easy to straighten if needed.

As greenfieldja noted, loosen the mounting bolts, apply the brakes, and re-tighten bolts to get the caliper in proper alignment with the rotor.

No, they shouldnt rub when adjusted properly.

-SP

hueyhoolihan

what's the point of the cards?

jmess

The cards provide a small gap between the brake pads and the rotor which should help center the caliper over the rotor.

Something I found that can help is rotating the wheel until you hear the pads rub. With the rub point under the brake pads loosen the bolts, you could try inserting the cards at this point also, then hold the brake lever down while you re-tighten the bolts.

Another thing to do before trying to center them is cleaning the rotors, calipers, pads, and the piston faces. I think shimano recommends using denatured alcohol as a cleaner. You don't want anything on the caliper piston faces that push against the pads.

fietsbob

Rotor needs to be dead Flat , Is It?

rmfnla

None of this is making a case for me to switch from rim brakes...

fietsbob

You live in a Desert.

CafeVelo

+1

rydabent

Some of the problem here is that they cycling community is stuck in the 1890s. Witness the fact that the cycling community rule makers the UCI dont even think that a recumbent is a bicycle. There seems to be total resistant to change. A LBS mechanic that dont seem to know how to adj disc brakes is IMO a throw back resistor of something new. LBS mechanics better learn quickly. If you read cycling news, disc brakes are coming on strong, including road racing bikes. Remember the cyclist and mechanics that didnt like click shift that came out in the mid 80s.

Disc brakes have a short sequence of steps that need to be followed, and if done correctly the pads dont rub.

dabac

Disc brakes have tight tolerances. Tighter than for rim brakes. With tighter tolerances comes less travel which is the main reason why discs gives more stopping power for a certain amount of hand effort than rim brakes.
But a consequence of the tighter tolerances is that everything needs to be pretty much bang on spec to run clean.
While brake rub is almost always annoying, it takes a fair amount of it before the drag becomes noticeable while riding. There really is very, very little energy lost when the brake isn't activated.

Zef

Not quite sure the tighter tolerance/less travel has much of anything to do with disc brakes having more stopping power...especially in a hydraulic system.

The tight tolerance between the pads and the rotor affect responsiveness to the point of engagement and possibly modulation of stopping power...but sopping power itself is affected by the cable pull ratio between the lever and the caliper in a cable operated disc brake, and the design of the hydraulic system in hydraulic disc brakes.

The tight tolerance of the disc brakes is more a function of the fact that the pads are only pulled back due to the fact that piston pushes further out of the hydraulic seal as the pads wear down...when the pressure is released on the brake lever the hydraulic seal of the piston pulls the piston back into the caliper body bud this travel back into the caliper body is not very far so the distance between the pads and rotor remain very small.

-j

FastJake

Wrong. Tolerances between the pads and rotors on bicycle disc brakes are so tight it's almost impossible and unreasonable to expect them to be setup not to rub. Rotors have to be true to fractions of a millimeter. One tiny bump and it will be out of true again.

On the plus side, this rubbing doesn't put much force on the rotor and hardly wastes any energy. But the noise can be annoying.

I've had a few bikes with mechanical and hydro disc brakes. They're gone and I don't miss them. I greatly prefer rim brakes.

rmfnla

I also don't like to ride in the rain...

Zef

I call BS as I have 4 mountain bikes in my stable (2 are mine and 2 are my kids) all have hydraulic disc brakes and neither of them drag on the rotor. I ride in the forests here in Belgium regularly, I remove wheels to put in or on the roof of the car depending on which I am driving and have no issues other than having to loosen the caliper to adapter bolts, squeeze the brake lever and re-tighten the bolts to ensure everything is aligned.

Although the tolerance between the pads and the rotor is miniscule it is sufficient and although the rotors can be bent, they are not as fragile ash you make them out to be...I have trued them once right after purchasing each of the bikes...not bad for 5 years of use.

-j

dabac

I disagree.
The starting point of the brake chain of events is the human hand.
The hand sets the amount of available lever travel.
This is what you have to work with as input.
At the other end there are brake pads.
When engaged, they need to push at the braked surface with sufficient power.
When disengaged, they need to retract enough to clear the braked surface.
With a disc brake caliper being a lot stiffer than just about any rim brake design, a 2-4 mm pad travel will get the job done.
By the time you've accounted for caliper flex, how much pad travel do you think a rim brake needs? 8 mm? 10 mm?
No matter what you do inbetween which doesn't include adding a brake servo, a set amount of lever travel turned into 2 mm pad travel will result in a stronger pinch than the same amount of lever travel turned into 8 mm pad travel.
The limited retraction capability of hydros then become a bit of a chicken or the egg line of consideration.
Hydros can't retract far, which means you need to engineer a tight-tolerance system. Which becomes a short pad travel system. Which, for a given amount of lever travel will pinch harder than a longer travel system.

Edit:
Hydros are short travel by choice, not by necessity.
Add a separate return spring instead of relying on the inherent characteristics of the sealing ring and you can have a considerably longer travel.

rydabent

Wrong!!! Disc brake adjusted right do not drag their pads.

Mine dont!!!

FastJake

You're still wrong. You must have different (better) disc brakes than the ones I used. The hydro discs I used didn't have any adjustments for pad clearance. There were no adjustments to do so there was nothing that could cure the rubbing besides a PERFECTLY true rotor. I spent some time getting it close but I wasn't going to bother trying for 0.1mm accuracy so I lived with it.

Rubbing is an inherent issue with bicycle disc brakes. Why do you think the question gets asked so much? It's not impossible to avoid, but with some systems it's extremely difficult to achieve.

rmfnla

Pad travel has nothing to do with braking power. All other things being equal, once the free play has been taken up it's still a matter of how hard you squeeze.

Hydraulics are more powerful because of the multiplicative effects of a master cylinder that is larger than the slave...

Hypno Toad

4 disc brake bikes in my house (1 hers & 3 his), none of them rub. My 3 bikes have a combined 20,000+ miles over 10 years. If the pads are rubbing, the calipers need to be adjusted; if your brakes don't allow you to adjust the calipers, you have the wrong brakes and need to replace them.

The question is asked so often because disc brakes are 'new' to road bikes. The MTB people aren't asking, 'cause they've been using disc brakes for 10+ years and figured them out.

hueyhoolihan

no rubbing on my XT's. they have a spring clip to help retract the pads.

in any case i know of no caliper mounting bracket that doesn't have enough inherent adjustability to allow the caliper to be set with the pads parallel to the rotor. if it's rubbing i would check the hub for excessive flexibility or the rotor as the source of a warp.