FatBottomedGirl

Hi,

First of all, in this question, I am only talking about a road bike used for training and racing if that can have any importance.

How close should I set my brake pads to the rim?
And should I toe them in? to what purpose? if it is only to avoid squeaking it really does not matter,... but if it allows better finely tuned feathering then sure... why not... And if yes, how toed-in should the shoes be?

From the documentations I read attached with the calipers, it says to leave a 1-2mm clearance on each side which does feel pretty close but on the other hand it does feel pretty well while using the lever...

But on the other hand, I am a heavy rider (~200 lbs), and even if my wheels are pretty stiff (in races I ride either Mavic Ksyrium SLRs or Mavic Cosmic Carbon SLEs) and my frame is ok, while not being a very high end one, full carbon fiber and my quick release is in good shape.
Where I am going with this is that when putting the pads 1-2mm of the rim, the rear wheel rubs when riding out of the saddle which is what makes me wonder about this whole pad clearance.

GlennR

If your rims are straight you can have them much closer than if they are not.

They just need to clear the rims so they don't rub.... anything more is a personal preference.

cderalow

i use the hold caliper tight to the rim and let it back off ever so slightly before tightening the pinch bolt.

probably 1-2mm i suppose if one was to measure.

Nachoman

As close as possible, without any rim contact.

milkbaby

My pads are probably about 2 to 3 mm away from the rims, enough for the levers to squeeze down a little before the pads hit the rim. I think it's argued that you get better leverage and more modulation that way?

I know some people use a business card or penny to set toe in, but I just do it by hand. I think it actually does more than just help eliminate squeal. If you think about it, the wheel rim is putting a twisting motion on the pads as the wheel rotates. So when you toe in the front, the rotation of the rim actually twists the pad to help braking.

cale

A good test of closeness is to squeeze the brake lever firmly. If it touches the handlebar, it isn't close enough.

79pmooney

Is there any play in the hub bearings? Can you rock the rim at the brakes? DO tis test with the wheel on the bike and quick-release tight. There should be play when the wheel is off the bike.) (I am hoping yes, because that means the out-of-the-saddle rubbing cause is known and fixable.)

Try some stiffer wheel and see if this still happens. (I am a retro so I know neither how stiff the Mavic wheels are nor what could be stiffer.) And if yes to both of the above, then it seems you have frame flex you will have to live with. Back off your rear brake until doesn't quite rub. Won't hurt anything, You will have to squeeze a little tighter but you will get used to it. (Don't make these changes the evening before a race!)

That 1-2mm isn't a magic number. A set-up that works for you is what matters. If you can back off a little on the brake and still have enough for a hard stop in the rain, you are good to go. (And this is a rear brake. In a really hard stop, it is your front doing all the work.)

Ben

RollCNY

As long as you can fully engage them, it is largely a matter of personal opinion. In a hard stop, how closed do you want the brake lever?

On the toe front, it can affect squealing, and can also impact pulsing. Anecdotally, I seem to recall running more toe on my wet weather bikes than dry weather ones. Really from a noise stand point.

merlinextraligh

If you have them as close as possible to the rim, it takes more pressure to get the same braking force.

So you want them far enough out you get leverage, but not so far out that the lever bottoms out before being at full force.

You can find the sweet spot by playing with the barrel adjuster.

Also they should be a millimeter or so closer on the leading edge, so that they don't squeal. (put a dime between the backside of the pad and the rim when you install new pads.

rpenmanparker 

Most of the time brake rub by the rim is due to the rim being too stiff and the build structure (spoke number, gauge, lacing pattern) not being stiff enough. If the rim were more flexible, it would bend at the horizontal diameter when stressed at the hub and the ground. In that case the top hf of the rim stays put and doesn't touch the rim. If it is too stiff for that, the whole rim rotates around the horizontal diameter and touches the brake. More or heavier spokes can help prevent that. The stiffer the rim you choose, the sturdier the build needs to be. Strange, but true.

Drew Eckhardt 

1mm is a good number which won't cause brake drag with minor problems.

Far enough the levers hit the bars is unacceptable, although without reaching that point you might increase clearance

- If you get brake rub climbing out-of-the-saddle

- If you can't get wheels out with the brake release open and not deflating tires

Wheel stiffness is a function of total spoke cross-sectional area which comes from gauge and count where your needs dictated by physics may be very different from what the market wants to buy.

Old and grumpy enough wheel builders would tell you not to expect gear made for 150 pound racers to work for you, and that they'd happily build you some 32 or 28 spoked wheels.

carpediemracing 

+1

With low spoke count wheels the rims are much stronger as they rely less on the spokes for strength. I can sit on an unlaced tall profile carbon rim without feeling much flex at all but if I did the same to an unlaced box section (much lighter) aluminum rim it'll bow outward as soon as I start putting weight on it.

The stiffer rims tilt around the hub. More flexible rims simply flex below the hub.

Therefore a stiffer rim will flex laterally relative to the brakes because it pivots around the hub. A more flexible rim won't because the bottom half of the wheel gets pushed to one side, leaving the top half (near the brakes) untouched.

As far as brake clearance, an independent tech guy found that for dual pivot brakes 2mm was the optimal rim-pad distance, far enough not to rub, close enough to stop well. He mentions it here but I don't know where the actual data sits.