cantilever brake pad adjustment

In article <[email hidden]>

Ben Barker said:

Apologies for very basic one here...

I've just had new pads fitted to the front of my bike. One pad is
parallel with the rim, the other is at a very slight angle such that
while the front of the pad rubs slightly, the rear is clear. I can't
work out how on a set of cantilever brakes to adjust this "tilt" -

Depends on the specific brake.

Quoted message said:

or why you would want to - surely paralell is always best...

It's normal to set the pads so the front touches slightly before the
back does - this is called 'toe-in' and helps to prevent squeal or
judder when braking. When you apply the brake hard the whole pad should
make contact with the rim.

in message <[email hidden]>, Ben Barker

(') said:

Apologies for very basic one here...

I've just had new pads fitted to the front of my bike. One pad is
parallel with the rim, the other is at a very slight angle such that
while the front of the pad rubs slightly, the rear is clear. I can't
work out how on a set of cantilever brakes to adjust this "tilt" - or
why you would want to - surely paralell is always best...

Parallel isn't best. You need a toe in because the brakes warp under load
and they need to be parallel at full braking effort. For instructions
see here: http://www.parktool.com/repair/readhowto.asp?id=19

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; I put the 'sexy' in 'dyslexia'

Ben Barker said:

Apologies for very basic one here...

I've just had new pads fitted to the front of my bike. One pad is
parallel with the rim, the other is at a very slight angle such that
while the front of the pad rubs slightly, the rear is clear. I can't
work out how on a set of cantilever brakes to adjust this "tilt" - or why
you would want to - surely paralell is always best...

AUSHTA. See <http://www.sheldonbrown.com/canti-trad.html> for the full
dope on adusting cantis.

--
Dave...

Ben Barker said the following on 05/07/2006 00:15:

Quoted message said:

Apologies for very basic one here...

No need to apologise.

Quoted message said:

I've just had new pads fitted to the front of my bike. One pad is
parallel with the rim, the other is at a very slight angle such that
while the front of the pad rubs slightly, the rear is clear. I can't
work out how on a set of cantilever brakes to adjust this "tilt" - or why
you would want to - surely paralell is always best...

Both blocks should be adjusted so that the front of the block touches
the rim just before the back, but obviously neither block should touch
the rim with the brakes off. You can do this by putting a piece of thin
cardboard between the back edge of the block and the rim, although some
blocks have a "designed-in" lip at the back for just this purpose. When
you say "had new pads fitted", was this by a bike shop? If so, I would
take it back and ask them to refit and adjust them properly, or read
http://www.parktool.com/repair/readhowto.asp?id=19 and have a go yourself.

If they are parallel, the odds are they will squeal like buggery!
They're set up at a slight angle so that the forward movement of the
wheel will pull the blocks parallel to the rim when you apply the
brakes. If they're parallel to start with, this same forward movement
will tend to lift the front of the block away from the rim.

--
Paul Boyd
http://www.paul-boyd.co.uk/

Paul Boyd said:

Both blocks should be adjusted so that the front of the block touches
the rim just before the back, but obviously neither block should touch
the rim with the brakes off. You can do this by putting a piece of thin
cardboard between the back edge of the block and the rim, although some
blocks have a "designed-in" lip at the back for just this purpose.

I think you'll find the lip on the back edge is not for setting toe-in
but is intended to displace water for quicker brake action with wet
rims.

--
Dave...

Ben Barker said:

I've just had new pads fitted to the front of my bike. One pad is
parallel with the rim, the other is at a very slight angle such that
while the front of the pad rubs slightly, the rear is clear. I can't
work out how on a set of cantilever brakes to adjust this "tilt" - or
why you would want to - surely paralell is always best...

Despite the prolific advice to toe-in, I've very rarey found that it, or
lack of it, actually makes any differenece to squeal or quality of
braking.

Personally, I prefer parallell because it allows the blocks to be set
nearer to the rim, meaning the lever doesn't have to be pulled so far
before it does something. But try toe-in if that's not an issue for you.

~PB

dkahn400 said the following on 05/07/2006 11:44:

Quoted message said:

I think you'll find the lip on the back edge is not for setting toe-in
but is intended to displace water for quicker brake action with wet
rims.

Oh well - it does at least provide a toe-in guide, even if that isn't
what it's for. :-)

--
Paul Boyd
http://www.paul-boyd.co.uk/

In article <[email hidden]>

Pete Biggs said:

Ben Barker said:

I've just had new pads fitted to the front of my bike. One pad is
parallel with the rim, the other is at a very slight angle such that
while the front of the pad rubs slightly, the rear is clear. I can't
work out how on a set of cantilever brakes to adjust this "tilt" - or
why you would want to - surely paralell is always best...

Despite the prolific advice to toe-in, I've very rarey found that it, or
lack of it, actually makes any differenece to squeal or quality of
braking.

As a former lbs mechanic I can assure you that it does.

Rob Morley said:

Quoted message said:

Despite the prolific advice to toe-in, I've very rarey found that
it, or lack of it, actually makes any differenece to squeal or
quality of braking.

As a former lbs mechanic I can assure you that it does.

I said "rarely" in /my/ experience, whether or not that's smaller than
your experience. My mere point is that it's not guaranteed to make a
difference in every case.

Lack of toe-in certainly does not cause squeal in every case, and toe-in
does not always cure squeal. It happens to have made no difference the
majority of times I've tried it. I can't explain why if that is not
typical, but it's with various bikes and brakes I've worked on over the
years.

~PB

Rob Morley said:

Quoted message said:

Despite the prolific advice to toe-in, I've very rarey found that it, or
lack of it, actually makes any differenece to squeal or quality of
braking.

As a former lbs mechanic I can assure you that it does.

The face of the block will soon wear to have the same angle to the rim
whether initially toed-in or not. So it's a short lived effect whatever
you do.

Anthony

In article <[email hidden]>

Pete Biggs said:

Rob Morley said:

Quoted message said:

Despite the prolific advice to toe-in, I've very rarey found that
it, or lack of it, actually makes any differenece to squeal or
quality of braking.

As a former lbs mechanic I can assure you that it does.

I said "rarely" in /my/ experience,

And I said often in my experience (or words to that effect).

Quoted message said:

whether or not that's smaller than your experience.

My experience is bigger than your experience - nah nah nah nah nah :-)

Quoted message said:

My mere point is that it's not guaranteed to make a difference in every case.

Agreed.

Anthony Jones said the following on 05/07/2006 13:01:

Quoted message said:

The face of the block will soon wear to have the same angle to the rim
whether initially toed-in or not. So it's a short lived effect whatever
you do.

I'm thinking about this as I type, rather than before, but I don't think
that's right. The face of the block will wear whilst it is being pulled
forwards by the wheel, and at that time it should be parallel to the
rim, so will wear parallel to the rim. When it is "let go" by releasing
the brakes, it will move back to it's rest position, which will still be
toed in.

Did that make sense? I haven't gone out to measure any remaining toe-in
on my worn blocks because it's raining!

--
Paul Boyd
http://www.paul-boyd.co.uk/

In article <[email hidden]>

Anthony Jones said:

Rob Morley said:

Quoted message said:

Despite the prolific advice to toe-in, I've very rarey found that it, or
lack of it, actually makes any differenece to squeal or quality of
braking.

As a former lbs mechanic I can assure you that it does.

The face of the block will soon wear to have the same angle to the rim
whether initially toed-in or not. So it's a short lived effect whatever
you do.

That will happen if you only ever brake lightly, in which case squeal
probably won't be much of a problem anyway. When you brake heavily with
toed-in blocks the block is pulled parallel with the rim so wears
evenly.

Paul Boyd said:

Anthony Jones said the following on 05/07/2006 13:01:

Quoted message said:

The face of the block will soon wear to have the same angle to the
rim whether initially toed-in or not. So it's a short lived effect
whatever you do.

I'm thinking about this as I type, rather than before, but I don't
think that's right. The face of the block will wear whilst it is
being pulled forwards by the wheel, and at that time it should be
parallel to the rim, so will wear parallel to the rim. When it is
"let go" by releasing the brakes, it will move back to it's rest
position, which will still be toed in.

Did that make sense? I haven't gone out to measure any remaining
toe-in on my worn blocks because it's raining!

That does make sense (when there's enough flex), but there might be
factors missing, including compression, and one end of the block being
pressed harder against the rim than the other.

~PB

Response to Rob Morley:

Quoted message said:

Quoted message said:

The face of the block will soon wear to have the same angle to the rim
whether initially toed-in or not. So it's a short lived effect whatever
you do.

That will happen if you only ever brake lightly, in which case squeal
probably won't be much of a problem anyway. When you brake heavily with
toed-in blocks the block is pulled parallel with the rim so wears
evenly.

I was just wondering about that, having been fettling my cantis this
morning [sounds like something Rambling Sid Rumpo might do]: I toe in
the blocks as a matter of course, and they're now worn parallel to the
rim on the rear brake [which I generally use for gently slowing down],
much more than on the front [which I generally use for stopping]. Just
one data point, YMMV, &c.

TBH, I never did it to stop squealing: IMlimitedE the brakes which
squealed still did it after toeing in, and the ones which didn't, um,
didn't; perhaps I was doing it wrong. In any case, I never really
objected to my brakes squealing, it tended to gain the attention of
dopey peds.

Now I come to think of it, on the bike which used to squeal, I got into
the habit of blipping the rear brake when approaching peds who were
about to step into the road, solely in order to gain their attention: is
there an easy way of making my present brakes squeal, I wonder?

--
Mark, UK
"One horse-laugh is worth ten thousand syllogisms."

Rob Morley said:

Quoted message said:

The face of the block will soon wear to have the same angle to the rim
whether initially toed-in or not. So it's a short lived effect whatever
you do.

That will happen if you only ever brake lightly, in which case squeal
probably won't be much of a problem anyway. When you brake heavily with
toed-in blocks the block is pulled parallel with the rim so wears
evenly.

You seem to be assuming that I'm saying that the block face will
necessarily wear to be parallel to the rim -- I'm not. Sorry if that
wasn't clear.

What you say above is completely correct, but similarly if the brake
block *isn't* toed-in to start with, and you brake heavily, it will wear
unevenly until it is toed-in.

For a given braking 'style', the end result (in terms of the resulting
angle between pad face and rim) will be the same whatever the starting
point.

The correct toe-in from the start has the benefit of even pad wear, and
minimal squealing from the start. Whether that's worth the extra hassle
is a moot point.

Anthony

Paul Boyd said:

Quoted message said:

The face of the block will soon wear to have the same angle to the rim
whether initially toed-in or not. So it's a short lived effect
whatever you do.

I'm thinking about this as I type, rather than before, but I don't think
that's right. The face of the block will wear whilst it is being pulled
forwards by the wheel, and at that time it should be parallel to the
rim, so will wear parallel to the rim. When it is "let go" by releasing
the brakes, it will move back to it's rest position, which will still be
toed in.

Yep, that's why I said 'the same angle' without specifying what the
angle was. See my other reply to Rob.

Anthony

Mark McNeill said:

Now I come to think of it, on the bike which used to squeal, I got
into the habit of blipping the rear brake when approaching peds who
were
about to step into the road, solely in order to gain their attention:
is there an easy way of making my present brakes squeal, I wonder?

Put a small dab of grease on the rim.... not that I would normally give
that advice!

~PB

In article <[email hidden]>

Pete Biggs said:

Paul Boyd said:

Anthony Jones said the following on 05/07/2006 13:01:

Quoted message said:

The face of the block will soon wear to have the same angle to the
rim whether initially toed-in or not. So it's a short lived effect
whatever you do.

I'm thinking about this as I type, rather than before, but I don't
think that's right. The face of the block will wear whilst it is
being pulled forwards by the wheel, and at that time it should be
parallel to the rim, so will wear parallel to the rim. When it is
"let go" by releasing the brakes, it will move back to it's rest
position, which will still be toed in.

Did that make sense? I haven't gone out to measure any remaining
toe-in on my worn blocks because it's raining!

That does make sense (when there's enough flex), but there might be
factors missing, including compression, and one end of the block being
pressed harder against the rim than the other.

The back of the block is pressed harder against the rim, it is
effectively self-energising - the more it grips the more it moves
towards the rim, while the front of the block moves away from the rim.
That's one of the reasons why squeal occurs in the first place - if the
rear of the block moves far enough forward the contact patch is reduced
to the point that it suddenly lets go, the block springs back and starts
to grip again. Toeing-in counters this by getting the front of the
block to take up some of the flex before the back of the block is
gripping hard, so there is less movement still available once the back
of the block starts to really bite.