Changing from 27" to 700c

Graham Ashton said:

I've got a fairly old touring bike with Weinmann centre pull brakes,
very much like these:

http://cgi.ebay.co.uk/WEINMANN-CENTRE-PULL-BRAKES-STRADLES-TOURER-RACER_W0QQitemZ260218566897QQcmdZViewItem?hash=item260218566897

They're fine. I want to get some new wheels for it though, and would
quite like to put some 700c wheels on it.

I get the impression that the front brake won't have enough reach to
hit a 700c rim, but the rear looks as though it will. Could I (or
should I?) get another rear calliper and stick it on the front, or
would that be a daft thing to do? I know of no reason why I shouldn't,
but then I also realise that I'm winging it here slightly...

I brake designed specifically for the rear wheel should not be used on
the front. The stresses involved in front wheel braking are higher than
in rear wheel braking, (and also the components flex the opposite way).

Why not get the new wheels, see if they fit, and if not then sort out
the new brakes. If you are buying the wheels from your LBS, then you can
check the wheel rim size whilst still in the shop, and look at brakes if
need be.

Martin.

On Fri, 14 Mar 2008 16:12:58 -0700 (PDT), Graham Ashton
<[email hidden]> said in
<[email hidden]>:

Quoted message said:

I've got a fairly old touring bike with Weinmann centre pull brakes,
very much like these:

http://cgi.ebay.co.uk/WEINMANN-CENTRE-PULL-BRAKES-STRADLES-TOURER-RACER_W0QQitemZ260218566897QQcmdZViewItem?hash=item260218566897

They're fine. I want to get some new wheels for it though, and would
quite like to put some 700c wheels on it.

I get the impression that the front brake won't have enough reach to
hit a 700c rim, but the rear looks as though it will. Could I (or
should I?) get another rear calliper and stick it on the front, or
would that be a daft thing to do? I know of no reason why I shouldn't,
but then I also realise that I'm winging it here slightly...

I would try it and see if the brakes can be adjusted to fit - the
Weinmann's on my 27" tourer fitted 700c wheels no problem.

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

Martin Dann said:

Graham Ashton said:

I've got a fairly old touring bike with Weinmann centre pull brakes,
very much like these:

http://cgi.ebay.co.uk/WEINMANN-CENTRE-PULL-BRAKES-STRADLES-TOURER-RACER_W0QQitemZ260218566897QQcmdZViewItem?hash=item260218566897

They're fine. I want to get some new wheels for it though, and would
quite like to put some 700c wheels on it.

I get the impression that the front brake won't have enough reach to
hit a 700c rim,

That is possible, though give it a go because only 4mm reach extra is
needed. If almost there, filing a bit off the bottom of the slots will do
the trick.

Quoted message said:

but the rear looks as though it will. Could I (or

Quoted message said:

should I?) get another rear calliper and stick it on the front, or
would that be a daft thing to do? I know of no reason why I
shouldn't, but then I also realise that I'm winging it here
slightly...

The shorter bolt makes that difficult.

The best solution, if your current brake doesn't have enough reach, is an
Alhonga deep-drop dual-pivot brake. This model provides an extra large
amount of reach. Dual-pivot brakes give you better braking and with a
lighter action than centre-pulls anyway.

Quoted message said:

I brake designed specifically for the rear wheel should not be used on
the front. The stresses involved in front wheel braking are higher
than in rear wheel braking, (and also the components flex the
opposite way).

Front and rear caliper brakes tend to be exactly the same except for the
length of the bolt. They can be interchanged safely if you get round the
bolt issues. More info on this is on the Sheldon Brown site. Look up
"recessed" in the Glossary.

~PB

Martin Dann said:

[A] brake designed specifically for the rear wheel should not be used on
the front. The stresses involved in front wheel braking are higher
than in rear wheel braking, (and also the components flex the
opposite way).

A front caliper is normally fitted in front of the forks and faces forwards.
A rear calper is normally fitted behind the stays and faces backwards.
Therefore if you swap them they will flex the same way.

As for handling the forces, except for a few special cases, manufacturers
don't bother making their rear caliper brakes weaker than their fronts.
Even the Campag "Differential" rear brake (special case) uses the
single-pivot design that used to be the norm for both rear and front brakes
some years ago. One of these would have no problem handling the stresses of
front-braking. You just have to pull the lever harder to get it to brake as
hard as a dual-pivot.

~PB

Pete Biggs said:

Martin Dann said:

[A] brake designed specifically for the rear wheel should not be used on
the front. The stresses involved in front wheel braking are higher
than in rear wheel braking, (and also the components flex the
opposite way).

A front caliper is normally fitted in front of the forks and faces forwards.
A rear calper is normally fitted behind the stays and faces backwards.
Therefore if you swap them they will flex the same way.

I don't agree with that statement. However I think that the direction of
stressing is less important than the strength of the brake.

Quoted message said:

As for handling the forces, except for a few special cases, manufacturers
don't bother making their rear caliper brakes weaker than their fronts.

When I replaced my front V brakes last year, I was told by the LBS that
front V brakes can be used on the rear, but not vice versa due to the
strength of the brakes.

I don't know whether this applies to callipers as well, but it makes
sense to me.

Martin.

Martin Dann said:

Pete Biggs said:

Martin Dann said:

[A] brake designed specifically for the rear wheel should not be
used on the front. The stresses involved in front wheel braking are
higher than in rear wheel braking, (and also the components flex the
opposite way).

A front caliper is normally fitted in front of the forks and faces
forwards. A rear calper is normally fitted behind the stays and
faces backwards. Therefore if you swap them they will flex the same
way.

I don't agree with that statement.

If I'm wrong then it would be helpful to explain what exactly you disagree
with in that statement.

Quoted message said:

However I think that the direction
of stressing is less important than the strength of the brake.

Quoted message said:

As for handling the forces, except for a few special cases,
manufacturers don't bother making their rear caliper brakes weaker
than their fronts.

When I replaced my front V brakes last year, I was told by the LBS
that front V brakes can be used on the rear, but not vice versa due
to the strength of the brakes.

Maybe that's true for V brakes, or some V brakes. I don't know so much
about V brakes, and the OP's bike doesn't have V brakes.

Quoted message said:

I don't know whether this applies to callipers as well, but it makes
sense to me.

It makes logical sense that rear brakes aren't as strong as front brakes,
but once you've looked closely at lots of caliper brakes and had lots of
experience using them, you realise that this isn't actually the case for
them - except perhaps for some very special cases.

I've had experience with Weinmann centre pulls as well as various single and
dual pivot sidepulls. With most of these, you wouldn't be able to tell if
it was a front or rear brake if I chopped the bolt off.

Well done for raising your concern - but there's no actual worry with the
particular brake in question as long as it's mounted adequately, etc.

~PB

Before I start I know I'll get all manner of [censored] from this reply
however here goes:

Take one round file roughly the same size as the brake pad slots and
file down until brake block is accommodated. Fit those 'tapered'
blocks the ones that in effect are narrower at the 'face' than they
are at the metal holders. Job done - well it works/worked for me on my
old Holdsworth frame. And to the horrified I only had to take off 2
mm! PS - still alive after about 5 years of doing this! But 2 mm is
about as much as I would recommend.

"Graham Ashton" <[email hidden]> wrote in message
news:[email hidden]...
I've got a fairly old touring bike with Weinmann centre pull brakes,
very much like these:

http://cgi.ebay.co.uk/WEINMANN-CENTRE-PULL-BRAKES-STRADLES-TOURER-RACER_W0QQitemZ260218566897QQcmdZViewItem?hash=item260218566897

They're fine. I want to get some new wheels for it though, and would
quite like to put some 700c wheels on it.

I get the impression that the front brake won't have enough reach to
hit a 700c rim, but the rear looks as though it will. Could I (or
should I?) get another rear calliper and stick it on the front, or
would that be a daft thing to do? I know of no reason why I shouldn't,
but then I also realise that I'm winging it here slightly...

Cheers,

Graham

Pete Biggs said:

I've had experience with Weinmann centre pulls as well as various single and
dual pivot sidepulls.  With most of these, you wouldn't be able to tell if
it was a front or rear brake if I chopped the bolt off.

Thanks all. I'll try offering a 700c wheel up to the bike and seeing
whether or not they'll reach as is. If not I now know what to do
next... :-)

Graham

In article <[email hidden]>, Pete Biggs
[email hidden] says...

Quoted message said:

Martin Dann said:

Pete Biggs said:

Martin Dann wrote:
> [A] brake designed specifically for the rear wheel should not be
> used on the front. The stresses involved in front wheel braking are
> higher than in rear wheel braking, (and also the components flex the
> opposite way).

A front caliper is normally fitted in front of the forks and faces
forwards. A rear calper is normally fitted behind the stays and
faces backwards. Therefore if you swap them they will flex the same
way.

I don't agree with that statement.

If I'm wrong then it would be helpful to explain what exactly you disagree
with in that statement.

Front brakes flex away from the forks, rear brakes flex towards the seat
stays. But the last time I checked, torsional stiffness isn't dependent
on the direction of rotation, just the axis (which remains pretty much
the same between front and rear brakes).

Quoted message said:

Quoted message said:

When I replaced my front V brakes last year, I was told by the LBS
that front V brakes can be used on the rear, but not vice versa due
to the strength of the brakes.

Maybe that's true for V brakes, or some V brakes.

It sounds like cow plops to me. In some situations you might want to
use a more compact brake on the back for clearance reasons, and the
reduced mechanical advantage is not a problem because it generally takes
less force to lock the rear wheel.

Quoted message said:

I don't know so much about V brakes, and the OP's bike doesn't have V brakes.

Quoted message said:

Quoted message said:

I don't know whether this applies to callipers as well, but it makes
sense to me.

It makes logical sense that rear brakes aren't as strong as front brakes,
but once you've looked closely at lots of caliper brakes and had lots of
experience using them, you realise that this isn't actually the case for
them - except perhaps for some very special cases.

In the case of the Suntour self energizing cantilever they only made the
more powerful brake available for rear fitment (apparently because of
concerns that people would be flying over the bars and suing), likewise
U brakes are very rigid and have high mechanical advantage but were
rarely used on the front, although more recently they have found favour
with some BMXers.

Quoted message said:

I've had experience with Weinmann centre pulls as well as various single and
dual pivot sidepulls. With most of these, you wouldn't be able to tell if
it was a front or rear brake if I chopped the bolt off.

You don't have to chop it off, just pull it out. When these brakes were
commonly used there was a tendency to fit a longer reach caliper on the
rear than on the front, but I don't think that had anything to do with
varying the mechanical advantage so much as allowing a bit more mudguard
clearance on the back wheel.

Rob Morley said:

In article <[email hidden]>, Pete Biggs
[email hidden] says...

Quoted message said:

Martin Dann said:

Pete Biggs wrote:
> Martin Dann wrote:
>> [A] brake designed specifically for the rear wheel should not be
>> used on the front. The stresses involved in front wheel braking are
>> higher than in rear wheel braking, (and also the components flex the
>> opposite way).
>
> A front caliper is normally fitted in front of the forks and faces
> forwards. A rear calper is normally fitted behind the stays and
> faces backwards. Therefore if you swap them they will flex the same
> way.

I don't agree with that statement.

If I'm wrong then it would be helpful to explain what exactly you disagree
with in that statement.

Front brakes flex away from the forks, rear brakes flex towards the seat
stays. But the last time I checked, torsional stiffness isn't dependent
on the direction of rotation, just the axis (which remains pretty much
the same between front and rear brakes).

Front brakes are theoretically more likely to suffer from fatigue of the
bolt holding them on because they are in tension rather than
compression.

But I don't know if front brake bolts are actually thicker or fail more
often in practice.

In article <[email hidden]>, archierob
[email hidden] says...

Quoted message said:

Before I start I know I'll get all manner of [censored] from this reply
however here goes:

Take one round file roughly the same size as the brake pad slots and
file down until brake block is accommodated. Fit those 'tapered'
blocks the ones that in effect are narrower at the 'face' than they
are at the metal holders. Job done - well it works/worked for me on my
old Holdsworth frame. And to the horrified I only had to take off 2
mm! PS - still alive after about 5 years of doing this! But 2 mm is
about as much as I would recommend.

There's not a problem doing that as long as it's only a couple of
millimetres, although it may be a good idea to fit a heavy washer each
side of the brake arm if there's enough thread to fit them in. One
thing that can catch people out when fitting different wheels is that
the blocks swing up on centrepulls as the calipers close, so fitting a
narrower rim effectively reduces the reach, and also brake wear can make
the blocks ride up onto the tyre sidewall (that's another reason why a
heavy washer inside the brake arm can help).

In article <[email hidden]>, Ben C
[email hidden] says...

Quoted message said:

Front brakes are theoretically more likely to suffer from fatigue of the
bolt holding them on because they are in tension rather than
compression.

Assuming you're talking about cantilevers, the rear bolts aren't in
compression, they're under a bit of tension but all they really do is
hold on the washer that keeps the brake arm on its boss - when braking
the force is transferred to the boss and the bolt just sits there. With
a front brake on conventionally mounted bosses it's the retaining washer
and bolt that transfers forward forces to the boss, so the bolt is more
stressed and the brake arm will fly off if it fails.

Quoted message said:

But I don't know if front brake bolts are actually thicker or fail more
often in practice.

Brake bolts are almost universally 6mm, whether the one holding a
caliper to the frame or the one holding a cantilever arm to its boss.
IME decent quality ones properly fitted just don't fail, if they did
then more manufacturers would put the bosses behind the fork blades, or
use exotic or oversized bolts. I think it's safe to assume that the
standard bolts are strong enough that fatigue isn't really an issue.

I did this, but had to gain an extra 5mm or so on the brake drop-outs
(if that's the term) on the Weinmann centre pulls. There was enough
meat on the to file out the slot the requisite amount. However I
rather think they didn't work as well after, perhaps because more
force was then needed on the levers. That said, I had replaced the
levers at some point, so perhaps the travel / leverage ratio was no
longer right in any case.

Basically it can be done, if you're prepared to file a bit off. You'll
need a small round file, and ally files quite easily, but may need
more force on the levers afterwards

Hywel

"Graham Ashton" <[email hidden]> wrote

Quoted message said:

I've got a fairly old touring bike with Weinmann centre pull brakes,
very much like these:

http://cgi.ebay.co.uk/WEINMANN-CENTRE-PULL-BRAKES-STRADLES-TOURER-RACER_W0QQitemZ260218566897QQcmdZViewItem?hash=item260218566897

They're fine. I want to get some new wheels for it though, and would
quite like to put some 700c wheels on it.

I get the impression that the front brake won't have enough reach to
hit a 700c rim, but the rear looks as though it will. Could I (or
should I?) get another rear calliper and stick it on the front, or
would that be a daft thing to do? I know of no reason why I shouldn't,
but then I also realise that I'm winging it here slightly...

For some reason, on my bike the front was ok, but the back wouldn't reach.
In any case I have now fitted a long reach dual pivot on the front which
cost a mere £11.

Quoting Pete Biggs <[email hidden]>:

Quoted message said:

Martin Dann said:

[A] brake designed specifically for the rear wheel should not be used on
the front. The stresses involved in front wheel braking are higher
than in rear wheel braking, (and also the components flex the
opposite way).

A front caliper is normally fitted in front of the forks and faces forwards.
A rear calper is normally fitted behind the stays and faces backwards.
Therefore if you swap them they will flex the same way.

Er, no. Front braking tries to pull the brake off the bolt; rear braking
tries to shove it onto the bolt.

Quoted message said:

As for handling the forces, except for a few special cases, manufacturers
don't bother making their rear caliper brakes weaker than their fronts.

This is more salient - I doubt for brakes of that era the "front" and
"rear" are different in any significant respect. I'm quite surprised by
the OP saying they're not identical.
--
David Damerell <[email hidden]> flcl?
Today is First Stilday, March - a weekend.

David Damerell said:

Quoting Pete Biggs
<[email hidden]>:

Quoted message said:

Martin Dann said:

[A] brake designed specifically for the rear wheel should not be
used on the front. The stresses involved in front wheel braking are
higher
than in rear wheel braking, (and also the components flex the
opposite way).

A front caliper is normally fitted in front of the forks and faces
forwards. A rear calper is normally fitted behind the stays and
faces backwards. Therefore if you swap them they will flex the same
way.

Er, no. Front braking tries to pull the brake off the bolt; rear
braking tries to shove it onto the bolt.

Er, Rob Morley already corrected my mistake three days ago. It's
irrelevant anyway.

"Front brakes flex away from the forks, rear brakes flex towards the
seat
stays. But the last time I checked, torsional stiffness isn't dependent
on the direction of rotation, just the axis (which remains pretty much
the same between front and rear brakes)."

Quoted message said:

Quoted message said:

As for handling the forces, except for a few special cases,
manufacturers don't bother making their rear caliper brakes weaker
than their fronts.

This is more salient - I doubt for brakes of that era the "front" and
"rear" are different in any significant respect. I'm quite surprised
by the OP saying they're not identical.

IIRC, there were different models of Weinmanns with different amounts of
reach. I think it's quite common to need more reach at the rear. Strangely
it seems the other way round on the OP's bike.

~PB

Pete Biggs said:

IIRC, there were different models of Weinmanns with different amounts of
reach.  I think it's quite common to need more reach at the rear.  Strangely
it seems the other way round on the OP's bike.

Correct. The front are labelled 610 and the rear 750, which I strongly
suspect indicates their respective dimensions.