rear rim seems to rub

Jim Flom said:

My rear rim seems to rub on a brake pad when I am standing on the pedals on
steep climbs. At least that's what I THINK it is. Off the bike, everything
appears trued up well with good clearance. It's my 1998 Raleigh R500 7005
alu frame with oversized tubes.

Any theories? Any suggestions?

--
JF

"A really great man is known by three signs,--generosity in the design,
humanity in the execution, and moderation in success."
- Karl Otto von Schonhausen Bismarck

What specific rim/wheel are you using on the rear of the bike? Highly
doubt the frame/bike matters. Any flexibility or lack thereof in the
frame/bottom bracket area will not get transferred to the seatstay
bridge where the brake caliper is mounted. If it did then you have
far more important/immediate issues to deal with.

It is somewhat common to see pro bicyclists with open brake quick
releases (calipers with Shimano and Ergo levers with Campagnolo) when
climbing mountains. Scan through pictures on the Cycling News website
and you will find them.

This is a link to tests Damon Rinard did measuring lateral flexibility
on wheels.

http://www.sheldonbrown.com/rinard/
http://www.sheldonbrown.com/rinard/wheel/index.htm

Jim Flom said:

My rear rim seems to rub on a brake pad when I am standing on the pedals on
steep climbs. At least that's what I THINK it is. Off the bike, everything
appears trued up well with good clearance. It's my 1998 Raleigh R500 7005
alu frame with oversized tubes.

Any theories? Any suggestions?

--
JF

"A really great man is known by three signs,--generosity in the design,
humanity in the execution, and moderation in success."
- Karl Otto von Schonhausen Bismarck

What specific rim/wheel are you using on the rear of the bike? Highly
doubt the frame/bike matters. Any flexibility or lack thereof in the
frame/bottom bracket area will not get transferred to the seatstay
bridge where the brake caliper is mounted. If it did then you have
far more important/immediate issues to deal with.

It is somewhat common to see pro bicyclists with open brake quick
releases (calipers with Shimano and Ergo levers with Campagnolo) when
climbing mountains. Scan through pictures on the Cycling News website
and you will find them.

This is a link to tests Damon Rinard did measuring lateral flexibility
on wheels.

http://www.sheldonbrown.com/rinard/
http://www.sheldonbrown.com/rinard/wheel/index.htm

Jim Flom said:

My rear rim seems to rub on a brake pad when I am standing on the pedals on
steep climbs. At least that's what I THINK it is. Off the bike, everything
appears trued up well with good clearance. It's my 1998 Raleigh R500 7005
alu frame with oversized tubes.

Any theories? Any suggestions?

This is normal (it's due to lateral frame and wheel flex) and became a
problem with the advent of dual pivot brakes and low-ratio levers, which
requires the pads to be set much closer to the rim to avoid the brake
lever hitting the bar. Just do what the pros do- flip your rear brake
QR open at the bottom of the hill.

Jim Flom said:

My rear rim seems to rub on a brake pad when I am standing on the pedals on
steep climbs. At least that's what I THINK it is. Off the bike, everything
appears trued up well with good clearance. It's my 1998 Raleigh R500 7005
alu frame with oversized tubes.

Any theories? Any suggestions?

This is normal (it's due to lateral frame and wheel flex) and became a
problem with the advent of dual pivot brakes and low-ratio levers, which
requires the pads to be set much closer to the rim to avoid the brake
lever hitting the bar. Just do what the pros do- flip your rear brake
QR open at the bottom of the hill.

Tim McNamara said:

Quoted message said:

My rear rim seems to rub on a brake pad when I am standing on the
pedals on steep climbs. At least that's what I THINK it is. Off
the bike, everything appears trued up well with good clearance.
It's my 1998 Raleigh R500 7005 alu frame with oversized tubes. Any
theories? Any suggestions?

Quoted message said:

This is normal (it's due to lateral frame and wheel flex) and became
a problem with the advent of dual pivot brakes and low-ratio levers,
which requires the pads to be set much closer to the rim to avoid
the brake lever hitting the bar. Just do what the pros do- flip
your rear brake QR open at the bottom of the hill.

Riders asked for it and got it. Old brake calipers, side/center/canti
were all 1:1 ratio and the hand lever 4:1 mechanical advantage
(measured from the lever crook to pivot and pivot to cable). That ws
not enough for the riders who couldn't stop as easily as they wanted
so the mechanical advantage was increased to a total of about 5.6:1.

This required reducing pad clearance or the whole hand lever travel
wold be used up getting the pads to touch the rim. To do that, a
precisely centered caliper was needed and the brute force method was
to use two pivot points, one on axis and the other off to one side.
This causes the pad on the short arm to climb into the tire with wear.

Accurate centering could have been achieved by coiling the return
spring around the center bolt instead of having a spring with
"elephant ears" on either side of center. The centers of rotation of
the return spring is the center of the elephant ears and that causes
cosine error, the sliding motion you can readily see on a dual pivot
caliper. They even have a sliding plastic sleeve to accommodate that
unnecessary motion.

Campagnolo was aware that riders climbed hills with open QR's on the
rear brake and offered a 1:1 single pivot brake with good pad
clearance for the rear, where heavy braking is not done anyway.

Today, closely spaced rear hub flanges work together with low pad
clearance to make brakes drag when climbing. This is more noticeable
when riding in rain, when wet road grit makes an audible complaint.

Jobst Brandt

Tim McNamara said:

Quoted message said:

My rear rim seems to rub on a brake pad when I am standing on the
pedals on steep climbs. At least that's what I THINK it is. Off
the bike, everything appears trued up well with good clearance.
It's my 1998 Raleigh R500 7005 alu frame with oversized tubes. Any
theories? Any suggestions?

Quoted message said:

This is normal (it's due to lateral frame and wheel flex) and became
a problem with the advent of dual pivot brakes and low-ratio levers,
which requires the pads to be set much closer to the rim to avoid
the brake lever hitting the bar. Just do what the pros do- flip
your rear brake QR open at the bottom of the hill.

Riders asked for it and got it. Old brake calipers, side/center/canti
were all 1:1 ratio and the hand lever 4:1 mechanical advantage
(measured from the lever crook to pivot and pivot to cable). That ws
not enough for the riders who couldn't stop as easily as they wanted
so the mechanical advantage was increased to a total of about 5.6:1.

This required reducing pad clearance or the whole hand lever travel
wold be used up getting the pads to touch the rim. To do that, a
precisely centered caliper was needed and the brute force method was
to use two pivot points, one on axis and the other off to one side.
This causes the pad on the short arm to climb into the tire with wear.

Accurate centering could have been achieved by coiling the return
spring around the center bolt instead of having a spring with
"elephant ears" on either side of center. The centers of rotation of
the return spring is the center of the elephant ears and that causes
cosine error, the sliding motion you can readily see on a dual pivot
caliper. They even have a sliding plastic sleeve to accommodate that
unnecessary motion.

Campagnolo was aware that riders climbed hills with open QR's on the
rear brake and offered a 1:1 single pivot brake with good pad
clearance for the rear, where heavy braking is not done anyway.

Today, closely spaced rear hub flanges work together with low pad
clearance to make brakes drag when climbing. This is more noticeable
when riding in rain, when wet road grit makes an audible complaint.

Jobst Brandt

Quoted message said:

Tim McNamara said:

Quoted message said:

My rear rim seems to rub on a brake pad when I am standing on the
pedals on steep climbs. At least that's what I THINK it is. Off
the bike, everything appears trued up well with good clearance.
It's my 1998 Raleigh R500 7005 alu frame with oversized tubes. Any
theories? Any suggestions?

This is normal (it's due to lateral frame and wheel flex) and became
a problem with the advent of dual pivot brakes and low-ratio levers,
which requires the pads to be set much closer to the rim to avoid
the brake lever hitting the bar. Just do what the pros do- flip
your rear brake QR open at the bottom of the hill.

Riders asked for it and got it. Old brake calipers, side/center/canti
were all 1:1 ratio and the hand lever 4:1 mechanical advantage
(measured from the lever crook to pivot and pivot to cable). That ws
not enough for the riders who couldn't stop as easily as they wanted
so the mechanical advantage was increased to a total of about 5.6:1.

This required reducing pad clearance or the whole hand lever travel
wold be used up getting the pads to touch the rim. To do that, a
precisely centered caliper was needed and the brute force method was
to use two pivot points, one on axis and the other off to one side.
This causes the pad on the short arm to climb into the tire with wear.

Accurate centering could have been achieved by coiling the return
spring around the center bolt instead of having a spring with
"elephant ears" on either side of center. The centers of rotation of
the return spring is the center of the elephant ears and that causes
cosine error, the sliding motion you can readily see on a dual pivot
caliper. They even have a sliding plastic sleeve to accommodate that
unnecessary motion.

Campagnolo was aware that riders climbed hills with open QR's on the
rear brake and offered a 1:1 single pivot brake with good pad
clearance for the rear, where heavy braking is not done anyway.

Today, closely spaced rear hub flanges work together with low pad
clearance to make brakes drag when climbing. This is more noticeable
when riding in rain, when wet road grit makes an audible complaint.

Jobst Brandt

Does your wheel wiggle back and forth when you tug on it? Your hub-
bearing adjustment may need attention. Hard torque will pull the wheel
to the drivetrain side, rubbing your brakes.

Quoted message said:

Tim McNamara said:

Quoted message said:

My rear rim seems to rub on a brake pad when I am standing on the
pedals on steep climbs. At least that's what I THINK it is. Off
the bike, everything appears trued up well with good clearance.
It's my 1998 Raleigh R500 7005 alu frame with oversized tubes. Any
theories? Any suggestions?

This is normal (it's due to lateral frame and wheel flex) and became
a problem with the advent of dual pivot brakes and low-ratio levers,
which requires the pads to be set much closer to the rim to avoid
the brake lever hitting the bar. Just do what the pros do- flip
your rear brake QR open at the bottom of the hill.

Riders asked for it and got it. Old brake calipers, side/center/canti
were all 1:1 ratio and the hand lever 4:1 mechanical advantage
(measured from the lever crook to pivot and pivot to cable). That ws
not enough for the riders who couldn't stop as easily as they wanted
so the mechanical advantage was increased to a total of about 5.6:1.

This required reducing pad clearance or the whole hand lever travel
wold be used up getting the pads to touch the rim. To do that, a
precisely centered caliper was needed and the brute force method was
to use two pivot points, one on axis and the other off to one side.
This causes the pad on the short arm to climb into the tire with wear.

Accurate centering could have been achieved by coiling the return
spring around the center bolt instead of having a spring with
"elephant ears" on either side of center. The centers of rotation of
the return spring is the center of the elephant ears and that causes
cosine error, the sliding motion you can readily see on a dual pivot
caliper. They even have a sliding plastic sleeve to accommodate that
unnecessary motion.

Campagnolo was aware that riders climbed hills with open QR's on the
rear brake and offered a 1:1 single pivot brake with good pad
clearance for the rear, where heavy braking is not done anyway.

Today, closely spaced rear hub flanges work together with low pad
clearance to make brakes drag when climbing. This is more noticeable
when riding in rain, when wet road grit makes an audible complaint.

Jobst Brandt

Does your wheel wiggle back and forth when you tug on it? Your hub-
bearing adjustment may need attention. Hard torque will pull the wheel
to the drivetrain side, rubbing your brakes.

Quoted message said:

Jim Flom said:

My rear rim seems to rub on a brake pad when I am standing on the pedals on
steep climbs. At least that's what I THINK it is. Off the bike, everything
appears trued up well with good clearance. It's my 1998 Raleigh R500 7005
alu frame with oversized tubes.

Any theories? Any suggestions?

--
JF

"A really great man is known by three signs,--generosity in the design,
humanity in the execution, and moderation in success."
- Karl Otto von Schonhausen Bismarck

What specific rim/wheel are you using on the rear of the bike? Highly
doubt the frame/bike matters. Any flexibility or lack thereof in the
frame/bottom bracket area will not get transferred to the seatstay
bridge where the brake caliper is mounted. If it did then you have
far more important/immediate issues to deal with.

It is somewhat common to see pro bicyclists with open brake quick
releases (calipers with Shimano and Ergo levers with Campagnolo) when
climbing mountains. Scan through pictures on the Cycling News website
and you will find them.

indeed. not a hard practice to copy!

Quoted message said:

This is a link to tests Damon Rinard did measuring lateral flexibility
on wheels.

http://www.sheldonbrown.com/rinard/
http://www.sheldonbrown.com/rinard/wheel/index.htm

Quoted message said:

Jim Flom said:

My rear rim seems to rub on a brake pad when I am standing on the pedals on
steep climbs. At least that's what I THINK it is. Off the bike, everything
appears trued up well with good clearance. It's my 1998 Raleigh R500 7005
alu frame with oversized tubes.

Any theories? Any suggestions?

--
JF

"A really great man is known by three signs,--generosity in the design,
humanity in the execution, and moderation in success."
- Karl Otto von Schonhausen Bismarck

What specific rim/wheel are you using on the rear of the bike? Highly
doubt the frame/bike matters. Any flexibility or lack thereof in the
frame/bottom bracket area will not get transferred to the seatstay
bridge where the brake caliper is mounted. If it did then you have
far more important/immediate issues to deal with.

It is somewhat common to see pro bicyclists with open brake quick
releases (calipers with Shimano and Ergo levers with Campagnolo) when
climbing mountains. Scan through pictures on the Cycling News website
and you will find them.

indeed. not a hard practice to copy!

Quoted message said:

This is a link to tests Damon Rinard did measuring lateral flexibility
on wheels.

http://www.sheldonbrown.com/rinard/
http://www.sheldonbrown.com/rinard/wheel/index.htm

Quoted message said:

Tim McNamara said:

Quoted message said:

My rear rim seems to rub on a brake pad when I am standing on the
pedals on steep climbs. At least that's what I THINK it is. Off
the bike, everything appears trued up well with good clearance.
It's my 1998 Raleigh R500 7005 alu frame with oversized tubes. Any
theories? Any suggestions?

Quoted message said:

This is normal (it's due to lateral frame and wheel flex) and became
a problem with the advent of dual pivot brakes and low-ratio levers,
which requires the pads to be set much closer to the rim to avoid
the brake lever hitting the bar. Just do what the pros do- flip
your rear brake QR open at the bottom of the hill.

Riders asked for it and got it. Old brake calipers, side/center/canti
were all 1:1 ratio and the hand lever 4:1 mechanical advantage
(measured from the lever crook to pivot and pivot to cable). That ws
not enough for the riders who couldn't stop as easily as they wanted
so the mechanical advantage was increased to a total of about 5.6:1.

so? dual pivot offer greater braking leverage and toe control. why do
you have a problem with that?

Quoted message said:

This required reducing pad clearance or the whole hand lever travel
wold be used up getting the pads to touch the rim.

so?

Quoted message said:

To do that, a
precisely centered caliper was needed and the brute force method was
to use two pivot points, one on axis and the other off to one side.
This causes the pad on the short arm to climb into the tire with wear.

so, maintain your bike more frequently!!

Quoted message said:

Accurate centering could have been achieved by coiling the return
spring around the center bolt instead of having a spring with
"elephant ears" on either side of center. The centers of rotation of
the return spring is the center of the elephant ears and that causes
cosine error, the sliding motion you can readily see on a dual pivot
caliper. They even have a sliding plastic sleeve to accommodate that
unnecessary motion.

1. shimano single pivots have exactly the same plastic sleeved sliders.
2. the motion is not "unnecessary", it's a function of the leverage!

Quoted message said:

Campagnolo was aware that riders climbed hills with open QR's on the
rear brake and offered a 1:1 single pivot brake with good pad
clearance for the rear, where heavy braking is not done anyway.

they "offer" it on chorus and record for weight savings, not for any
mysterious geometrical reasoning. the lower end models remain as dual
pivot. try checking facts for a change by reading campy's own literature.

Quoted message said:

Today, closely spaced rear hub flanges work together with low pad
clearance to make brakes drag when climbing. This is more noticeable
when riding in rain, when wet road grit makes an audible complaint.

this is exactly the same as old bikes with single pivot if pads are run
that close to the rim. don't demonize what you yourself don't have
experience of.

Quoted message said:

Tim McNamara said:

Quoted message said:

My rear rim seems to rub on a brake pad when I am standing on the
pedals on steep climbs. At least that's what I THINK it is. Off
the bike, everything appears trued up well with good clearance.
It's my 1998 Raleigh R500 7005 alu frame with oversized tubes. Any
theories? Any suggestions?

Quoted message said:

This is normal (it's due to lateral frame and wheel flex) and became
a problem with the advent of dual pivot brakes and low-ratio levers,
which requires the pads to be set much closer to the rim to avoid
the brake lever hitting the bar. Just do what the pros do- flip
your rear brake QR open at the bottom of the hill.

Riders asked for it and got it. Old brake calipers, side/center/canti
were all 1:1 ratio and the hand lever 4:1 mechanical advantage
(measured from the lever crook to pivot and pivot to cable). That ws
not enough for the riders who couldn't stop as easily as they wanted
so the mechanical advantage was increased to a total of about 5.6:1.

so? dual pivot offer greater braking leverage and toe control. why do
you have a problem with that?

Quoted message said:

This required reducing pad clearance or the whole hand lever travel
wold be used up getting the pads to touch the rim.

so?

Quoted message said:

To do that, a
precisely centered caliper was needed and the brute force method was
to use two pivot points, one on axis and the other off to one side.
This causes the pad on the short arm to climb into the tire with wear.

so, maintain your bike more frequently!!

Quoted message said:

Accurate centering could have been achieved by coiling the return
spring around the center bolt instead of having a spring with
"elephant ears" on either side of center. The centers of rotation of
the return spring is the center of the elephant ears and that causes
cosine error, the sliding motion you can readily see on a dual pivot
caliper. They even have a sliding plastic sleeve to accommodate that
unnecessary motion.

1. shimano single pivots have exactly the same plastic sleeved sliders.
2. the motion is not "unnecessary", it's a function of the leverage!

Quoted message said:

Campagnolo was aware that riders climbed hills with open QR's on the
rear brake and offered a 1:1 single pivot brake with good pad
clearance for the rear, where heavy braking is not done anyway.

they "offer" it on chorus and record for weight savings, not for any
mysterious geometrical reasoning. the lower end models remain as dual
pivot. try checking facts for a change by reading campy's own literature.

Quoted message said:

Today, closely spaced rear hub flanges work together with low pad
clearance to make brakes drag when climbing. This is more noticeable
when riding in rain, when wet road grit makes an audible complaint.

this is exactly the same as old bikes with single pivot if pads are run
that close to the rim. don't demonize what you yourself don't have
experience of.

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Tim McNamara said:

Quoted message said:

My rear rim seems to rub on a brake pad when I am standing on the
pedals on steep climbs. At least that's what I THINK it is. Off
the bike, everything appears trued up well with good clearance.
It's my 1998 Raleigh R500 7005 alu frame with oversized tubes. Any
theories? Any suggestions?

Quoted message said:

This is normal (it's due to lateral frame and wheel flex) and became
a problem with the advent of dual pivot brakes and low-ratio levers,
which requires the pads to be set much closer to the rim to avoid
the brake lever hitting the bar. Just do what the pros do- flip
your rear brake QR open at the bottom of the hill.

Riders asked for it and got it. Old brake calipers, side/center/canti
were all 1:1 ratio and the hand lever 4:1 mechanical advantage
(measured from the lever crook to pivot and pivot to cable). That ws
not enough for the riders who couldn't stop as easily as they wanted
so the mechanical advantage was increased to a total of about 5.6:1.

This required reducing pad clearance or the whole hand lever travel
wold be used up getting the pads to touch the rim. To do that, a
precisely centered caliper was needed and the brute force method was
to use two pivot points, one on axis and the other off to one side.
This causes the pad on the short arm to climb into the tire with wear.

Accurate centering could have been achieved by coiling the return
spring around the center bolt instead of having a spring with
"elephant ears" on either side of center. The centers of rotation of
the return spring is the center of the elephant ears and that causes
cosine error, the sliding motion you can readily see on a dual pivot
caliper. They even have a sliding plastic sleeve to accommodate that
unnecessary motion.

Campagnolo was aware that riders climbed hills with open QR's on the
rear brake and offered a 1:1 single pivot brake with good pad
clearance for the rear, where heavy braking is not done anyway.

Today, closely spaced rear hub flanges work together with low pad
clearance to make brakes drag when climbing. This is more noticeable
when riding in rain, when wet road grit makes an audible complaint.

And it is precisely in the fall BC rain that I'm noticing it. Never noticed
it before this (or last?) year, but I'm riding in the rain a lot more right
now.

Someone asked about the rim. It's a Mavic something P-10 (it looks like),
but the label is pretty worn so I am not sure.

I have never liked this hub. I think it's a low end Shimano, possibly an RX
100. It was impossible to repack the hub without some wobble, until this
fall. I managed to eliminate any lateral looseness in the hub, and it spun
well, and quietly. But I've been riding in so much crud, so much rain and
road grit that the hub has become audible when I spin it. I gave it to my
LBS last year to repack and they did such a crappy job (they're otherwise
good -- few complaints -- I support them) that I repacked it myself two
weeks later. I _never_ have this kind of problem with my Campy components
on my other bike.

Brakes are Ultegra. I guess I'll open up the quick release. I'll just have
to man up on that one steep descent.

I'm tempted to get a new hub and get a well-built wheel. Sounds like it
won't eliminate the rubbing when I climb but at least it may be easier to
maintain.

Thanks fellas,

Jim

--
JF

"A really great man is known by three signs,--generosity in the design,
humanity in the execution, and moderation in success."
- Karl Otto von Schonhausen Bismarck

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Tim McNamara said:

Quoted message said:

My rear rim seems to rub on a brake pad when I am standing on the
pedals on steep climbs. At least that's what I THINK it is. Off
the bike, everything appears trued up well with good clearance.
It's my 1998 Raleigh R500 7005 alu frame with oversized tubes. Any
theories? Any suggestions?

Quoted message said:

This is normal (it's due to lateral frame and wheel flex) and became
a problem with the advent of dual pivot brakes and low-ratio levers,
which requires the pads to be set much closer to the rim to avoid
the brake lever hitting the bar. Just do what the pros do- flip
your rear brake QR open at the bottom of the hill.

Riders asked for it and got it. Old brake calipers, side/center/canti
were all 1:1 ratio and the hand lever 4:1 mechanical advantage
(measured from the lever crook to pivot and pivot to cable). That ws
not enough for the riders who couldn't stop as easily as they wanted
so the mechanical advantage was increased to a total of about 5.6:1.

This required reducing pad clearance or the whole hand lever travel
wold be used up getting the pads to touch the rim. To do that, a
precisely centered caliper was needed and the brute force method was
to use two pivot points, one on axis and the other off to one side.
This causes the pad on the short arm to climb into the tire with wear.

Accurate centering could have been achieved by coiling the return
spring around the center bolt instead of having a spring with
"elephant ears" on either side of center. The centers of rotation of
the return spring is the center of the elephant ears and that causes
cosine error, the sliding motion you can readily see on a dual pivot
caliper. They even have a sliding plastic sleeve to accommodate that
unnecessary motion.

Campagnolo was aware that riders climbed hills with open QR's on the
rear brake and offered a 1:1 single pivot brake with good pad
clearance for the rear, where heavy braking is not done anyway.

Today, closely spaced rear hub flanges work together with low pad
clearance to make brakes drag when climbing. This is more noticeable
when riding in rain, when wet road grit makes an audible complaint.

And it is precisely in the fall BC rain that I'm noticing it. Never noticed
it before this (or last?) year, but I'm riding in the rain a lot more right
now.

Someone asked about the rim. It's a Mavic something P-10 (it looks like),
but the label is pretty worn so I am not sure.

I have never liked this hub. I think it's a low end Shimano, possibly an RX
100. It was impossible to repack the hub without some wobble, until this
fall. I managed to eliminate any lateral looseness in the hub, and it spun
well, and quietly. But I've been riding in so much crud, so much rain and
road grit that the hub has become audible when I spin it. I gave it to my
LBS last year to repack and they did such a crappy job (they're otherwise
good -- few complaints -- I support them) that I repacked it myself two
weeks later. I _never_ have this kind of problem with my Campy components
on my other bike.

Brakes are Ultegra. I guess I'll open up the quick release. I'll just have
to man up on that one steep descent.

I'm tempted to get a new hub and get a well-built wheel. Sounds like it
won't eliminate the rubbing when I climb but at least it may be easier to
maintain.

Thanks fellas,

Jim

--
JF

"A really great man is known by three signs,--generosity in the design,
humanity in the execution, and moderation in success."
- Karl Otto von Schonhausen Bismarck

Quoted message said:

Tim McNamara said:

Quoted message said:

My rear rim seems to rub on a brake pad when I am standing on the
pedals on steep climbs. At least that's what I THINK it is. Off
the bike, everything appears trued up well with good clearance.
It's my 1998 Raleigh R500 7005 alu frame with oversized tubes. Any
theories? Any suggestions?

Quoted message said:

This is normal (it's due to lateral frame and wheel flex) and became
a problem with the advent of dual pivot brakes and low-ratio levers,
which requires the pads to be set much closer to the rim to avoid
the brake lever hitting the bar. Just do what the pros do- flip
your rear brake QR open at the bottom of the hill.

Riders asked for it and got it. Old brake calipers, side/center/canti
were all 1:1 ratio and the hand lever 4:1 mechanical advantage
(measured from the lever crook to pivot and pivot to cable). That ws
not enough for the riders who couldn't stop as easily as they wanted
so the mechanical advantage was increased to a total of about 5.6:1.

actually, the total is more like 8:1 - the ratio of arm lengths on the
"C" arm of a dual pivot caliper is ~2:1. [62mm:31mm for dura-ace 7700.]
the mechanical ratio is not affected by the 1:1 ratio on the "Y" arm
side of the caliper because the lateral stiffness of the rim is many
orders of magnitude less than that of the caliper so the rim simply
"floats".

Quoted message said:

This required reducing pad clearance or the whole hand lever travel
wold be used up getting the pads to touch the rim. To do that, a
precisely centered caliper was needed and the brute force method was
to use two pivot points, one on axis and the other off to one side.
This causes the pad on the short arm to climb into the tire with wear.

Accurate centering could have been achieved by coiling the return
spring around the center bolt instead of having a spring with
"elephant ears" on either side of center. The centers of rotation of
the return spring is the center of the elephant ears and that causes
cosine error, the sliding motion you can readily see on a dual pivot
caliper. They even have a sliding plastic sleeve to accommodate that
unnecessary motion.

Campagnolo was aware that riders climbed hills with open QR's on the
rear brake and offered a 1:1 single pivot brake with good pad
clearance for the rear, where heavy braking is not done anyway.

Today, closely spaced rear hub flanges work together with low pad
clearance to make brakes drag when climbing. This is more noticeable
when riding in rain, when wet road grit makes an audible complaint.

Jobst Brandt

Quoted message said:

Tim McNamara said:

Quoted message said:

My rear rim seems to rub on a brake pad when I am standing on the
pedals on steep climbs. At least that's what I THINK it is. Off
the bike, everything appears trued up well with good clearance.
It's my 1998 Raleigh R500 7005 alu frame with oversized tubes. Any
theories? Any suggestions?

Quoted message said:

This is normal (it's due to lateral frame and wheel flex) and became
a problem with the advent of dual pivot brakes and low-ratio levers,
which requires the pads to be set much closer to the rim to avoid
the brake lever hitting the bar. Just do what the pros do- flip
your rear brake QR open at the bottom of the hill.

Riders asked for it and got it. Old brake calipers, side/center/canti
were all 1:1 ratio and the hand lever 4:1 mechanical advantage
(measured from the lever crook to pivot and pivot to cable). That ws
not enough for the riders who couldn't stop as easily as they wanted
so the mechanical advantage was increased to a total of about 5.6:1.

actually, the total is more like 8:1 - the ratio of arm lengths on the
"C" arm of a dual pivot caliper is ~2:1. [62mm:31mm for dura-ace 7700.]
the mechanical ratio is not affected by the 1:1 ratio on the "Y" arm
side of the caliper because the lateral stiffness of the rim is many
orders of magnitude less than that of the caliper so the rim simply
"floats".

Quoted message said:

This required reducing pad clearance or the whole hand lever travel
wold be used up getting the pads to touch the rim. To do that, a
precisely centered caliper was needed and the brute force method was
to use two pivot points, one on axis and the other off to one side.
This causes the pad on the short arm to climb into the tire with wear.

Accurate centering could have been achieved by coiling the return
spring around the center bolt instead of having a spring with
"elephant ears" on either side of center. The centers of rotation of
the return spring is the center of the elephant ears and that causes
cosine error, the sliding motion you can readily see on a dual pivot
caliper. They even have a sliding plastic sleeve to accommodate that
unnecessary motion.

Campagnolo was aware that riders climbed hills with open QR's on the
rear brake and offered a 1:1 single pivot brake with good pad
clearance for the rear, where heavy braking is not done anyway.

Today, closely spaced rear hub flanges work together with low pad
clearance to make brakes drag when climbing. This is more noticeable
when riding in rain, when wet road grit makes an audible complaint.

Jobst Brandt

To assess the mechanical advantage of a dual pivot caliper, measure
the cable stroke and pad closure. The caliper has the same effect of
the centerpull with two arms, each twice as long as the pivot-to-pad
dimension, but there are two of them, each providing half the motion.
It was this geometric gimmick that led people to believe that hey were
twice as powerful grabbers as sidepull brakes of that time. It wasn't
so.

Jobst Brandt

To assess the mechanical advantage of a dual pivot caliper, measure
the cable stroke and pad closure. The caliper has the same effect of
the centerpull with two arms, each twice as long as the pivot-to-pad
dimension, but there are two of them, each providing half the motion.
It was this geometric gimmick that led people to believe that hey were
twice as powerful grabbers as sidepull brakes of that time. It wasn't
so.

Jobst Brandt

Quoted message said:

To assess the mechanical advantage of a dual pivot caliper, measure
the cable stroke and pad closure.

that's inaccurate and pointless. the lever ratios are easy and much
more accessible. maybe that's why you got it wrong?

Quoted message said:

The caliper has the same effect of
the centerpull with two arms, each twice as long as the pivot-to-pad
dimension, but there are two of them, each providing half the motion.

doesn't matter - the rim effectively floats. one pad could be static
for all it matters to mechanical advantage. indeed, avid mechanical
disk brakes use this principle.

Quoted message said:

It was this geometric gimmick that led people to believe that hey were
twice as powerful grabbers as sidepull brakes of that time. It wasn't
so.

maybe to people that didn't measure their lever ratios correctly.