Bottom Bracket Drag

HarryB said:

How much drag is considered normal for a cartridge bearing BB?

Very damn little. A new unit will feel a little stiff at first for a
variety of reasons, but a used one should spin freely.

Quoted message said:

I note
Sheldon Brown's advice on adjusting a cone-and-cup BB as a reference:
"Make a mental note of how easily the spindle turns when the bearing
is too loose-it should turn just as freely when you have finished
adjusting it." Does this same comparison apply to cartridge bearings -
IOW, the spindle's drag should not increase when the cartridge is
properly tightened?

If the unit is properly constructed *and* the BB shell in the frame is
faced and threaded correctly, then tightening it down should make no
difference.

Quoted message said:

I posted a question a few days ago about problems with tight BB's
("Bottom Bracket Question"😉 on a tandem. I followed the advice given
and had both shells faced and chased. This really improved the BB that
was very tight and marginally improved the other. But, there is still
more drag after the BB's have been torqued than when they are loose.
In fact, the drag increases as soon as the drive side of the BB is
tightened and increases even more when the adjustable cup is
tightened.

The BBs in question are TruVativ GigaPipes and only have a couple of
thousand miles on them.

It sounds like the threads on one side are not cut squarely.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

HarryB said:

How much drag is considered normal for a cartridge bearing BB? I note
Sheldon Brown's advice on adjusting a cone-and-cup BB as a reference:
"Make a mental note of how easily the spindle turns when the bearing
is too loose-it should turn just as freely when you have finished
adjusting it." Does this same comparison apply to cartridge bearings -
IOW, the spindle's drag should not increase when the cartridge is
properly tightened?

I posted a question a few days ago about problems with tight BB's
("Bottom Bracket Question"😉 on a tandem. I followed the advice given
and had both shells faced and chased. This really improved the BB that
was very tight and marginally improved the other. But, there is still
more drag after the BB's have been torqued than when they are loose.
In fact, the drag increases as soon as the drive side of the BB is
tightened and increases even more when the adjustable cup is
tightened.

The BBs in question are TruVativ GigaPipes and only have a couple of
thousand miles on them.

TIA,
Harry

Cart BBs are just that, cartridge bearings with rubber seals that
automatically are more draggy than loose ball BBs. Some lower end BBs
DO get more sluggish when installed, shimano UN-series is a good
example. Never been a big fan of ISIS in general or Truvativ
specifically. BUT if they are smooth, not notchey or crunchy, best it's
gonna be.

HarryB said:

How much drag is considered normal for a cartridge bearing BB? I note
Sheldon Brown's advice on adjusting a cone-and-cup BB as a reference:
"Make a mental note of how easily the spindle turns when the bearing
is too loose-it should turn just as freely when you have finished
adjusting it." Does this same comparison apply to cartridge bearings -
IOW, the spindle's drag should not increase when the cartridge is
properly tightened?

Perhaps drag shouldn't increase theory, but it always does in my
experience - with several different BBs in several bikes.

~PB

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

Quoted message said:

HarryB said:

How much drag is considered normal for a cartridge bearing BB?

Very damn little. A new unit will feel a little stiff at first for a
variety of reasons, but a used one should spin freely.

Quoted message said:

I note
Sheldon Brown's advice on adjusting a cone-and-cup BB as a reference:
"Make a mental note of how easily the spindle turns when the bearing
is too loose-it should turn just as freely when you have finished
adjusting it." Does this same comparison apply to cartridge

bearings -

Quoted message said:

Quoted message said:

IOW, the spindle's drag should not increase when the cartridge is
properly tightened?

If the unit is properly constructed *and* the BB shell in the frame is
faced and threaded correctly, then tightening it down should make no
difference.

Quoted message said:

I posted a question a few days ago about problems with tight BB's
("Bottom Bracket Question"😉 on a tandem. I followed the advice given
and had both shells faced and chased. This really improved the BB

that

Quoted message said:

Quoted message said:

was very tight and marginally improved the other. But, there is still
more drag after the BB's have been torqued than when they are loose.
In fact, the drag increases as soon as the drive side of the BB is
tightened and increases even more when the adjustable cup is
tightened.

The BBs in question are TruVativ GigaPipes and only have a couple of
thousand miles on them.

It sounds like the threads on one side are not cut squarely.
--

My thoughts too.

The BB should be faced and the threads chased using a BB tool like one
from VAR, Campy, Park etc. that has a pilot that goes through the BB
into a mating part to keep the cutting tools aligned.

If some used a single sided tool to face, tap or chase the threads the
two sides could be out of alignment.

Chas.

HarryB said:

How much drag is considered normal for a cartridge bearing BB?

Don't know about normal, but if I give my cranks a good push with no chain
connected they continue to spin for several minutes.

Veloce cartridge BB (2006 model I think)

--
Jim

Jim Higson said:

HarryB said:

How much drag is considered normal for a cartridge bearing BB?

Don't know about normal, but if I give my cranks a good push with no chain
connected they continue to spin for several minutes.

Veloce cartridge BB (2006 model I think)

Several minutes??? That's not normal.

Lou
--
Posted by news://news.nb.nu

In article <[email hidden]>,

Lou Holtman said:

Jim Higson said:

HarryB said:

How much drag is considered normal for a cartridge bearing BB?

Don't know about normal, but if I give my cranks a good push with no chain
connected they continue to spin for several minutes.

Veloce cartridge BB (2006 model I think)

Several minutes??? That's not normal.

The Veloce bottom brackets are pretty smooth turning- smoother than most
of Campy's other BBs including (the last ones I tried) Chorus and Record.

Tim McNamara said:

In article <[email hidden]>,

Lou Holtman said:

Jim Higson said:

HarryB wrote:

>How much drag is considered normal for a cartridge bearing BB?

Don't know about normal, but if I give my cranks a good push with no chain
connected they continue to spin for several minutes.

Veloce cartridge BB (2006 model I think)

Several minutes??? That's not normal.

The Veloce bottom brackets are pretty smooth turning- smoother than most
of Campy's other BBs including (the last ones I tried) Chorus and Record.

We are talking of minutes. That is a very loooong time. I can't believe
that.
Last week I installed a Shimano XT hollotech II crankset (outboard
bearings). I gave it a swing and it wouldn't turn even one revolution,
but that's just the drag of the seals and you don't notice that while
riding.

Lou
--
Posted by news://news.nb.nu

Lou Holtman said:

Tim McNamara said:

In article <[email hidden]>,

Lou Holtman said:

Jim Higson wrote:

>HarryB wrote:
>
>
>>How much drag is considered normal for a cartridge bearing BB?
>
>Don't know about normal, but if I give my cranks a good push with no chain
>connected they continue to spin for several minutes.
>
>Veloce cartridge BB (2006 model I think)

Several minutes??? That's not normal.

The Veloce bottom brackets are pretty smooth turning- smoother than most
of Campy's other BBs including (the last ones I tried) Chorus and Record.

We are talking of minutes. That is a very loooong time. I can't believe
that.
Last week I installed a Shimano XT hollotech II crankset (outboard
bearings). I gave it a swing and it wouldn't turn even one revolution,
but that's just the drag of the seals and you don't notice that while
riding.

Lou

Dear Lou,

For fun, I tested a 1998 Schwinn Le Tour triple with 170 mm cranks,
pretty much unused and bought for spares, a ten-year-old bottom of the
line example of a crank.

With no pedals, the level crank will support two dimes over the left
pedal eye, but it starts to turn under the weight when a third dime is
added.

According to the US Mint, a dime is around 2.268 grams, plus or minus
a smidgen for grime and wear:

http://www.usmint.gov/about_the_mint/index.cfm?flash=yes&action=coin_specifications

So the initial bearing resistance (higher than the moving resistance)
is a bit less than 170 mm / 6 grams of torque, which works out to the
surprisingly high value of about 0.1 foot-lbs of torque.

Bracing the frame and giving the pedals a brisk turn produces about 13
seconds of spin on average.

Adding some light pedals increases the inertia and angular momentum
more than the wind drag and produces about 20 seconds of spin on
average.

So maybe really smooth modern bearings can spin for minutes. I'd love
to see some quick and dirty tests involving how many coins (or half or
quarter coins) a level crank can support before it starts to turn.

It's difficult to compare how hard one poster's hand twirls a crank,
so that's probably not as good a measure as weights on the ends of
pedals, even though it's fun. But a few spin-down times would be
interesting.

Since we're talking about at most the downward force of 3 dimes on a
motionless horizontal pedal, I suspect that in real life random air
current variations are more important. There just isn't much drag
available to reduce.

Cheers,

Carl Fogel

Quoted message said:

Lou Holtman said:

Tim McNamara said:

In article <[email hidden]>,
Lou Holtman <[email hidden]> wrote:

>Jim Higson wrote:
>
>
>>HarryB wrote:
>>
>>
>>
>>>How much drag is considered normal for a cartridge bearing BB?
>>
>>Don't know about normal, but if I give my cranks a good push with no chain
>>connected they continue to spin for several minutes.
>>
>>Veloce cartridge BB (2006 model I think)
>
>
>Several minutes??? That's not normal.

The Veloce bottom brackets are pretty smooth turning- smoother than most
of Campy's other BBs including (the last ones I tried) Chorus and Record.

We are talking of minutes. That is a very loooong time. I can't believe
that.
Last week I installed a Shimano XT hollotech II crankset (outboard
bearings). I gave it a swing and it wouldn't turn even one revolution,
but that's just the drag of the seals and you don't notice that while
riding.

Lou

Dear Lou,

For fun, I tested a 1998 Schwinn Le Tour triple with 170 mm cranks,
pretty much unused and bought for spares, a ten-year-old bottom of the
line example of a crank.

With no pedals, the level crank will support two dimes over the left
pedal eye, but it starts to turn under the weight when a third dime is
added.

According to the US Mint, a dime is around 2.268 grams, plus or minus
a smidgen for grime and wear:

http://www.usmint.gov/about_the_mint/index.cfm?flash=yes&action=coin_specifications

So the initial bearing resistance (higher than the moving resistance)
is a bit less than 170 mm / 6 grams of torque, which works out to the
surprisingly high value of about 0.1 foot-lbs of torque.

I think your arithmetic is a little off. I get .00738 ft-lb, which at
90 RPM takes .094 watt. While pedaling, seal drag may be lower, but
bearing drag higher due to the load. It isn't going to be much power
loss unless the bearings are really awful.

Quoted message said:

Bracing the frame and giving the pedals a brisk turn produces about 13
seconds of spin on average.

Adding some light pedals increases the inertia and angular momentum
more than the wind drag and produces about 20 seconds of spin on
average.

So maybe really smooth modern bearings can spin for minutes. I'd love
to see some quick and dirty tests involving how many coins (or half or
quarter coins) a level crank can support before it starts to turn.

It's difficult to compare how hard one poster's hand twirls a crank,
so that's probably not as good a measure as weights on the ends of
pedals, even though it's fun. But a few spin-down times would be
interesting.

Since we're talking about at most the downward force of 3 dimes on a
motionless horizontal pedal, I suspect that in real life random air
current variations are more important. There just isn't much drag
available to reduce.

Cheers,

Carl Fogel

Dave Lehnen

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

Quoted message said:

Jim Higson said:

HarryB said:

How much drag is considered normal for a cartridge bearing BB?

Don't know about normal, but if I give my cranks a good push with no

chain

Quoted message said:

Quoted message said:

connected they continue to spin for several minutes.

Veloce cartridge BB (2006 model I think)

Several minutes??? That's not normal.

Lou
--

Well, it depends on how heavy your chainrings are, just like the
flywheel on a car. If you used nice heavy steel chainrings not the
flimsy alloy [censored] you see today, then yes they could possibly keep
spinning for quite some time.

Chas.

Dave Lehnen said:

[email hidden] wrote:

[snip]

Quoted message said:

Quoted message said:

So the initial bearing resistance (higher than the moving resistance)
is a bit less than 170 mm / 6 grams of torque, which works out to the
surprisingly high value of about 0.1 foot-lbs of torque.

I think your arithmetic is a little off. I get .00738 ft-lb, which at
90 RPM takes .094 watt. While pedaling, seal drag may be lower, but
bearing drag higher due to the load. It isn't going to be much power
loss unless the bearings are really awful.

[snip]

Quoted message said:

Dave Lehnen

Dear Dave,

You're right--I goofed.

When I went back to my spreadsheet, I found that I'd used the newtons
column instead of the pounds column and then multiplied instead of
dividing.

Now I think I've caught up with you.

We're converting 6 grams * 0.17 meters to X lbs * 1 foot.

6 grams x (1 lb/454 grams) = 6/454 lbs = 0.0132 lbs

0.170 meters x (39.4 inches/meter) = 0.17 x 39.4 = 6.7 inches

6.7 inches / (12 inches/foot) = 6.7/12 feet = 0.5583 feet

0.0132 lbs * 0.5583 feet = Dave's 0.0074 foot-lbs

So the force of 2~3 2.6 gram dimes on a 170 mm horizontal lever is
pleasantly smaller than the goofy figure that surprised me.

The really embarrassing part is that I made my careful miscalculations
while feeling fine, not after I woke up feeling fuzzy just now and had
to creep through things while feeling even dimmer than usual.

Thanks for checking the idle rumors from Fogel Labs.

Cheers,

Carl Fogel

* * Chas said:

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

Quoted message said:

HarryB said:

How much drag is considered normal for a cartridge bearing BB?

Very damn little. A new unit will feel a little stiff at first for a
variety of reasons, but a used one should spin freely.

Quoted message said:

I note
Sheldon Brown's advice on adjusting a cone-and-cup BB as a reference:
"Make a mental note of how easily the spindle turns when the bearing
is too loose-it should turn just as freely when you have finished
adjusting it." Does this same comparison apply to cartridge

bearings -

Quoted message said:

Quoted message said:

IOW, the spindle's drag should not increase when the cartridge is
properly tightened?

If the unit is properly constructed *and* the BB shell in the frame is
faced and threaded correctly, then tightening it down should make no
difference.

Quoted message said:

I posted a question a few days ago about problems with tight BB's
("Bottom Bracket Question"😉 on a tandem. I followed the advice given
and had both shells faced and chased. This really improved the BB

that

Quoted message said:

Quoted message said:

was very tight and marginally improved the other. But, there is still
more drag after the BB's have been torqued than when they are loose.
In fact, the drag increases as soon as the drive side of the BB is
tightened and increases even more when the adjustable cup is
tightened.

The BBs in question are TruVativ GigaPipes and only have a couple of
thousand miles on them.

It sounds like the threads on one side are not cut squarely.
--

My thoughts too.

The BB should be faced and the threads chased using a BB tool like one
from VAR, Campy, Park etc. that has a pilot that goes through the BB
into a mating part to keep the cutting tools aligned.

If some used a single sided tool to face, tap or chase the threads the
two sides could be out of alignment.

Chas.

After the mechanic had finished the work and I was discussing with him
that I was disappointed that the BB's still seemed tight, he said that
he used a tool that cost upwards of $400. When I called back to find
out exactly which tool had been used, the mechanic had gone home, but
the person who answered the phone said it was a Park Tool.

When I screw the BB into the shell, I can turn it in with my fingers
until it bottoms out against the shell. The same for the other side
(although it apparently bottoms out against a ridge in the BB, not
against the BB shell.) It seems to me that if one of the threads was
not cut square relative to the centerline of the BB or concentric
relative to the other threads, that I wouldn't be able to screw both
sides of the BB all the way in with my fingers.

Harry

Quoted message said:

Lou Holtman said:

Tim McNamara said:

In article <[email hidden]>,
Lou Holtman <[email hidden]> wrote:

>Jim Higson wrote:
>
>
>>HarryB wrote:
>>
>>
>>
>>>How much drag is considered normal for a cartridge bearing BB?
>>
>>Don't know about normal, but if I give my cranks a good push with no chain
>>connected they continue to spin for several minutes.
>>
>>Veloce cartridge BB (2006 model I think)
>
>
>Several minutes??? That's not normal.

The Veloce bottom brackets are pretty smooth turning- smoother than most
of Campy's other BBs including (the last ones I tried) Chorus and Record.

We are talking of minutes. That is a very loooong time. I can't believe
that.
Last week I installed a Shimano XT hollotech II crankset (outboard
bearings). I gave it a swing and it wouldn't turn even one revolution,
but that's just the drag of the seals and you don't notice that while
riding.

Lou

Dear Lou,

For fun, I tested a 1998 Schwinn Le Tour triple with 170 mm cranks,
pretty much unused and bought for spares, a ten-year-old bottom of the
line example of a crank.

With no pedals, the level crank will support two dimes over the left
pedal eye, but it starts to turn under the weight when a third dime is
added.

According to the US Mint, a dime is around 2.268 grams, plus or minus
a smidgen for grime and wear:

http://www.usmint.gov/about_the_mint/index.cfm?flash=yes&action=coin_specifications

So the initial bearing resistance (higher than the moving resistance)
is a bit less than 170 mm / 6 grams of torque, which works out to the
surprisingly high value of about 0.1 foot-lbs of torque.

Bracing the frame and giving the pedals a brisk turn produces about 13
seconds of spin on average.

Adding some light pedals increases the inertia and angular momentum
more than the wind drag and produces about 20 seconds of spin on
average.

So maybe really smooth modern bearings can spin for minutes. I'd love
to see some quick and dirty tests involving how many coins (or half or
quarter coins) a level crank can support before it starts to turn.

Carl, I gave my front wheel (with tire) with a recently overhauled and
very smooth running Record hub a very firm spin (I hurt myself) and it
stopped after 45 seconds. So I think 'several' minutes is a ridiculous
claim.

Lou
--
Posted by news://news.nb.nu

* * Chas said:

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

Quoted message said:

Jim Higson said:

HarryB wrote:

>How much drag is considered normal for a cartridge bearing BB?

Don't know about normal, but if I give my cranks a good push with no

chain

Quoted message said:

Quoted message said:

connected they continue to spin for several minutes.

Veloce cartridge BB (2006 model I think)

Several minutes??? That's not normal.

Lou
--

Well, it depends on how heavy your chainrings are, just like the
flywheel on a car. If you used nice heavy steel chainrings not the
flimsy alloy [censored] you see today, then yes they could possibly keep
spinning for quite some time.

Oh please, alloy chainrings are fine. For several minutes spin time
those clunky chainrings must be very heavy and large in diameter.

Lou
--
Posted by news://news.nb.nu

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

Quoted message said:

* * Chas said:

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

Quoted message said:

On Fri, 01 Dec 2006 22:05:30 -0600, HarryB <[email hidden]> wrote:

>How much drag is considered normal for a cartridge bearing BB?

Very damn little. A new unit will feel a little stiff at first for a
variety of reasons, but a used one should spin freely.

>I note
>Sheldon Brown's advice on adjusting a cone-and-cup BB as a

reference:

Quoted message said:

Quoted message said:

Quoted message said:

>"Make a mental note of how easily the spindle turns when the bearing
>is too loose-it should turn just as freely when you have finished
>adjusting it." Does this same comparison apply to cartridge

bearings -

Quoted message said:

>IOW, the spindle's drag should not increase when the cartridge is
>properly tightened?

If the unit is properly constructed *and* the BB shell in the frame

is

Quoted message said:

Quoted message said:

Quoted message said:

faced and threaded correctly, then tightening it down should make no
difference.

>I posted a question a few days ago about problems with tight BB's
>("Bottom Bracket Question"😉 on a tandem. I followed the advice given
>and had both shells faced and chased. This really improved the BB

that

Quoted message said:

>was very tight and marginally improved the other. But, there is

still

Quoted message said:

Quoted message said:

Quoted message said:

>more drag after the BB's have been torqued than when they are loose.
>In fact, the drag increases as soon as the drive side of the BB is
>tightened and increases even more when the adjustable cup is
>tightened.
>
>The BBs in question are TruVativ GigaPipes and only have a couple of
>thousand miles on them.

It sounds like the threads on one side are not cut squarely.
--

My thoughts too.

The BB should be faced and the threads chased using a BB tool like one
from VAR, Campy, Park etc. that has a pilot that goes through the BB
into a mating part to keep the cutting tools aligned.

If some used a single sided tool to face, tap or chase the threads the
two sides could be out of alignment.

Chas.

After the mechanic had finished the work and I was discussing with him
that I was disappointed that the BB's still seemed tight, he said that
he used a tool that cost upwards of $400. When I called back to find
out exactly which tool had been used, the mechanic had gone home, but
the person who answered the phone said it was a Park Tool.

When I screw the BB into the shell, I can turn it in with my fingers
until it bottoms out against the shell. The same for the other side
(although it apparently bottoms out against a ridge in the BB, not
against the BB shell.) It seems to me that if one of the threads was
not cut square relative to the centerline of the BB or concentric
relative to the other threads, that I wouldn't be able to screw both
sides of the BB all the way in with my fingers.

Harry

There is a possibility that the BB cartridge is contacting a tube or tubes
or a lump of braze protruding into the BB shell that doesn't get fully
cleaned up with the thread chasers. When you tighten the BB cup this could
be applying pressure to the OD of the BB cartridge causing a slight
deflection. Look inside the BB shell to rule this out.

BB tools like those made by Park are designed to work with a pilot and
bushings or both chasing taps together to keep the tool aligned . I've
seen guys who were lazy (I've done it myself) or didn't know better use
the BB threading tool with one side only. Also, one side of the BB threads
could be mis-aligned from the factory and the "mechanic" found it too hard
to use both sides on the of the Park thread chasers to correct the
problem... DOH!

Check out the Park BB tools at these links to Park's web site:

Facing Tool - there are detailed instructions on how to use both of these
tools at this site:

http://www.parktool.com/products/detail.asp?cat=25&item=BFS%2D1

Threading Tool:

http://www.parktool.com/products/detail.asp?cat=25&item=BTS%2D1

I would take your tandem back to the shop and request to watch while they
run the chasers through again.

One other thing is the possibility of over torquing the cups. IRD
recommends tightening their BBs to 24 to 30 Foot Lbs. of torque, Shimano
21.6 to 29 Foot Lbs. of torque and Phil 25 Foot Lbs.

If you don't have a torque wrench maybe you can borrow or rent one with
the proper sized socket. A "good" bike shop should have a torque wrench
since many of the newer BBs and crank arm need to be accurately tightened.

Chas.

Lou Holtman said:

Quoted message said:

Lou Holtman said:

Tim McNamara wrote:

>In article <[email hidden]>,
> Lou Holtman <[email hidden]> wrote:
>
>
>
>>Jim Higson wrote:
>>
>>
>>>HarryB wrote:
>>>
>>>
>>>
>>>>How much drag is considered normal for a cartridge bearing BB?
>>>
>>>Don't know about normal, but if I give my cranks a good push with no chain
>>>connected they continue to spin for several minutes.
>>>
>>>Veloce cartridge BB (2006 model I think)
>>
>>
>>Several minutes??? That's not normal.
>
>
>The Veloce bottom brackets are pretty smooth turning- smoother than most
>of Campy's other BBs including (the last ones I tried) Chorus and Record.

We are talking of minutes. That is a very loooong time. I can't believe
that.
Last week I installed a Shimano XT hollotech II crankset (outboard
bearings). I gave it a swing and it wouldn't turn even one revolution,
but that's just the drag of the seals and you don't notice that while
riding.

Lou

Dear Lou,

For fun, I tested a 1998 Schwinn Le Tour triple with 170 mm cranks,
pretty much unused and bought for spares, a ten-year-old bottom of the
line example of a crank.

With no pedals, the level crank will support two dimes over the left
pedal eye, but it starts to turn under the weight when a third dime is
added.

According to the US Mint, a dime is around 2.268 grams, plus or minus
a smidgen for grime and wear:

http://www.usmint.gov/about_the_mint/index.cfm?flash=yes&action=coin_specifications

So the initial bearing resistance (higher than the moving resistance)
is a bit less than 170 mm / 6 grams of torque, which works out to the
surprisingly high value of about 0.1 foot-lbs of torque.

Bracing the frame and giving the pedals a brisk turn produces about 13
seconds of spin on average.

Adding some light pedals increases the inertia and angular momentum
more than the wind drag and produces about 20 seconds of spin on
average.

So maybe really smooth modern bearings can spin for minutes. I'd love
to see some quick and dirty tests involving how many coins (or half or
quarter coins) a level crank can support before it starts to turn.

Carl, I gave my front wheel (with tire) with a recently overhauled and
very smooth running Record hub a very firm spin (I hurt myself) and it
stopped after 45 seconds. So I think 'several' minutes is a ridiculous
claim.

Lou

Dear Lou,

Since a front wheel is not a bottom bracket, the two may behave
differently.

For one thing, the wheel has considerably greater wind drag from all
the spokes--you can feel the fan effect off to the side of a spun
front wheel.

The drag is partly due to the area of the spokes, which is
surprisingly large. With ~275 mm of exposed spoke at mostly 1.8 mm for
a butted spoke, each spoke has ~500 mm^2 of area. At 16 spokes, that's
8,000 mm^2. For 32 spokes, it's 16,000 mm^2.

The two 170 mm pedal arms on the crank that I tested are about 15 mm
wide by 160 mm exposed length, so 2 x 15 x 160 = 4,800 mm^2. So the
crank has considerably less raw fan surface than any normal spoked
wheel.

The other aspect of the wheel's increased wind drag is that the wheel
is much larger in diameter and therefore spins the spokes at a much
higher speed. About half the spoke length sticks out further than the
crank, so at the same rpm the spoke travels faster--and wind drag
rises wildly as speed increases.

So wheels may not compare very well to cranks.

In any case, your 45 second front wheel hand-spin turns out to be well
under what can be achieved:

"In one test, the wheel is accelerated to 70km/h before being
released; time is recorded until it comes to a complete standstill.
The best performing Cometes, used by Meares for her record, can spin
for over 12 minutes."

http://www.cyclingnews.com/tech.php?id=tech/2006/features/meares_bt_stealth

So some front wheels can go over 720 seconds when spun up to about 43
mph.

Sorry that you hurt yourself, but it's unlikely that your hand-spin
for 45 seconds reached even 20 mph.

When I tested hand-spinning of front wheels, I found that about 15 mph
was the maximum, due to the extremely limited span and awkward angle
at which our arms engage wheels. Your hand must change direction 90
degrees in only a quarter-turn of the wheel, so your hand comes off
the wheel long before you reach even the speed of a casual
stone-throw:

http://groups.google.com/group/rec.bicycles.tech/msg/9b36efb8133cd8a7

The current RBT record for hand-spinning a 700c front wheel [modest
cough] still stands at 16.2 mph.

Anyway, my initial reaction was disbelief when a crank was said to
spin for minutes, but I'm willing to be convinced. A 2006 crank,
beautifully finished and designed and so forth, with heavy pedals,
should certainly be able to beat my cheap 1998 test crank's 20 seconds
with light pedals.

I'd love to have someone with a nice new crank give it a whirl without
the chain and report actual seconds.

Cheers,

Carl Fogel

Lou Holtman said:

* * Chas said:

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

Quoted message said:

Jim Higson wrote:

>HarryB wrote:
>
>
>
>>How much drag is considered normal for a cartridge bearing BB?
>
>
>Don't know about normal, but if I give my cranks a good push with no

chain

Quoted message said:

>connected they continue to spin for several minutes.
>
>Veloce cartridge BB (2006 model I think)
>

Several minutes??? That's not normal.

Lou
--

Well, it depends on how heavy your chainrings are, just like the
flywheel on a car. If you used nice heavy steel chainrings not the
flimsy alloy [censored] you see today, then yes they could possibly keep
spinning for quite some time.

Oh please, alloy chainrings are fine. For several minutes spin time
those clunky chainrings must be very heavy and large in diameter.

Lou

Dear Lou,

Actually, heavy pedals would probably be more helpful, since they're
further out and provide more angular momentum.

When I attached some light pedals to my test crank, spin time
increased about 50%, from around 13 seconds to over 20 seconds. The
extra mass overwhelmed the increased wind drag.

As always, I'm amused by the willingness of RBT posters to argue
yes-it-does and no-it-can't without taking the trouble to do something
as simple as testing how long a crank will spin.

Surely someone out there must want to take the current 20-second
crank-spin record away from me and my 1998 Shimano triple.

(Be warned that the record-holder craftily performed the test at
nearly 5,000 feet to take advantage of thinner air and reduced wind
drag.)

Cheers,

Carl Fogel

Quoted message said:

Lou Holtman said:

Quoted message said:

On Sun, 03 Dec 2006 23:48:19 +0100, Lou Holtman
<[email hidden]> wrote:

>Tim McNamara wrote:
>
>
>>In article <[email hidden]>,
>>Lou Holtman <[email hidden]> wrote:
>>
>>
>>
>>
>>>Jim Higson wrote:
>>>
>>>
>>>
>>>>HarryB wrote:
>>>>
>>>>
>>>>
>>>>
>>>>>How much drag is considered normal for a cartridge bearing BB?
>>>>
>>>>Don't know about normal, but if I give my cranks a good push with no chain
>>>>connected they continue to spin for several minutes.
>>>>
>>>>Veloce cartridge BB (2006 model I think)
>>>
>>>
>>>Several minutes??? That's not normal.
>>
>>
>>The Veloce bottom brackets are pretty smooth turning- smoother than most
>>of Campy's other BBs including (the last ones I tried) Chorus and Record.
>
>
>We are talking of minutes. That is a very loooong time. I can't believe
>that.
>Last week I installed a Shimano XT hollotech II crankset (outboard
>bearings). I gave it a swing and it wouldn't turn even one revolution,
>but that's just the drag of the seals and you don't notice that while
>riding.
>
>Lou

Dear Lou,

For fun, I tested a 1998 Schwinn Le Tour triple with 170 mm cranks,
pretty much unused and bought for spares, a ten-year-old bottom of the
line example of a crank.

With no pedals, the level crank will support two dimes over the left
pedal eye, but it starts to turn under the weight when a third dime is
added.

According to the US Mint, a dime is around 2.268 grams, plus or minus
a smidgen for grime and wear:

http://www.usmint.gov/about_the_mint/index.cfm?flash=yes&action=coin_specifications

So the initial bearing resistance (higher than the moving resistance)
is a bit less than 170 mm / 6 grams of torque, which works out to the
surprisingly high value of about 0.1 foot-lbs of torque.

Bracing the frame and giving the pedals a brisk turn produces about 13
seconds of spin on average.

Adding some light pedals increases the inertia and angular momentum
more than the wind drag and produces about 20 seconds of spin on
average.

So maybe really smooth modern bearings can spin for minutes. I'd love
to see some quick and dirty tests involving how many coins (or half or
quarter coins) a level crank can support before it starts to turn.

Carl, I gave my front wheel (with tire) with a recently overhauled and
very smooth running Record hub a very firm spin (I hurt myself) and it
stopped after 45 seconds. So I think 'several' minutes is a ridiculous
claim.

Lou

Dear Lou,

Since a front wheel is not a bottom bracket, the two may behave
differently.

For one thing, the wheel has considerably greater wind drag from all
the spokes--you can feel the fan effect off to the side of a spun
front wheel.

The drag is partly due to the area of the spokes, which is
surprisingly large. With ~275 mm of exposed spoke at mostly 1.8 mm for
a butted spoke, each spoke has ~500 mm^2 of area. At 16 spokes, that's
8,000 mm^2. For 32 spokes, it's 16,000 mm^2.

The two 170 mm pedal arms on the crank that I tested are about 15 mm
wide by 160 mm exposed length, so 2 x 15 x 160 = 4,800 mm^2. So the
crank has considerably less raw fan surface than any normal spoked
wheel.

The other aspect of the wheel's increased wind drag is that the wheel
is much larger in diameter and therefore spins the spokes at a much
higher speed. About half the spoke length sticks out further than the
crank, so at the same rpm the spoke travels faster--and wind drag
rises wildly as speed increases.

So wheels may not compare very well to cranks.

In any case, your 45 second front wheel hand-spin turns out to be well
under what can be achieved:

"In one test, the wheel is accelerated to 70km/h before being
released; time is recorded until it comes to a complete standstill.
The best performing Cometes, used by Meares for her record, can spin
for over 12 minutes."

http://www.cyclingnews.com/tech.php?id=tech/2006/features/meares_bt_stealth

So some front wheels can go over 720 seconds when spun up to about 43
mph.

Sorry that you hurt yourself, but it's unlikely that your hand-spin
for 45 seconds reached even 20 mph.

When I tested hand-spinning of front wheels, I found that about 15 mph
was the maximum, due to the extremely limited span and awkward angle
at which our arms engage wheels. Your hand must change direction 90
degrees in only a quarter-turn of the wheel, so your hand comes off
the wheel long before you reach even the speed of a casual
stone-throw:

http://groups.google.com/group/rec.bicycles.tech/msg/9b36efb8133cd8a7

The current RBT record for hand-spinning a 700c front wheel [modest
cough] still stands at 16.2 mph.

Anyway, my initial reaction was disbelief when a crank was said to
spin for minutes, but I'm willing to be convinced. A 2006 crank,
beautifully finished and designed and so forth, with heavy pedals,
should certainly be able to beat my cheap 1998 test crank's 20 seconds
with light pedals.

I'd love to have someone with a nice new crank give it a whirl without
the chain and report actual seconds.

Cheers,

Carl Fogel

OK I'm challenged. I now go back to my garage, remove the chain and spin
my 2006 Campagnolo Carbon Compact crank, with smooth running Record BB.
I'll be back..

Lou
--
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