Frictional losses?

"oyvey1948" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

How does drivetrain frictional drag change with speed?

Under a constant load, frictional drag would be directly proportional to speed.

Quoted message said:

Do watts generated create the same losses regardless of gearing?

Most of the frictional drag is incurred through the derailleur pulleys in the non-drive tensioned
part of the chain. The main drivechain tension is handled by only 2 or 3 teeth on the chainring/cog.
However, a very small increase will be incurred with a tighter chain wrap around smaller cogs. Drive
chain losses at normal cycling speeds are approx. 1%.

Phil Holman

Phil Holman said:

"oyvey1948" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

How does drivetrain frictional drag change with speed?

Under a constant load, frictional drag would be directly proportional to speed.

Quoted message said:

Do watts generated create the same losses regardless of gearing?

Most of the frictional drag is incurred through the derailleur pulleys in the non-drive tensioned
part of the chain. The main drivechain tension is handled by only 2 or 3 teeth on the
chainring/cog. However, a very small increase will be incurred with a tighter chain wrap around
smaller cogs. Drive chain losses at normal cycling speeds are approx. 1%.

I don't think this is accurate. Numbers I've seen range from 2% for a fixed gear up to 15% or more
for extreme cross-gears w/ triple chain rings, with 5% typical for a typical geared bike.

My reference for this is data reproduced in [email hidden] back in 1997 (Feb,
I think). However, the list archives have recently been blitzed, it seems (cycling.org seems to be
active again, to some degree).

Dan

Dan Connelly said:

Phil Holman said:

smaller cogs. Drive chain losses at normal cycling speeds are approx. 1%.

I don't think this is accurate. Numbers I've seen range from 2% for a fixed gear up to 15% or more
for extreme cross-gears w/ triple chain rings, with 5% typical for a typical geared bike.

I found some numbers. The cross-gears are more efficient than I remembered. Losses go from 5% to
1.5% for a 3x5 gear. Cross-gears will of course be worse on a 3x9 or 3x10, but maybe a 2x9 or 2x10
will be comparable to the 3x5.

selbst-machen.despeedhub vs xt.gifOpen ↗

Dan

"Dan Connelly" <d_j_c_o_n_n_e_l@i_e_e_e.o_r_g> wrote in message
"]news:[email hidden]...

Quoted message said:

Phil Holman said:

"oyvey1948" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

How does drivetrain frictional drag change with speed?

Under a constant load, frictional drag would be directly

proportional to

Quoted message said:

Quoted message said:

speed.

Quoted message said:

Do watts generated create the same losses regardless of gearing?

Most of the frictional drag is incurred through the derailleur

pulleys

Quoted message said:

Quoted message said:

in the non-drive tensioned part of the chain. The main drivechain tension is handled by only 2
or 3 teeth on the chainring/cog.

However, a

Quoted message said:

Quoted message said:

very small increase will be incurred with a tighter chain wrap

around

Quoted message said:

Quoted message said:

smaller cogs. Drive chain losses at normal cycling speeds are

approx.

Quoted message said:

Quoted message said:

1%.

I don't think this is accurate. Numbers I've seen range from 2% for a fixed gear up to 15% or more
for extreme cross-gears w/ triple chain rings, with 5% typical for a typical geared bike.

My reference for this is data reproduced in

[email hidden]

Quoted message said:

back in 1997 (Feb, I think). However, the list archives have recently

been

Quoted message said:

blitzed, it seems (cycling.org seems to be active again, to some

degree).

Quoted message said:

That surprises me. We would see a much greater difference between an SRM and a Powertap. Not that
what you say isn't correct but I've never heard of 15% differences in power measurement between
these 2 systems.

Phil Holman

Dan Connelly said:

Dan Connelly said:

Phil Holman said:

smaller cogs. Drive chain losses at normal cycling speeds are approx. 1%.

I don't think this is accurate. Numbers I've seen range from 2% for a fixed gear up to 15% or
more for extreme cross-gears w/ triple chain rings, with 5% typical for a typical geared bike.

I found some numbers. The cross-gears are more efficient than I remembered. Losses go from 5% to
1.5% for a 3x5 gear. Cross-gears will of course be worse on a 3x9 or 3x10, but maybe a 2x9 or 2x10
will be comparable to the 3x5.

selbst-machen.despeedhub vs xt.gifOpen ↗

Correction #2 : those data don't include extreme cross-gears. The drivetrain is 3x9, with only 15 of
the 27 possible gears used in the test:

11 12 14 16 18 21 24 28 32 22 - - - - - + + + + 32 - - + + + + + + - 44 + + + + + - - - -

Dan

Phil Holman said:

That surprises me. We would see a much greater difference between an SRM and a Powertap. Not that
what you say isn't correct but I've never heard of 15% differences in power measurement between
these 2 systems.

Right. I modify this with data posted in a followup, which nevertheless doesn't have extreme cross-
gears. However, just backspinning a 3x9 drivetrain in an extreme cross-gear makes it clear the
losses are quite substantial.

On a previous post, before the h-b-s archives fried, I claimed 10%, so it's probably closer to 10%:
groups.google.comgroupsOpen ↗

Dan

"Dan Connelly" <d_j_c_o_n_n_e_l@i_e_e_e.o_r_g> wrote in message
"]news:[email hidden]...

Quoted message said:

Phil Holman said:

That surprises me. We would see a much greater difference between

an SRM

Quoted message said:

Quoted message said:

and a Powertap. Not that what you say isn't correct but I've never

heard

Quoted message said:

Quoted message said:

of 15% differences in power measurement between these 2 systems.

Right. I modify this with data posted in a followup, which

nevertheless

Quoted message said:

doesn't have extreme cross-gears. However, just backspinning a 3x9 drivetrain in an extreme cross-
gear makes it clear the losses are quite substantial.

On a previous post, before the h-b-s archives fried, I claimed 10%, so it's probably closer to
10%: groups.google.comgroupsOpen ↗

Since we're discussing friction losses I have to add that I had a pair of 32 mm tires on my century
bike figuring that if 28 mm were good then 32 would be better. I couldn't feel any difference riding
the bike but MAN, at the end of a century I was really beat. Changing to 23's made a huge difference
in expended energy on that sort of measurement.

"Dan Connelly" <d_j_c_o_n_n_e_l@i_e_e_e.o_r_g> wrote in message
"]news:[email hidden]...

Quoted message said:

Phil Holman said:

That surprises me. We would see a much greater difference between an

SRM

Quoted message said:

Quoted message said:

and a Powertap. Not that what you say isn't correct but I've never

heard

Quoted message said:

Quoted message said:

of 15% differences in power measurement between these 2 systems.

Right. I modify this with data posted in a followup, which

nevertheless

Quoted message said:

doesn't have extreme cross-gears. However, just backspinning a 3x9 drivetrain in an extreme cross-
gear makes it clear the losses are quite substantial.

Here is another reference ihpva.orgHP52.pdfOpen ↗ that supports your numbers. Remind me
not to run a severe cross chain in my next TT. This still leaves the question about which power
measuring system is best. I found this tinyurl.com2xxfvOpen ↗ that hints at a 2% difference but I
also researched a bunch of other google data that was unfortunately fraught and muddled with
calibration and accuracy issues. Thanks for keeping me honest.

Quoted message said:

On a previous post, before the h-b-s archives fried, I claimed 10%, so it's probably closer to
10%: groups.google.comgroupsOpen ↗

Phil Holman

Phil Holman said:

This still leaves the question about which power measuring system is best. I found this
tinyurl.com2xxfvOpen ↗ that hints at a 2% difference but I also researched a bunch of other
google data that was unfortunately fraught and muddled with calibration and accuracy issues.

That link points to a message by Andy Coggan in which he speculates what would be found when a Power
Tap and an SRM were placed on the same bike. Two reports are available on the web that look at this
(actually, in both cases the bikes were equipped with the SRM, the Power Tap, and the Polar power
module). They come to different conclusions, but for various reasons I tend to think the second test
is better.

mywebpage.netscape.comrosetta.htmlOpen ↗
bike.comtemplate.aspOpen ↗

I said:

That link points to a message by Andy Coggan in which he speculates what would be found when a
Power Tap and an SRM were placed on the same bike. Two reports are available on the web that look
at this (actually, in both cases the bikes were equipped with the SRM, the Power Tap, and the
Polar power module). They come to different conclusions, but for various reasons I tend to think
the second test is better.

mywebpage.netscape.comrosetta.htmlOpen ↗

Sorry. A better link is: mywebpage.netscape.comrosetta details.htmlOpen ↗

Nonetheless, as I said above, I tend to think this one is a little better:

Quoted message said:

bike.comtemplate.aspOpen ↗

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

Quoted message said:

How does drivetrain frictional drag change with speed?

Do watts generated create the same losses regardless of gearing?

this belongs in rec.bicycles.tech, not here.
------------
Alex

Phil Holman said:

Here is another reference ihpva.orgHP52.pdfOpen ↗ that supports your numbers.

This is a really good article. But note from the text, and the final figure, that most of the data,
which are uncorrected for the energy loss in the test apparatus, reads a few % low on efficiency.
This makes the loss in the cross gear around 8-9% on the 3x9 drivetrain. So the numbers can't easily
be compared with other studies.

Dan

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

Quoted message said:

Since we're discussing friction losses I have to add that I had a pair of 32 mm tires on my
century bike figuring that if 28 mm were good then 32 would be better. I couldn't feel any
difference riding the bike but MAN, at the end of a century I was really beat. Changing to 23's
made a huge difference in expended energy on that sort of measurement.

You've confused power loss due to drivetrain inefficiency with power required to overcome rolling
resistance. Both are directly proportional to velocity. In your case the power difference required
to overcome rolling resistance associated with a 32 mm tire and a 23 mm tire could be as much as 20W
at a speed of 18mph. The major factor with rolling resistance is choice of tyre AND road surface.

The bicycle is the most efficient transport mechanism ever invented. A state of the art single speed
track bike is about 98% efficient i.e. only 2% of the power that you generate is wasted due to the
drive train inefficiency, the rest goes into the forward propulsion of the bike.

For Chris Boardman's last World Hour record (49.442 km/h) only about 8W were lost due to the drive
train. As other posters have indicated for deraileur geared bikes and a bad gear selection (one were
the chain is at an angle between the front and rear cogs) the power loss can be more significant,
but generally the efficeny of a derailleur bike with appropriate gear selection is 96-97%.