53 X 16 vs. 50 X 15 gearing

I've had some advice saying that a 53 X 16 gear (on a track bike) which
corresponds to 89.4" will have less internal resistance than a 50 X 15
(90") or 47 X 14 (90.6"). The logic being that larger cogs and/or
chainrings have cause less chain bending and therefore will have less
energy losses.

Any thoughts on whether this might be correct? One might think the
opposite since there's more chain contact on the larger chainrings /
cogs.

I can quite readily convince myself to believe either side of the
argument.

The application here is to elite pursuit racing where loss or victory
can be a matter of inches after 3 km of racing.

Any and all thoughts, opinions, etc. looked forward to. Especially any
references to real studies or science.

Thanks.

Steve Karpik

Dear Steve,

This study mentions that bigger is better:

The researchers found two factors that seemed to affect the bicycle
chain drive's efficiency. Surprisingly, lubrication was not one of
them.

"The first factor was sprocket size," Spicer says. "The larger the
sprocket, the higher the efficiency we recorded." The sprocket is the
circular plate whose teeth catch the chain links and move them along.
Between the front and rear sprockets, the chain links line up straight.
But when the links reach the sprocket, they bend slightly as they curl
around the gear. "When the sprocket is larger, the links bend at a
smaller angle," Spicer explains. "There's less frictional work, and as
a result, less energy is lost."

The second factor that affected efficiency was tension in the chain.
The higher the chain tension, Spicer says, the higher the efficiency
score. "This is actually not in the direction you'd expect, based
simply on friction," he says. "It's not clear to us at this time why
this occurs."

The Johns Hopkins engineers made another interesting discovery when
they looked at the role of lubricants. The team purchased three popular
products used to "grease" a bicycle chain: a wax-based lubricant, a
synthetic oil and a "dry" lithium-based spray lubricant. In lab tests
comparing the three products, there was no significant difference in
energy efficiency. "Then we removed any lubricant from the chain and
ran the test again," Spicer recalls. "We were surprised to find that
the efficiency was essentially the same as when it was lubricated."

http://www.jhu.edu/news_info/news/ho...ug99/bike.html

Carl Fogel

Thanks for the info.

The advice that I got was from renowned bicycle coach Eddie B. I guess
you're not one of the world's most successful coaches without knowing a
thing or two.

It is cool to see actual experimental data though.

Steve Karpik

-----BEGIN PGP SIGNED MESSAGE-----

In article . com,
Steve Karpik wrote:
I've had some advice saying that a 53 X 16 gear (on a track bike) which
corresponds to 89.4" will have less internal resistance than a 50 X 15
(90") or 47 X 14 (90.6"). The logic being that larger cogs and/or
chainrings have cause less chain bending and therefore will have less
energy losses.

Any thoughts on whether this might be correct? One might think the
opposite since there's more chain contact on the larger chainrings /
cogs.

_ It's correct[1], but it's also an incomplete analysis. Bigger
gears have less frictional loss, but they also weigh more. I'm
sure there is a point somewhere where the extra weight to carry
more than cancels out the efficiency advantage. A fixed gear
bicycle is already remarkably efficient, so any gains between the
two extremes are fairly minimal. The weight difference between
53 x 16 and 47 x 14 is also probably fairly trivial. The trade
off point would also depend quite a bit on how much you
weigh... Unless you've got numbers for all these factors, nobody
can really answer the question analytically.


The application here is to elite pursuit racing where loss or victory
can be a matter of inches after 3 km of racing.

Any and all thoughts, opinions, etc. looked forward to. Especially any
references to real studies or science.


_ There is remarkably little science done on the mechanics of a
bicycle. I found one study on chain efficiency on derailleur
bikes and there is some very old work on gear ratio
efficiency. I think your best bet is to use the gears of the
person that beat you. It at least has the advantage of tradition
on it's side.

_ Booker C. Bense

[1]- Well, Richard Feynman thought so, and that's good enough for
me. The one empirical study I've found supports that idea as
well.

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Steve Karpik wrote:

The advice that I got was from renowned bicycle coach Eddie B. I guess
you're not one of the world's most successful coaches without knowing a
thing or two.

Like scarfing down a ham & cheese sandwich while racing? His
description of sprints in his coaching book was great, though.

I don't know what the friction variation is between smaller and larger
sprockets, but the smaller the rear sprocket the greater the chordal effect
and the greater the vibration. That is, a chain accelerates and decelerates
because the pitch line of the chain rises and falls as it goes around the
sprocket. For a 17t sprocket the speed variation is about 1.5%. For an 11t
sprocket it rises to about 4.5%, which is why a 53x11 feels rough.

Nick

"Steve Karpik" wrote in message
ups.com...
I've had some advice saying that a 53 X 16 gear (on a track bike) which
corresponds to 89.4" will have less internal resistance than a 50 X 15
(90") or 47 X 14 (90.6"). The logic being that larger cogs and/or
chainrings have cause less chain bending and therefore will have less
energy losses.

Any thoughts on whether this might be correct? One might think the
opposite since there's more chain contact on the larger chainrings /
cogs.

I can quite readily convince myself to believe either side of the
argument.

The application here is to elite pursuit racing where loss or victory
can be a matter of inches after 3 km of racing.

Any and all thoughts, opinions, etc. looked forward to. Especially any
references to real studies or science.

Thanks.

Steve Karpik

Nick Payne wrote:
I don't know what the friction variation is between smaller and larger
sprockets, but the smaller the rear sprocket the greater the chordal
effect and the greater the vibration. That is, a chain accelerates
and decelerates because the pitch line of the chain rises and falls
as it goes around the sprocket. For a 17t sprocket the speed
variation is about 1.5%. For an 11t sprocket it rises to about 4.5%,
which is why a 53x11 feels rough.

I thought this was because the side plates of the chain hit/dig into the
integrated spacer on 11t and 12t cogs. All my 11 and 12t cogs exhibit this.
--
Phil, Squid-in-Training

On 12 May 2005 08:57:21 -0700, "Steve Karpik"
wrote:

I've had some advice saying that a 53 X 16 gear (on a track bike) which
corresponds to 89.4" will have less internal resistance than a 50 X 15
(90") or 47 X 14 (90.6"). The logic being that larger cogs and/or
chainrings have cause less chain bending and therefore will have less
energy losses.

Any thoughts on whether this might be correct? One might think the
opposite since there's more chain contact on the larger chainrings /
cogs.

I can quite readily convince myself to believe either side of the
argument.

The application here is to elite pursuit racing where loss or victory
can be a matter of inches after 3 km of racing.

Any and all thoughts, opinions, etc. looked forward to. Especially any
references to real studies or science.

Thanks.

Steve Karpik


Dear Steve,

Here's another, but rather denser study that addresses
gear-size in passing:

http://www.ihpva.org/pubs/HP52.pdf

The study notes that "a 12-tooth sprocket seems to cause
inefficiency. In the Shimano 27-speed, gears 4, 9, 15, 18,
and 24 have the lowest efficiency. The two gears with the
lowest efficiency of the 15 tested both use a 12-tooth
sprocket. The gears with the 12-tooth sprockets (18, 24, and
27) have an average efficiency of 91.2%, while those
involving 16-tooth sprockets (11, 20, and 25) have an
average efficiency of 93.5%."

This suggests that what really matters is increasing the
size of the smallest sprocket, not the largest one, and that
the difference between a 12 and a 16 tooth sprocket might be
around 91.2% versus 93.5%.

Annoyingly, the transmission efficiency rises with
increasing power. At 80 watts, gear 24 is 86.9% efficient,
but at 200 watts, the same gear's efficiency rises to 91.4%.

Meanwhile, gear 25 has reached 95.5% efficiency at the same
200 watts, 4.1% higher. At 370 watts, gear 25 reaches 97.2%
efficiency.

The transmission loss acts more like a fixed cost, rising at
a much slower rate than power.

gear25
input 54 80 150 200 307 370
watts watts watts watts watts watts
efficiency 90.6% 93.8% 94.8% 95.5% 97.1% 97.2%
loss % 9.4% 6.2% 5.2% 4.5% 2.9% 2.8%
watts lost 5.1w 5.0w 7.8w 9.0w 8.9w 10.4w

gear24
input 54 80 150 200 307 370
watts watts watts watts watts watts
efficiency n/a 86.9% 91.0% 91.4% n/a n/a
loss % n/a 13.1% 9.0% 8.6% n/a n/a
watts lost n/a 10.5w 8.2w 17.2w n/a n/a

gear25
advantage 5.5w 0.4w 8.2w

As these tables make clear, the results were not consistent
and may past the limits of accuracy. (Or they may be showing
weird efficiency patterns--chain speed, chain line, and
input power might cause efficiency to fall off in both
directions from some maxium point.)

However, the pattern of losses staying fixed after 200 watts
on the more widely tested gear25 suggests that the same
pattern for gear24 would lead to steady 8-10 watt difference
at 200 watts and higher.

Trying different gear combinations on a metered trainer
might be a better way to show the size of any practical
advantage to larger rear gears, which would require larger
front gears to maintain roughly the same ratio.

Carl Fogel

Steve Karpik wrote:
I've had some advice saying that a 53 X 16 gear (on a track bike)
which corresponds to 89.4" will have less internal resistance than a
50 X 15 (90") or 47 X 14 (90.6"). The logic being that larger cogs
and/or chainrings have cause less chain bending and therefore will
have less energy losses.

Any thoughts on whether this might be correct? One might think the
opposite since there's more chain contact on the larger chainrings /
cogs.

I can quite readily convince myself to believe either side of the
argument.

The application here is to elite pursuit racing where loss or victory
can be a matter of inches after 3 km of racing.

Any and all thoughts, opinions, etc. looked forward to. Especially
any references to real studies or science.

Herewith something reported in "The Times" in 1998:

"A SCIENTIST at Bristol University has discovered that cyclists should start
thinking bigger.

A bigger sprocket wheel - the toothed wheel that carries the chain - cuts
friction and enhances efficiency,
Stuart Burgess says.

Had Chris Boardman fitted one when he achieved his world record of 56.38km
in an hour in 1996, he
would have covered another 100 metres.

A tiny increase, perhaps, but it could be enough to separate first from
second in a race determined by
fractions of a second, as cycling races often are. Over 25 miles, the bigger
sprocket wheels would save
six seconds, Mr Burgess says in New Scientist.

Cycle designers have concentrated on saving weight by making the sprocket
wheels smaller but that is
the wrong approach, Mr Burgess's tests have shown. Modern sprocket wheels
are made of aluminium
and are already so light that doubling their size makes hardly any
difference. What it does, however, is
reduce the tiny frictional losses that occur as the chain flexes around the
sprocket wheels. These losses
increase with the force exerted on the chain.

Making the sprocket wheels bigger reduces the force on the chain, which in
turn reduces the frictional
losses. Chain drives are very efficient already but bigger sprocket wheels
improve things still further. The
smaller wheels typically used by competition cyclists are 98.8 per cent
efficient but wheels twice as big
are 99.4 per cent efficient.

The ordinary cyclist would not notice the difference but a racing cyclist
might. The only limit is set by the
need for ground clearance at the front sprockets but it would be relatively
easy to double the size of the
sprocket wheels without catching the ground."

I'm sure, however, that I've read of another study which maintains smaller
chainrings & sprockets are the way to go...

--
Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/
Pepperoni and green peppers, mushrooms, olives, chives!

hope is not too late for my answer...


as an older track racer and panamerican junior champion... i would say
that for pursuit racing the best is use maybe 53(52)x16 or maybe 51x15
(usualy people use this one)... I saw a lot of scientific explanations
and stuff... they are right but it depends of the racer too... for
example... 50x15 and 47x14 are almost the same but when u have to "move
it" it makes a lot of difference... 50x15 is a lot easier to move than
47x14, but when sprinting with 47x14 u can get more final speed.. so one
thing for another... as i said it depends of the racer.. and another
thing... basically the one that commands in how "hard to move" the
multiplication is.. will be the cog... WHY? simply because the torque
between the Cog and the chain.. so the chainring influence is minimal
somehow although all depends on what do u want to acchieve... for example
with 50x15 on per points racing will be easier to sprint than with 47x14
but with 47x14 u can continue the acceleration almost endlesly.. at the
sametime with 52 or 53x16 is a little bit easier to move or advance
because with a 16 cog u have more torque (less power to move the rear
wheel) but when srpinting ull have problems because ull get to some point
where ull be pedaling and pedaling w/o the chance to accelerate
anymore... i think u guys have the idea now... sorry for my terrible
english ok?...

If u are a strong racer put 51 or 52 x15 that will be enough...47x14 will
give u a few inches more but after 1 km your legs will be out of power
because u cant do high cadence in loger periods in a track using
47x14... i'm not saying that is imposible but 47x14 is not comfortable
for tha porpouse.. u'll loose the pace...and it is harder to mantain high
cadence.. by the opposite with 50 51 or 52x15 is nice and easier to get
an even cadence, even accelerate...

Well do your own tests... experience is all that it takes... and how i
said before depends on the racer too...

cya





"Steve Karpik" wrote in
ups.com:

I've had some advice saying that a 53 X 16 gear (on a track bike) which
corresponds to 89.4" will have less internal resistance than a 50 X 15
(90") or 47 X 14 (90.6"). The logic being that larger cogs and/or
chainrings have cause less chain bending and therefore will have less
energy losses.

Any thoughts on whether this might be correct? One might think the
opposite since there's more chain contact on the larger chainrings /
cogs.

I can quite readily convince myself to believe either side of the
argument.

The application here is to elite pursuit racing where loss or victory
can be a matter of inches after 3 km of racing.

Any and all thoughts, opinions, etc. looked forward to. Especially any
references to real studies or science.

Thanks.

Steve Karpik