Gear ratios
Tim Brandt
I am currios as to effect of the front chainrings size. I just bought
a Cannondale H200 and it has a 24/32/38 front chainring set. If I
were to get 22/34/42 or 24/36/46 front chainring, how much of a
difference would it make in the speed of the bike.
Tim Brandt
Sergio
David Martin (dama...@bioslave.uio.no) wrote:
: In article <31FCC3EB...@kcco.com>, Tim Brandt <bra...@kcco.com> wrote:
: ]I am currios as to effect of the front chainrings size. I just bought
: ]a Cannondale H200 and it has a 24/32/38 front chainring set. If I
: ]were to get 22/34/42 or 24/36/46 front chainring, how much of a
: ]difference would it make in the speed of the bike.
: It all depends on the engine.....
Not as simple!
It would marginally depend on the fuelling power-bars, too.
Sergio
Pisa
David Martin
In article <4tkvfs$10...@serra.unipi.it>,
serv...@ipifidpt.difi.unipi.it (Sergio) wrote:
Ok.. I take your point. Most MTBs seem IMHO to be way undergeared. Is it just
me or does a 38 big ring seem just a tad titchy? Maybe its because my road
bike has a shortest gear of 54" (gear ratio of 2, 42/21) and that gets me up
most road hills, I can't imagine not running out of gear at 38/11 (93") or
what ever even off road. Is micro drive really a big con?
If it were me I'd go for 24/36/48, with a 12-23 rear block (or slightly wider
ratio if you wish/need). That should do fine if you're after speed. For more
relaxed pootling you may want a wider block but with the bottom gears its
going to be quicker to get off and walk...
Then again my advice is complete cack so ignore it..
70lbs luggage and a bottom gear of 42/32 made interesting touring .. those 12%
grades really get to you after a while.
Alternatively pedal faster and spend the money you save on something for the
wife/girlfriend/kids to keep them happy whilst you're out riding.
.d (Whos bike budget is less than what he saves in transport costs by
commuting on the bike)
* David Martin, PhD - Post-Doctoral Research Fellow *
* Atherosclerosis and Thrombosis research group *
* Biotechnologisenteret i Oslo *
* Postboks 1125 Blindern, N-0316 Oslo, Norway *
* Tel: +47 22 95 84 54 Fax: +47 22 69 41 30 *
* http://www.uio.no/~damartin/ david....@biotek.uio.no *
David Martin
In article <31FCC3EB...@kcco.com>, Tim Brandt <bra...@kcco.com> wrote:
]I am currios as to effect of the front chainrings size. I just bought
]a Cannondale H200 and it has a 24/32/38 front chainring set. If I
]were to get 22/34/42 or 24/36/46 front chainring, how much of a
]difference would it make in the speed of the bike.
It all depends on the engine.....
.d
David Martin
In article <4tnfci$k...@tuegate.tue.nl>,
Camiel Rouweler <cami...@surf.phys.tue.nl> wrote:
<bits on optimum speed/gear snipped>
]Assuming a 26" wheel with a circumference of 2 m, a smallest cog with
]twelve teeth and you are pedalling at a rate of 90 rpm, this will give
]you the following optimum speeds in top gear:
]
] opt. speed
]teeth: (km/h) (mph)
]38 34.2 21.1
]42 37.8 23.6
]46 41.4 25.9
]
Now if you want a flat cruising speed of that you are looking at 52/14 or
thereabouts which leaves you an extra couple of gears for those wicked
downhills..
]Unless you often ride faster than 34 km/h 38 teeth will be fine.
]A relatively small chainring also has the advantage that the gears
]are spaced close to each other
disadvantage.. it overlaps your rear block more so you get less fine
adjustment.
If you are after lots of speed you want lots of gear. If you want lots of
torque (for vicious hills/heavy loads/crappy conditions) you need little tiny
gears.
What you are constrained by is the amount of extra chain your rear derailleur
can cope with and the capacity (largest front-smallest front) of your front
derailleur.
I prefer to have my cruising speed somewhere about 1/3 of the way up the block
(3rd/4th smallest cog) and have chainrings that then match the conditions. (so
I'm after a 39 tooth small ring for my road bike if anyone wants to throw one
in my direction, shimano road compatible 130mm BCD) so I have a flat/downhill
chainring, and an uphill chainring, and do fine adjustment on the back. (I'm
going to install a granny to take towing the trailer).
If you work mostly on the rear then the slight difficulties in shifting up to
the big rings at the front are negligible, typically you can take more time as
the conditions are easing. going the other way there is virtually no
difference.
One other thing, hacking on your 11/12 tooth rear sprocket as a cruising gear
will knacker your chain faster than using the middle of the block.
Camiel Rouweler
Tim Brandt <bra...@kcco.com> wrote:
>I am currios as to effect of the front chainrings size. I just bought
>a Cannondale H200 and it has a 24/32/38 front chainring set. If I
>were to get 22/34/42 or 24/36/46 front chainring, how much of a
>difference would it make in the speed of the bike.
Gears are used to be able to keep the optimum pedal rate at any
speed. A pedal rate of 90 rpm seems to deliver the most power. This
is for racer who want top performance. If you're after efficiency,
a rate of 60 or 70 rmp is probably better (but will kill your knees
on demanding climbs).
The optimum speed for a given gear is than given by:
speed = #teeth on chainring/#teeth on cog*rpm*60*circumference(m)/1000
(in km/h, divide by 1.6 to get mph)
Assuming a 26" wheel with a circumference of 2 m, a smallest cog with
twelve teeth and you are pedalling at a rate of 90 rpm, this will give
you the following optimum speeds in top gear:
opt. speed
teeth: (km/h) (mph)
38 34.2 21.1
42 37.8 23.6
46 41.4 25.9
Unless you often ride faster than 34 km/h 38 teeth will be fine.
A relatively small chainring also has the advantage that the gears
are spaced close to each other
--
Camiel Rouweler (cami...@surf.phys.tue.nl)
"I don't want to be called 'boy' anymore. I find that term
sexist and demeaning!". "How do you want to be called then?"
"I want to be called 'chromosomally advantaged youth." (Calvin&Hobbes)
Ozzie123
The Physics books are packed away. If I know my crank cadence, what chain
ring and cog I am in, how can I calculate power? I would like to know
this to assess for the same power output the relative speeds in the
various chainring/cog combinations. Any insite would be appreciated.
Thanks,
Paul Oswald
Ozzi...@aol.com
Geoffrey Levand
I was asking for something specific and perfect for my city,
Whereupon lo! upsprang the post of dama...@bioslave.uio.no (David
Martin):
>If it were me I'd go for 24/36/48, with a 12-23 rear block (or slightly wider
>ratio if you wish/need). That should do fine if you're after speed. For more
>relaxed pootling you may want a wider block but with the bottom gears its
>going to be quicker to get off and walk...
I guess you've never pushed a bike up a steep mountain before. It may
be slower, but its damn easier to ride. My racing friends were
wishing they had the 24/32 gearing of my touring bike when we went up
Mt. Fuji...
Larry Schuldt
ozzi...@aol.com (Ozzie123) wrote:
>Thanks,
>Paul Oswald
>Ozzi...@aol.com
Quick answer: You can't.
If you also factor in your wheel size, you CAN calculate speed. Power
would depend on grade, wind speed, wind direction, your riding
position, etc.
larry
============================================================================
Larry Schuldt Opinions expressed herein are
Chicago Title & Trust hardly ever those of management.
(312) 223-2512
schu...@ctt.com (work) or
lsch...@ix.netcom.com (home)
============================================================================
Tho X. Bui (bleep@mwci.net)
Larry Schuldt wrote:
> Paul Oswald wrote:
> >The Physics books are packed away. If I know my crank cadence,
> >what chain ring and cog I am in, how can I calculate power? I
> >would like to know this to assess for the same power output the
> >relative speeds in the various chainring/cog combinations. Any
> >insite would be appreciated.
> Quick answer: You can't.
"Power" is how hard you're working, as in energy produced
for a given period in time.
Probably the easiest way to get a feel of how much power you're
putting out is find a steep hill, climb up it and time your climb.
Then use mass times gravitational acceleration times the height of
climb divided by time to get your average power output--assuming
zero rolling and air friction. This is probably possible only for
very steep hill at very low speeds (7-10 mph?).
Then try to equate that on how hard you work on the flats...
The other option is measure the torque produced at your pedal,
then multiply it to the rpm....A more accurate measurement of power,
but the measuring hardware can be expensive.
tho
Steve Hendrix
In article <4toc7b$7...@newsbf02.news.aol.com>, ozzi...@aol.com (Ozzie123) writes:
|> The Physics books are packed away. If I know my crank cadence, what chain
|> ring and cog I am in, how can I calculate power? I would like to know
|> this to assess for the same power output the relative speeds in the
|> various chainring/cog combinations. Any insite would be appreciated.
|>
|> Paul Oswald
|> Ozzi...@aol.com
Power is Force times distance divided by time. One horsepower is 550 foot pounds per second. The force is missing from the list of givens you provide so you will not be able to calculate power.
To do what I think you want to do I would assume a force holding back the bicycle
and back calculate to get the force on the pedals (this may require unpacking
the physics book) , then knowing pedal force and speed you can calculate
the relative cadence required to maintain the same power output for various
gear ratios. I am not sure where you would get data for the mechanical losses
which will affect the power somewhat.
The book The Science of Cycling by Burke has a chart showing how many calories
per hour a cyclist uses at various sppeds.( calories per hour is a unit of power
and can be converted to horsepower or whatever you would like to use.
Steve Hendrix
Steve Hendrix
In article <4tqbj1$c...@Nntp1.mcs.net>, schu...@ctt.com (Larry Schuldt) writes:
|> hen...@sdd.hp.com (Steve Hendrix) wrote:
|>
|> >The book The Science of Cycling by Burke has a chart showing how many calories
|> >per hour a cyclist uses at various sppeds.( calories per hour is a unit of power
|>
|> what riding position? That's why I implied in my previous post that
|> power would be difficult to quantify. Actually, all you'd really need
|> would be a wheel pickup for speed and a straing gauge placed in the
|> drive train somewhere... Didn't Look make a rear hub set up for this a
|> couple years ago?
|> ============================================================================
|> Larry Schuldt Opinions expressed herein are
|> Chicago Title & Trust hardly ever those of management.
|> (312) 223-2512
|> schu...@ctt.com (work) or
|> lsch...@ix.netcom.com (home)
|>
|>
|>
|> ============================================================================
to calculate power. Charts such as the one in BUrkes book are quite approximate.
I find them useful for disputing those who say cycling does not burn many
calories. (which is true if you are going the 12mph listed on most exercise
comparison charts.)
Do you think people are actually interested enough in power
to buy and attach a sensor to theit bike? And if so, how interested? $500 and
2 pounds? $50 and 6 ounces? A few years ago I made some prototype segmants
of the system which would be needed for this. One measures forces and sppeds
at the crank and one at the chain. Either could be developed but I do not
have the resources to develop or market the Idea.
The hub you mentioned sounds interesting. Do you have any idea how
athe strain data from the hub was transmittes accross the rotating interface? t
Steve Hendrix
>
Larry Schuldt
David Martin
In article <4toni4$q...@gol2.gol.com>, gle...@gol.com (Geoffrey Levand) wrote:
]I was asking for something specific and perfect for my city,
I have.. my touring bike (due to economic factors) had a low gear of 42/32.
That still went up 12% grades though with 50lbs luggage.
At the moment I'm wanting to get something a little easier than 42/21 for the
race biek for some of the hills around here. That'll have to wait for some
money though. The tourer will go to a triple on the front to pull the trailer
when I get it.
Anyway, you asked about gears to go fast in the city, not to wander up long
mountain roads at a snails pace.
Doug Milliken
On 31 Jul 1996, Ozzie123 wrote:
> The Physics books are packed away. If I know my crank cadence, what chain
> ring and cog I am in, how can I calculate power? I would like to know
The other posters are right... you need to know more than cadence & gear.
You might look at the Bikepower program -- see the FAQ to find this.
Also, check out the book, "Bicycling Science" by Whitt & Wilson, MIT Press.
There is an expensive (US$3000??) computer/crank made by SRM (Germany?)
that reads out and records power while you are riding.
-- Doug
Rick Tengdin
Larry Schuldt wrote:
>
> ozzi...@aol.com (Ozzie123) wrote:
>
> >The Physics books are packed away. If I know my crank cadence, what chain
> >ring and cog I am in, how can I calculate power? I would like to know
> >various chainring/cog combinations. Any insite would be appreciated.
>
>
> would depend on grade, wind speed, wind direction, your riding
> position, etc.
>
If you know crank force vs. time you can calculate your power
output. The relative crank speed you see in different chainring/cog
settings will show up in crank force, time, or both. AFAIK this is
how the power meters that are out there work.
Just knowing crank cadence, chainring, and cog doesn't give you enough
information. Look at the difference in doing 100 rpm in a 48x12 gear
on the workstand, on a 3% downgrade, or a 5% upgrade. Same numbers,
very different power output.
--
Richard Tengdin Senior Systems Integration Engineer
VLSystems, Inc. NT/Alpha specialist
#include <disclaimer.h>
"GUIs are wonderful until you have to do the same thing *twice*."
Rob & LeAnne Platt
Doug Milliken wrote:
>
> On 31 Jul 1996, Ozzie123 wrote:
>
> > The Physics books are packed away. If I know my crank cadence, what chain
> > ring and cog I am in, how can I calculate power? I would like to know
>
You could put tour bike in a stand and run a small (<1KVA) DC generator
connected to a resistive load,
and measure the voltage (or current) at various levels of effort.
P=V*V/R or P=V*I or P=I*I*R, depending on which values you measure.
This is called a dynomometer, and it's very accurate.
I'm not being very serious, but if you do try some of these suggestions, let
us know the results.
-------------------------------------------------------
Rob & LeAnne Platt 'Better software through Espresso!'
mailto:rjp...@gti.net http://www.gti.net/rjplatt
mailto:Robert_Platt%SCHI...@notes.worldcom.com
Mark T. Takeuchi
> The Physics books are packed away. If I know my crank cadence, what chain
> ring and cog I am in, how can I calculate power? I would like to know
> this to assess for the same power output the relative speeds in the
> various chainring/cog combinations. Any insite would be appreciated.
>
> Thanks,
> Paul Oswald
> Ozzi...@aol.com
If you know your cadence and gear ratio you can calculate your speed. If
you know your speed you can generate a rough model for power if some
assumptions are made.
P = drag force x velocity
drag force aero = (1/2) rho x frontal area x Cd x velocity^2
rho is the density of air, and
Cd is the drag coefficient, a measure of the aero efficiency of a
particular shape
P aero = (1/2) rho x frontal area x Cd x velocity^3
If the following are assumed:
rho = 1.197 g/l at 22 C and 76 cm of pressure and
frontal area = 3.2 ft^2
Cd = .76 (Alec Brooks, 12/89 Cycling Science)
velocity = 20 mph
P = 97 W = 0.13 hp
The interesting (and perhaps discouraging) part of the equation is the
velocity^3 term. If you double the amount of power, you only get a 25%
increase in speed.
A rough model for the power required to climb a hill can also be generated.
If the backward force due to the uphill is
drag force hill = weight x Sine (alpha)
weight is the weight of the rider + bicycle
alpha is the angle the hill makes with horizontal
If the hill isnšt too steep the following approximation can be made.
drag force hill = weight x %grade
P hill = drag force hill x velocity
= weight x %grade x velocity
If the following are assumed:
weight = 170 lbf
%grade = .05
velocity = 20 mph
p hill = 340 W = 0.45 hp
You can assume that the power due to bearing friction and rolling
resistance is small compared to the power required to move a bicycle and
rider through the air and up a hill.
Working backwards, given a particular power you can calculate the speed,
and knowing the speed you can then calculate the gear ratios and cadences
required to produce that speed.
A related interesting question is more a physiological question than one
of physics. For a given power, at what cadence is a rider most efficient?
The summer 1996 Cycling Science has an article on what determines optimal
cadence.
Interested people can contact Cycling Science at:
Cycling Science
Penner Publishing Inc.,
PO Box 926, Hightstown, New Jersey 08520
Phone 609-443-0038
Fax 609-443-4471
~Mark.
Jim Campbell
> The hub you mentioned sounds interesting. Do you have any idea how
> athe strain data from the hub was transmittes accross the rotating
interface? t
> Steve Hendrix
> >
Never seen this device. I would use slip rings. Common practice for
transmitting electrical current or signal through a rotating interface
such as a rate table, etc. They can be very small indeed, and we have
even made our own.
Jim Campbell
--
James R. Campbell, Jr.
d.cam...@main.mmf.umn.edu
Doug Milliken
On Fri, 2 Aug 1996, Rob & LeAnne Platt wrote:
> Doug Milliken wrote:
> > On 31 Jul 1996, Ozzie123 wrote:
> > > The Physics books are packed away. If I know my crank cadence, what chain
> > > ring and cog I am in, how can I calculate power? I would like to know
> > The other posters are right... you need to know more than cadence & gear.
>
> You could put tour bike in a stand and run a small (<1KVA) DC generator
> connected to a resistive load,
> and measure the voltage (or current) at various levels of effort.
> P=V*V/R or P=V*I or P=I*I*R, depending on which values you measure.
> This is called a dynomometer, and it's very accurate.
>
> I'm not being very serious, but if you do try some of these suggestions, let
> us know the results.
We did this over 10 years ago to determine our rider's power curve vs rpm
and time-of-exercise. We used a rewound golf cart motor capable of ~10 hp
peaks (~7.5kw) and a servo control - which meant that we could actually run
as a true constant rpm dynomometer, even with the most powerful sprinters.
We have the motor mounted in gimbals and measure the reaction torque,
rather than trying to deal with the thermal changes in the motor (bearing
and brush friction, etc.) One of the controls available is a 10-turn pot
that sets the "can't exceed" rpm... It's interesting to put a
non-engineer-bike-racer on this machine and watch as they try to exceed the
set-point! They can't.
This data was then used in a simple model to determine the best
"acceleration schedule" for our streamlined human powered vehicle. I guess
we were successful -- our flying 200 meter record with the Moulton 'Liner
(streamlined, normal position, i.e., _not_recumbent_) of 51+ mph at sea
level still stands 10 years later.
-- Doug
Carsten Dieter Wolf
: > The Physics books are packed away. If I know my crank cadence, what chain
: > ring and cog I am in, how can I calculate power? I would like to know
: > various chainring/cog combinations. Any insite would be appreciated.
: >
: > Thanks,
: > Paul Oswald
: > Ozzi...@aol.com
Hi - look over the prog. form ftp: draco.acs.uci.edu/pub/rec.bicycles
bikei_power.c
Compile it, every C-Copiler make the job and look over the examples
discribed in bike_power.doc.
carsten
Daniel Connelly
In article <4u9php$i...@dm2.uibk.ac.at>,
Power output depends on bike speed, which can be calculated from cadence
and the gear development. bike_power converts speed to power and vice-versa.
The equations are implemented in a Java applet available through
the Western Wheeler's pages,
http://www.webville.com/oak/ww/BikePowerApplet.html
(the interface is slightly buggy, but it mostly works.)
Also there is a link the the bike_power.c source on draco.acs.uci.edu.
Dan
Larry Schuldt
hen...@sdd.hp.com (Steve Hendrix) wrote:
> Do you think people are actually interested enough in power
>to buy and attach a sensor to theit bike? And if so, how interested? $500 and
>2 pounds? $50 and 6 ounces? A few years ago I made some prototype segmants
>of the system which would be needed for this. One measures forces and sppeds
>at the crank and one at the chain. Either could be developed but I do not
>have the resources to develop or market the Idea.
> The hub you mentioned sounds interesting. Do you have any idea how
>athe strain data from the hub was transmittes accross the rotating interface? t
>Steve Hendrix
>>
Steve,
I'd be interested, but certainly not $500 + 2 lbs worth.
Anyway, I don't think I ever say details on how the Look hub worked. I
remember seeing articles on it in the bike mags. It was anodized red
in color as I recall. The rear hub would be the logical place for it,
because you can also measure rpm there and get wheel speed. The only
additional input you'd need would be for wheel size. Of course, if
you're picky, you wouldn't know about losses in the drive train, but
it WOULD measure power actually reaching the rear wheel.
Bicycling Magazine ran an article a few years ago about computing
power/actual calories burned with the conclusion that x miles/hour = y
calories/power type charts are next to worthless... 20 mph on a
mountain bike in an upright position != 20 mph on a road bike on the
aero bars as far as power is concerned.
============================================================================
Larry Schuldt Opinions expressed herein are
Chicago Title & Trust hardly ever those of management.
(312) 223-2512
schu...@ctt.com (work) or
lsch...@mc.net (home)
============================================================================