Granny vs. the hill

Dave said:

Is there any reasonable table of granny ratios to hill inclines for a
typical rider? Thanks.

Not that I know of. But in general, with all other things being equal and for grades steeper than about 8%, the gear you need is roughly inversely proportional to the steepness of the hill. So if you need a 30/21 to get up a 10% grade, you'll need a 30/25 to get up a 12% grade.

Can anything be determined from this "Gain ratio" stuff? I have no
clue how to interpret it. Does this provide any way to relate an
incline to a required torque?

http://www.sheldonbrown.com/gain.html

Gonzo Bob said:

Not that I know of. But in general, with all other things being equal
and for grades steeper than about 8%, the gear you need is roughly
inversely proportional to the steepness of the hill. So if you need a
30/21 to get up a 10% grade, you'll need a 30/25 to get up a 12% grade.

Dave said:

Is there any reasonable table of granny ratios to hill inclines for a
typical rider? Thanks.

[email hidden] (Dave) wrote in
news:[email hidden]:

Quoted message said:

Can anything be determined from this "Gain ratio" stuff? I have no
clue how to interpret it. Does this provide any way to relate an
incline to a required torque?

It's a ratio between *force* at the pedal spindle and *force* at the rear
wheel rim. You can't relate force to incline unless you have numbers for
things like air resistance and rolling resistance.

However, the gravitational force along the ground (pushing you down the
hill) is mg sin \theta, where m is your total mass, g is the local
gravitational field strength, and \theta is the slope angle. For small
\theta, sin \theta ~= \theta (in radians); I think this works up to about
1 in 10.

--
to email me, run my email address through /usr/bin/caesar
(or rotate by -4)

RE/

Quoted message said:

Is there any reasonable table of granny ratios to hill inclines for a
typical rider? Thanks.

I back into that ratio. For my upper gear, I choose a ratio where I'm spun
out at about 5 mph faster than the highest speed I can maintain aerobically.

For me, that gives a really low, stump-pulling granny gear. Others might want
to start with the high ration as described, then kick it up a couple steps if
the resulting granny is just *too* low.
--
PeteCresswell

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

Quoted message said:

[email hidden] (Dave) wrote in
news:[email hidden]:

Quoted message said:

Can anything be determined from this "Gain ratio" stuff? I have no
clue how to interpret it. Does this provide any way to relate an
incline to a required torque?

It's a ratio between *force* at the pedal spindle and *force* at the rear
wheel rim. You can't relate force to incline unless you have numbers for
things like air resistance and rolling resistance.

However, the gravitational force along the ground (pushing you down the
hill) is mg sin \theta, where m is your total mass, g is the local
gravitational field strength, and \theta is the slope angle. For small
\theta, sin \theta ~= \theta (in radians); I think this works up to about
1 in 10.

Maybe what I need to ask is this -- at what gear ratio will you simply
lack enough wheelspeed to maintain adequate balance and instead tend
to fall over?

Dave said:

Quoted message said:

Quoted message said:

Can anything be determined from this "Gain ratio" stuff? I have no
clue how to interpret it. Does this provide any way to relate an
incline to a required torque?

It's a ratio between *force* at the pedal spindle and *force* at the rear
wheel rim. You can't relate force to incline unless you have numbers for
things like air resistance and rolling resistance.

However, the gravitational force along the ground (pushing you down the
hill) is mg sin \theta, where m is your total mass, g is the local
gravitational field strength, and \theta is the slope angle. For small
\theta, sin \theta ~= \theta (in radians); I think this works up to about
1 in 10.

Maybe what I need to ask is this -- at what gear ratio will you simply
lack enough wheelspeed to maintain adequate balance and instead tend
to fall over?

Actually, when you get "too low" the limit is often the tendency of the
bike to "wheelie" which is partly related to the frame geometry and
rider height.

Once you get below about a 1.5 gain ratio (20 inches, 1 meter) the gears
tend to become impractical for a bicycle.

Tricycles can effectively use lower gears than this in some cases.

Sheldon "Greenspeed" Brown
+------------------------------------------------+
| I’ll be appearing in: |
| Gilbert & Sullivan's Iolanthe at M.I.T. |
| November 12, 13, 14 and 18, 19, 20, 21 |
| http://web.mit.edu/gsp/www |
| http://sheldonbrown.com/music.html |
+------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Sheldon Brown said:

Actually, when you get "too low" the limit is often the tendency of the
bike to "wheelie" which is partly related to the frame geometry and
rider height.

Once you get below about a 1.5 gain ratio (20 inches, 1 meter) the gears
tend to become impractical for a bicycle.

Tricycles can effectively use lower gears than this in some cases.

Sheldon "Greenspeed" Brown

Sheldon Brown has been assimilated. 😉
<http://www.sheldonbrown.com/harris/greenspeed/index.html>.

--
Tom Sherman