backpacks

On 09/04/14 00:32, jbeattie wrote:

Loaded panniers take a while to get used to, and if you have a cheap
rack and flexible frame, it can feel like you're driving a fire
truck. But there is no way I'm going to carry significant weight on
my back. It hurts my back; it's hot, and it makes it hard for me to
climb out of the saddle. When I'm riding a heavily loaded touring
bike, I feel like a flea on the back of a dog. With a heavily loaded
back pack, I feel like a flea with a dog on my back.

Obviously. I'm not advocating carrying 20kg on your back. Some lunch
and clean clothes, etc., doesn't usually weigh much more than 5kg I
would guess.

--
JS

with Mars from ?



https://www.youtube.com/watch?v=q8q44GjqZ-0

On Tue, 08 Apr 2014 14:57:57 -0400, Frank Krygowski
wrote:

On 4/8/2014 12:42 PM, wrote:
On Tue, 08 Apr 2014 19:51:02 +0700, John B.
wrote:

On Tue, 08 Apr 2014 14:10:35 +1000, James
wrote:

On 08/04/14 12:41, John B. wrote:
On Mon, 07 Apr 2014 08:25:37 -0400, Duane
wrote:

On 4/7/2014 8:09 AM, John B. wrote:
On Mon, 07 Apr 2014 13:56:47 +1000, James
wrote:

On 07/04/14 11:45, John B. wrote:
On Mon, 07 Apr 2014 07:46:59 +1000, James
wrote:

On 06/04/14 10:37, John B. wrote:
On Sun, 06 Apr 2014 07:39:45 +1000, James
wrote:


When you stand on the pedals the backpack weight adds to your body
weight, assisting in pushing down on the pedals.


This theory might indicate that fat people can pedal harder and thus
go up hill quicker?


No.

Weight on the body doesn't hinder as much as weight on the bike.

Err... so how come all the top "climbers" are light weight guys :-?


We are not talking about *body* weight, but a dead weight added to the
body or bike.


I'm not sure that it makes any difference what you call the weight. At
least every example I've seen of calculating climbing effort used
speed, gross weight and angle of climb to calculate the effort
required.



Right but we're talking about dead weight that affects the bike's
handling. Weight on the back of the bike is going to make you work
harder when the bike is moving side to side. Like on a standing climb.

Maybe Jay or Dan could explain this better. I think they both commute
in the hills. For me, I'm not usually carrying anything when I'm
climbing. Last time I did that was on a road trip and I did have
panniers and it sucked big time going up hills. I remember that between
the crosswinds and the heavy handling the ride was a bitch.

I agree with you as to the effect of added weight to the "weight and
balance" of the bike. I was mainly thinking of the effort to climb a
hill where weight seems to be the dominant figure in the calculation.


Also, consider the point at which standing on a pedal with the crank
horizontal, on an up hill gradient and in such a gear that with the
extra weight on your back you can just move forward. Then move the
weight to the bike and see if you can still move forward under the same
circumstances.

Like a lot of things, "yes in theory". But does one climb by standing
on the pedals alone? I don't think so, so in real life your thesis
probably doesn't happen although theoretically you may be correct.

I believe that what happens is that while the added weight does apply
a force to the pedal that force is less than the force needed to move
the added weight up the hill. Out of curiosity I looked up a formula
(total weight x 9.8 x elevation) / time and got:
total weight Watts Required
70 Kg = 228.6 watts
71 Kg = 312.9
72 Kg = 235

I wonder, does an extra weight of 1 kg on the pedal produce 3.3 watts
of power?
You forget the weight is going to be there in any case, in this
situation. Only difference is whether it is "sprung" or "unsprung" -
is it bike weight or "engine" weight. Shifting weight from the bike
to the "engine" WOULD make for better efficiency.

How, exactly?
Strictly in the scenario mentioned, the weight on the "engine"
provides more torque on the crank than having the weight on the bike.
More torque gives more climbing power.
The weight of the bike/ "engine" combination does not change.
Of course, no advantage if NOT standing on the pedals.

On Wed, 09 Apr 2014 08:46:56 +1000, James
wrote:

On 09/04/14 01:17, Frank Krygowski wrote:
On 4/8/2014 12:10 AM, James wrote:



Also, consider the point at which standing on a pedal with the crank
horizontal, on an up hill gradient and in such a gear that with the
extra weight on your back you can just move forward. Then move the
weight to the bike and see if you can still move forward under the same
circumstances.

If the extra weight on your back allows the bike to just move forward in
that circumstance, it's because you previously lifted that extra weight.
If you did get some work out of it, it's only because you earlier put
the work in.

Obviously. The mechanical work done is the same regardless of where the
extra weight is.

To apply the same torque at the cranks with the extra weight on the
bike, you would need to pull more on the handlebars, or lift harder with
the other leg. These muscles are usually not as adept as the ones
designed to lift your body weight, over and over again.

If you're climbing while seated, I think weight on your back won't make
much difference. If you're climbing out of the saddle, you are
repeatedly lifting and dropping that backpack's weight. I suspect there
are inefficiencies in doing so.


That depends greatly on how much of your weight is on the seat. It's
pretty easy to lift your bum off the seat with one leg.
And extra weight on your back will help keep your bum on the seat!!!

On 09/04/14 10:27, wrote:
On Wed, 09 Apr 2014 08:46:56 +1000, James
wrote:

On 09/04/14 01:17, Frank Krygowski wrote:
On 4/8/2014 12:10 AM, James wrote:



Also, consider the point at which standing on a pedal with the crank
horizontal, on an up hill gradient and in such a gear that with the
extra weight on your back you can just move forward. Then move the
weight to the bike and see if you can still move forward under the same
circumstances.

If the extra weight on your back allows the bike to just move forward in
that circumstance, it's because you previously lifted that extra weight.
If you did get some work out of it, it's only because you earlier put
the work in.

Obviously. The mechanical work done is the same regardless of where the
extra weight is.

To apply the same torque at the cranks with the extra weight on the
bike, you would need to pull more on the handlebars, or lift harder with
the other leg. These muscles are usually not as adept as the ones
designed to lift your body weight, over and over again.

If you're climbing while seated, I think weight on your back won't make
much difference. If you're climbing out of the saddle, you are
repeatedly lifting and dropping that backpack's weight. I suspect there
are inefficiencies in doing so.


That depends greatly on how much of your weight is on the seat. It's
pretty easy to lift your bum off the seat with one leg.
And extra weight on your back will help keep your bum on the seat!!!


Precisely.

--
JS

polyester oxford