low-air= how much more work?

Mike Jacoubowsky said:

I've seen all that data for how much weight change will affect a given
climb, but what about a tire running at sub-optimal pressure?

http://groups.google.com/groups?selm=6erog5%24imk%40hplntx.hpl.hp.com

--
Still a proud member of the reality-based community.

Mike Jacoubowsky said:

So, since I'm looking for excuses for how I felt this morning, how much more
effort does an underinflated tire create? Hopefully a lot! :>😉

Check out the curves of resistance vs. pressure on my web page:

http://bike.terrymorse.com/rolres.html

Short answer: pressure makes a real difference, but not a huge
difference.

--
terry morse Palo Alto, CA http://bike.terrymorse.com/

Mike Jacoubowsky said:

I've seen all that data for how much weight change will affect a given
climb, but what about a tire running at sub-optimal pressure?

Not much. I rode into work for a week with a slow puncture without even
realising. The final pressure was probably about 25psi in a 1.3" tyre.

Quoted message said:

Quoted message said:

So, since I'm looking for excuses for how I felt this morning, how much
more
effort does an underinflated tire create? Hopefully a lot! :>😉

Check out the curves of resistance vs. pressure on my web page:

http://bike.terrymorse.com/rolres.html

Short answer: pressure makes a real difference, but not a huge
difference.

Terry: I've gone through the old threads (again), and looked (again) at the
charts on your site showing what happens to rolling resistance as pressure
increases, but I'm *still* not sure what it all means. For example, if you
increase the rolling resistance from 240 to 290 grams (as you decrease
pressure from about 125psi to 82), you're talking about a 20% difference.

But 20% greater rolling resistance means what exactly? On flat land at
moderate speeds, rolling resistance is probably a much smaller part of the
equation than air resistance. But climbing, you (well, at least I) don't
have the speed for air resistance to be much of a factor, but obviously
you're doing a lot of work gaining elevation.

I went to this site- http://w3.iac.net/~curta/bp/velocity/velocity.html- and
played around a bit with the numbers. From what I can tell, the change in
rolling resistance is linear and thus changes might be best estimated by
making changes in the "transmission efficiency" part of the equation. But,
of course, we're talking about only one tire having a 20% increase in
rolling resistance, with the other being inflated to normal pressure.

An awful lot of trouble to try and rationalize why I felt slow!

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

Mike Jacoubowsky said:

Terry: I've gone through the old threads (again), and looked (again) at the
charts on your site showing what happens to rolling resistance as pressure
increases, but I'm *still* not sure what it all means. For example, if you
increase the rolling resistance from 240 to 290 grams (as you decrease
pressure from about 125psi to 82), you're talking about a 20% difference.

But 20% greater rolling resistance means what exactly? On flat land at
moderate speeds, rolling resistance is probably a much smaller part of the
equation than air resistance. But climbing, you (well, at least I) don't
have the speed for air resistance to be much of a factor, but obviously
you're doing a lot of work gaining elevation.

I plugged in a few numbers here:

http://analyticcycling.com/ForcesSource_Page.html

Using default everything, except 4 m/s speed and 0.07 grade, gives
5913 gm of force on the rider. Increasing the rolling resistance
coefficient from 0.004 to 0.005 gives 5990 gm, or a 1.3% increase.

1.3% is about 20 seconds on Kings Mountain.

--
terry morse Palo Alto, CA http://bike.terrymorse.com/

Quoted message said:

I plugged in a few numbers here:

http://analyticcycling.com/ForcesSource_Page.html

Using default everything, except 4 m/s speed and 0.07 grade, gives
5913 gm of force on the rider. Increasing the rolling resistance
coefficient from 0.004 to 0.005 gives 5990 gm, or a 1.3% increase.

1.3% is about 20 seconds on Kings Mountain.

Good enough for me... clearly, I would have kept up with the other guy then.
He finished 30 seconds ahead of me, but had I been a bit closer, no doubt I
would have been spurred on to a fast finish!

You're never too old to dream.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

I'm no expert, but I don't think 82 lbs is all that low. I have different
road bikes that I ride regularly with different sizes and pressures. My
race bike with 23s gets 110 rear and 100 front. I have a bike with 28s
that I run at 85 rear and 80 front, and a bike with 32s that I run 75 to
65lbs. There is a feeling quality difference for me between them, but,
I feel the variation in how I feel from day to day makes more of a
difference in my ease and speed up hills than the tires do. Also I have had
times on the race bike where I hadn't filled them in several rides and came
back with them at 80 lbs. I can feel the front wheels softness on standing
climbs, but I don't think it would cause me to get dropped.

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

Quoted message said:

Quoted message said:

So, since I'm looking for excuses for how I felt this morning, how much
more
effort does an underinflated tire create? Hopefully a lot! :>😉

Check out the curves of resistance vs. pressure on my web page:

http://bike.terrymorse.com/rolres.html

Short answer: pressure makes a real difference, but not a huge
difference.

Terry: I've gone through the old threads (again), and looked (again) at the
charts on your site showing what happens to rolling resistance as pressure
increases, but I'm *still* not sure what it all means. For example, if you
increase the rolling resistance from 240 to 290 grams (as you decrease
pressure from about 125psi to 82), you're talking about a 20% difference.

But 20% greater rolling resistance means what exactly? On flat land at
moderate speeds, rolling resistance is probably a much smaller part of the
equation than air resistance. But climbing, you (well, at least I) don't
have the speed for air resistance to be much of a factor, but obviously
you're doing a lot of work gaining elevation.

I went to this site- http://w3.iac.net/~curta/bp/velocity/velocity.html- and
played around a bit with the numbers. From what I can tell, the change in
rolling resistance is linear and thus changes might be best estimated by
making changes in the "transmission efficiency" part of the equation. But,
of course, we're talking about only one tire having a 20% increase in
rolling resistance, with the other being inflated to normal pressure.

An awful lot of trouble to try and rationalize why I felt slow!

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com