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Re: More Data From Silca - Tire Pressure & Comfort [TRIing2Run] [ In reply to ]
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Thanks, currently working on the last details of next week's piece on Crr... gonna be a fun one!
J

http://www.SILCA.cc
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Re: More Data From Silca - Tire Pressure & Comfort [joshatsilca] [ In reply to ]
Quote | Reply
joshatsilca wrote:
Thanks, currently working on the last details of next week's piece on Crr... gonna be a fun one!

J


It will be interesting to see how things align with the late Jobst Brandt's thoughts on the topic:

jbrandt wrote:
From: jbrandt@hpl.hp.com (Jobst Brandt)

Newsgroups: rec.bicycles.tech Subject: Re: Tire question for Jobst
Date: 11 Jun 1999 18:49:16 GMT Brian Nystrom writes:
> In your rolling resistance testing, did you ever do any comparison
> of the effects of tire pressure on rolling resistance on a rough
> surface or was it all done on smooth surfaces? I've heard that high
> tire pressures can increase rolling resistance on rough surfaces,
> since they are less able to absorb the irregularities. Any credence
> to this?

Rough surface tests are not generally performed because they affect tires equally with varying inflation. I suppose for curiosity, a test on a drum with intermittent ribs widely spaced could do this, but I believe it has nothing to do with practical tire performance. The possibility that RR increases for tires on some surfaces is an often discussed subject, especially by riders who do not ride on a variety of surfaces with high pressure tires. In theory an increase would occur on a regular saw toothed surface riding up successive ramps only to land after a short free flight on the next ramp, thereby not rolling off the back side of the crest to gain any forward thrust. For those who ride over cattle guards either at the critical speed, this is a real effect and exactly emulates the ramp model. However, since road roughness is random and far smaller than the compliance of the tire, this scenario is unreal and does not occur. Tire deflection does not go to zero with high inflation. I have gotten snake bites with maximum safe inflation pressure on rough dirt roads. This is evidence of how much compliance a tire has even when inflated to these theoretical retarding pressures. It doesn't happen!

> I realize that the term "rough" is not descriptive, so for arguments
> sake, let's define it at as irregularities up to 1/2" in height or
> depth, which would be reasonably representative
> of.patched/cracked/erroded pavement.

Yes, any singular feature that causes lift-off has a retarding effect if there is not a series of randomly spaced similar ones on whose backside the tire lands as often as it lifts off. This occurs on an adversely ordered surface, such as a cattle guard or a series of botts dots. However, a tire that is run at lower inflation absorbs energy all the time including the larger bumps that it cannot entirely absorb anyway. Jim Papadopoulos has argued for lower inflation at great length ins this subject here on the net. Having ridden many miles on pave' and cobbles, I am convinced that although it may not be comfortable, high tire pressure is faster on even such rough surfaces. Jobst Brandt <jbrandt@hpl.hp.com>



My own personal findings indicate that on super duper rough chip seal, a modest increase in Crr can be observed with modestly higher pressures - maybe 10% or so in terms of watts @ 40 kph:


other field test data I've collected in the past suggests higher pressures aren't as bad as have been posited:

http://biketechreview.com/...-on-road-crr-results


...though, drawing conclusions based on field testing Crr and CxA is a tough piece of work when methodology lacks statistical power.

also, FWIW, bumpy roller tests conducted by two separate individuals (myself and Al Morrision) indicate decreasing Crr with increasing pressure:

http://www.biketechreview.com/...py_Data_BTR_rev1.pdf

ymmv,

=================
Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
=================
Quote Reply
Re: More Data From Silca - Tire Pressure & Comfort [BikeTechReview] [ In reply to ]
Quote | Reply
BikeTechReview wrote:
joshatsilca wrote:
Thanks, currently working on the last details of next week's piece on Crr... gonna be a fun one!

J


It will be interesting to see how things align with the late Jobst Brandt's thoughts on the topic:

jbrandt wrote:
From: jbrandt@hpl.hp.com (Jobst Brandt)

Newsgroups: rec.bicycles.tech Subject: Re: Tire question for Jobst
Date: 11 Jun 1999 18:49:16 GMT Brian Nystrom writes:
> In your rolling resistance testing, did you ever do any comparison
> of the effects of tire pressure on rolling resistance on a rough
> surface or was it all done on smooth surfaces? I've heard that high
> tire pressures can increase rolling resistance on rough surfaces,
> since they are less able to absorb the irregularities. Any credence
> to this?

Rough surface tests are not generally performed because they affect tires equally with varying inflation. I suppose for curiosity, a test on a drum with intermittent ribs widely spaced could do this, but I believe it has nothing to do with practical tire performance. The possibility that RR increases for tires on some surfaces is an often discussed subject, especially by riders who do not ride on a variety of surfaces with high pressure tires. In theory an increase would occur on a regular saw toothed surface riding up successive ramps only to land after a short free flight on the next ramp, thereby not rolling off the back side of the crest to gain any forward thrust. For those who ride over cattle guards either at the critical speed, this is a real effect and exactly emulates the ramp model. However, since road roughness is random and far smaller than the compliance of the tire, this scenario is unreal and does not occur. Tire deflection does not go to zero with high inflation. I have gotten snake bites with maximum safe inflation pressure on rough dirt roads. This is evidence of how much compliance a tire has even when inflated to these theoretical retarding pressures. It doesn't happen!

> I realize that the term "rough" is not descriptive, so for arguments
> sake, let's define it at as irregularities up to 1/2" in height or
> depth, which would be reasonably representative
> of.patched/cracked/erroded pavement.

Yes, any singular feature that causes lift-off has a retarding effect if there is not a series of randomly spaced similar ones on whose backside the tire lands as often as it lifts off. This occurs on an adversely ordered surface, such as a cattle guard or a series of botts dots. However, a tire that is run at lower inflation absorbs energy all the time including the larger bumps that it cannot entirely absorb anyway. Jim Papadopoulos has argued for lower inflation at great length ins this subject here on the net. Having ridden many miles on pave' and cobbles, I am convinced that although it may not be comfortable, high tire pressure is faster on even such rough surfaces. Jobst Brandt <jbrandt@hpl.hp.com>



My own personal findings indicate that on super duper rough chip seal, a modest increase in Crr can be observed with modestly higher pressures - maybe 10% or so in terms of watts @ 40 kph:


other field test data I've collected in the past suggests higher pressures aren't as bad as have been posited:

http://biketechreview.com/...-on-road-crr-results


...though, drawing conclusions based on field testing Crr and CxA is a tough piece of work when methodology lacks statistical power.

also, FWIW, bumpy roller tests conducted by two separate individuals (myself and Al Morrision) indicate decreasing Crr with increasing pressure:

http://www.biketechreview.com/...py_Data_BTR_rev1.pdf

ymmv,

What size rim and what tire were you using? Also, how much do you weigh.


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Re: More Data From Silca - Tire Pressure & Comfort [BikeTechReview] [ In reply to ]
Quote | Reply
BikeTechReview wrote:

also, FWIW, bumpy roller tests conducted by two separate individuals (myself and Al Morrision) indicate decreasing Crr with increasing pressure:

http://www.biketechreview.com/...py_Data_BTR_rev1.pdf

Some important notes about Al's testing, of which you may, or may not be aware...but which are important for others to put it into context:

1. Al applied wire "bumps" to only 1 roller of a 2-roller rear setup. This means that only have the contact patch load of the rear wheel was being "energized" (i.e. only slightly more than half the load on the "bumpy" contact).

2. The wires were fairly small diameter. As we've seen in the previous Silca data (and data from Damon Rinard) the smaller the object, the lower the effective spring constant for a given tire/wheel at a given pressure.

3. Al's rollers are plastic, which will have more inherent flexibility than aluminum rollers, or even a typical road surface.

Knowing all of that, even Al has told me himself that he doesn't think his original "bumpy roller" test was particularly enlightening.

http://bikeblather.blogspot.com/
Quote Reply
Re: More Data From Silca - Tire Pressure & Comfort [Thomas Gerlach] [ In reply to ]
Quote | Reply
Thomas Gerlach wrote:
BikeTechReview wrote:
joshatsilca wrote:
Thanks, currently working on the last details of next week's piece on Crr... gonna be a fun one!

J


It will be interesting to see how things align with the late Jobst Brandt's thoughts on the topic:

jbrandt wrote:
From: jbrandt@hpl.hp.com (Jobst Brandt)

Newsgroups: rec.bicycles.tech Subject: Re: Tire question for Jobst
Date: 11 Jun 1999 18:49:16 GMT Brian Nystrom writes:
> In your rolling resistance testing, did you ever do any comparison
> of the effects of tire pressure on rolling resistance on a rough
> surface or was it all done on smooth surfaces? I've heard that high
> tire pressures can increase rolling resistance on rough surfaces,
> since they are less able to absorb the irregularities. Any credence
> to this?

Rough surface tests are not generally performed because they affect tires equally with varying inflation. I suppose for curiosity, a test on a drum with intermittent ribs widely spaced could do this, but I believe it has nothing to do with practical tire performance. The possibility that RR increases for tires on some surfaces is an often discussed subject, especially by riders who do not ride on a variety of surfaces with high pressure tires. In theory an increase would occur on a regular saw toothed surface riding up successive ramps only to land after a short free flight on the next ramp, thereby not rolling off the back side of the crest to gain any forward thrust. For those who ride over cattle guards either at the critical speed, this is a real effect and exactly emulates the ramp model. However, since road roughness is random and far smaller than the compliance of the tire, this scenario is unreal and does not occur. Tire deflection does not go to zero with high inflation. I have gotten snake bites with maximum safe inflation pressure on rough dirt roads. This is evidence of how much compliance a tire has even when inflated to these theoretical retarding pressures. It doesn't happen!

> I realize that the term "rough" is not descriptive, so for arguments
> sake, let's define it at as irregularities up to 1/2" in height or
> depth, which would be reasonably representative
> of.patched/cracked/erroded pavement.

Yes, any singular feature that causes lift-off has a retarding effect if there is not a series of randomly spaced similar ones on whose backside the tire lands as often as it lifts off. This occurs on an adversely ordered surface, such as a cattle guard or a series of botts dots. However, a tire that is run at lower inflation absorbs energy all the time including the larger bumps that it cannot entirely absorb anyway. Jim Papadopoulos has argued for lower inflation at great length ins this subject here on the net. Having ridden many miles on pave' and cobbles, I am convinced that although it may not be comfortable, high tire pressure is faster on even such rough surfaces. Jobst Brandt <jbrandt@hpl.hp.com>



My own personal findings indicate that on super duper rough chip seal, a modest increase in Crr can be observed with modestly higher pressures - maybe 10% or so in terms of watts @ 40 kph:


other field test data I've collected in the past suggests higher pressures aren't as bad as have been posited:

http://biketechreview.com/...-on-road-crr-results


...though, drawing conclusions based on field testing Crr and CxA is a tough piece of work when methodology lacks statistical power.

also, FWIW, bumpy roller tests conducted by two separate individuals (myself and Al Morrision) indicate decreasing Crr with increasing pressure:

http://www.biketechreview.com/...py_Data_BTR_rev1.pdf

ymmv,


What size rim and what tire were you using? Also, how much do you weigh.

brake track to brake track measured 19.6mm - I have used many different tires over the years to create demand plots similar to the above; however for this particular plot I used a vittoria 700x20c zaffiro that had an installed width of 20.8mm at 120 psi.

All-up bike/kit/rider mass at the time was 84kg IIRC.

=================
Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
=================
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Re: More Data From Silca - Tire Pressure & Comfort [Tom A.] [ In reply to ]
Quote | Reply
Tom A. wrote:
BikeTechReview wrote:


also, FWIW, bumpy roller tests conducted by two separate individuals (myself and Al Morrision) indicate decreasing Crr with increasing pressure:

http://www.biketechreview.com/...py_Data_BTR_rev1.pdf



Some important notes about Al's testing, of which you may, or may not be aware...but which are important for others to put it into context:

1. Al applied wire "bumps" to only 1 roller of a 2-roller rear setup. This means that only have the contact patch load of the rear wheel was being "energized" (i.e. only slightly more than half the load on the "bumpy" contact).


that's what I did in my testing as well. At the time, my well-calibrated meat in the seat/supercomputer sensor said - "whoa, that's f'in bumpy!". It's also interesting to note that Al's reported bumpy Crr increased by about 30% over the smooth roller configuration with his "half-load-energized" setup. Does this make his setup more lossy than what is reported elsewhere? I dunno...but, my setup was f'in bumpy!

Quote:
2. The wires were fairly small diameter. As we've seen in the previous Silca data (and data from Damon Rinard) the smaller the object, the lower the effective spring constant for a given tire/wheel at a given pressure.

I had small bump heights as well: 1-2 mm tall. They were pretty wide, though, and I had quite a few of them - rubber deposited on the bumps too. I took some video when I did this experiment back in 2010 and there was some discussion on the BTR forum as well:

video here (woohoo - hear those bumps hum!):


www.biketechreview.com/images/bumpy_rollers_090610_lores.wmv

thread here:
http://biketechreview.com/...losses-in-human-body


Quote:
3. Al's rollers are plastic, which will have more inherent flexibility than aluminum rollers, or even a typical road surface.

mine were 4.5" aluminum as shown in the video above.

=================
Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
=================
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