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  1. #1
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    Schwalbe tire pressure study question....

    Ive read the study. How do you reconcile those results with how much harder it is to pedal 28 psi tires with 35 psi tires. Or is it my imagination? Thanks?

  2. #2
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    The rougher the terrain, the greater benefit of lower PSI (compliance) for maintaining momentum.

    There are other benefits such as traction with lower PSI as well.

    P

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    Your perception of what "feels fast" and what is actually lower rolling resistance on rough terrain are two completely different things

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    Quote Originally Posted by briscoelab
    Your perception of what "feels fast" and what is actually lower rolling resistance on rough terrain are two completely different things
    And none of those things address the question at hand. Is it harder to power forward a softer tire?

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    The definition of rolling resistance would lead you to the conclusion that it is not harder to pedal a softer tire over rough terrain (less power for the same speed). Sorry that's such a hard connection to make.

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    Quote Originally Posted by bing!
    And none of those things address the question at hand. Is it harder to power forward a softer tire?
    Did you just change over to talking about durometers of the rubber?

    A tire isn't "softer" at a lower PSI, it just isn't as full.

    You can debate the feel of it, but you cannot argue with numbers.

    One of my favorite parts is how tires don't tend to spin-out as much climbing in the wet/rocky/rooty areas when running super low PSI. Always faster to not have to get off your bike and walk.

  7. #7
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    Quote Originally Posted by briscoelab
    The definition of rolling resistance would lead you to the conclusion that it is not harder to pedal a softer tire over rough terrain (less power for the same speed). Sorry that's such a hard connection to make.
    What "feels fast" has nothing to do with my question. Youre smugness is amusing but is not productive. The rest of this response is not addressed to you.

    A characteristic of a deformable material such that the energy of deformation is greater than the energy of recovery. The rubber compound in a tire exhibits hysteresis. As the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy loss as heat. Hysteresis is the main cause of energy loss associated with rolling resistance.

    -- National Academy of Sciences[3]

    The Schwalbe study begins with a comparison of 2.1 tires at 57 psi vs. 2.4 at 21. It moves on to compare the same tire at 57 and 21 psi. As with anything, there must be a curve. Both pressure samples seem too far apart with the high pressure value selected looking unrealistic. Id be very interested to know where that curve is as in my experience, the difference between effort exerted at 35 psi and 28 psi is apparent.

    I am a bit puzzled why only two air pressures, and why those two, were selected. That is like taking the race times of an 8 and a 65 year old among 25 differently aged racers as the average race time for cyclists in a given sample. (disclaimer: basic analogy, could be better).
    Last edited by bing!; 02-28-2011 at 02:00 PM.

  8. #8
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    Quote Originally Posted by CharacterZero
    Did you just change over to talking about durometers of the rubber?

    A tire isn't "softer" at a lower PSI, it just isn't as full.

    You can debate the feel of it, but you cannot argue with numbers.

    One of my favorite parts is how tires don't tend to spin-out as much climbing in the wet/rocky/rooty areas when running super low PSI. Always faster to not have to get off your bike and walk.
    Besides playing with words, to which I am sure you understand what I mean, you seem to be honest in your answer. Thank you.

    Let me refine the question as below - The Schwalbe study begins with a comparison of 2.1 tires at 57 psi vs. 2.4 at 21. It moves on to compare the same tire at 57 and 21 psi. As with anything, there must be a curve. Both pressure samples seem too far apart. Id be very interested to know where that curve is as in my experience, the difference between effort exerted at 35 psi and 28 psi is apparent and favors the slightly higher pressure.

    I am not denying the Schwalbe results. However, I am sure you will accept that lower tire pressure will only give productivity up to a certain point, after which it will trail off to lesser efficiency. Given my own experience, in my environs, which is more specific than 57 to 21 psi, I am questioning if 28 is more efficient that 35.

    Not trying to be controversial. Just a questioning mind. That other guy seems to take the study as gospel

  9. #9
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    Quote Originally Posted by bing!
    Besides playing with words, to which I am sure you understand what I mean, you seem to be honest in your answer. Thank you.

    Let me refine the question as below - The Schwalbe study begins with a comparison of 2.1 tires at 57 psi vs. 2.4 at 21. It moves on to compare the same tire at 57 and 21 psi. As with anything, there must be a curve. Both pressure samples seem too far apart. Id be very interested to know where that curve is as in my experience, the difference between effort exerted at 35 psi and 28 psi is apparent and favors a slightly higher pressure.

    I am not denying the Schwalbe results. However, I am sure you will accept that lower pressure will only give productivity to a certain point. Given my own experience, which is more specific than 57 to 21 psi, I am questioning if 28 is more efficient that 35.

    Not trying to controversial. Just a questioning mind. That other guy seems to take a study as gospel
    Did you time your laps or a section that you feel is most relevant to your riding?
    Are your legs more sore after riding at 28 psi?

  10. #10
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    Quote Originally Posted by CharacterZero
    Did you time your laps or a section that you feel is most relevant to your riding?
    Are your legs more sore after riding at 28 psi?
    Yes, they are definitely more sore, and I did a blind test on my son I let air out off his tires from 32 to 28, and he was complaining the whole ride that there was something wrong with his bike

    I am not sure of my observations. They are just that, observations. I might explore it further, just looking for an honest discussion at this point so I can make a more informed choice.
    Last edited by bing!; 02-28-2011 at 02:15 PM.

  11. #11
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    Quote Originally Posted by bing!
    Ive read the study. How do you reconcile those results with how much harder it is to pedal 28 psi tires with 35 psi tires. Or is it my imagination? Thanks?

    Tire pressure is always going to be a trade-off between rolling resistance, grip and pinch flat or rim damage resistance. Add to that the rolling resistance at different pressures will depend on how smooth the trail surface is.
    The wider the tire the more you can lower the pressure, gain grip, minimise rolling resistance and gain pinch flat resistance at the expense of weight.

    Maybe for where you are testing the tires the right pressure is 35 psi but it might be worth checking that with some qualitative measurements. Tire pressure is a tuning tool, there's no perfect number that you should always set it to, some trails will need higher pressure just to keep from dinging rims or getting pinch flats, some will need lower pressure to keep the tires from skittering in turns.

    I changed from 700x23c @120psi to 700x25c @95 psi on my road bike a couple of years ago. Initially they felt slow (though with noticeably better grip and comfort) but my average speed on rides never changed so there can't be much difference in rolling resistance, it was just the softer feel of the lower pressure tire that felt slow because I was used to the rock hard tires = fast feel.

    For mountain bike tires I generally start at whatever pressure will get all the knobs but the edge knobs touching the ground when I'm riding straight on flat ground then adjust up or down from there in 5 psi increments depending on how they feel. It's amazing how much difference a change as small as 2-3 psi will make.

  12. #12
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    Quote Originally Posted by Surestick Malone
    Tire pressure is always going to be a trade-off between rolling resistance, grip and pinch flat or rim damage resistance. Add to that the rolling resistance at different pressures will depend on how smooth the trail surface is.
    The wider the tire the more you can lower the pressure, gain grip, minimise rolling resistance and gain pinch flat resistance at the expense of weight.

    ......... It's amazing how much difference a change as small as 2-3 psi will make.
    I was thinking it................but not as well Great stuff.

    Given that I spend 3/4 of my riding time going up and only 1/4 down, I think I will be fine tuning my pressure accordingly. Not to mention that Im unable to climb some stuff at 35 psi

    Thanks.

  13. #13
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    Quote Originally Posted by bing!
    What "feels fast" has nothing to do with my question. Youre smugness is amusing but is not productive. The rest of this response is not addressed to you.

    A characteristic of a deformable material such that the energy of deformation is greater than the energy of recovery. The rubber compound in a tire exhibits hysteresis. As the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy loss as heat. Hysteresis is the main cause of energy loss associated with rolling resistance.

    -- National Academy of Sciences[3]

    The Schwalbe study begins with a comparison of 2.1 tires at 57 psi vs. 2.4 at 21. It moves on to compare the same tire at 57 and 21 psi. As with anything, there must be a curve. Both pressure samples seem too far apart with the high pressure value selected looking unrealistic. Id be very interested to know where that curve is as in my experience, the difference between effort exerted at 35 psi and 28 psi is apparent.

    I am a bit puzzled why only two air pressures, and why those two, were selected. That is like taking the race times of an 8 and a 65 year old among 25 differently aged racers as the average race time for cyclists in a given sample. (disclaimer: basic analogy, could be better).
    If you are conducting a study you chose variables that are enough different to show significant results. You need to run a large number of tests with each variable to have consistent data. Adding variables vastly increases the time and cost of the test.

    After you have established that there is a performance difference, then you can start narrowing the gaps in setup, if you have funding.

    I have had a plan for real-world tire performance. I would love to use 3-4 different pressures, but realistically I would not have time to do enough runs in a day with 4-5 setups (including controls) to record enough data points to have valid results.

    And my butt and legs tell me that most tires roll better at 28psi than 35 on trails, though the lower pressure does feel harder to pedal on pavement.
    Last edited by shiggy; 02-28-2011 at 03:59 PM.
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  14. #14
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    Quote Originally Posted by bing!
    The Schwalbe study begins with a comparison of 2.1 tires at 57 psi vs. 2.4 at 21. It moves on to compare the same tire at 57 and 21 psi. As with anything, there must be a curve. Both pressure samples seem too far apart. Id be very interested to know where that curve is as in my experience, the difference between effort exerted at 35 psi and 28 psi is apparent and favors the slightly higher pressure.
    so people can see what you're talking about here's a link.
    There are four points going from 21 to 57 psi, not just two. The curve is on page 7, and there are other presentations of the results as well.
    Quote Originally Posted by bing!
    I am not denying the Schwalbe results. However, I am sure you will accept that lower tire pressure will only give productivity up to a certain point, after which it will trail off to lesser efficiency. Given my own experience, in my environs, which is more specific than 57 to 21 psi, I am questioning if 28 is more efficient that 35.
    If by "lesser efficiency" you mean pinch flats, then yes.
    21 psi is lower than most people can ride w/out getting pinch flats, and 57 psi is much higher than most people ride, so they covered the whole operating range (more-or-less) and the results are pretty clear. According to the study, 28psi is more efficient than 35 psi on rough surfaces. The rougher the surface, the greater the effect. On the road, the opposite is true. This transition happens somewhere between "meadow" and "road." If you're riding smooth hardpack, you very well might be on the other side of the transition. The roughness of the surface is key.
    Quote Originally Posted by bing!
    Not trying to be controversial. Just a questioning mind. That other guy seems to take the study as gospel
    questioning minds are good! studies are not gospel, they have to be taken for what they are, with all the facts and limitations they have.
    Last edited by meltingfeather; 02-28-2011 at 04:15 PM.
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    Time to stop believing the hype and start doing some science.
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  15. #15
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    Quote Originally Posted by meltingfeather
    so people can see what you're talking about here's a link.
    There are four points going from 21 to 57 psi, not just two. The curve is on page 7, and their are other presentations of the results as well.

    If by "lesser efficiency" you mean pinch flats, then yes.
    21 psi is lower than most people can ride w/out getting pinch flats, and 57 psi is much higher than most people ride, so they covered the whole operating range (more-or-less) and the results are pretty clear. According to the study, 28psi is more efficient than 35 psi on rough surfaces. The rougher the surface, the greater the effect. On the road, the opposite is true. This transition happens somewhere between "meadow" and "road." If you're riding smooth hardpack, you very well might be on the other side of the transition. The roughness of the surface is key.

    questioning minds are good! studies are not gospel, they have to be taken for what they are, with all the facts and limitations they have.
    Totally agree with you MF.
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  16. #16
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    Quote Originally Posted by shiggy

    After you have established that there is a performance difference, then you can start narrowing the gaps in setup, if you have funding.

    I have had a plan for real-world tire performance. I would love to use 3-4 different pressures, but realistically I would not have time to do enough runs in a day with 4-5 setups (including controls) to record enough data points to have valid results.

    And my butt and legs tell me that most tires roll better at 28psi than 35 on trails, though the lower pressure does feel harder to pedal on pavement.
    IMHO, a larger sample than just two wouldve have been more conclusive. In a post above, it was actually shown that there was inded 4 samples, instead of the 2 that I thought.

    I looked into the SRM training system used to measure results in the the Schwalbe test and it seems to be dependent on rider input. The controlled properties of a human rider is debatable (re: ability to produce the exactly same amount of power repeatedly). THe SRM system is better suited for.....training. FYI, the SRM system is 950 dollars for the head unit only.

    Ideally, I think an MTB wheel travelling on a large self powered offroad surface drum wouldve been more conclusive. However, I'm sure, nobody is going to bother.

    Appreciate the input. Thanks.
    Last edited by bing!; 02-28-2011 at 04:47 PM.

  17. #17
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    Quote Originally Posted by meltingfeather
    There are four points going from 21 to 57 psi, not just two. The curve is on page 7, and there are other presentations of the results as well.

    questioning minds are good! studies are not gospel, they have to be taken for what they are, with all the facts and limitations they have.
    You are correct regarding the samples.



    The gravel results suggest that MTB tires exhibit no hysteresis (increased rolling resistance due to tire folding) effect in off road conditions. That is surprising. With those results, and momentarily dismissing pinch flats, it would be interesting to see how efficient a tire could be made by further reducing air pressure.

    Thanks for the correction.

    EDIT: There is a significant error in that chart. According to the study, the highest rolling resistance is in the MEADOW tests. If you look at the chart, the gravel shows the highest rolling resistance. If we are to assume that the meadow result is actually that of gravel, the difference between 1.5 bar to 4 bar is less than 4 watts. Almost negligible between 1.5 and 2 bar, and probably less than the standard deviation for the study considering the human input. I wonder what 1 watt feels like?
    Last edited by bing!; 02-28-2011 at 05:06 PM.

  18. #18
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    Quote Originally Posted by bing!
    Ideally, I think a self propelled cart on MTB wheels travelling on a rail would be the way to go. Or an MTB wheel travelling on a large offroad surface drum. However, I'm sure, nobody is going to bother.

    Assuming you want to go as fast as possible for a given effort the best way to measure would be to ride the same trail with a power meter or heart rate monitor and different tire pressures. Try and keep similar power outputs or heart rates for the different pressures and see which gives you the best time.
    A drum won't tell you anything about behaviour under braking and turning at different pressures and those can have as much of an effect on speed as rolling resistance.

    I'm in Quebec so Northern East-coast roots & rocks. I'd bet that for my local trails I'm faster going to the lowest pressure I can without pinch flatting because it means I can carry more speed through turns and brake harder and later.

    Quote Originally Posted by bing!



    The gravel results suggest that MTB tires exhibit no hysteresis (increased rolling resistance due to tire folding) effect in off road conditions. That is surprising. With those results, and momentarily dismissing pinch flats, it would be interesting to see how efficient a tire could be made by further reducing air pressure.
    My understanding is that while you still lose more energy to hysteresis at lower pressures you save more energy by deforming around bumps instead of bouncing off them. That's why the rolling resistance on the road decreases a bit with pressure and increase on gravel

  19. #19
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    This bikeradar.com article about the Wheel Energy company's tyre testing in Finland is quite an interesting read on the same subject.

    http://www.bikeradar.com/gear/articl...he-myths-29245

    .

  20. #20
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    Quote Originally Posted by Surestick Malone
    My understanding is that while you still lose more energy to hysteresis at lower pressures you save more energy by deforming around bumps instead of bouncing off them. That's why the rolling resistance on the road decreases a bit with pressure and increase on gravel
    Good point.

    Ergo, by looking at the charts, it is highly possible that hysteresis is a factor that exerts an influence of less than +/- 3 watts. Terrain resistance(?) must supersede the tires rolling resistance at that point.

    Thanks.

  21. #21
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    Quote Originally Posted by bing!
    The gravel results suggest that MTB tires exhibit no hysteresis (increased rolling resistance due to tire folding) effect in off road conditions. That is surprising. With those results, and momentarily dismissing pinch flats, it would be interesting to see how efficient a tire could be made by further reducing air pressure.
    I don't think it shows that there's no hysteresis (which we know to be false), I think it shows that whatever other effect is playing out has a greater overall effect than hysteresis does.
    I have a bit of a theory about why we see this effect. I'll try and wrap it in a nutshell, which I haven't done before:
    Thinking about tire deflection on a flat surface, all force arrows from the road on the tire and tire on road are vertical (there is no horizontal component at all). I'm not sure how efficient the friction of tire and road as the tire re-takes it's shape at the back of the contact is at propelling the bike forward, so you might even see rolling resistance in a mythical tire that didn't have hysteresis.
    Now change to a tire rolling over a simple object (say a triangular block). As the tire rolls over the block, there comes a point when, as the tire rolls off the block, there is an angled surface that the tire pressure is pushing against that does have a horizontal component. Essentially, the tire has the backside of the obstacle to "push off" of, recovering some energy that was used to deflect the tire.
    If a hard tire hits the same obstacle and kicks the tire up, you lose forward momentum from the upward movement of the bike, but I think you also lose the effectiveness of this theoretical "push off" energy recovery, because on small surfaces you are less likely to come down in time to get the push-off. On large-amplitude surfaces, like a BMX double, you are able to recover some of the energy stored when you get air by rolling down the tranny, which propels you forward.

    Note that this is totally untested, off-the-cuff, theoretical musing on my part.

    Quote Originally Posted by bing!
    Thanks for the correction.

    EDIT: There is a significant error in that chart. According to the study, the highest rolling resistance in the MEADOW tests. If you look at the chart, the gravel shows the highest rolling resistance. If we are to assume that the meadow result is actually that of gravel, the difference between 1.5 bar to 4 bar is less than 4 watts. Almost negligible between 1.5 and 2 bar, and probably less than the standard deviation for the study considering the human input. I wonder what 1 watt feels like?
    Great catch!
    I think that they have flipped the results (mislabeled).
    There's some study somewhere about the human perception limit of rolling resistance. Of course, the results wouldn't apply to everyone.
    Even if rolling resistance were the same across the board, I'd still ride pressure as low as possible for comfort and traction.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  22. #22
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    Quote Originally Posted by bing!
    Ideally, I think an MTB wheel travelling on a large self powered offroad surface drum wouldve been more conclusive. However, I'm sure, nobody is going to bother.
    Don't know about that:

    I'd also like to see this overall power measurement technique used on a hybrid of a drum and a rider on an open course, like this:
    <iframe title="YouTube video player" width="480" height="390" src="http://www.youtube.com/embed/AKEHoA_xl-U" frameborder="0" allowfullscreen></iframe>
    Attached Thumbnails Attached Thumbnails Schwalbe tire pressure study question....-rr%2520surfaces.jpg  

    Last edited by meltingfeather; 03-01-2011 at 10:06 AM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  23. #23
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    The typical MTBR argument thread:

    General opinions - check
    Reference of general data - check
    Charts - check
    Pictures - check
    Equations - incoming
    Arguments over equations - incoming

    We are still missing the comparison between 26 & 29" wheels and we will have met the requirements.

    Oh by the way Shiggy and Melting Feather are right!

  24. #24
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    Quote Originally Posted by bing!
    IMHO, a larger sample than just two wouldve have been more conclusive. In a post above, it was actually shown that there was inded 4 samples, instead of the 2 that I thought.

    I looked into the SRM training system used to measure results in the the Schwalbe test and it seems to be dependent on rider input. The controlled properties of a human rider is debatable (re: ability to produce the exactly same amount of power repeatedly). THe SRM system is better suited for.....training. FYI, the SRM system is 950 dollars for the head unit only.

    Ideally, I think an MTB wheel travelling on a large self powered offroad surface drum wouldve been more conclusive. However, I'm sure, nobody is going to bother.

    Appreciate the input. Thanks.
    A larger sample of a few variables will give better results than few samples of more variables. Basic experimental protocol.

    As already posted, there are testing drums. But I do not ride my bike on 3-4-foot metal drums.
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  25. #25
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    Quote Originally Posted by OLx6
    The typical MTBR argument thread:

    General opinions - check
    Reference of general data - check
    Charts - check
    Pictures - check
    Equations - incoming
    Arguments over equations - incoming

    We are still missing the comparison between 26 & 29" wheels and we will have met the requirements.

    Oh by the way Shiggy and Melting Feather are right!
    the 26/29 test is in the BikeRadar article
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  26. #26
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    Right on for the 26/29. Can someone throw out some equations? Preferably one that takes an assumption as a factor that everyone can disagree on?

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    Quote Originally Posted by shiggy
    But I do not ride my bike on 3-4-foot metal drums.
    Hehehehehe, sounds good to the ear, but I'm sure you know better.

    When testing for stuff like rolling resistance, a controlled experiment requires a controlled and repeatable test, hence the drum. Then, results can be comparable.

  28. #28
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    Quote Originally Posted by bing!
    Hehehehehe, sounds good to the ear, but I'm sure you know better.

    When testing for stuff like rolling resistance, a controlled experiment requires a controlled and repeatable test, hence the drum. Then, results can be comparable.
    Jep, true that. The only question is if that drum simulates your riding surface well enough. I guess for generic results such as what is discussed in this thread it won't be so critical, then again the Finnish company (pumps chest with national pride) seemed to be releasing quite little information and most of that related to road bikes.

    There was a thread regarding this on a Finnish board too, I believe at least part of the people behind the company are members, but no comments or details till now.

  29. #29
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    I just realized no one has referenced the testing as done in this thread:
    http://forums.mtbr.com/showthread.php?t=419392

  30. #30
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    If anyone's wondering which Schwalbe tyre study is being discussed there's a link to the original article here:

    http://www.mtbonline.co.za/downloads...llustrated.pdf

    The study was originally carried out by Peter Nilges, for his graduate dissertation at the German College of Physical Education, Cologne.

    There are also Pages 16-17 from this Schwalbe PDF which mention rolling resistance and tyre pressure:

    http://www.schwalbe.co.uk/shopdata/f...chInfo2-GB.pdf

    .
    Last edited by WR304; 03-01-2011 at 10:59 AM.

  31. #31
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    Quote Originally Posted by CharacterZero
    I just realized no one has referenced the testing as done in this thread:
    http://forums.mtbr.com/showthread.php?t=419392
    i think because this thread is specifically about the correllation between lower pressure and lower rolling resistance that only happens on rough surfaces. all of those tests were conducted on standard RR machines (smooth drums).
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  32. #32
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    Quote Originally Posted by shiggy
    A larger sample of a few variables will give better results than few samples of more variables. Basic experimental protocol.

    As already posted, there are testing drums. But I do not ride my bike on 3-4-foot metal drums.

    Well a larger sample with fewer variables may or may not give "better results" that would depend upon a statistical analysis of the data obtained.

    Tests without inherent errors in measurement will give "better results" than tests with inherent errors in measurement. (ie a rolling drum rather than a flat track).

    What is certain is increasing the number of variables increases the number of test points required. ( proportional to the power of the number of variables tested)

    If a large data spread is noted than the number of data points must be increased. If the testing results in a small data spread then the number of data points maybe decreased. When examined by valid statiscal methods.

    That is basic experimental protocol.
    Last edited by jeffscott; 03-01-2011 at 11:29 AM.

  33. #33
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    Quote Originally Posted by bing!
    You are correct regarding the samples.



    The gravel results suggest that MTB tires exhibit no hysteresis (increased rolling resistance due to tire folding) effect in off road conditions. That is surprising. With those results, and momentarily dismissing pinch flats, it would be interesting to see how efficient a tire could be made by further reducing air pressure.

    Thanks for the correction.

    EDIT: There is a significant error in that chart. According to the study, the highest rolling resistance is in the MEADOW tests. If you look at the chart, the gravel shows the highest rolling resistance. If we are to assume that the meadow result is actually that of gravel, the difference between 1.5 bar to 4 bar is less than 4 watts. Almost negligible between 1.5 and 2 bar, and probably less than the standard deviation for the study considering the human input. I wonder what 1 watt feels like?

    Yeah, I think that is wrong too. I read the article and saw the same thing. That discrepancy in the chart doesn't make sense.

    The article does make some some sense especially the how a wider tire is less rolling resistance than narrower. It is just finding the right tire pressure for the terrain that you ride. That is no exact answer but you probably can get it close. However, you wouldn't know whether it is right or wrong unless you have some way to quantify the energy used at different tire pressures for your home ride.

  34. #34
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    Quote Originally Posted by aliikane

    The article does make some some sense especially the how a wider tire is less rolling resistance than narrower. It is just finding the right tire pressure for the terrain that you ride. That is no exact answer but you probably can get it close. However, you wouldn't know whether it is right or wrong unless you have some way to quantify the energy used at different tire pressures for your home ride.
    If you read the study carefully, the lower rolling resistance of the wider tire, is due to is larger diameter, not the width.

    I thought that was interesting considering that a tire with less air pressure actually has a smaller rolling diameter. So given the same tire, how do you reconcile both? Personally, I duhno

  35. #35
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    Quote Originally Posted by jeffscott
    Well a larger sample with fewer variables may or may not give "better results" that would depend upon a statistical analysis of the data obtained.

    Tests without inherent errors in measurement will give "better results" than tests with inherent errors in measurement. (ie a rolling drum rather than a flat track).

    What is certain is increasing the number of variables increases the number of test points required. ( proportional to the power of the number of variables tested)

    If a large data spread is noted than the number of data points must be increased. If the testing results in a small data spread then the number of data points maybe decreased. When examined by valid statiscal methods.

    That is basic experimental protocol.
    And if you do not make a large sample in the first place, you can not know for sure if there can be a wide range of results or if it is just an anomaly.

    In real-world testing, such as the Schwalbe study with actual riding on natural surfaces, there is inherently going to be a larger range in the results than a lab test on metal rollers.
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    Quote Originally Posted by bing!
    Hehehehehe, sounds good to the ear, but I'm sure you know better.

    When testing for stuff like rolling resistance, a controlled experiment requires a controlled and repeatable test, hence the drum. Then, results can be comparable.
    Comparable but not necessarily transferable to real-world performance, especially for mtb tires, but even for road tires.
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  37. #37
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    Quote Originally Posted by shiggy
    Comparable but not necessarily transferable to real-world performance, especially for mtb tires, but even for road tires.

    I dont look at hp ratings on cars either. I dont drive on a dyno.

  38. #38
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    Quote Originally Posted by bing!
    If you read the study carefully, the lower rolling resistance of the wider tire, is due to is larger diameter, not the width.

    I thought that was interesting considering that a tire with less air pressure actually has a smaller rolling diameter. So given the same tire, how do you reconcile both? Personally, I duhno
    I didn't read that the same way. They said the wider, shorter contact patch results in less casing deformation, with the increased diameter being an additional factor, but not the primary one:
    "The wider tyre's contact area is wider, but shorter. This then means that the 'retarding' lever that the typre has to overcome ('F' in the diagram) also shortens. Moreover wider tyres have larger diameters, and again that improves rolling."
    F is half the length of the contact patch.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by meltingfeather
    I didn't read that the same way. They said the wider, shorter contact patch results in less casing deformation, with the increased diameter being an additional factor, but not the primary one:
    "The wider tyre's contact area is wider, but shorter. This then means that the 'retarding' lever that the typre has to overcome ('F' in the diagram) also shortens. Moreover wider tyres have larger diameters, and again that improves rolling."
    F is half the length of the contact patch.
    That's how i read it also. Diameter is a factor but not primary factor. It says that the weight of the rider and bike flatten the narrower tire more than a wide tire causing more resistance of the narrow tire.

    I'm just getting some wide tires. Haha.

  40. #40
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    Quote Originally Posted by OLx6
    The typical MTBR argument thread:

    General opinions - check
    Reference of general data - check
    Charts - check
    Pictures - check
    Equations - incoming
    Arguments over equations - incoming

    We are still missing the comparison between 26 & 29" wheels and we will have met the requirements.

    Oh by the way Shiggy and Melting Feather are right!
    self important dumb ass - check!

  41. #41
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    Quote Originally Posted by bing!
    self important dumb ass - check!

    Whoa. Don't hate, relate. LOL.


    I emailed schwalbe to see some clarification of some of the information. It is definitely a big argument for having bigger tires. Now the question is " when does the weight counteract the rolling resistance of a bigger tire?" So many factors.

  42. #42
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    Quote Originally Posted by aliikane
    Whoa. Don't hate, relate. LOL.


    I emailed schwalbe to see some clarification of some of the information. It is definitely a big argument for having bigger tires. Now the question is " when does the weight counteract the rolling resistance of a bigger tire?" So many factors.
    The rolling resistance measurements of the SRM system is given in watts/power required to keep an X amount of speed, you can safely assume that weight effects are pretty much reflected. This is assuming that your concern is regarding the amount of power required to move a specific weight of tire, and keep it moving.

  43. #43
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    I just got a reply from Schwalbe. They are very helpful. Makes me wanna buy the tires more. Anyway, he did say that there was a typo in the chart. Meadow needs to be switched with the gravel line in the chart.



    I think it is difficult to do a really accurate test in real world conditions on a trail with a rider unless it was a robot. Too many variables affect speed of the rider. He may be tired, malnourished that day, dehydrated, mind not into the ride, muscles looser, etc. all would have an affect on the results.

  44. #44
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    you can hear all the experts say what is the "ideal" presure to run your tires at but at the end of the day isnt it really up to what seems to work best for you?

  45. #45
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    Quote Originally Posted by aliikane

    I think it is difficult to do a really accurate test in real world conditions on a trail with a rider unless it was a robot. Too many variables affect speed of the rider. He may be tired, malnourished that day, dehydrated, mind not into the ride, muscles looser, etc. all would have an affect on the results.
    Bingo! Given that they used a person as the motor the only thing you can really draw from those numbers is a 'rough idea' of what rolling resistance is like. The other thing to keep in mind is rider weight which plays a huge roll in what kind of tire pressure one needs to run. What would be nice is if they measure the air pressure in tire deflection instead of PSI.

  46. #46
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    Quote Originally Posted by aliikane
    I think it is difficult to do a really accurate test in real world conditions on a trail with a rider unless it was a robot. Too many variables affect speed of the rider. He may be tired, malnourished that day, dehydrated, mind not into the ride, muscles looser, etc. all would have an affect on the results.
    They didn't measure speed except to keep it relatively low and constant. They measured power, which is independent of the rider's condition.
    I agree that there are flaws in the tests (no test is perfect), but there's a wealth of information to be gained too.
    Establishing control is difficult in an open environment, but if you move it to a lab, trail hounds will accuse you of being a caliper-toting, pencil neck and tell you the results aren't relevant because what happens on the trail is all that matters.
    Catch 22
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  47. #47
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    Quote Originally Posted by b-kul
    you can hear all the experts say what is the "ideal" presure to run your tires at but at the end of the day isnt it really up to what seems to work best for you?
    i agree absolutely, but for many years myths have been propagated in the cycling world that lead cyclists not to experiment outside the window of what the 'experts' say will work best.
    this particular discovery aims at the heart of a long-held myth: that rolling resistance decreases with increasing tire pressure no matter the application.
    plus, with the amount if "which one should i get" threads on this forum, i think many rely completely on input/validation from others in their cycling choices.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  48. #48
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    Quote Originally Posted by meltingfeather
    They didn't measure speed except to keep it relatively low and constant. They measured power, which is independent of the rider's condition.
    I agree that there are flaws in the tests (no test is perfect), but there's a wealth of information to be gained too.
    Establishing control is difficult in an open environment, but if you move it to a lab, trail hounds will accuse you of being a caliper-toting, pencil neck and tell you the results aren't relevant because what happens on the trail is all that matters.
    Catch 22
    A couple of points.

    Power is entirely dependent on the rider that produces it. Less in, less out (as measured). Give the guy a 4x Gu shot and watch the watts go up

    RR as measured off an all terrain drum/dyno is better than a field test. This method provides a standardized comparison for making a tire and pressure selection.

    At the end of the day, the study exhibits a trend. However, a 1 watt difference, 2.5% of 40 watts, between 1.5 and 2 bar as provided by an unregulated power source is almost neglible.

    Good of Schwalbe to answer your question.

  49. #49
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    Quote Originally Posted by bing!
    Power is entirely dependent on the rider that produces it. Less in, less out (as measured). Give the guy a 4x Gu shot and watch the watts go up
    The body has a max power regardless of Gu shots. Gu would only be able to maintain your maximum for longer. Not increase power.

    Quote Originally Posted by bing!
    RR as measured off an all terrain drum/dyno is better than a field test. This method provides a standardized comparison for making a tire and pressure selection.
    This is the first field test, so this is relevant to whether trends in labs match up with trends in the field. I think that is important. To me it equates to more myth busting.

    Quote Originally Posted by bing!
    At the end of the day, the study exhibits a trend. However, a 1 watt difference, 2.5% of 40 watts, between 1.5 and 2 bar as provided by an unregulated power source is almost neglible.
    But it backs up the drum test trend and my 2.5% advantage over over 1000 yards (or whatever unit of measurement) = 25 yards ahead of you at the finish line.

    Quote Originally Posted by bing!
    Good of Schwalbe to answer your question.
    Good for Schwalbe to release this information to the public, as opposed to more marketing drivel.

    Work with the information we do have, not the info we wish we had.

    P

  50. #50
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    Quote Originally Posted by bing!
    A couple of points.

    Power is entirely dependent on the rider that produces it. Less in, less out (as measured). Give the guy a 4x Gu shot and watch the watts go up
    If the rider is maintaining a constant, low speed his power output will be a function of grade. Many runs on the course & averaging results also helps to dampen minute variations.
    Quote Originally Posted by bing!
    RR as measured off an all terrain drum/dyno is better than a field test. This method provides a standardized comparison for making a tire and pressure selection.
    This is true and an interesting point, because I think it has been pointed out and generally accepted that the absorbtion of bumps rather than losing momentum to upward motion of a hard tire bouncing off of them is a mechanism at play. Upward motion is not possible on a rolling resistance machine. So we get to the definition of rolling resistance. Is it as measured by X method, as so many standard analytical results are reported, or is it a more open definition of the power required to maintain speed on an open course, which is no doubt more relevant to a rider? Controlled rolling resistance tests are what promulgated the myth in he first place. How many "standard" rough-surface drum tests should there be? By limiting the number of standards you limit the amount of relevance to real off-road conditions a rider experiences. That's what allowed for this 'breakthrough' in the first place, the limitation of rolling resistance testing to one standard-- smooth drums.

    Quote Originally Posted by bing!
    At the end of the day, the study exhibits a trend. However, a 1 watt difference, 2.5% of 40 watts, between 1.5 and 2 bar as provided by an unregulated power source is almost neglible.
    I think the trend is the important thing, not any particular value or percentage reduction, as that is condition dependent as demonstrated by the study. What I think is important is that there does not seem to be a limit or point of diminishing returns as you seem to seek based on your own much less controlled "tests."
    Last edited by meltingfeather; 03-02-2011 at 10:45 PM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  51. #51
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    Quote Originally Posted by meltingfeather

    I think the trend is the important thing, not any particular value or percentage reduction, as that is condition dependent as demonstrated by the study. What I think is important is that there does not seem to be a limit or point of diminishing returns as you seem to seek based on your own much less controlled "tests."
    You'll get no argument from me. I pose no conclusions, just thoughts.

    I think this entire conversation helped me understand this subject much better.

  52. #52
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    Quote Originally Posted by Mr.P
    "The body has a max power regardless of Gu shots. Gu would only be able to maintain your maximum for longer. Not increase power."
    - I was being facetious with the GU comment.


    Quote Originally Posted by Mr.P
    "This is the first field test, so this is relevant to whether trends in labs match up with trends in the field. I think that is important. To me it equates to more myth busting."
    - I too think it was relevant. I was not being dismissive.


    Quote Originally Posted by Mr.P
    But it backs up the drum test trend and my 2.5% advantage over over 1000 yards (or whatever unit of measurement) = 25 yards ahead of you at the finish line.
    - only if the guy with an 2.5% advantage was racing a robot. you fail to account for differences in strength and motivational effect of being 25 yards behind the lead guy.


    Quote Originally Posted by Mr.P
    "Work with the information we do have, not the info we wish we had."
    - ask questions to build knowledge and understanding, as knowledge without understanding is simply blind faith.
    Last edited by bing!; 03-02-2011 at 10:51 PM.

  53. #53
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    Quote Originally Posted by bing!
    You'll get no argument from me. I pose no conclusions, just thoughts.

    I think this entire conversation helped me understand this subject much better.
    Me too.
    While this topic is something I've thought a lot about, this thread has taught me some things and caused me to think of things I previously hadn't. That's why I'm here after all.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  54. #54
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    Quote Originally Posted by bing!
    If you read the study carefully, the lower rolling resistance of the wider tire, is due to is larger diameter, not the width.
    duhno
    They concluded that's an additional benefit of the wider tire not the main contributor. Ref page 4 along with other tire mfg studies.
    Last edited by gvs_nz; 03-03-2011 at 12:31 AM.

  55. #55
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    Quote Originally Posted by bing!
    A couple of points.

    At the end of the day, the study exhibits a trend. However, a 1 watt difference, 2.5% of 40 watts, between 1.5 and 2 bar as provided by an unregulated power source is almost neglible.

    Good of Schwalbe to answer your question.
    And relating to your OP, from 35 to 28 psi, the difference in watts is even less.. But it is less. And for you to contest that you would have to do the 350 test rides,150km and 8500m of elevation in the test.But that small difference, what looks to me more like 5 watts on the graph, is on pea gravel and I don't ride on pea gravel.I don't ride on meadow either and there was 18 watts difference. If you look at the back of the study rolling resistance makes up about 46% on the meadow and only 24% on gravel anyway.


    It's not the flashest of of tests, and taking an excerpt from the conclusion, you can probably see his reason for doing it.
    He says "off road tires should be as wide and as low a pressure as necessary in contrast to the narrow and high pressure".

    He knew the result he would get . He designed a test to debunk the myth. Not specifically air pressure but the narrow tire high pressure mindset.

    As you have alluded to in previous posts you can't be conclusion from this test. You have to do your own tests on your own terrain on your tires. If your son's bike has cheap heavy narrow tires then they may well be slower at lower pressure. The hysteresis losses from deformation of the poorly designed plasticky compound thick walled casing at low pressure may well override any benefits over rough terrain? Schwalbe and other good quality tires' casings will be designed with low pressure in mind.

    You'll have to do some tests with your tires vs your son's and let us know how you got on.
    Last edited by gvs_nz; 03-03-2011 at 01:33 AM.

  56. #56
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    Quote Originally Posted by bing!

    A characteristic of a deformable material such that the energy of deformation is greater than the energy of recovery. The rubber compound in a tire exhibits hysteresis. As the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy loss as heat. Hysteresis is the main cause of energy loss associated with rolling resistance.

    -- National Academy of Sciences[3]
    I haven't ready every post, so I'm at risk of sounding like an idiot...but.

    When a tire is rolling you have to worry not only about hysteresis of the tire materials, but also the ground. The ground sees whatever pressure is in your tires. The lower the pressure, the more the tire compresses (strains), and the less the soil compresses (strains). Nearly all soils have MUCH higher hysteresis than tire materials.

    So yes, your compressing the tire materials more at a lower pressure, but the dirt is compressed less...offseting the energy lost into the tire. The softer the surface, the more benefit there is to low pressure.

    Smoothing the tires response the terrain by lowering pressure probably has an affect as well, but to I would bet to a lesser extent.

    I've done roll down tests on hills to flat before at different pressures. (Total energy into the system controlled by start height on the hill). There was a statistically significant difference in rollout distances when only the pressure was changed. I've done it with different brand tires at the same pressures too, and there was a difference, but at a lower confidence interval than changing pressures.

  57. #57
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    Quote Originally Posted by shiggy
    I have had a plan for real-world tire performance. I would love to use 3-4 different pressures, but realistically I would not have time to do enough runs in a day with 4-5 setups (including controls) to record enough data points to have valid results.
    Limit the experiment to pressures only, or tire model only; granted you'll lose interactions between the two.

    Collect variables data (not pass/fail attribute), and you'd be surprised how few sample runs you need (30 or less). Make the test short in duration, and it becomes not so time consuming.

    Granted changing setups is more difficult than just changing tire pressures, and adds significant amounts of time.
    Last edited by brentos; 03-03-2011 at 04:48 PM.

  58. #58
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    Makes sense. Some tires are definitely faster than others and generally higher volume tires with good quality casing respond better to low pressure. As bing says in his OP some can feel and probably are slower at lower pressure[cheap, narrow, poor quality casing tires].

  59. #59
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    Are clipless or flat pedals faster?








    Just joking......

  60. #60
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    Quote Originally Posted by kmorast
    Are clipless or flat pedals faster?








    Just joking......
    Yes.

    OP should just spend a few hundred on ceramic bearings and it will even out that killer rolling resistance increase from a 10psi drop.

  61. #61
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    Quote Originally Posted by gvs_nz
    And relating to your OP, from 35 to 28 psi, the difference in watts is even less.. But it is less. And for you to contest that you would have to do the 350 test rides,150km and 8500m of elevation in the test.But that small difference, what looks to me more like 5 watts on the graph, is on pea gravel and I don't ride on pea gravel.I don't ride on meadow either and there was 18 watts difference. If you look at the back of the study rolling resistance makes up about 46% on the meadow and only 24% on gravel anyway.
    I am at a loss for words.

  62. #62
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    When I got my tubeless setup, I was interested in testing Schwalbe's hypothesis firsthand. It makes sense that the more the tires can crawl over stuff by deformation, instead of lifting the entire bike & rider over them, the better the ride and the less power will be needed.

    However, I didn't like how that played out in reality. Too much casing deformation caused control issues on narrow hill-slope trails, and the bike didn't accelerate well. I'm at about 152 pounds, but I'd still go with at least 33-35psi to make the bike handle and accelerate the way I want.

    I also see this play out in an entirely different arena: my winter commuting bike has ~1100-gram Schwalbe Marathon Winter studded tires. When I bring the pressure down to ~20-25psi in those to lay down the maximum amount of studs on ice, the rolling resistance skyrockets. My top speed across the bridge on the way to work takes a huge hit compared to ~50-55psi, and considering I'm in the mid-20mph range, that's saying something... you'd think air drag would trump every other factor, wouldn't you? But it's empirical results, repeatable and predictable.

    Bottom line, I'm pretty confident that a timed assault on our local racecourses would bear out my seat-of-the-pants findings... there's such a thing as too much casing deformation. I recommend picking what works best for you, unless you're one of my XC race rivals, in which case you're welcome to run 21psi

  63. #63
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    I read they did the measurements by power. How do they measure power and can it be an accurate reading?

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    Quote Originally Posted by mechBgon
    I also see this play out in an entirely different arena: my winter commuting bike has ~1100-gram Schwalbe Marathon Winter studded tires. When I bring the pressure down to ~20-25psi in those to lay down the maximum amount of studs on ice, the rolling resistance skyrockets. My top speed across the bridge on the way to work takes a huge hit compared to ~50-55psi, and considering I'm in the mid-20mph range, that's saying something... you'd think air drag would trump every other factor, wouldn't you? But it's empirical results, repeatable and predictable.
    Why is that surprising? Smooth surface and RR increases with decreasing pressure... that's nothing new.
    Quote Originally Posted by mechBgon
    Bottom line, I'm pretty confident that a timed assault on our local racecourses would bear out my seat-of-the-pants findings... there's such a thing as too much casing deformation.
    Then you've kind of missed the point, unless you ride on pavement or very smooth surfaces, in which case I'm sure it would.
    You being unable to control your bike, which is probably related to how quickly you made the transition, doesn't have anything to do with rolling resistance and pressure.
    Riding your studs over an icy bridge is irrelevant.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  65. #65
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    Quote Originally Posted by aliikane
    I read they did the measurements by power. How do they measure power and can it be an accurate reading?
    With an SRM power meter. It measures roder-applied torque with a load cell and with cadence calculates power output. +/-2% accuracy.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  66. #66
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    Quote Originally Posted by mechBgon
    ...Bottom line, I'm pretty confident that a timed assault on our local racecourses would bear out my seat-of-the-pants findings... there's such a thing as too much casing deformation. I recommend picking what works best for you, unless you're one of my XC race rivals, in which case you're welcome to run 21psi
    Can I run 24 psi? I did that last season and was seated accelerating through the embedded rock sections while my competition stood and absorbed (SS class so all hardtails).

    Most of the course had benefits to low PSI. And it is almost all loose over hard.

    It is a 12 race series on the same course that I have been doing for years. I have tried many tire & pressure combinations, and found a high volume, thin (light), minimum knob, low pressure tire kills it.

    P

  67. #67
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    Quote Originally Posted by aliikane
    I just got a reply from Schwalbe. They are very helpful. Makes me wanna buy the tires more. Anyway, he did say that there was a typo in the chart. Meadow needs to be switched with the gravel line in the chart.



    I think it is difficult to do a really accurate test in real world conditions on a trail with a rider unless it was a robot. Too many variables affect speed of the rider. He may be tired, malnourished that day, dehydrated, mind not into the ride, muscles looser, etc. all would have an affect on the results.
    The real world testing protocol I have designed is a coasting test. 2-3 mile course, no brakes required, no chain on the bike, includes turns, grade changes that show how a tire can acclerate and hold speed, max speed under 20mph with the average around 12mph. And run where brakes are used or the line is "off" is thrown out.
    All on the same bike with the same rider, same spec wheels.
    Data with a stopwatch and a Garmin Edge GPS.

    Fastest elapsed time = fastest tire. There is more to a tire being fast than just its rolling resistance.

    I had a good course for the test but could not get the number of wheels I needed. Now I could likely get the wheels, but I moved and. Can not find a suitable course.
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  68. #68
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    Quote Originally Posted by Mr.P
    Can I run 24 psi? I did that last season and was seated accelerating through the embedded rock sections while my competition stood and absorbed (SS class so all hardtails).

    Most of the course had benefits to low PSI. And it is almost all loose over hard.

    It is a 12 race series on the same course that I have been doing for years. I have tried many tire & pressure combinations, and found a high volume, thin (light), minimum knob, low pressure tire kills it.

    P

    Like I said, use what works for you

    Riding your studs over an icy bridge is irrelevant.
    I disagree. It's not an off-road scenario with off-road tires, but it demonstrates that there's a break point at which casing deformation becomes detrimental to actual speed. Because like it or not, hysteresis does consume some energy. These very heavy, thick tires just make it very apparent.

    Then you've kind of missed the point, unless you ride on pavement or very smooth surfaces, in which case I'm sure it would.
    Maybe we're not interested in the same thing. I'm interested in going fast and reaching the finish line first, not discussing rolling resistance in the abstract as if it's the only factor involved in going fast on a bike on a racecourse.

    For some perspective, on our local 24-hour course, my best laps are about 17.4mph average speed. That includes 1300 feet of climbing, lots of loose over hard and some limited rock gardens. It's a semi-desert climate, so it tends to be a firm surface too. The local race series is a little more varied, but still in the 16mph-17mph range. So yeah, rather smooth and fast. I'm a Masters-age rider racing with the younger age bracket by choice, and have been on the podium for the last... what, 11 XC races in a row, so I'm getting results, at any rate

  69. #69
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    Quote Originally Posted by meltingfeather
    Why is that surprising? Smooth surface and RR increases with decreasing pressure... that's nothing new.

    Then you've kind of missed the point, unless you ride on pavement or very smooth surfaces, in which case I'm sure it would.
    You being unable to control your bike, which is probably related to how quickly you made the transition, doesn't have anything to do with rolling resistance and pressure.
    Riding your studs over an icy bridge is irrelevant.
    And every tire/rim/rider combo (plus terrain) has a pressure sweetspot where the tire performs best. Very generally, the heavier the rider and/or narrower the rim, the higher the pressure will be. The best pressure range is affected by the characteristics of the tire casing, tread and compound, as well as size/volume.
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  70. #70
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    Quote Originally Posted by shiggy
    And every tire/rim/rider combo (plus terrain) has a pressure sweetspot where the tire performs best. Very generally, the heavier the rider and/or narrower the rim, the higher the pressure will be. The best pressure range is affected by the characteristics of the tire casing, tread and compound, as well as size/volume.
    100% agree.
    I wasn't meaning to imply that anyone should ride a pressure other than what they feel is best.
    mechBgon's pressure threshold is much higher than mine. In his case, control is a trade-off for increased rolling resistance off-road. It doesn't make his choice bad, but it also doesn't really have a relevance to Schwalbe's results or refute them at all.
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  71. #71
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    Quote Originally Posted by mechBgon
    For some perspective, on our local 24-hour course, my best laps are about 17.4mph average speed. That includes 1300 feet of climbing, lots of loose over hard and some limited rock gardens. It's a semi-desert climate, so it tends to be a firm surface too. The local race series is a little more varied, but still in the 16mph-17mph range. So yeah, rather smooth and fast. I'm a Masters-age rider racing with the younger age bracket by choice, and have been on the podium for the last... what, 11 XC races in a row, so I'm getting results, at any rate
    How could I have known that you are a good bit faster than the fastest pros and endurance racers riding "XC" courses (see below)?!?
    Keep doing what works for you.

    Two examples:
    In a local 24-hour race, the fastest Open class riders, who typically cover ~180 miles, only ride a little over half as fast as you (link).
    At a local XC race Jeremy Horgan-Kobelski (heard of him?) smoked even our fastest local pros and only managed a feeble 13.5mph (link).
    At the speeds you're going, a TT helmet is probably a good idea.
    Maybe you should consider going pro.
    Forgive me if I'm a bit skeptical that you can manage to average 2.5-3 mph faster than top-tier american pro riders in their prime.
    Quote Originally Posted by mechBgon
    I disagree. It's not an off-road scenario with off-road tires, but it demonstrates that there's a break point at which casing deformation becomes detrimental to actual speed. Because like it or not, hysteresis does consume some energy. These very heavy, thick tires just make it very apparent.
    Just to make sure we're on the same page, you do realize that Schwalbe's results, and the "lower pressure = lower rolling resistance" trend is only applicable off road, and particularly on rough surfaces, right?
    We've known for many years that decreasing tire pressure on smooth surfaces increases rolling resistance.
    Therefore, your smooth-surface "test" doesn't really have any bearing on these results.
    Quote Originally Posted by mechBgon
    Maybe we're not interested in the same thing. I'm interested in going fast and reaching the finish line first, not discussing rolling resistance in the abstract as if it's the only factor involved in going fast on a bike on a racecourse.
    We are interested in the same thing. Your pressure threshold is much higher than mine (I run 21psi in 2.2s on my rigid ss and weigh 210lbs riding very rocky terrain), and I won't tell you that's wrong. You choose a pressure that works for you. However, you used your experience to essentially refute Schwalbe's results. Schwalbe's rolling resistance results are but one factor (control is another, for example). The reason why it's important is that it debunks a paradigm about pressure and rolling resistance specifically in off-road conditions.
    It seems like you ride on extremely smooth terrain, so you very well could be in the range where increasing tire pressure decreases resistance. Again, that does not refute Schwalbe's results.
    Last edited by meltingfeather; 03-04-2011 at 01:29 PM.
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  72. #72
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    Quote Originally Posted by meltingfeather
    With an SRM power meter. It measures roder-applied torque with a load cell and with cadence calculates power output. +/-2% accuracy.
    How much does power measured in this way relate to actual physical exertion? For example, just the weight of your foot from gravity only pushing down on one pedal creates power, but no physical exertion. If you hit a big bump and stall, pushing hard on the pedal but not actually moving, then there is exertion but no measured power.

    I would guess that the more jagged the terrain, the less measured power actually related to physical exertion. You might have to strap on a respirator and measure oxygen consumption like they do in the labs.

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    Quote Originally Posted by beanbag
    How much does power measured in this way relate to actual physical exertion? For example, just the weight of your foot from gravity only pushing down on one pedal creates power, but no physical exertion. If you hit a big bump and stall, pushing hard on the pedal but not actually moving, then there is exertion but no measured power.

    I would guess that the more jagged the terrain, the less measured power actually related to physical exertion. You might have to strap on a respirator and measure oxygen consumption like they do in the labs.
    Interesting points, and valid, I think. I imagine that the relationship between power and exertion is just as you say, different depending on conditions. Power meters are typically used for road training, where riders focus on riding "quietly" to reduce exertion outside of pedal-applied power, and I think for the low-exertion and relatively smooth (sounding) test conditions, the power measurements are probably pretty reliable. The power measurement is what the rider delivers to the cranks. I think that the idea of exertion is an interesting one, but would probably add a level of complexity to interpreting the results, because you would then be looking through the window of the rider's efficiency, which I don't think adds anything but the increased complexity for this particular scope.
    These tests don't consider, for example, the increased fatigue that comes with high pressure and being bounced around a lot... that would be yet another interesting factor to consider.
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  74. #74
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    The notable thing about the meadow and gravel isn't so much that they're rough, but that they're soft. My hypothesis is that when you run high pressure on a soft surface you encounter two problems

    1) You have to displace the rocks or dirt to sink down, creating friction
    2) You're constantly climbing out of your own little trench.

    Lower the pressure, and you don't sink as far. Simple as that. This sinking would be far more significant than the added hystersis in the tire.

    On rough surfaces, I suppose I agree with the comment above. When you go up a little ramp, you exchange speed for altitude. If there's a ramp down the other side, you exchange that altitude for speed. But, on small bumps you just fly over'em. There's nothing to accelerate you off the back side, so you just fall and absorb that altitude energy in your shocks, arms, and legs instead. Conforming over obstacle should be more efficient.

  75. #75
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    Quote Originally Posted by brentos
    I haven't ready every post, so I'm at risk of sounding like an idiot...but.

    When a tire is rolling you have to worry not only about hysteresis of the tire materials, but also the ground. The ground sees whatever pressure is in your tires. The lower the pressure, the more the tire compresses (strains), and the less the soil compresses (strains). Nearly all soils have MUCH higher hysteresis than tire materials.

    So yes, your compressing the tire materials more at a lower pressure, but the dirt is compressed less...offseting the energy lost into the tire. The softer the surface, the more benefit there is to low pressure.

    Smoothing the tires response the terrain by lowering pressure probably has an affect as well, but to I would bet to a lesser extent.

    I've done roll down tests on hills to flat before at different pressures. (Total energy into the system controlled by start height on the hill). There was a statistically significant difference in rollout distances when only the pressure was changed. I've done it with different brand tires at the same pressures too, and there was a difference, but at a lower confidence interval than changing pressures.
    salient points.
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  76. #76
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    Hmm, beanbag and meltingfeather in the same thread again talking about rolling resistance. Only one direction for this thread to go...

  77. #77
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    Quote Originally Posted by beanbag
    How much does power measured in this way relate to actual physical exertion? For example, just the weight of your foot from gravity only pushing down on one pedal creates power, but no physical exertion. If you hit a big bump and stall, pushing hard on the pedal but not actually moving, then there is exertion but no measured power.
    Kind of like someones brain working real hard about this but not actually understanding any of it, is any thought actually done?

  78. #78
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    Quote Originally Posted by meltingfeather
    How could I have known that you are a good bit faster than the fastest pros and endurance racers riding "XC" courses (see below)?!?
    I do happen to be our 2009 Masters C state road-racing champion. I hope that never happens again, though

    Incidentally, the pros at our 24-hour race were turning 49-minute laps at >18mph. My own PR is just under 51m and my best lap in the actual event was 52:15. Results yonder, if your skepticisms need proof: https://www.cadencesportsonline.com/..._divisions.pdf

    Just to make sure we're on the same page, you do realize that Schwalbe's results, and the "lower pressure = lower rolling resistance" trend is only applicable off road, and particularly on rough surfaces, right?
    I'd put it this way: Schwalbe's study measures power consumption, not rolling resistance per se. As my studded-tire example illustrates, the actual rolling resistance IS higher with low pressure. If the terrain were rough, then the tires' ability to conform to obstacles might save me more power than they waste, but you have to find that optimum trade-off point for yourself.

    And if the bike corners like trash because the tires are too soft and you're getting casing roll, then they cost time in corners. I went into the low-pressure thing with an open mind, but having the rear end that loose wasn't helpful.

    Oh, and

    At the speeds you're going, a TT helmet is probably a good idea.
    I do use supercruise wherever practical, which is good for an easy ~1mph boost at 18-22mph and about 2mph on the fast sections of the course... the final section includes a nice rampdown where I typically hit 35mph and decay that down to 25mph on the way in to the finish line. Aerodynamics is a serious factor, yep.

  79. #79
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    Quote Originally Posted by mechBgon
    Incidentally, the pros at our 24-hour race were turning 49-minute laps at >18mph. My own PR is just under 51m and my best lap in the actual event was 52:15. Results yonder, if your skepticisms need proof: http://www.cadencesportsonline.com/p..._divisions.pdf
    I saw a handful of laps over 18mph on relay teams, but it doesn't really matter.
    Obviously what you guys call XC is very different from the "XC" terrain around here. The speeds the elite of you are able to maintain are typical for road training rides around here. That's a factor, and definitely a driver. No doubt it's extremely smooth and hard tires help with rolling resistance. I don't think that's what the study was aimed at.
    Quote Originally Posted by mechBgon
    I'd put it this way: Schwalbe's study measures power consumption, not rolling resistance per se. As my studded-tire example illustrates, the actual rolling resistance IS higher with low pressure.
    The study measures total resistance, and they tried to keep drag down by keeping speed down. Your studded tire doesn't demonstrate anything that we didn't know already. Just like a standard RR test on a smooth drum, increased pressure reduces rolling resistance on a smooth surface. I know you like your example, but it's old hat, and I'm not really sure why you keep bringing it up unless you've never looked at rolling resistance testing before.
    Quote Originally Posted by mechBgon
    If the terrain were rough, then the tires' ability to conform to obstacles might save me more power than they waste, but you have to find that optimum trade-off point for yourself.
    Uh... that's the whole point.
    Quote Originally Posted by mechBgon
    And if the bike corners like trash because the tires are too soft and you're getting casing roll, then they cost time in corners. I went into the low-pressure thing with an open mind, but having the rear end that loose wasn't helpful.
    Personal preference. No doubt you're on terrain that's not suited to low pressure. I run 110psi in my road tires.
    I think you may be taking the study as telling you what to do, and there are some sentences that hint at that, but I think that's just the author having a bit of fun with an informal(ish) report. All in all you have to take it for what it's worth. If you're riding smooth hardpan, well, it's not applicable to you and clearly you're in the more road-like range of rolling resistance trends.
    Denying the results isn't really supported by anything you've said.
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    Time to stop believing the hype and start doing some science.
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  80. #80
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    Quote Originally Posted by meltingfeather
    Obviously what you guys call XC is very different from the "XC" terrain around here. The speeds the elite of you are able to maintain are typical for road training rides around here. That's a factor, and definitely a driver. No doubt it's extremely smooth and hard tires help with rolling resistance. I don't think that's what the study was aimed at.
    Well, here's a small sample of two riding areas I hit a lot. This is unfortunately limited to what I can ride while shooting video with a camera in one hand, but you can judge for yourself whether it's all buff hardpack or whatever...

    http://www.youtube.com/profile?user=...11/wq985UJ6ID0
    This is the South Hill bluff. The hillside trail shown in the video is one of the wide hillside trails; the narrow ones call for pretty precise tire position, one reason I don't like the bike wallowing around too much due to overly-soft tires.

    http://www.youtube.com/profile?user=...23/IG8vaBrwsMk
    This is Beacon Hill. I wish I had helmet-cam footage of the Easy Ezzy trail, which involves some serious railing of banked singletrack, another place where I don't want casing roll.

    I think you may be taking the study as telling you what to do, and there are some sentences that hint at that,
    Well put. They lay it on pretty thick: use fat tires and minimal pressure because it results in lower steady-state power consumption when riding slowly uphill at a near-constant speed (yeah, that sounds like an XC race all right... not). I have the fattest tires that'll fit my frame & fork, but at minimal pressure, I found the benefits are outweighed by the drawbacks. And honestly, plowing my way across rock gardens at 25psi, the "magic carpet" effect didn't wow me that much.

    So yes, I'm suggesting people read the study, but also think for themselves. If you like the low-PSI approach, go for it. If you don't, you're not a fool for saying "been there, tried that" either.

  81. #81
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    Quote Originally Posted by mechBgon
    Well, here's a small sample of two riding areas I hit a lot. This is unfortunately limited to what I can ride while shooting video with a camera in one hand, but you can judge for yourself whether it's all buff hardpack or whatever...

    http://www.youtube.com/profile?user=...11/wq985UJ6ID0
    This is the South Hill bluff. The hillside trail shown in the video is one of the wide hillside trails; the narrow ones call for pretty precise tire position, one reason I don't like the bike wallowing around too much due to overly-soft tires.

    http://www.youtube.com/profile?user=...23/IG8vaBrwsMk
    This is Beacon Hill. I wish I had helmet-cam footage of the Easy Ezzy trail, which involves some serious railing of banked singletrack, another place where I don't want casing roll.
    Those trails are pretty buff, but if you can manage 16-17mph on them, which looks to be about 3X as fast as anybody in the vids, you are definitely skilled and in incredible shape. Kudos.
    Here's a typical ATX trail (don't know the shooter, just searched youtube), and as you can see, the terrain is much more rough. No wonder you're able to maintain 20% higher pace than super bad @ss JHK can on our local trails.

    Quote Originally Posted by mechBgon
    So yes, I'm suggesting people read the study, but also think for themselves. If you like the low-PSI approach, go for it.
    That about sums it up.
    Quote Originally Posted by mechBgon
    If you don't, you're not a fool for saying "been there, tried that" either.
    I don't think anybody said that you're a fool for not running lower pressure, but OK.
    p.s. I posted a thread when I was experimenting with low pressure and ended up racing rigid ss at ~210lbs on ~21psi in my Geax 2.2s on a very rocky (similar to the video course). People called BS and said I must have been creeping along, etc. For some reason many peeps have a problem with "live and let live" and think that what they do must be the only thing that works.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    I run a little more air in my tires on my full suspension than hard tail, i let the suspension soak up the trail imperfections more than the tires, as opposed to a hard tail where you need all the help you can get. I would like to see a study comparing the two different bikes..

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    Quote Originally Posted by BitterDave
    Hmm, beanbag and meltingfeather in the same thread again talking about rolling resistance. Only one direction for this thread to go...
    Bitter, Dave?
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by meltingfeather
    Interesting points, and valid, I think. I imagine that the relationship between power and exertion is just as you say, different depending on conditions. Power meters are typically used for road training, where riders focus on riding "quietly" to reduce exertion outside of pedal-applied power, and I think for the low-exertion and relatively smooth (sounding) test conditions, the power measurements are probably pretty reliable. The power measurement is what the rider delivers to the cranks. I think that the idea of exertion is an interesting one, but would probably add a level of complexity to interpreting the results, because you would then be looking through the window of the rider's efficiency, which I don't think adds anything but the increased complexity for this particular scope.
    These tests don't consider, for example, the increased fatigue that comes with high pressure and being bounced around a lot... that would be yet another interesting factor to consider.

    Interesting points. I dont doubt the test, i just think it could have been done another way. The srm is for training. Not ideal for a test of rolling resistance. Imho, an electric bicycle set to propel the bike at a set amount of power, say a constant 50 Watts over a course would have been better. Highest average speed wins. Simple and controlled.

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    Quote Originally Posted by meltingfeather
    Those trails are pretty buff, but if you can manage 16-17mph on them, which looks to be about 3X as fast as anybody in the vids, you are definitely skilled and in incredible shape. Kudos.
    16-17mph average speeds on the Bluff or the Beacon would certainly be remarkable, yeah. My average speeds in those areas is probably pretty low, because I'm going out of my way to hit the most difficult climbs for training, at least when riding solo. The XC and 24-hour courses here are definitely faster, and have places to pass.


    Here's a typical ATX trail (don't know the shooter, just searched youtube), and as you can see, the terrain is much more rough. No wonder you're able to maintain 20% higher pace than super bad @ss JHK can on our local trails.
    Our seriously-rocky trails are literally nothing BUT a non-stop path of large angular volcanic rocks, so I think we have that guy beat If this thread drags on long enough, I'll try to get out there and snag some pics. We call it the Tour de Moon.

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    Quote Originally Posted by pindowngirl25
    I run a little more air in my tires on my full suspension than hard tail, i let the suspension soak up the trail imperfections more than the tires, as opposed to a hard tail where you need all the help you can get. I would like to see a study comparing the two different bikes..
    Thats is same concept that developed low profile tires. A well adjusted susension is assumed to be better at soaking bumps than an undampened tire.

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    Quote Originally Posted by mechBgon
    Our seriously-rocky trails are literally nothing BUT a non-stop path of large angular volcanic rocks, so I think we have that guy beat If this thread drags on long enough, I'll try to get out there and snag some pics. We call it the Tour de Moon.
    I wasn't so much trying to compare our local trails or establish who "wins" as much as establish a frame of reference. In the context of this discussion the trails that you can average 16-17mph on are relevant. The gnarliest terrain you can find is not.
    The section of the Barton Creek Greenbelt in the vid is typical and similar to the terrain JHK was riding on, and is much rougher than either the terrain you showed in your example video or the 24-hour course you raced on. In fact, the beginners in the video are very near the trail head and another well-used access point, so what they're riding is heavily traveled and relatively tame compared to the "serious" rocks. Again, though, comparing our rockiest terrain to see who "beats" who is not the point, or at least not my point, and definitely irrelevant regardless.
    Steering this tangent back to topic, you might find that overall resistance decreases with pressure on rough trails, if you can keep your bike under control with less than 33psi in the tires. Maybe not, though.
    Last edited by meltingfeather; 03-06-2011 at 12:55 PM.
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    Quote Originally Posted by bing!
    Interesting points. I dont doubt the test, i just think it could have been done another way. The srm is for training. Not ideal for a test of rolling resistance. Imho, an electric bicycle set to propel the bike at a set amount of power, say a constant 50 Watts over a course would have been better. Highest average speed wins. Simple and controlled.
    I'm sure there are a number of ways to do it.
    I disagree that constant power is better, though. Changing speed introduces changes in drag and handling. I'm not sure why you so distrust power metering. It is remarkably accurate and I've already reasoned why variability in the motors condition is not the significant detriment you suspect.
    As I have mentioned, there's a question of defining rolling resistance that has not been answered. If "rolling resistance" is the number you get by "x" method, then that's not what we're talking about. It's important to keep in mind that standard rolling resistance testing left a glaring omission in the results. That to me is part of the point and no small discovery. I personally think the study did a fantastic job of illustrating the point. It is not without fault though.
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    Quote Originally Posted by bing!
    Interesting points. I dont doubt the test, i just think it could have been done another way. The srm is for training. Not ideal for a test of rolling resistance. Imho, an electric bicycle set to propel the bike at a set amount of power, say a constant 50 Watts over a course would have been better. Highest average speed wins. Simple and controlled.
    When you read the prelude the tests were carried out at 5-6mph to exclude wind resistance.
    His rolling resistance measurements were backed up in the lab by Schwalbe rolling drum tests. His power measurements were also adjusted for the different weights of the tire
    Unless the rider is accelerating the SRM readings is accurate steady state power measurement. No speed testing is done because he wants power only. When you do speed testing you introduce variables like wind resistance, the energy to accelerate the bike and rider and the accuracy of repeatability of rider input[ pretty easy to maintain consistent 5-6mph].
    Last edited by gvs_nz; 03-06-2011 at 05:14 PM.

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    Quote Originally Posted by mechBgon
    16-17mph average speeds on the Bluff or the Beacon would certainly be remarkable, yeah. My average speeds in those areas is probably pretty low, because I'm going out of my way to hit the most difficult climbs for training, at least when riding solo. The XC and 24-hour courses here are definitely faster, and have places to pass.
    Let me get this straight: I say that to average 16-17mph the trails have got to be pretty damn smooth hardpack. So you post an example vid of two places you ride a lot. I note that it's pretty buff, but even so 16-17mph is impressive. You respond that at neither of these places can you average 16-17mph.
    Needless to say, I'm having trouble following the logic here...
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

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