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#21
June 16th 05, 01:07 AM
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Nobody knows about RR
On Wed, 15 Jun 2005 00:21:55 +0200, "Ivar Hesselager"
wrote: I trust, that if mr Walde knew of ane measurable difference, he would be willing to tell me about it. Therefore he and Continental Tires don't know of a difference. And if they don't know, most likely nobody knows. I find that surprising and interesting. It is not a given that any tire company representative's failure to be forthcoming with actual test data indicates that they don't know. Several alternate analyses are just as likely, among them very possibly that they know precisely what the answers would be, but that their own products would not be shown in a beneficial light by those numbers. (I will posit that it's very likely that every maker would have tires whose performace in such testing is at both ends of the spectrum as well as all across the middle, and there also may be sample variation known which renders the data less than useful.) It's equally likely that the testing is done only infrequently and not very comprehensively, in which case it's very possible that what they could provide would not be currently informative. Perhaps most likely of all, however, is the possibility that the company's management considers such data proprietary and does not permit it to be shared. It is obvious that if you give priority to comfort and tracking, you should prefer af 25 mm to a 23 mm. But even if you give priority to speed, the 25 mm tire appears to be the better choice. But nobody knows. Or, more probably, those who know are not forthcoming with the data. For a specialty product with relatively low production and significant price pressure, it would amaze me if they were spending the time in product evaluation that would be required in order to know how their tire compared to all of its principal competitors. Even if they did, the data would be stale as soon as any significant percentage of the competition changed its tech specs or model designations, making the collected data largely irrelevant. And, last but not least, there may not be as much variance in the results for road tires (where it would matter most) as might be expected. It's quite possible that the people who have the data (however much of it there is) are reticent about sharing it because it primarily reveals a lack of important differentiation in the products...and doesn't always show that theirs is the best. I doubt that there is any tire maker whose products *always* earn the highest marks in rolling resistance testing, so the expected tendency would be to say little about the subject for any product unless the advatange for a given tire was remarkable against all potential competitors...and somehow, I doubt that this is going to be the case. Thus far, you have queried precisely one maker; it is premature to draw the conclusion that *nobody knows" based on one non-response, and even if all possible responses ended up being essentially the same as the one collected, it would still not prove a lack of knowledge, but rather only a lack of publicly released data. Here is an uncovered field for an engineer student or for a bicycle magazine to look in to. One can find research grants with less justification, certainly! I suspect, though, that the end result would be a finding that there's less difference between the various tires than some might expect. -- Typoes are a feature, not a bug. Some gardening required to reply via email. Words processed in a facility that contains nuts. 
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#22
June 16th 05, 01:09 AM
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Nobody knows about RR
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#23
June 16th 05, 02:29 AM
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Nobody knows about RR
David L. Johnson wrote:
On Wed, 15 Jun 2005 12:15:01 +0100, David Damerell wrote: No, it's not. If you want to maximise speed, you should use in both tyres the maximum pressure that does not cause the increase in RR we see with track-style pressures (eg 170psi), Um, what increase in RR is that? I haven't seen any data anywhere, but it makes intuitive sense to me that if the tire is so hard that road bumps significantly increase vibrations in bike and rider, that this is energy being wasted. produce an intolerably hard ride; that will be equal in both cases and the 25mm tyre will have lower RR. I don't think either of those conclusions are true. For one thing, a 25mm tire may reach blow-off pressures before it is "intolerably hard", and at that pressure I would assume the RR of the two sizes would be close to the same. Do blow-off pressures vary with tire width? How and why? -- Benjamin Lewis Seeing is deceiving. It's eating that's believing. -- James Thurber
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#24
June 16th 05, 02:59 AM
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Nobody knows about RR
On Wed, 15 Jun 2005 18:29:30 -0700, Benjamin Lewis
wrote: David L. Johnson wrote: On Wed, 15 Jun 2005 12:15:01 +0100, David Damerell wrote: No, it's not. If you want to maximise speed, you should use in both tyres the maximum pressure that does not cause the increase in RR we see with track-style pressures (eg 170psi), Um, what increase in RR is that? I haven't seen any data anywhere, but it makes intuitive sense to me that if the tire is so hard that road bumps significantly increase vibrations in bike and rider, that this is energy being wasted. [snip] Dear Benjamin, Like you, I haven't seen actual data about increasing pressure eventually causing rock-hard tires slow down becaue they bounce like kangaroos. But the theory is explained (without marsupials) in Lennard Zinn's reply to Tom he http://www.ottawabicycleclub.ca/phpB...pic.php?t=137& Zinn gaves no details or data, but he did say that he "saw results" and was "told of similar results": "Years ago, for example, I saw results like this at the Continental tire factory. I was told of similar results at a number of other tire factories I have visited." Like Ivar, of course, I yearn for oodles of details. Carl Fogel
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#25
June 16th 05, 03:23 PM
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Nobody knows about RR
Quoting Ivar Hesselager :
skrev: Why would you use a lower pressure in the 25mm tyre if the aim is to maximise speed? Because overinflated tires are not faster: they jump too much, and have too little grip. What makes you suppose this limit varies with width? The ideal comparison would be between the two sizes of tires, each with their ideal pressure (for road quality and rider weight). This should be reflected in their "recommended pressure" - not in the same pressure. There cannot be any single recommended or ideal pressure when riders have different desires vis-a-vis comfort and speed. -- David Damerell flcl? Today is Second Gouday, June.
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#26
June 17th 05, 12:07 AM
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Nobody knows about RR
16 Jun 2005 15:23:47 +0100 (BST), David Damerell
skrev: What makes you suppose this limit varies with width? Because Sheldon says so, thats why! Read this: http://www.sheldonbrown.com/tires.html#pressure If that doesn't convince you, look at the side of a 23 mm tire and a 25 mm tire. The max pressure will vary with width, and if there is a recommended pressure there also, that will vary with width as well. There cannot be any single recommended or ideal pressure when riders have different desires vis-a-vis comfort and speed. Right and wrong! We all have to look for our own ideal compromise if we want to make the intelligent choise of width and the pressure in our tires based on information about different road quality, different weights, different preferences concerning comfort, traction and speed. The ideal pressure that YOU will reach for YOUR tires will be higher for a 23 mm than for a 25 mm. The recommended pressure is a place to start your personal investigation, as it is the tire makers compromise for the same factors, but for an imagined average cyclist, that much I can predict. So if you want to make the ideal choice of tire width and pressure you must make an calculation/assumption of which tire and which pressure will give you the lower RR. Since it is impossible to ask you and me and everybody else about our experiences and preferences, the practical way to find the relevant data is to compare RR for the two tire sizes, each with their recommended pressure. We already know that an overinflated 25 mm tire has less rolling resistance than a correctly infalted 23 mm tire. We still need to know the result of a comparisen of two (for an imagninary average cyclist) correctly inflated tires. Cheers Ivar
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#27
June 17th 05, 07:49 AM
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Nobody knows about RR
See: http://www.zipp.com
They have done extensive testing in windtunnels. Neither exhaustive nor definitive, windtunnels are like that, Zipp have come to conclusions that bear witness to a multiplicity. Tests have confirmed that RR is not determinative but aerodynamics is. Zipp have analysed the data between test of differing sized tyres which results in conclusions of the First Order. The First Order in play is the "chord length" effect a larger dia tyre exerts upon a rim profile. Zipp have data which maps to the results of aerodynamic wings. Bottomline takeaway is that a larger dia tyre may destroy the aerodynamic advantage of a wheel. Further, Zipp show that airplane wing mfg'r teach that "where" along the length of a foil the widest (thickest) chord occurs affects aerodynamic efficiency. In the case of a wider tyre for a given rim, Zipp detail moving the widest chord point back (away from the rim edge) to achieve max. efficiency. Tire width relative to rim width and the point of max. chord width are the variables of First Order magnitude. Its an interesting take on the 25 .vs. 23 tyre size debate... -r
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#28
June 17th 05, 01:34 PM
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Nobody knows about RR
Quoting Ivar Hesselager :
skrev: What makes you suppose this limit varies with width? Because Sheldon says so, thats why! Read this: http://www.sheldonbrown.com/tires.html#pressure I have, many times. That does not say that the point at which there is an increase in RR or loss in traction from overinflation - the limit I am asking about - varies with width. [And, even if it did, Sheldon has no more done any research there than you or I.] If that doesn't convince you, look at the side of a 23 mm tire and a 25 mm tire. The max pressure will vary with width, and if there is a recommended pressure there also, that will vary with width as well. Yes. The maximum pressure, however, is concerned with blowoff, not with the limit I am asking about. So, why do you suppose that limit varies with width? There cannot be any single recommended or ideal pressure when riders have different desires vis-a-vis comfort and speed. Right and wrong! Not wrong at all. How is that wrong? Manifestly I cannot make a sensible recommendation to Joe Racer who wants to go as fast as possible and to Bob Tourist who wants as much comfort as won't give him pinch flats. The ideal pressure that YOU will reach for YOUR tires will be higher for a 23 mm than for a 25 mm. No, it won't. Not at all. I pump up my tyres as much as doesn't actually rattle my nuts on bad tarmac, because that way when I forget to do it for a few weeks I don't get pinch flats. That's the same pressure in both widths of tyre. The same would apply to someone who wants to minimise RR without suffering what is to them unacceptable discomfort. Same pressure never mind the width. their recommended pressure. We already know that an overinflated 25 mm tire has less rolling resistance than a correctly infalted 23 mm tire. We still need to know the result of a comparisen of two (for an imagninary average cyclist) correctly inflated tires. This is just returning to the assumption that the manufacturer's recommended pressure, which we know is basically bogus, is "correct". If a 23 and 25mm tyre are at the same pressure, the pressure which produces acceptable rider comfort, and that pressure is nowhere near the blowoff point, why is one "overinflated" and the other "correctly" inflated? -- David Damerell flcl? Today is Second Chedday, June - a weekend.
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#29
June 17th 05, 02:58 PM
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Nobody knows about RR
Conti doesn't know anything about RR...until/unless they have something
new to sell. http://www.cyclingnews.com/tech/?id=...res/conti_tech This article (really an ad for new Conti 25mm tubs with a Vectran anti-puncture belt) actually has a little discussion of RR vs. aerodynamics plus a nice visualization of contact patches for fat vs narrow tires. JLS
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#30
June 17th 05, 09:08 PM
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Nobody knows about RR
David Damerell wrote:
Quoting Ivar Hesselager : skrev: What makes you suppose this limit varies with width? http://www.sheldonbrown.com/tires.html#pressure I have, many times. That does not say that the point at which there is an increase in RR or loss in traction from overinflation - the limit I am asking about - varies with width. It's not a "point" it's a "region." where two curves intersect. Where in the region is best for you will depend on your priorities. It is not possible for anybody to specify a "perfect" tire pressure for a given situation, any more than anybody can tell you what gear ratio you should choose for a given piece of road. You need to figure this out for yourself by experimentation. [And, even if it did, Sheldon has no more done any research there than you or I.] No less either. Like many cyclists I have a lot of personal experience riding different tires at different pressures on different surfaces, and have been able to make some broad generalizations that may well be useful to beginners, or to those who have been mindlessly following rote specifications provided by tire makers. If that doesn't convince you, look at the side of a 23 mm tire and a 25 mm tire. The max pressure will vary with width, and if there is a recommended pressure there also, that will vary with width as well. This is less than a 10% difference in width, it would not be surprising that the various attributes of different pressure settings don't clearly favor one or t'other. There cannot be any single recommended or ideal pressure when riders have different desires vis-a-vis comfort and speed. Right and wrong! Not wrong at all. How is that wrong? Manifestly I cannot make a sensible recommendation to Joe Racer who wants to go as fast as possible and to Bob Tourist who wants as much comfort as won't give him pinch flats. The ideal pressure that YOU will reach for YOUR tires will be higher for a 23 mm than for a 25 mm. Theoretically this is true No, it won't. Not at all. I pump up my tyres as much as doesn't actually rattle my nuts on bad tarmac, because that way when I forget to do it for a few weeks I don't get pinch flats. That's the same pressure in both widths of tyre. Considering all of the variables involved, the difference probably gets lost in the noise. If a 23 and 25mm tyre are at the same pressure, the pressure which produces acceptable rider comfort, and that pressure is nowhere near the blowoff point, why is one "overinflated" and the other "correctly" inflated? The same pressure _doesn't_ produce the same rider comfort, but the difference is likely too subtle to evaluate with any precision. Sheldon "Season To Taste" Brown +---------------------------------------------------------+ | To be good is noble; but to show others how to be good | | is nobler and no trouble. --Mark Twain | +---------------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide http://captainbike.com http://sheldonbrown.com
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