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  1. #76
    Senior Member Chesha Neko's Avatar
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    Quote Originally Posted by Commodus View Post
    I have chosen to believe that Jan Heine is essentially truthful. Surely not always right (no one is), but based on the fact that he is perfectly willing to put his real name on tests results found using methodology that he is happy to share points to transparency and honesty in my opinion.
    I agree. I have the last few issues of BQ. He shares his data, but I don't always agree with his conclusions. The data remains useful for making one's own choices.
    "I stick to my basic plan of simply keeping the pedals turning."
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  2. #77
    Senior Member Homeyba's Avatar
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    Quote Originally Posted by Commodus View Post
    I have chosen to believe that Jan Heine is essentially truthful. Surely not always right (no one is), but based on the fact that he is perfectly willing to put his real name on tests results found using methodology that he is happy to share points to transparency and honesty in my opinion.

    Sure it could be some extravagant conspiracy, but I have a hard time swallowing the idea that he spends so much time and energy pushing old timey French rando bikes. I could be wrong, I suppose. If anyone has a better source of information, I would like to see it!...
    I don't think Jan is a bad guy. I know him (in a we've talked way, not a we hang out way) and I don't think he's out to deliberately deceive anyone but that really isn't the point. Bias is Bias, especially in reporting. If he really wanted to put forth an impartial test, or at least the appearance of such, he wouldn't include products that he helped develop and sells. Be honest, if he wasn't espousing something you agreed with you would completely dismiss him.
    It doesn't get harder, you just go slower.

  3. #78
    Senior Member Commodus's Avatar
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    Quote Originally Posted by Homeyba View Post
    I don't think Jan is a bad guy. I know him (in a we've talked way, not a we hang out way) and I don't think he's out to deliberately deceive anyone but that really isn't the point. Bias is Bias, especially in reporting. If he really wanted to put forth an impartial test, or at least the appearance of such, he wouldn't include products that he helped develop and sells. Be honest, if he wasn't espousing something you agreed with you would completely dismiss him.
    I used to completely disagree with him, and was very happy with my race bikes and 23mm tires. As time went on, I grew frustrated with various aspects of them, and tried more 'conservative' solutions. Then one day after a 300 I tried a friend's Boulder and it was a relevation...shortly after I discovered his website as a source of parts and then his blog.

    Basically, I like data. My experiences have led me to favour 'classic' French rando bikes, but generally speaking when I'm making my mind up about something I want to see some information. Years ago, everyone thought 20mm tires were best because the contact patch was thought to be smaller, and thus there was less friction. This turned out to be mostly false, but it persisted for years. Why not test it? Why not publish how the tests were done, so people can make up their own minds? Why not 'real-world' tests? Heine seems to be the only one who really does this...I don't want to hear a bike is 'laterally stiff, blah blah'. Why not try and quantify which one is actually faster? This has value to me. Where else can I get this?

    I understand what you're saying about bias, but I don't agree with your conclusion. If you set up a little online bike shop, doesn't it make sense to offer your customers some actual data about why your tires are better? Alternately, if you test fifty tires why would you not sell the best of them?

    Edit: Additionally, I don't think 'impartiality' is really necessary. It's okay to have an opinion, or even a bias, if the data is accurate and provided in a transparent fashion.
    Last edited by Commodus; 04-01-13 at 10:56 AM.

  4. #79
    Senior Member Homeyba's Avatar
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    That's kind of funny because I started randoneuring on a 70's Peugeot I used that bike for a number of years and did my first 1200k on it. I switched to the modern bike because the Peugeot beat the crap out of me. My C-40HP accepted 25's and that's pretty much what I rode. When I got the C-50 I was a little chagrined that the 25's rubbed on the rear chainstays so I had to switch to the 23's on that bike. To be honest I couldn't tell the difference between them. I think most people would be hard pressed to tell the difference between a 23mm and 25mm tire of the same make and manufacturer.
    The important thing to take from this is that there is no right or wrong way to do this. The right way is the way that gets you to the finish and allows you to meet whatever goals you might have along the way.
    As far as the bias at BQ we'll just have to agree to disagree. As far as I'm concerned it's no better than the "engineering" that comes from Santana's journal or any other proprietary journal. As long as the writer has a personal or financial stake in the outcome I treat it as if there is a bias.
    It doesn't get harder, you just go slower.

  5. #80
    Senior Member Commodus's Avatar
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    Quote Originally Posted by Homeyba View Post
    ....
    The important thing to take from this is that there is no right or wrong way to do this. The right way is the way that gets you to the finish and allows you to meet whatever goals you might have along the way....


    No one can disagree with this.

  6. #81
    Senior Member Steamer's Avatar
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    Quote Originally Posted by Commodus View Post
    Basically, I like data. My experiences have led me to favour 'classic' French rando bikes, but generally speaking when I'm making my mind up about something I want to see some information. Years ago, everyone thought 20mm tires were best because the contact patch was thought to be smaller, and thus there was less friction. This turned out to be mostly false, but it persisted for years. Why not test it? Why not publish how the tests were done, so people can make up their own minds? Why not 'real-world' tests? Heine seems to be the only one who really does this...I don't want to hear a bike is 'laterally stiff, blah blah'. Why not try and quantify which one is actually faster? This has value to me. Where else can I get this?
    IF you are serious, there are ways to do real world field tests all by yourself that allow you to determine rolling resistance of various tires at whatever inflation pressures you chose, on road surfaces of your choosing. These methods have better accuracy and precision than the simplified roll downs that Jan does. And since you'll do your own test, there is no reason to worry about bias, etc. These methods do require having a bike computer that can reliably measure and record velocity on a second by second basis. Something as simple as a Garmin 500 with an auxillary speed sensor will do. If you have, or have access to, a power meter, that is even better (but a PM is not 100% necessary either). The coolest thing is that you'll be able to measure the aero effect of the different tires at the same time - with the same test runs.

    If anyone is interested, PM me.

  7. #82
    Senior Member Commodus's Avatar
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    Quote Originally Posted by Steamer View Post
    IF you are serious, there are ways to do real world field tests all by yourself that allow you to determine rolling resistance of various tires at whatever inflation pressures you chose, on road surfaces of your choosing. These methods have better accuracy and precision than the simplified roll downs that Jan does. And since you'll do your own test, there is no reason to worry about bias, etc. These methods do require having a bike computer that can reliably measure and record velocity on a second by second basis. Something as simple as a Garmin 500 with an auxillary speed sensor will do. If you have, or have access to, a power meter, that is even better (but a PM is not 100% necessary either). The coolest thing is that you'll be able to measure the aero effect of the different tires at the same time - with the same test runs.

    If anyone is interested, PM me.
    Frankly, I have little interest in buying several dozen pairs of tires, and setting up at least two bikes identically...but feel free to post your methodology, it is maybe interesting.

  8. #83
    Senior Member Steamer's Avatar
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    Quote Originally Posted by Commodus View Post
    Frankly, I have little interest in buying several dozen pairs of tires, and setting up at least two bikes identically...but feel free to post your methodology, it is maybe interesting.
    Well, it doesn't take two bikes, all it takes is two different sets of tires, each set tested on a given bike. Perhpas two sets of tires you already own? I don't go out and spend hundreds of dollars on stuff to test, and neither would you or most other people. This info is accumulated a peice at a time, and shared with like minded individuals when possible. Mostly, I just do the tests to inform myself in an objective and quantifiable way as to how different equipment performs. I find I don't repeately buy the same tires over and over - I keep searching for something I hope I will like better, that will roll more efficiently, etc. So if I test tires as I get them, over time I can gain more insight into what tires perform better than others, and by how much. I can even calculate how many watts are at stake for varying riding speeds. I find this ability to answer my own questions liberating.

    It's not my method. Google 'robert chung virtual elevation' and you can read about it and see how people are making use of the technique.

    I just happen to be willing to help people get started with doing it themselves. It's a 'pay it forward' kind of thing for me.

  9. #84
    totally louche Bekologist's Avatar
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    Quote Originally Posted by Homeyba View Post
    To be honest I couldn't tell the difference between them. I think most people would be hard pressed to tell the difference between a 23mm and 25mm tire of the same make and manufacturer.
    I'd disagree.

    You switched from 27" to 25c to 23c, kind of a backwards progression to most riders' experiments. most riders will first stick a 25c tire under the ganks of their bike which previously only saw 23c tires because thats' what the bike came with.

    The feeling changing to 25c is going to be tangible to riders attuned to their bikes. The rider may not be able to qualify what exactly it is about the 25c that felt different, but noticeable it will be.

    observations like "I felt a little faster" "the chipseal seemed smoother" "The bike stuck in corners better" "less tired on normal routes" and "less vibration" will be widespread, not infrequent.

    I've seen this happen in a number of regulars at the shop making the switch to 25c tires, and the shop monkeys too.


    Quote Originally Posted by homeyba
    As far as the bias at BQ we'll just have to agree to disagree. As far as I'm concerned it's no better than the "engineering" that comes from Santana's journal or any other proprietary journal. As long as the writer has a personal or financial stake in the outcome I treat it as if there is a bias.
    The world view is extensively colored with studies funded by interests with a financial stake in the outcome. For example- do you think cholesterol in eggs is good or bad for us? Or, how's chocolate milk as a recovery drink?

    Yep, companies often fund studies to further their interests. In the case of Jan's "rando rollout", I don't think there's much bias evidenced in the tire roll-out test data.


    ----------------------------------
    Quote Originally Posted by steamer
    This info is accumulated a peice at a time, and shared with like minded individuals when possible.
    You mean, like how Jan Heine has done it.
    Last edited by Bekologist; 04-02-13 at 04:35 AM.
    "Evidence, anecdote and methodology all support planning for roadway bike traffic."

  10. #85
    Senior Member Steamer's Avatar
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    Quote Originally Posted by Bekologist View Post
    You mean, like how Jan Heine has done it.
    In a few minor senses, yes. The test method and number crunching approach is different, though. I also don't have any agenda except to share my enthusiasm for individuals to do their own testing. It seems to me that Jan kinda does have an agenda that is possibly less begin. At the least, I perceive that his agenda is to 'prove' to the world that what he likes and uses is what everyone else should like and use. That's how it seems to me, at least. It's possible that this characterization is unfair. But perception can become reality at a certain point. The appearance of a conflict of interest is almost as much of a problem as an actual one.

  11. #86
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    Quote Originally Posted by Steamer View Post
    In a few minor senses, yes. The test method and number crunching approach is different, though. I also don't have any agenda except to share my enthusiasm for individuals to do their own testing. It seems to me that Jan kinda does have an agenda that is possibly less begin. At the least, I perceive that his agenda is to 'prove' to the world that what he likes and uses is what everyone else should like and use. That's how it seems to me, at least. It's possible that this characterization is unfair. But perception can become reality at a certain point. The appearance of a conflict of interest is almost as much of a problem as an actual one.
    I think that Jan's "journey" from riding "racing" bikes and tires to his current espousal of wider tires, front loads, and geometry to suit is more one where his prior preconceptions were challenged by a proposed alternative and then he did his best to test whether the proposed alternative actually is either faster or is more comfortable at the same speed. See http://janheine.wordpress.com/2011/0...-used-to-ride/ and successive articles.

    I'm skeptical about his test results, but only in the sense that everyone should always be skeptical about test results. Fortunately, as you point out, one can always do one's own testing, which I've done to the extent reasonable and possible. With rare exceptions, I coast downhill on my 650Bx42 Hetres at least as fast as anyone I know on whatever tires they are riding and faster than many. It's pretty clear that quality of construction and materials is a major influence on rolling resistance, just based on my own experience riding different tires. In 700x32 tires, Panaracer TServ's are clearly slugs compared with Panaracer Pasela's with Tourguard, which are clearly slugs compared with Panaracer Pasela's without Tourguard, which are clearly slugs compared with Grand Bois Cypres. No big surprise there, TServ's are designed for heavy-duty city riding with flatproofness as a premium and rolling resistance is not even a consideration--they even say on the sidewall "TServ for Messengers". The Pasela's of either category are designed more as a touring tire. The GB Cypres is designed with rolling resistance as the primary consideration and assume that you will be fast enough that any flats encountered will still leave you faster on net. That's been my experience with the Cypres, I've only rarely gotten flats. But it's my understanding that areas with Goat's Head Thorns will provide a different experience!

    Nick

  12. #87
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    WRT "bias", it's a reasonable concern. But Jan published the methodology and the numbers. It's kind of hard to see how bias could intrude. Which is why I consider the "bias" claims more Ad hominem than reasonable counterargument.

  13. #88
    Hopelessly addicted... photogravity's Avatar
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    Do Wider Tires Really Make A Bicycle Slower?

    Quote Originally Posted by Six jours View Post
    WRT "bias", it's a reasonable concern. But Jan published the methodology and the numbers. It's kind of hard to see how bias could intrude. Which is why I consider the "bias" claims more Ad hominem than reasonable counterargument.
    I agree with your thoughts, Six jours. From my personal experience, I know that the recent change on my Norman Rapide from narrow Vittoria tires (26mm, 25mm measured on the rim) to Grand Bois Cypres (30mm, 31mm measured on the rim), did not result in slower speeds on one of my regular rides. Road irregularities that would have had me out of my saddle using the previous tires instead were approached sitting in the saddle and pedaling. Now I'm accustomed to the feel of the new setup, I'm going to get more measurements on the loop and see if my time drops when compared to the old setup.

    Another data point is my Bilenky 650B tandem. On some rides I've been on with other tandems, when they would get into sections of road where the surface was rough (they were riding on narrow tires, 25-28mm typically), they'd be out of their saddles standing on the pedals while my wife and I would continue pedaling. On those sections, we would close the gap and sometimes pass them. When the road smoothed out, the other tandems would start pulling away or catch up and pass us because they were strong teams. Given the strength of the other teams, they should have consistently stayed out front, but they didn't and I attribute that to the tires we were riding.

    I again want to repeat that my comments and thoughts on the matter are purely anecdotal, but appear to be in line with testing that Jan Heine has done in recent years.
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  14. #89
    Senior Member Homeyba's Avatar
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    Quote Originally Posted by Six jours View Post
    WRT "bias", it's a reasonable concern. But Jan published the methodology and the numbers. It's kind of hard to see how bias could intrude. Which is why I consider the "bias" claims more Ad hominem than reasonable counterargument.
    I don't really understand why you'd consider bias an irrelevant claim. Just because someone publishes a methodology and data doesn't mean the data is relevant or hasn't been fudged. I'm not saying BQ does that but, do you think BQ's going to print data that says the tires they personally helped developed and sell are crap?
    Cigarettes are good for you too, Marlboro has the research that says so. They have methodology and data too. You can call that ad hominem but then maybe you could point to all the back up research by unbiased researchers that verifies BQ's findings? That may come and it may not but until then I'll view their findings as just another baised sales pitch.
    It doesn't get harder, you just go slower.

  15. #90
    Senior Member Commodus's Avatar
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    Quote Originally Posted by Homeyba View Post
    I don't really understand why you'd consider bias an irrelevant claim. Just because someone publishes a methodology and data doesn't mean the data is relevant or hasn't been fudged. I'm not saying BQ does that but, do you think BQ's going to print data that says the tires they personally helped developed and sell are crap?
    Cigarettes are good for you too, Marlboro has the research that says so. They have methodology and data too. You can call that ad hominem but then maybe you could point to all the back up research by unbiased researchers that verifies BQ's findings? That may come and it may not but until then I'll view their findings as just another baised sales pitch.
    Actually they have done that...so yea I'd say they would. If I can find the info I'll post it here.

  16. #91
    Senior Member Commodus's Avatar
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    Ah yes, here it is:

    When the Mitsuboshi 650B x 38 mm tires were discontinued, I had an idea for a stop-gap replacement: What about using the mold of the Panaracer “Col de la Vie,” but with the Grand Bois casing and tread material? The result was the Grand Bois “Ourson.” Unfortunately, the “micro-knob” tread pattern of the Col de la Vie dominated the experience of riding the Ourson: It was not as fast as the other Grand Bois tires, and the knobs squirmed and flexed, making the Ourson less than ideal both in a straight line and in corners.

    Others did not share our concerns, and raved about these tires online. It would have been easy leave it at that, and not review the Ourson at all, but that would not have been honest. The review in Bicycle Quarterly was harsh: “We do not feel that the Ourson warrants the extra cost [over the Col de la Vie].” When we did this, we knew that sales of these tires would collapse. Our stocks of these tires remained in the warehouse for years, until we finally closed them out when the completely new and excellent Grand Bois Lierre was announced.
    From the blog post in which Heine address this very issue: http://janheine.wordpress.com/2012/0...-what-we-like/

  17. #92
    Senior Member Homeyba's Avatar
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    Let me make this clear because I don't want anyone to think that I'm trying to besmirch BQ's reputation. I've not seen anything that makes me question their integrity. My point here is that BQ is a sales tool just like the Rivendell newsletter, Tandems and Tandeming by Santana and many others. If you choose to take what they write as gospel and free from bias you are more than free to do so.
    It doesn't get harder, you just go slower.

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    That's apparently where we differ: I don't see BQ as a sales tool. I mean, I suppose it is possible that Jan started the magazine as part of a far-reaching conspiracy-type thing (he didn't start selling bike parts until years after introducing the magazine) but I figure that's pretty unlikely. I think his answer ("I couldn't find the parts I wanted to use myself, so decided to start importing them) makes more sense.

    As you point out, he could actually be fudging his numbers. I simply choose to believe that he (along with the people working with him, assuming he didn't make them up too) is not publishing a magazine filled with blatant lies for the purpose of selling small numbers of high-end bike parts to a tiny minority of cyclists.

  19. #94
    totally louche Bekologist's Avatar
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    At least Jan took the time to do a rollout test and publish the numbers. He's got some hard proof that 25c tires are faster than 20c tires generally speaking. We don't have to rely on the whims of racing to trickle down to rando....



    BQ a sales tool?
    Egads, the world must look like one huge rolling advertisement. Avoid all magazines and television.

    BQ is definitely something more than a J Peterman catalog, It's a magazine targeting the rando/classic cycling community, dedicated to the traditions and origins of randonneuring, or something thereabouts.

    Jeesh. So the guy wanted faster, big volume tires.
    Last edited by Bekologist; 04-04-13 at 03:41 AM.
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    Quote Originally Posted by Steamer View Post
    People who think differences in rolling resistance coefficient between different, outwardly similar tires doesn't matter much mainly think that (IMO) because they have no good way to perceive the difference moment by moment. Extra rolling resistance kills you by a thousand cuts. The extra work it makes you do is present on every foot traveled.

    Quoting a friend of mine:

    One handy way to "envision" the cost of rolling resistance is to compare it to slope. If you go back and look at the power equation, the amount of power needed to overcome rolling resistance is Crr*mass*gravity*speed while the amount of power needed to overcome a change in altitude is mass*gravity*height/time. But height/time is approximately slope*speed. So rolling resistance is Crr*m*g*v and climbing is slope*m*g*v. So Crr scales exactly like slope in terms of power demand.
    So a Crr of .005 is exactly equivalent to a slope of .005, or .5%.
    Suppose you had a choice of two tires, Crr(A) = .005 and Crr(B) = .004. That's a difference of .001, or equivalent to a change in slope of 0.1%. Over the course of a 1200k randonnee, that's like climbing a 1200m hill.
    The difference between a pretty good and sorta-bad tire can be about .002 in Crr. Which is 2x the example given. That's like adding 1,950 feet of climbing to a 300K just due to a poor choice in tires. No thanks. This stuff is hard enough without handicapping myself with crappy tires.
    Nice. Not that you should ignore durability, comfort, and ease of repair but if, for the purposes of this discussion, you do, then it makes sense to take the entire drag profile into account, not just the Crr piece of the story. A reasonable rule of thumb for racing speeds is that a difference in Crr of .001 is roughly equivalent to a difference in CdA of .01 m^2. At randonee speeds, a more reasonable rule of thumb is that a difference in Crr of .001 is roughly equivalent to a difference in CdA of around .02 m^2 (the exact threshold will depend on your actual "cruising" speed). That is, if you're willing to switch to wider tires whose Crr decreases by .001, you'll end up to the net good as long as it increases your CdA by less than .02 m^2. What this means is that racers use narrower tires not because they're clueless about the rolling resistance differences between narrow and wide tires but because they understand the net trade-off for their particular purpose. Plus, they don't usually have to worry about puncture-resistance.

    The virtue of the newer "wide" wheels (for example, like the Zipp Firecrests or the new Heds) is that you don't take as much of an aerodynamic hit when you use wider tires (though we're still talking 25mm as opposed to 20's or 21's). If you take a look at the cross-section of these new rims they're sort of like a tailbox on a recumbent bike: they don't affect the frontal area but they do affect the Cd of the tire-rim combination. That's at zero yaw -- at non-zero yaw (and randonneurs are likely to see a wider range of yaw angles than racers) the newer rims do even better than box rims. Bottom line, if randonneuring were a larger segment of the market more effort would be spent on designing "wide, low-speed, high yaw" wheels and tires.

    As a comment on the BQ Crr testing methodology, note that it requires at least two other people as timers (one at the "entry" to the timing trap and another at the exit), and you have to have a way to synchronize their timing so you can get a true estimate of your elapsed time as you roll through the trap. Since they're only measuring elapsed time, you're limited in the error estimation. As you know, there are ways to get around these limitations.

  21. #96
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    Quote Originally Posted by Bekologist View Post
    At least Jan took the time to do a rollout test and publish the numbers. He's got some hard proof that 25c tires are faster than 20c tires generally speaking. We don't have to rely on the whims of racing to trickle down to rando....
    The amusing bit is that the case could be made that Jan is largely responsible for the re-introduction of wider tubulars to pro cycling. Homeyba would rather eat worms than admit the possibility of any such thing, but then, that may be why I find it amusing!

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    totally louche Bekologist's Avatar
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    Quote Originally Posted by Six jours View Post
    The amusing bit is that the case could be made that Jan is largely responsible for the re-introduction of wider tubulars to pro cycling. Homeyba would rather eat worms than admit the possibility of any such thing, but then, that may be why I find it amusing!
    but the tire don't fit!
    Last edited by Bekologist; 04-05-13 at 03:28 AM.
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    Quote Originally Posted by RChung View Post
    Nice. Not that you should ignore durability, comfort, and ease of repair but if, for the purposes of this discussion, you do, then it makes sense to take the entire drag profile into account, not just the Crr piece of the story. A reasonable rule of thumb for racing speeds is that a difference in Crr of .001 is roughly equivalent to a difference in CdA of .01 m^2. At randonee speeds, a more reasonable rule of thumb is that a difference in Crr of .001 is roughly equivalent to a difference in CdA of around .02 m^2 (the exact threshold will depend on your actual "cruising" speed). That is, if you're willing to switch to wider tires whose Crr decreases by .001, you'll end up to the net good as long as it increases your CdA by less than .02 m^2. What this means is that racers use narrower tires not because they're clueless about the rolling resistance differences between narrow and wide tires but because they understand the net trade-off for their particular purpose. Plus, they don't usually have to worry about puncture-resistance.

    The virtue of the newer "wide" wheels (for example, like the Zipp Firecrests or the new Heds) is that you don't take as much of an aerodynamic hit when you use wider tires (though we're still talking 25mm as opposed to 20's or 21's). If you take a look at the cross-section of these new rims they're sort of like a tailbox on a recumbent bike: they don't affect the frontal area but they do affect the Cd of the tire-rim combination. That's at zero yaw -- at non-zero yaw (and randonneurs are likely to see a wider range of yaw angles than racers) the newer rims do even better than box rims. Bottom line, if randonneuring were a larger segment of the market more effort would be spent on designing "wide, low-speed, high yaw" wheels and tires.

    As a comment on the BQ Crr testing methodology, note that it requires at least two other people as timers (one at the "entry" to the timing trap and another at the exit), and you have to have a way to synchronize their timing so you can get a true estimate of your elapsed time as you roll through the trap. Since they're only measuring elapsed time, you're limited in the error estimation. As you know, there are ways to get around these limitations.
    Thanks. Particularly for those rules of thumb. .01 isn't a huge change in CdA, but not insignifcant either. I don't personally yet have a sense of how different tire widths would impact CdA by that amount. Do you have any examples / points of reference on this? I am sure they are for two tires that are both narrower than what I like to use, but the example might still be illustrative.

    I have a test planned soon to compare my 25mm Duranos (actual width: 24 mm) to my 32mm Vittoria Rando Hypers (actual width 31.5mm). I suspect the Hypers will produce a lower Crr (based on how they feel to ride), but of course will most certainly have a higher CdA. I am mounting both tires on 19mm wide rims, so the CdA penalty for the fatter rubber will be in full effect. I suppose the more detailed way (i.e. not a rule of thumb way) of looking at the tradeoff issue is to just plug and chug the Crr and CdA figures associated with different tires into a calculator (like the online Gribble calculator) for some anticipated moving average on a randonee and see which CdA/Crr pair results in lower power required.

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    Quote Originally Posted by Steamer View Post
    Thanks. Particularly for those rules of thumb. .01 isn't a huge change in CdA, but not insignifcant either. I don't personally yet have a sense of how different tire widths would impact CdA by that amount. Do you have any examples / points of reference on this? I am sure they are for two tires that are both narrower than what I like to use, but the example might still be illustrative.
    The change in frontal area (A) is easy to calculate but the change in the drag area (CdA) isn't -- the rim shape doesn't affect A at all, so the change in CdA is entirely due to how it affects Cd. That said, going from a 25mm tire to a 32mm tire should increase A by roughly .005, and the Cd will probably increase as well.

    As a timely and perhaps interesting aside (interesting if you're obsessed about these kinds of things and if you are there may be therapy indicated in your future) a rim manufacturer was just in the A2 wind tunnel yesterday checking out which tires of which widths had the lowest CdA when mated with their rims. To repeat, this was a wind tunnel -- they weren't checking out the Crr characteristics but just the aero characteristics.

    [Edited to add] Of course, this doesn't have much to do with rando speeds (except for the non-zero yaw part) but it does give you an idea of how people are interested in the trade-off between Crr and CdA.
    Last edited by RChung; 04-05-13 at 09:46 AM.

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    Quote Originally Posted by RChung View Post
    As a comment on the BQ Crr testing methodology, note that it requires at least two other people as timers (one at the "entry" to the timing trap and another at the exit), and you have to have a way to synchronize their timing so you can get a true estimate of your elapsed time as you roll through the trap. Since they're only measuring elapsed time, you're limited in the error estimation. As you know, there are ways to get around these limitations.
    Ah, I see from the most recent issue of BQ that they've switched to a new testing protocol. It appears they're using a power meter now, though the description doesn't give quite enough information about the methodology and protocol to determine exactly how it is done or its precision.

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