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  1. #101
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    Quote Originally Posted by garage sale GT View Post
    So first it's not what everybody else notices, then it isn't?
    Quote Originally Posted by garage sale GT View Post
    Gauging from what you said so far, it's not particularly amazing that you never noticed that narrow tires at a given pressure vibrate less also.
    I missed the "at a given pressure" part. The problem is that people almost always use higher pressure with narrower tires. To keep the load capacity the same (eg, the same resistance to pinch flats), you have to use more pressure in a narrower tire. That is, a narrower tire run at lower pressure to reduce vibration is a less functional tire in other areas (eg, more prone to pinch flats and more rolling-resistance).

    Quote Originally Posted by garage sale GT View Post
    Someone pointed out that you can't go by graphs that say a 28 rolls easier on a steel drum than 23s, at the same pressure, because you don't use the same pressure.
    You don't ride on steel drums either (except for rollers).

    Quote Originally Posted by garage sale GT View Post
    Sounds like they don't think 28s have less RR than 23s, doesn't it? What does that tell you about the steel drum tests that predicted the opposite? Does that include the aforementioned race teams?
    You really can't talk about tire widths without talking about tire pressure. Narrower tires (as tires are made) allow the use of higher pressure. That means, we'd have to know what pressure they were using in the different tires to even begin talking about why they use 23s on smooth roads.

    ===============

    Quote Originally Posted by garage sale GT View Post
    Gauging from what you said so far, it's not particularly amazing that you never noticed that narrow tires at a given pressure vibrate less also.
    Quote Originally Posted by garage sale GT View Post
    That's why narrower tires are good, incidentally. They can be run at a higher PSI without bouncing or shaking. This factor is not testable by the steel drum tests in the picture on the first page of this thread.
    If you want contradiction, look at your own posts. From what you said in these, increasing and decreasing pressure in a narrow tire decreases "vibration/bouncing/shaking".
    Last edited by njkayaker; 04-16-11 at 05:12 PM.

  2. #102
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    Quote Originally Posted by njkayaker View Post
    I missed the "at a given pressure" part. The problem is that people almost always use higher pressure with narrower tires. To keep the load capacity the same (eg, the same resistance to pinch flats), you have to use more pressure in a narrower tire. That is, a narrower tire run at lower pressure to reduce vibration is a less functional tire in other areas (eg, more prone to pinch flats and more rolling-resistance).
    It's not about the strength of the tire.

    The reason steel drum tests show less rolling resistance for wider tires at the same pressure is because the carcass deforms less. That's also why you can't use as high a maximum pressure when riding on smooth asphalt. They will start to eat up your power generating road buzz at a lower PSI.
    You don't ride on steel drums either (except for rollers).
    You really can't talk about tire widths without talking about tire pressure. Narrower tires (as tires are made) allow the use of higher pressure. That means, we'd have to know what pressure they were using in the different tires to even begin talking about why they use 23s on smooth roads.
    I don't think so. You would simply have to realize that generating road buzz eats up a lot of energy, and you won't get less RR in the real world on smooth asphalt from a 28 until it is run at sufficiently low pressure to deform as easily as the 23, which will prevent road buzz, which eats power. It is larger so it will deform more at that pressure, generating more RR when run at a real-world max determined by the need not to waste pedal power forcing the bike to vibrate up and down.

    Also, assuming the airflow closes nicely behind an aero rim, a 28 has about 1% more frontal area than a 23.

  3. #103
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    Here is a graph which suggests that in the real world, a tire simply starts to generate rapidly increasing RR due to starting to bounce. It's only one test and I don't claim to have analyzed a lot of data for my theory. I just kind of stumbled upon this. You can see that as PSI goes up, at a certain point the RR of the real world result goes through the roof. I am assuming that is because the pressure is so high it starts to bounce over the aggregate in the asphalt rather than conforming to the road.

  4. #104
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    Quote Originally Posted by njkayaker View Post
    If you want contradiction, look at your own posts. From what you said in these, increasing and decreasing pressure in a narrow tire decreases "vibration/bouncing/shaking".
    Show me where.

  5. #105
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    Quote Originally Posted by garage sale GT View Post
    Here is a graph ...
    Generally, it's considered proper to reference your sources. If not to give due credit, at least so others can evaluate the credibility on their own.

  6. #106
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    Quote Originally Posted by asgelle View Post
    Generally, it's considered proper to reference your sources. If not to give due credit, at least so others can evaluate the credibility on their own.
    I don't remember. It was some blog. First graph I pulled up. I don't base my views on the graph; I didn't do the search that brought it up until after this thread hit page 5. Having inserted it so casually, I don't really know where to find it.
    Last edited by garage sale GT; 04-17-11 at 12:02 PM.

  7. #107
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    Quote Originally Posted by garage sale GT View Post
    I don't remember. It was some blog. First graph I pulled up. I don't base my views on the graph; I didn't do the search that brought it up until after this thread hit page 5.
    It's not for your evaluation, it's so the rest of us know what to make of the data you chose to share with us (and let's not forget that credit thing). Anyway, it comes from here http://forum.slowtwitch.com/cgi-bin/...engine#1909561

    You might even have gotten to it from here http://www.bikeforums.net/showthread...der-the-better

  8. #108
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    Quote Originally Posted by garage sale GT View Post
    Show me where.
    Here.

    You are saying basically opposite things in these two paragraphs.

    Quote Originally Posted by garage sale GT View Post
    Gauging from what you said so far, it's not particularly amazing that you never noticed that narrow tires at a given pressure vibrate less also.
    That is, you are saying using the same pressure in wider and narrower tires reduces "vibration" comparitively. You are basically describing the case where the narrower tires is "under inflated" and the wider tire is "over inflated" (more or less). What you are describing is the same effect as using a lower pressure in the same tire (that is, reducing pressure reduces "vibration"). The problem with running a lower pressure in narrower tires is that it reduces the load that can be accommodated (eg, for a given tire, heavy people use higher pressure and lighter people can use less).

    Quote Originally Posted by garage sale GT View Post
    That's why narrower tires are good, incidentally. They can be run at a higher PSI without bouncing or shaking. This factor is not testable by the steel drum tests in the picture on the first page of this thread.
    That is, you are saying using a higher pressure in narrow tires reduces "bouncing/shaking". But narrower tires run at higher pressures are less comfortable.

    ====================

    Quote Originally Posted by garage sale GT View Post
    I am assuming that is because the pressure is so high it starts to bounce over the aggregate in the asphalt rather than conforming to the road.
    The tires have to "give" enough (but not too much) to absorb shocks and variations in road surface. The pressure certainly can be too high.

    Interesting graph (let's assume it's accurate for different tires).

    I suspect that the upward turn in RR with increased pressure occurs earlier on rougher roads. If so, that's why one uses wider tires for rougher roads. The basic effect is the same with cars: race cars driven on smooth tracks have stiff suspensions.

    http://en.wikipedia.org/wiki/Suspension_(vehicle)
    Last edited by njkayaker; 04-17-11 at 02:55 PM.

  9. #109
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    Quote Originally Posted by njkayaker View Post
    Here.

    You are saying basically opposite things in these two paragraphs.


    That is, you are saying using the same pressure in wider and narrower tires reduces "vibration" comparitively. You are basically describing the case where the narrower tires is "under inflated" and the wider tire is "over inflated" (more or less). What you are describing is the same effect as using a lower pressure in the same tire (that is, reducing pressure reduces "vibration"). The problem with running a lower pressure in narrower tires is that it reduces the load that can be accommodated (eg, for a given tire, heavy people use higher pressure and lighter people can use less).


    That is, you are saying using a higher pressure in narrow tires reduces "bouncing/shaking". But narrower tires run at higher pressures are less comfortable.
    I actually said narrow tires can tolerate being run at higher pressure before they start to vibrate. I'm not sure how you decided that meant you get less vibration by adding more pressure.

  10. #110
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    Quote Originally Posted by garage sale GT View Post
    I actually said narrow tires can tolerate being run at higher pressure before they start to vibrate. I'm not sure how you decided that meant you get less vibration by adding more pressure.
    "Start to vibrate"? You mean it's binary? What do you mean by "vibrate". Why do people tend to prefer wider tires and lower pressure on rough roads?

    Quote Originally Posted by garage sale GT View Post
    Gauging from what you said so far, it's not particularly amazing that you never noticed that narrow tires at a given pressure vibrate less also.
    Do this mean that people should be using under inflated narrower tires on rough roads?

    Why are you taking about comparing an under-inflated narrow tire with a wider-tire or an narrow tire with an over-inflated wider tire?

    You are basically comparing a soft suspension with a hard suspension.

    The amount of pressure one uses for a given load is lower in wider tires and higher in narrower tires. Increasing the pressure (in any tire) makes the suspension harder.
    Last edited by njkayaker; 04-17-11 at 04:54 PM.

  11. #111
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    Quote Originally Posted by njkayaker View Post
    "Start to vibrate"? You mean it's binary? What do you mean by "vibrate". Why do people tend to prefer wider tires and lower pressure on rough roads?
    By "vibrate" I mean when the bike shakes i.e. the plain speech meaning of the word "vibrate." If you increase tire pressure, you will eventually experience the onset of road buzz. I am theorizing that too much road buzz can eat energy.
    Do this mean that people should be using under inflated narrower tires on rough roads?
    No, they'd snakebite. That's a different issue than rolling resistance. And I'm not talking about rough roads but about any road. In case you never noticed, an asphalt road has little bits of gravel stuck together with asphalt. It is not nearly as smooth as a steel drum. Also in case you never noticed, if you keep increasing tire pressure, at some point you can feel a vibration through the bars, seat and pedals, even if you're riding on unbroken asphalt.
    Why are you taking about comparing an under-inflated narrow tire with a wider-tire or an narrow tire with an over-inflated wider tire?
    My whole point is that this is NOT done in the real world, so the steel drum data which show wider road tires rolling easier than narrow ones at a given pressure does not prove that wider tires have less rolling resistance.
    You are basically comparing a soft suspension with a hard suspension.

    The amount of pressure one uses for a given load is lower in wider tires and higher in narrower tires. Increasing the pressure (in any tire) makes the suspension harder.
    Therefore you can't say the steel drum tests prove wider tires have less rolling resistance since the curve for the wide tires is below the curve for the narrow ones. Which is my point.

    That "suspension" is also necessary for a smooth roll over most types of unbroken pavement. Maybe that's what you people don't get about my argument. A larger tire pumped up to the same pressure as a narrower tire may deform less on a steel roller test, but it will roll rough over asphalt for the same reason it rolls easier on the steel drum, i.e. the casing is harder to deform, i.e. its ability to deform to absorb shock is also less. Casing deformation causes RR!!! And when you let the pressure out till the wide tire rolls smooth, then you have probably more RR than a narrow tire at its best pressure, because the reason the ride smoothed out is because you're letting the casing deform over bumps. It's wider and can bear more load, so the pressure has to be let out even more than to make it sag as much as the narrow tire, for equivalent smoothness.

    My friend, I think you lack the patience to try to grasp my point. Why don't you either give it the time it needs or do something else?
    Last edited by garage sale GT; 04-17-11 at 05:38 PM.

  12. #112
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    Incidentally, besides snakebiting, overly narrow tires would worsen resistance because when the rim bottomed out, a portion of the bike's forward momentum would be converted into upward momentum as the rim bounced the bike upward. But the main reason not to use overly narrow tires is that they would snakebite. A wider tire would also bridge certain gaps in some surfaces better, leading to a smoother, more even ride.

    But all this stuff comes into play only if a tire is TOO narrow for the surface you're riding on.

  13. #113
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    Quote Originally Posted by garage sale GT View Post
    By "vibrate" I mean when the bike shakes i.e. the plain speech meaning of the word "vibrate." If you increase tire pressure, you will eventually experience the onset of road buzz. I am theorizing that too much road buzz can eat energy.
    I'm not sure it "starts" at a particular pressure. We have no idea what "too much" is and how much energy would be eaten. It's possible that the rider's tolerance for road buzz would be hit before any appreciable energy loss.

    Quote Originally Posted by garage sale GT View Post
    <snip>
    This makes sense.

    Quote Originally Posted by garage sale GT View Post
    My friend, I think you lack the patience to try to grasp my point. Why don't you either give it the time it needs or do something else?
    No, you just weren't being that clear before.

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