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  1. #1
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    26" - 650B: no difference in contact patch? Drawing!

    Question:

    I get that a slightly bigger wheel has a slightly bigger contact patch with the ground, that is a FLAT/SMOOTH wheel.

    What about a knobbly MTB tire?

    Unless you are in fine sand, both 650B and 26" wheels have probably the same amount of rubber knobs hooked to the ground? See image:

    26" - 650B: no difference in contact patch? Drawing!-screenshot-2014-02-11-10.19.23.jpg

    Highly realistic rendering made in PowerPoint....

  2. #2
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  3. #3
    bikeaholic
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    I don't know about contact patch, but your drawing really makes me want a Reese's peanut butter cup.

  4. #4
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    Quote Originally Posted by Dougie View Post
    I don't know about contact patch, but your drawing really makes me want a Reese's peanut butter cup.
    I'll second that.
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  5. #5
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    Yea ill take the 650b cup please.

  6. #6
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    29" cups are where its at.

  7. #7
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    Go big or go home muhfahkers!


  8. #8
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    Quote Originally Posted by mrmentallo View Post
    go big or go home muhfahkers!

    ftw!!!!
    If I had a black light this place would look like a Jackson Pollock painting.

  9. #9
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    Quote Originally Posted by MrMentallo View Post
    Go big or go home muhfahkers!

    +2 cups

  10. #10
    dwt
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    26" - 650B: no difference in contact patch? Drawing!

    Quote Originally Posted by Jan Schultink View Post
    Question:

    I get that a slightly bigger wheel has a slightly bigger contact patch with the ground, that is a FLAT/SMOOTH wheel.

    What about a knobbly MTB tire?

    Unless you are in fine sand, both 650B and 26" wheels have probably the same amount of rubber knobs hooked to the ground? See image:

    Click image for larger version. 

Name:	Screenshot 2014-02-11 10.19.23.jpg 
Views:	829 
Size:	46.8 KB 
ID:	868874

    Highly realistic rendering made in PowerPoint....
    OMG. You've pulled back the curtain, the wizard is a fraud. Oh, wait, nobody has marketed this wheel size based on contact patch. That would be 29", and there are still arguments about that. It is common knowledge that so called 650b wheels are very close in size to so called 26" ( which are actually 26.5"-- except close is not and never was identical.

    Except for Giant, the marketing is not that 650b is "better" than 26" or 29"; rather that it is somewhere in between for people that are not happy for whatever reason with either 26" or 29". A compromise size might or might not suit such folks. The point it's another choice with good and bad characteristics, like everything else. Only the individual can decide what works or doesn't for them.
    Old enough to know better. And old enough not to care. Best age to be.

  11. #11
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    But that's a bit simplistic comparing fully inflated at rest, what about real world performance with the tyre squished mid corner???
    You need to get a 650B and a 26 both at 18psi and squish them in those peanut butter cups for a real 3d comparison

    oh and that's leaned over too so its relevant
    Last edited by SlashNZ; 02-11-2014 at 03:45 PM. Reason: more blah added

  12. #12
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    Where can I get some tires like that?
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  13. #13
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    Get wheels that offer a full spectrum of sizes between 24"-29" and be happy.


  14. #14
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    Re: 26" - 650B: no difference in contact patch? Drawing!

    Quote Originally Posted by Dougie View Post
    I don't know about contact patch, but your drawing really makes me want a Reese's peanut butter cup.
    I'd like a couple D cups.

    Not for me. Right about... here.

    OP, I'd urge you to consider the size of a knob compared to the overall size of the tire. Though you can probably get away with a little less tire pressure in a big wheel.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  15. #15
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    I knew you guys would have a sense of humour!

  16. #16
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    NICE WHEELS!!!
    SPYDER MOTORCYLES is MAKING - 3 WHEEL BIKES NOW!!

  17. #17
    dwt
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    26" - 650B: no difference in contact patch? Drawing!

    Quote Originally Posted by Jan Schultink View Post
    I knew you guys would have a sense of humour!
    Old enough to know better. And old enough not to care. Best age to be.

  18. #18
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    To be serious for a moment:

    Contact patch doesn't change with wheel size like people think.

    If you have 3 different size wheels and tires with 50 psi in each, and you put a 100 lb load on them, they will all deform to make a 2 square inch contact patch (50 lb/sq in x 2 sq in = 100 lb). The shape of the contact patch will be different but not the amount of contact patch.

  19. #19
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    I think the contact patch size changes too. Here's why...

    I think when different wheel sizes are in play, psi isn't quite the right conversation to have. There's an article kicking around that claims that there's an optimal amount of deformation for a road tire. They measure it based on how far the rim drops relative to its height above the pavement. Their optimal is 15%. I suspect ours is higher, but I think it still exists, and as long as pinch flats or something don't get in the way, I think it's the same from wheel size to wheel size.

    Since the outside of a bigger tire has a larger radius, it doesn't take as much wheel drop to get the same contact patch. So one lets a little air out.

    I got to thinking about this after I noticed that I can get away with less air in the miserly 29x2.2 tires that came on my bike than in the generous 26x2.25s on my older bike. One of my coworkers mentioned a bunch of modeling finding something similar about the difference in wheel sizes - basically that the only things a 29er wheel has going for it are getting to use a little less pressure and the change in angle of attack for square-edged hits.

    Anyway, I think it bears thinking about. And I'd encourage anyone who runs the same pressure in similar-width tires across different wheel sizes to try dropping a few psi and see what you think.

    I agree with the idea that same psi means same contact patch size. It would violate the laws of physics if it didn't. I just don't think pressure is the right thing to try to hold constant in making this comparison.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  20. #20
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    26" - 650B: no difference in contact patch? Drawing!

    Quote Originally Posted by AndrwSwitch View Post
    I think the contact patch size changes too. Here's why...

    I think when different wheel sizes are in play, psi isn't quite the right conversation to have. There's an article kicking around that claims that there's an optimal amount of deformation for a road tire. They measure it based on how far the rim drops relative to its height above the pavement. Their optimal is 15%. I suspect ours is higher, but I think it still exists, and as long as pinch flats or something don't get in the way, I think it's the same from wheel size to wheel size.

    Since the outside of a bigger tire has a larger radius, it doesn't take as much wheel drop to get the same contact patch. So one lets a little air out.

    I got to thinking about this after I noticed that I can get away with less air in the miserly 29x2.2 tires that came on my bike than in the generous 26x2.25s on my older bike. One of my coworkers mentioned a bunch of modeling finding something similar about the difference in wheel sizes - basically that the only things a 29er wheel has going for it are getting to use a little less pressure and the change in angle of attack for square-edged hits.

    Anyway, I think it bears thinking about. And I'd encourage anyone who runs the same pressure in similar-width tires across different wheel sizes to try dropping a few psi and see what you think.

    I agree with the idea that same psi means same contact patch size. It would violate the laws of physics if it didn't. I just don't think pressure is the right thing to try to hold constant in making this comparison.
    Except in practice, I run about the same pressure for tires of the same actual cross section (not the nominal size on the label) and construction on the same width rims, regardless of diameter.

    Same pressure = same contact patch area.
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  21. #21
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    Interesting. Have you tried using less for same-width tires on bigger wheels?
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  22. #22
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    Quote Originally Posted by AndrwSwitch View Post
    basically that the only things a 29er wheel has going for it are getting to use a little less pressure and the change in angle of attack for square-edged hits.
    I think overall rolling resistance is less as well.


    I agree with the idea that same psi means same contact patch size. It would violate the laws of physics if it didn't. I just don't think pressure is the right thing to try to hold constant in making this comparison.
    I agree with you in theory. You many be able to run lower pressure with 29ers, and that indeed changes the size of the contact patch. For me though, I don't usually do that. I just have a pressure that feels right, but I haven't experimented that much.

    The whole theory of the tire pressure equalizing to the weight on the tire is a good approximation, but there are some variables with contact patch. For example, if you hit a patch of soft dirt or sand the tire will sink, and the 29er tire curves away from the ground more slowly, so I envision that more knobs would be on the ground for a 29er in that situation.
    Stiff sidewalls, like on UST tires, also have some effect on the contact patch size.

  23. #23
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    26" - 650B: no difference in contact patch? Drawing!

    Quote Originally Posted by AndrwSwitch View Post
    Interesting. Have you tried using less for same-width tires on bigger wheels?
    If you are talking to me, I have tried almost everything. Literally many hundreds of tires on dozens of rims at all pressures.
    Usually the use the lowest pressure possible (functional) for the setup, but some combos perform better at higher pressures.
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  24. #24
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    If trails were flat ............

  25. #25
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    Wait... who here cares about contact patch? Are you trying to set records on the skidpad?

  26. #26
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    I care when I am cornering but thats about it.

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  27. #27
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    Re: 26" - 650B: no difference in contact patch? Drawing!

    Quote Originally Posted by shiggy View Post
    If you are talking to me, I have tried almost everything. Literally many hundreds of tires on dozens of rims at all pressures.
    Usually the use the lowest pressure possible (functional) for the setup, but some combos perform better at higher pressures.
    I'll have to put a caliper to my rim and tire next time I shuffle things around. The 26" bike and 29er both have 2.25" Rocket Ron Evos on the front, but the one on the old bike is a year or two old and the one on the new bike is this year's. I'm also not controlling for the rim. Regardless, it's a small difference - 2.5 psi.
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