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  1. #26
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    Quote Originally Posted by Berkeley Mike View Post
    We disagree but probably ride differently in different places.
    Some riders happily add a pound to their bike with a dropper post while others don't see any value. Both are right.

    At one end you have rubber weighing 1000+ grams and some new interest in tires in ~3 inch widths. It may be that this approach can accomplish similar goals with superior weight/size tradeoffs. That's why it's not clear to me that it represents a "weight penalty" even though it clearly would to an XC racer.

    It may turn out that you can get "1000 gram" performance out of an 800 gram tire with the added benefit of no burps or rim strikes. That's a win at no weight penalty plus tire clearance may improve. On the other hand, you'll never see "400 gram" performance out of a 200 gram tire so it just won't translate on that end of the range.

    Of course, it's also possible that it's a dead end.

    I'm someone whose weight and terrain limit my pressures through rim strikes. It's not clear, though, how much lower I could go before other factors come into play. I'd like to experiment with it, just not excited to drill out a carbon rim only to find that my preferred tires don't like the lowered pressures or that the solution doesn't agree with my rim width. Seems like a good idea to me to build a front wheel with a Dually to experiment with before going all in.

  2. #27
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    Quote Originally Posted by half_man_half_scab View Post
    So wouldn't adding this system reduce the volume inside of your tire, making it more progressive?
    It would make the spring rate somewhat more progressive but not nearly enough. It's really just a nice, soft bump stop. Technically, the volume of the tire is unchanged.

  3. #28
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    It's two separate air chambers, both of which are small when you add the insert. I guess the progressive is the point, but I'd like to try before reserving judgement.

  4. #29
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    How the overall volume reacts is what counts

    Quote Originally Posted by craigsj View Post
    It would make the spring rate somewhat more progressive but not nearly enough. It's really just a nice, soft bump stop. Technically, the volume of the tire is unchanged.
    It changes the spring rate feel in the tire/wheel noticeably and has more rebound or bounce on certain hits,, or a sort of bob off of g-outs. There is less "travel" in the low pressure tire portion.. and that initial feel will now have to do more with the construction of the tire casing..


    The higher pressure portion will only save the rim if psi is high enough. That higher psi restricts the volume in the lower psi portion and how the overall volume reacts, that is what counts. It is definitely changed

  5. #30
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    Quote Originally Posted by Deerhill View Post
    It changes the spring rate feel in the tire/wheel noticeably and has more rebound or bounce with certain hits. There is less "travel" in the low pressure tire portion.. and that initial feel will now have to do more with the construction of the tire casing..
    Are you speaking from experience?

    If you estimate the overall volume of air in a typical tire, then estimate how much volume is reduced when the tire is loaded, you'll see that the change is quite small (less than 1%). Now, if this system cuts the low pressure volume in half, which it won't, the percentage change doubles but is still nothing.

    I seriously doubt the "feel" is changed "noticably" or has more "rebound or bounce". It is true mathematically but it's 1 or 2 orders of magnitude away from significance.

    Volume of 29er trail tire (torus, 720x53): ~2x10^7 mm^3
    Volume lost, 20 psi 100 pound load: ~2x10^4 mm^3
    relative change: 0.1%

    I think that's a generous estimate of volume change, but even at 10x more than that, it's still only 1%. Changes in progression here are very small. Any change in feel will come from the drop in pressure and the additional support at the bead. Spring progression is the same until the tire engages the inner chamber.

    Quote Originally Posted by Deerhill View Post
    The higher pressure portion will only save the rim if psi is high enough. That higher psi restricts the volume in the lower psi portion and how the overall volume reacts, that is what counts. It is definitely changed
    It would be pretty dumb to set the inner chamber too low to accomplish that. It doesn't take huge pressure after all. How many rim strikes does anyone get at 50 psi today? None.

    As I said before, the high pressure chamber changes the lower pressure chamber's behavior mathematically, just not significantly.

  6. #31
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    Can't believe no one else has brought up the dual core tire concept

    Quote Originally Posted by Deerhill View Post
    It changes the spring rate feel in the tire/wheel noticeably and has more rebound or bounce on certain hits,, or a sort of bob off of g-outs. There is less "travel" in the low pressure tire portion.. and that initial feel will now have to do more with the construction of the tire casing..


    The higher pressure portion will only save the rim if psi is high enough. That higher psi restricts the volume in the lower psi portion and how the overall volume reacts, that is what counts. It is definitely changed
    I doubt there is going to be any significant change in the outer tire pressure.

    The dual chamber systems are more about bead locks, rim protection, and run-flat possibilities.

    This is more of a two-stage spring rate. When the low pressure outer tire compresses it hits the high pressure (80-90psi) inner tire.

    For a given "hit", whether or not the inner tire spring rate comes into play depends on the volume of the outer tire, the outer tire pressure, the inner tire volume (I have experimented with various size road and 'cross tires as inners), and rim width.
    The less difference between inner and outer volume, the more you will be bouncing on the inner tire.
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  7. #32
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    Quote Originally Posted by craigsj View Post
    I seriously doubt the "feel" is changed "noticably" or has more "rebound or bounce". It is true mathematically but it's 1 or 2 orders of magnitude away from significance.

    Volume of 29er trail tire (torus, 720x53): ~2x10^7 mm^3
    Volume lost, 20 psi 100 pound load: ~2x10^4 mm^3
    relative change: 0.1%

    I think that's a generous estimate of volume change, but even at 10x more than that, it's still only 1%. Changes in progression here are very small. Any change in feel will come from the drop in pressure and the additional support at the bead. Spring progression is the same until the tire engages the inner chamber.
    It's like any shock in that the bottom out protection will change with rider preference and weight, but it does act like a volume spacer/reducer when at the pressure needed for protection of high speed compression impacts (too simplify).


    Quote Originally Posted by craigsj View Post
    It would be pretty dumb to set the inner chamber too low to accomplish that. It doesn't take huge pressure after all. How many rim strikes does anyone get at 50 psi today? None.

    As I said before, the high pressure chamber changes the lower pressure chamber's behavior mathematically, just not significantly.
    And the application is heavier duty.. you are leaving out the fact that there's a VERY small distance above the rim sidewall to stop the high speed compression impact of a rock strike. Lowering the inner chamber to 50 psi will not protect the rim from a HSC hit like that unless you obviously raise the tire pressure.. or smooth trails

    The other fact you are leaving out is that if you want to ride with lower pressures, you need more rim protection if you're using this to prevent breaking the rim.

  8. #33
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    Quote Originally Posted by shiggy View Post
    I doubt there is going to be any significant change in the outer tire pressure.

    The dual chamber systems are more about bead locks, rim protection, and run-flat possibilities.

    This is more of a two-stage spring rate. When the low pressure outer tire compresses it hits the high pressure (80-90psi) inner tire.

    For a given "hit", whether or not the inner tire spring rate comes into play depends on the volume of the outer tire, the outer tire pressure, the inner tire volume (I have experimented with various size road and 'cross tires as inners), and rim width.
    The less difference between inner and outer volume, the more you will be bouncing on the inner tire.
    The rider preference for outer tire pressure won't change much, lets say it is 20 psi for reference.

    The tire expands when it takes a hit. The increase in rebound/ bouncing/ progression is also affected by reducing the 20 psi volume (increasing the rigidity of inner chamber with more psi), and it's also affected by the construction of the casings (how they increase contraction/rebound)

  9. #34
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    Quote Originally Posted by Deerhill View Post
    It changes the spring rate feel in the tire/wheel noticeably and has more rebound or bounce on certain hits,, or a sort of bob off of g-outs. There is less "travel" in the low pressure tire portion.. and that initial feel will now have to do more with the construction of the tire casing..


    The higher pressure portion will only save the rim if psi is high enough. That higher psi restricts the volume in the lower psi portion and how the overall volume reacts, that is what counts. It is definitely changed
    How do you know this?
    You seem very certain... how much experience do you have riding this system?
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  10. #35
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    This is not new

  11. #36
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    Quote Originally Posted by Deerhill View Post
    It's like any shock in that the bottom out protection will change with rider preference and weight, but it does act like a volume spacer/reducer when at the pressure needed for protection of high speed compression impacts (too simplify).
    Yes, it's a volume reducer just not a sufficiently effective one. From a spring rate perspective, the air volume in a tire is far too great.

    What shiggy is saying is the correct answer---the system acts as a two stage spring. The designers have to get the inner size right and it sounds like shiggy has some experience playing with that.

    Quote Originally Posted by Deerhill View Post
    And the application is heavier duty.. you are leaving out the fact that there's a VERY small distance above the rim sidewall to stop the high speed compression impact of a rock strike. Lowering the inner chamber to 50 psi will not protect the rim from a HSC hit like that unless you obviously raise the tire pressure.. or smooth trails
    I'm not leaving that out nor is it necessarily true. I was not advocating for a 50 psi inner pressure, just using that as an example of a pressure where rim strikes are typically eliminated in a conventional tire. The inner pressure will depend on the rider and the diameter of the inner tube.

    Quote Originally Posted by Deerhill View Post
    The other fact you are leaving out is that if you want to ride with lower pressures, you need more rim protection if you're using this to prevent breaking the rim.
    It's hard to leave that out when it's the entire point of the system.

    I don't know why you are suggesting that rim strikes can't be eliminated when they most certainly can be. We can eliminate rim strikes now. Like you said, the system isn't new.

  12. #37
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    Look I was not trying to be hostile.. and wasn't trying to say shiggy is incorrect, in fact the way he words it sounds right.. I might not always type it out in the best way for someone to read it. The extra bounce/rebound in the system is there though



    * edit

    shiggy have you tried different combos on 26" or 650b? I have not tried 29er
    Last edited by Deerhill; 06-29-2014 at 05:46 PM.

  13. #38
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    Can't believe no one else has brought up the dual core tire concept

    Quote Originally Posted by Deerhill View Post
    The extra bounce/rebound in the system is there though
    I'm curious why you think rider preference for tire pressure wouldn't change. If either burping or rim strikes are the limiting factors (they are for me), and you take those limitations away, then I can lower the tire pressure until I hit whatever the next barrier is... likely handling.
    Once more, how much ride experience do you have on these systems?
    It would be good to know which system it was and when you did this riding.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  14. #39
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    Quote Originally Posted by shiggy View Post
    You could still cut or puncture the outer tire, but as long as the inner tire is inflated the tire would stay in place and could be ridden with little or no damage to the rim.
    I know I can still get a sidewall tear, but compared to pinch flats that's a rarity for me.

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