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  1. #26
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    Quote Originally Posted by mad dog26 View Post
    I am not an exierienced wheel builder but my 1st thought was a wheel should not need to be tensioned to every tire but perhaps overtensioning spokes before fitting tires is what needs to be done with light rims?
    I think I said this in another thread, but I suspect the tension drop problem is not with light rims, but with Stan's rims + tubeless ready tires. The reason being that Stan's rims overstretch the tire bead, and so the tires really squeezes down on the rim.

  2. #27
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    I think the significantly lower and variable spoke tension after airing up a tire to various pressures is mostly from lateral rim wall flex and rim wall elongation from the lateral force from aired up tire beads. There is some minor nipple bead-in, spoke stretch, and flange hub hole bed-in too. The rim's tire-bead walls, flex outward from tire pressure, and "pivot" at the constraint of the bead seats and inner channel shelf, and then the rim walls below the bead seats are leveraged inward and elongate. Net effect is the spoke tension is relaxed.

    Tire Pressure and Spoke Tension-reducedspoketension.png

    Thanks to Bike Whisperer in the this thread, for the reference to Melting Feather's thread here
    Spoke tension change after tire install
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  3. #28
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    Hello Derby,

    I think you are two years late, and also wrong. (sorry if that sounds mean)
    It's the tire mounting that causes the loss of spoke tension. The tire bead squeezes downwards on the spoke bed and compresses the whole rim. If the rim is light, then it's overall cross section is not as good at resisting circumferential compress, so the whole rim shrinks inwards. Tire PSI has very little effect, as Meltingfeather has measured. This is due to cancellation of forces, as pointed out earlier.

    Your picture doesn't apply because although it might be true in cross section, it is not true in a complete rim. The spoke hole section is prevented from moving downwards because it would circumferentially compress that section. This constraint means that any section of the rim can only deflect laterally, plus other length-conserving constraints.

    The "Derby mystery lever" (LOL there I go again about levers) that goes from the bead hook to the spoke hole bed is too floppy and constrained to transmit much force to the end.

  4. #29
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    Quote Originally Posted by beanbag View Post
    Hello Derby,

    I think you are two years late, and also wrong. (sorry if that sounds mean)
    It's the tire mounting that causes the loss of spoke tension.
    I support Derby's position on this topic. Or at least I find his observations above plausible as a contributing factor. But on a more fervent note, I'm highly opposed to beanbag's absolute dismissal of tire pressure as a contributing factor to the de-tensioning of spokes.

    I've tested three different rim/tire combinations (all "typical" road rims with conventional beads, 28 or 32H, and road tires 23-37c in width, and no-tire spoke tension at ~90-110kgF). In every case, the difference in spoke tension was ~15kgF less when measured at 90-100psi versus measuring at 20-30 PSI (but bead still tightly seated). But the difference in tension between 20-30 PSI and zero PSI (bead unseated) was undetectable on my gauge.

  5. #30
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    Tire Pressure and Spoke Tension

    Quote Originally Posted by derby View Post
    I think the significantly lower and variable spoke tension after airing up a tire to various pressures is mostly from lateral rim wall flex and rim wall elongation from the lateral force from aired up
    That may be the case with your rims, but not what the measurements show for my experiment.
    I think you need to send me a pair if your rims so I can conduct a conclusive experiment.
    I'm going to work on my Nancy Wides once I get back from vacation.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  6. #31
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    Tire Pressure and Spoke Tension

    Quote Originally Posted by InertiaMan View Post
    I support Derby's position on this topic. Or at least I find his observations above plausible as a contributing factor. But on a more fervent note, I'm highly opposed to beanbag's absolute dismissal of tire pressure as a contributing factor to the de-tensioning of spokes.

    I've tested three different rim/tire combinations (all "typical" road rims with conventional beads, 28 or 32H, and road tires 23-37c in width, and no-tire spoke tension at ~90-110kgF). In every case, the difference in spoke tension was ~15kgF less when measured at 90-100psi versus measuring at 20-30 PSI (but bead still tightly seated). But the difference in tension between 20-30 PSI and zero PSI (bead unseated) was undetectable on my gauge.
    Post your measurements please.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  7. #32
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    Quote Originally Posted by meltingfeather View Post
    Post your measurements please.
    I did this months ago, long before running across these threads, so I don't have the "original data." But its a very simple measurements, and I still have all the wheels, so I'll be happy to run through it later today when I get home and post the results. I can also include some Chinese carbon rim examples as well.

  8. #33
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    Quote Originally Posted by InertiaMan View Post
    I did this months ago, long before running across these threads, so I don't have the "original data." But its a very simple measurements, and I still have all the wheels, so I'll be happy to run through it later today when I get home and post the results. I can also include some Chinese carbon rim examples as well.
    I would find this very interesting. Could you please also state what type of rim, whether it's sleeved/pinned or welded, and what type of tire, bead type, and what the 'bead seat pressure' was (the pressure at which the beads seated onto the bead seat shelf)?

    I've noticed a drop in rim tension frequently, typically when mounting UST or tubeless ready tires onto Stan's rims or similar. The most drastic drop I've seen was when mounting tubeless road tires onto Stan's Alpha 340 rims; I resorted to final spoke tensioning while the tire was mounted and inflated. I always assumed it was a combination of the compressive force from the beads, and from the air pressure X the surface of the inner rim bed. But in some rim designs, derby's explanation above makes sense. Unfortunately, I can't think of a way to isolate one force from the other.

    On second thought, maybe I can. Derby, send me a pair of your rims, also, for testing!
    Tire Design & Development Engineer. The opinions expressed in this forum are solely my own.

  9. #34
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    Tension vs. PSI for Five Wheel/Tire combinations

    Here's some fresh measurements:

    Wheel 1: 700c Velocity Synergy ASYM 36H, DB14, Marathon Supreme 32c tubed
    TIRE . . . . . . . . . TENSION kgF
    80 psi . . . . . . . . . . . . 80
    30 psi . . . . . . . . . . . . 86
    5 psi & seated . . . . . . 90
    tire off . . . . . . . . . . . 92

    Wheel 2: Shimano MT75 UST 29er 24H, 2.0mm spoke, Big Apple 29x2.35 tubed
    TIRE PSI . . . . . . . TENSION kgF
    60 . . . . . . . . . . . 77
    25 . . . . . . . . . . . 95
    10 . . . . . . . . . . .105
    ~0 & seated . . . .110
    no tire . . . . . . . .110

    Wheel 3: EC90 XC UST 29er 24H, 2.0/1.7, Wild Racer 2.1 TR tubeless
    TIRE PSI . . . . . . . . TENSION kgF
    45 psi . . . . . . . . . . 95
    30 psi . . . . . . . . . . 105
    20 psi . . . . . . . . . . 110
    4 psi & seated . . . . 118
    no tire . . . . . . . . . .130

    Wheel 4: LB Wider 29er 28H, 2.0/1.8, Rocket Ron 2.25 TR tubeless
    TIRE PSI . . . . . . . . TENSION kgF
    45 psi . . . . . . . . . . 76
    20 psi . . . . . . . . . . 84
    5 psi . . . . . . . . . . . 87
    0 psi & seated . . . . 92
    no tire . . . . . . . . . 100

    Wheel 5: 700c RR1.1 28H, 2.0/1.7mm, Conti Grand Prix 25c tubed
    TIRE PSI . . . . . . . TENSION kgF
    120 . . . . . . . . . . . 73k
    70 . . . . . . . . . . . . 75
    30 . . . . . . . . . . . . 79
    5 . . . . . . . . . . . . . 84
    no tire . . . . . . . . . 90

    METHODS/NOTES:
    To save time, I selected 4 spokes on one wheel side which were representative of the nominal tension & measured those same spokes for each tire state.
    As I went, I made some anecdotal measurements on the other side of the wheel which indicated that they were tracking with the measured side, so I didn't bother recording those, preferring to keep the table above simple.
    All wheels are in good condition, never been wonky, no damage.
    On any given wheel, spoke tension was pretty consistent +/- 5% or so.
    The RR on the LB rim fits pretty normal, not tight, not loose during installation.
    The Wild Racer goes on the UST rim with normal/modest effort if your technique is good, but the bead after seating is TIGHT. I had a real struggle getting the second wheel side bead off.
    Anecdotal measurements seem to distinguish one bead off versus both beads off in the cases where bead seating did show de-tensioning.

  10. #35
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    Observations/Comments based on data above

    There are a few observations which seem sort of beyond debate:
    - PSI definitely affects spoke tension on all wheel types
    - Bead seating definitely affects spoke tension on rim/tire types which are designed for tight seating aka tubeless applications
    - The de-tensioning contribution from bead seating appears to be higher with tighter rim/tire combinations.
    - On road wheels with commonly high pressures and (traditionally) non-tight bead interfaces, the total de-tensioning is pretty significant, and it is dominated and perhaps entirely caused by tire pressure.
    - On MTB wheels with a relatively low common tire pressure in real world use, the total de-tensioning is less substantial, and the bead seating plays an increasingly higher role in the de-tensioning.

    Hopefully this is a starting point for some objective discussion.

    I know I've convinced myself that bead seating plays a meaningful role in this phenomenon in the case of tight MTB tires at lower pressures. I was initially skeptical. I guess that (relatively) unstretchable bead, when subject to sufficient tire pressure, forces the rim to compress in circumference and "accept" the bead into the rim channel.

    Hopefully I've also convinced others that tire pressure has a roughly equal role here, and is the dominant/only factor in many common road wheel scenarios.

  11. #36
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    Quote Originally Posted by InertiaMan View Post
    - On MTB wheels with a relatively low common tire pressure in real world use, the total de-tensioning is less substantial, and the bead seating plays an increasingly higher role in the de-tensioning.
    I want to correct myself on this point. Once I compared the spoke de-tension between raw rim and a typical real world tire pressure in each case above, it seems the scale of the effect is pretty similar on both road/high-pressure and MTB/tubeless/low-pressure cases. In my limited sample set, the de-tension effect is 10-20kgF, with 15kgF being a rough proxy for an average.

  12. #37
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    I also noticed a big change in tension on my road wheel and only a very minor change on my mountain wheel. So that means I have to revise my explanation.

    It depends on whether the tire bead squeezes against the rim or pulls up against the bead hook. In MeltingFeather's case, he uses the bead-overstretching Stan's rims, so that means the bead always compresses tightly against the rim. He observes no change in spoke tension with pressure because the increased force of the air pressure down against the spoke bed is cancelled out by the tire sidewalls pulling up on the bead more, reducing its pressure on the rim.

    On a road tire where the bead does not squeeze down hard, the tire pressure pushes down on the spoke bed as before, but now the bead just lifts up and does not exert a pressure on the spoke bed, so there is no counteracting force. When the tire pressure is higher yet, the tire bead catches on the bead hook, and now there is an opposing force again. That's why in InertiaMan's data, there isn't much more decrease in tension at the highest pressures.

    Of course, Derby's explanation is still wrong because it would predict a linear decrease in spoke tension vs tire pressure.

  13. #38
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    While the data is leading us to similar conclusions, I have a hard time agreeing with some of Beanbag's conceptualizations to explain the data, specifically the idea of the bead "pulling up" on the rim lip and acting as a counter force to the air pressure.

    We assume that the bead is essentially unstretchable, and this explains the compressing forces on the rim circumference as the bead moves up out of the center channel and onto the bead shelf. We can't then also assume the bead is stretchable enough to grow in diameter and cause a circumference expanding force against the rim lip.

    I think there are better explanations for the "non-linearity" in the de-tensioning that is somewhat apparent in the data (keeping in mind this data isn't highly precise).

    I think there are 3 dominant elements to explain the de-tensioning behavior, and it is the interplay of these factors that lead to non-linear results in some of the data:
    1) Tire pressure
    2) Relative difference between (a) diameter of the bead shelf of the rim cross section, and (b) the true bead diameter of the tire
    3) Rim structure (ie fundamental rigidity, strength, integrity, etc)

    #1 and #2 seem to be the bulk of the factor in the wheels for which we have data, but I'm confident that #3 plays a role in the scale or limits of impact by #1 and #2.

    Meltingfeather's data demonstrates an example which has a relatively extreme case of #2, and I would argue is further exacerbated by the Crest being a relatively light rim that would be more vulnerable to these forces. I'm still surprised that his data shows virtually zero impact by tire pressure; perhaps if these were re-measured on the "adjusted" (ie properly tensioned) wheel, we would see some minor but measureable de-tensioning from tire pressure?

    Classic road rims represent the opposite case: the rim's bead shelf basically has a smaller diameter than the tire's bead. So the bead seating contributes almost nothing to the de-tensioning.

    But with a sufficiently stout rim, I'd bet that neither the air pressure OR the bead seating would de-tension spokes. Say, an imaginary 1500g rim with an 80mm tall cross section. In fact, a bead may not even seat in such a case, if the rim's dimensional design was like a Crest (large bead shelf diameter) because the rim structure of a would not compress sufficiently for the bead to move onto the shelf.

    No one makes such an impractical rim, of course. But I'd love to see some data on a super stiff rim like, say, a DT R465. My prediction is that one would see a lesser de-tensioning effect from tire pressure. If so, such data would support my assertion above that #3 rim structure plays a role here.

    Ultimately, what do we do with this information?

    If I were building a wheel with a Crest rim, I would be inclined to bring it up to final tension WITH a tire installed. Otherwise, the severe de-tensioning that occurs as a consequence of seating a tight bead will result in actual spoke tensions during wheel use which are insufficient to maintain a robust wheel.

    On other wheels we've measured, the de-tensioning effect isn't as pronounced, so its less critical, but I'd probably still skew toward the higher end of good-practice tension ranges when measured without a tire installed.

    I'd love to see some more data from wheel/tire cases that aren't represented here. For example:
    - Stan's Arch or Flow. This might help illustrate the different contributions of a tight rim/bead design versus rim structure. In other words, I would expect these to behave similar to the Crest w.r.t. the tight rim/bead being proportionally higher contributor than air pressure in the de-tensioning, but perhaps be less pronounced in total de-tensioning due to a much stronger overall rim structure.
    - an uber-stiff tall profile rim, so see if sufficient rim structure would reduce the total de-tensioning from air pressure.

    As for Derby's explanation, I can't categorically reject it. It seems the Crest's weak rim structure is playing a role, but is it due to general compressibility? Or to leverage forcing a change in rim cross section as Derby theorizes? I can't think of a practical experiment to help determine this. One could use a caliper to measure rim width at the sidewall with and without tire installed? I don't have any wheels with Stan's rims, certainly no Crest, so I can't really try.

  14. #39
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    Quote Originally Posted by InertiaMan View Post
    While the data is leading us to similar conclusions, I have a hard time agreeing with some of Beanbag's conceptualizations to explain the data, specifically the idea of the bead "pulling up" on the rim lip and acting as a counter force to the air pressure.

    We assume that the bead is essentially unstretchable, and this explains the compressing forces on the rim circumference as the bead moves up out of the center channel and onto the bead shelf. We can't then also assume the bead is stretchable enough to grow in diameter and cause a circumference expanding force against the rim lip.
    Think these two assumptions are wrong. Yes, the bead is stretchable. That explains why tires can even mount on Stan's rims in the first place.

    Yes, the bead hook has capturing abilities. That's why the rim/tire system is called a "clincher".

    The degree to which bead and pressure affects spoke tension change has to do with how easy it is to compress the rim, which is related to its cross sectional area, which is proportional to its weight. Of course the bead is more stretchy than the rim because a few grams of kevlar is more stretchy than 500g of aluminum.

    The whole system can be modeled with a bunch of different pre-loaded springs tugging on each other with different stiffnesses.

  15. #40
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    [QUOTE=InertiaMan;11112260]Here's some fresh measurements:

    Wheel 1: 700c Velocity Synergy ASYM 36H, DB14, Marathon Supreme 32c tubed
    TIRE . . . . . . . . . TENSION kgF
    80 psi . . . . . . . . . . . . 80
    30 psi . . . . . . . . . . . . 86
    5 psi & seated . . . . . . 90
    tire off . . . . . . . . . . . 92

    Wheel 2: Shimano MT75 UST 29er 24H, 2.0mm spoke, Big Apple 29x2.35 tubed
    TIRE PSI . . . . . . . TENSION kgF
    60 . . . . . . . . . . . 77
    25 . . . . . . . . . . . 95
    10 . . . . . . . . . . .105
    ~0 & seated . . . .110
    no tire . . . . . . . .110

    Wheel 3: EC90 XC UST 29er 24H, 2.0/1.7, Wild Racer 2.1 TR tubeless
    TIRE PSI . . . . . . . . TENSION kgF
    45 psi . . . . . . . . . . 95
    30 psi . . . . . . . . . . 105
    20 psi . . . . . . . . . . 110
    4 psi & seated . . . . 118
    no tire . . . . . . . . . .130

    Wheel 4: LB Wider 29er 28H, 2.0/1.8, Rocket Ron 2.25 TR tubeless
    TIRE PSI . . . . . . . . TENSION kgF
    45 psi . . . . . . . . . . 76
    20 psi . . . . . . . . . . 84
    5 psi . . . . . . . . . . . 87
    0 psi & seated . . . . 92
    no tire . . . . . . . . . 100

    Wheel 5: 700c RR1.1 28H, 2.0/1.7mm, Conti Grand Prix 25c tubed
    TIRE PSI . . . . . . . TENSION kgF
    120 . . . . . . . . . . . 73k
    70 . . . . . . . . . . . . 75
    30 . . . . . . . . . . . . 79
    5 . . . . . . . . . . . . . 84
    no tire . . . . . . . . . 90

    I'm really interested in this thread - brilliant!. I'm surprised to see the de tensioning with the LB wide carbon rims!, I've just had them laced up and they came back in my opinion with pretty slack spoke tensions, I don't have a tension meter but comparing them with my other mountain bike wheelsets they would appear to have half the tension!. The Maxxis HRII tyres were very tight to get on and believe that the tight beads are indeed playing their part in the tension of the spokes. I think I will retension the spokes with the tyres on and see how they perform.
    (650B 35mm wide rim)

    Thanks guys

  16. #41
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    The change in spoke tension is caused by the tire pressure

    InertiaMan's tests pretty much shows this ( thanks for the info )

    "air pressure exerts equal force in all directions"
    a simple calculation to find out the total compressive force the tire pressure exerts on the rim

    tire pressure in bar * bead seat circumference in cm * internal rim width in cm= total compressive force in kgf exerted on the wheel by the tire air pressure

    (note * the internal rim width will be the distance between the inside tire bead edges)

    I did the calculation for a 26AM ENVE carbon wheel with tire pressure at 2bar (30psi)
    internal rim width between the UST beads 20mm
    2bar * 176cm * 2cm = 705 kgf

    I did actual test on a Enve 26" AM carbon rim and had 117kgf spoke tension without tire mounted
    mounted tire and pump to 2bar recheck spoke tension reading indeed went down to 95kgf

    32 spokes x 117kgf = 3744kgf total compressive force exerted on the rim from spoke tension
    3744kgf - 704kgf = 3040kgf
    3040kgf/32= 95kgf

    this is no coincidence...

    some rims may not show the total calculated amount of de-tensioning, as depending on the rim material, thickness and rim profile we can have internal resistance to the compressive forces, (the tire pressure and spoke tension are not exerted on the same part of the rim)
    example of this would be deep profile rims where you probably would get less de-tensioning effect...

  17. #42
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    Tire Pressure and Spoke Tension

    Quote Originally Posted by WaXed64 View Post
    The change in spoke tension is caused by the tire pressure

    InertiaMan's tests pretty much shows this ( thanks for the info )
    If you ignore almost every other post in the thread, including my measurements and data reporting that started it.

    "It depends" is about as good as you can get looking at my original results vs. yours (and his).
    Your categorical proclamation that tire pressure is responsible is... how u say... wrong.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  18. #43
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    Quote Originally Posted by meltingfeather View Post
    He also didn't show anything... he told us about what he did and never posted his measurements as requested.
    Seriously? Apparently it is YOU that hasn't read the thread. I posted extensive data one day after you asked for it. I posted 4 to 5 tension measurements each for 5 different wheels and fully documented the wheel builds, tires and measuring methods. What more could I have posted?

    Quote Originally Posted by meltingfeather View Post
    Your categorical proclamation that tire pressure is responsible is... how u say... wrong.
    Actually it is your original categorical proclamation that tire pressure is NOT responsible that is wrong.

    Meltingfeather, your condescending tone is irritating in any context, but in this particular thread it is wholly unjustified since you've been proven wrong by a substantial body of empirical data.

    Why is it so hard for folks to acknowledge/agree on the reality here? Tire pressure and bead/rim interface issues BOTH contribute to de-tensioning, and both are significant contributors. This is both intuitive and supported by my data above.

  19. #44
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    Tire Pressure and Spoke Tension

    Quote Originally Posted by InertiaMan View Post
    Seriously? Apparently it is YOU that hasn't read the thread. I posted extensive data one day after you asked for it. I posted 4 to 5 tension measurements each for 5 different wheels and fully documented the wheel builds, tires and measuring methods. What more could I have posted?
    My apologies... don't know how I missed that. Need to look back at it.
    I'll correct the post.

    Quote Originally Posted by InertiaMan View Post
    Actually it is your original categorical proclamation that tire pressure is NOT responsible that is wrong.
    I made no such proclamation. It was clearly not contributing in my case, but I'm not one to take one data point and try to write a law.
    My measurements/results as well as the experiences of others posted here demonstrate that bead seating is definitely dominant in some cases.
    Sorry for missing your post, but let's redirect this back to what the various measurements are showing.
    Tire pressure was clearly not contributing in my case.
    It was in yours... as I said, "it depends."

    Quote Originally Posted by InertiaMan View Post
    Meltingfeather, your condescending tone is irritating in any context, but in this particular thread it is wholly unjustified since you've been proven wrong by a substantial body of empirical data.
    Again... look at the data. Clearly both can contribute in different circumstances.
    "Proven wrong" is BS... the data is what it is. Your experience doesn't mean my measurements were in error.

    Quote Originally Posted by InertiaMan View Post
    Why is it so hard for folks to acknowledge/agree on the reality here? Tire pressure and bead/rim interface issues BOTH contribute to de-tensioning, and both are significant contributors. This is both intuitive and supported by my data above.
    So which is it... my data and conclusions are "proven wrong" as you just said or both bead seating and pressure are contributors as you now say?
    I agree with the latter statement, and whether each or the other is dominant depends on circumstances. I have never said anything different. The guy I responded to concluded that tire pressure (alone) is responsible, which is wrong, and you obviously agree... at least at one point.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  20. #45
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    Tire Pressure and Spoke Tension

    Quote Originally Posted by InertiaMan View Post
    Here's some fresh measurements:
    This is great data!
    Thanks for posting. So sorry I missed it the first time.
    Need to think some about it...
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  21. #46
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    Experiment suggestion: Measure precise ERD of un-laced rim. Mount a tire on bare-rim, re-measure ERD. Inflate tire, measure ERD again at various pressures, 5psi increments for repeatability.

    Lace/tension rim, re-mount tire. measure tensions at same pressures. Create charts.

    I'm curious about this, as I had a set of Crest rims (32hole, laced 3x to CK hubs), which I just removed because the damn things were so flexy. I wish I'd seen this thread beforehand so I could add some data.

    I had initially set the tension at 85kgf, bumped it up to 95 because of flex. I don't recall the tension being low when I started to increase tension, but also wasn't looking for it. I replaced them with Arch EX, tensioned to 120kgf. Kenda Nevegals with fairly loose fitting beads. just riding around the yard it felt like a different bike, significant change in the feel.

    I'm on the road for 3 wks, or I would try it now.
    My bike MCA kinda climbs like a billy-goat. WOO WOO!

  22. #47
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    Quote Originally Posted by meltingfeather View Post
    I made no such proclamation.
    These two statements seem like proclamations to me:

    Quote Originally Posted by meltingfeather View Post
    What you find when you actually do it and measure it (reality) is that bead seating causes the drop. Pressure does virtually nothing.
    Quote Originally Posted by meltingfeather View Post
    It's not the pressure it's the bead seating tightly.
    Both of your statements above were directed specifically at the Chinese carbon rims, not your Crest experience. Yet you have no data for those rims to support your statement, and I've posted data which directly contradicts your statements.

    For clarity, I never suggested that your observation of bead seating influencing spoke tension was wrong. Rather, I contend that your earlier statements that tire pressure does NOT influence spoke tension is wrong.

    Similarly, I never said that Waxed64's position (implying that tire pressure was the only factor) was correct -- its clearly not, at least in cases where beads seat with any tightness -- though I can see how the timing of my response might suggest I was supporting him.

    Quote Originally Posted by meltingfeather View Post
    "Proven wrong" is BS... the data is what it is. Your experience doesn't mean my measurements were in error.

    So which is it... my data and conclusions are "proven wrong" as you just said or both bead seating and pressure are contributors as you now say?
    :
    What I believe is "proven wrong" is the notion that tire pressure has no role in de-tensioning. I associated you with that position (perhaps unjustifiably?) due to your statements I noted above.

    Also "proven wrong" is the opposite notion that tire pressure is solely responsible for de-tensioning.

    I have no doubt your Crest measurements are correct, and I've never contested that data. Its what inspired me to do my own measurements to expand the data set.

    So enough with the nitpicking, and back to the interesting stuff, since we both agree "it depends" . . . but I'd be interested in further study/discussion to see what it depends upon.

    I see two ends of the spectrum:
    1) classic tire/rim combo where the tire bead is loose relative to the rim BSD. In this case, tire pressure seems to be virtually 100% responsible for the de-tensioning. And worst case de-tensioning is on the order of 15k-20kgF.
    2) the lightest Stan's rims matched with tires with tight beads. The worst case de-tensioning in this case can be far higher, as MF's data shows. And the bead/rim interface is the dominant factor.

    Given my data on tubeless designs other than Stans, it seems that the Stans rim designs exhibit more de-tensioning than other designs of similar weight/application. Anecdotal data on this thread and others seems to support this even for Stans rims other than Crests (Arch, etc). Though clearly the Crest example is understandably an extreme case (combination of very light rim and a design that isn't robust against de-tensioning).

    Can someone post up some hard data on Arch or Flows? Or maybe a Shimano road tubeless wheel? That would be interesting.

  23. #48
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    Quote Originally Posted by shupack View Post
    Experiment suggestion: Measure precise ERD of un-laced rim. Mount a tire on bare-rim, re-measure ERD. Inflate tire, measure ERD again at various pressures, 5psi increments for repeatability.
    I like the concept, but the precision required is challenging. My rough math suggests that the ERD/tension delta is something on the order of 1mmERD/20kgF. So we need to consistently measure ERD at, say, 0.1mm precision. I personally don't have the tools to do that. A digital caliper across spoke heads would be my best option, but I'm not confident I could be consistent enough.

  24. #49
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    Quote Originally Posted by InertiaMan View Post
    These two statements seem like proclamations to me:

    Both of your statements above were directed specifically at the Chinese carbon rims, not your Crest experience. Yet you have no data for those rims to support your statement, and I've posted data which directly contradicts your statements.
    taking posts from historical threads completely out of context is seemingly intentionally misleading and complicating.
    Quote Originally Posted by InertiaMan View Post
    FRather, I contend that your earlier statements that tire pressure does NOT influence spoke tension is wrong.
    Arguments you take out of context are hardly relevant... and hack tactics. Buck the tilt and let's talk about what's interesting, not your juvenile emotional reactions to to something I said in another thread/context ages ago.
    Quote Originally Posted by InertiaMan View Post
    Similarly, I never said that Waxed64's position (implying that tire pressure was the only factor) was correct -- its clearly not, at least in cases where beads seat with any tightness -- though I can see how the timing of my response might suggest I was supporting him.
    You're almost starting to sound reasonable...
    I said it was wrong and you responded with an emotionally laden rebuke with obscure references and lacking specificity... hardly relevant or even recognizable.

    Quote Originally Posted by InertiaMan View Post
    What I believe is "proven wrong" is the notion that tire pressure has no role in de-tensioning. I associated you with that position (perhaps unjustifiably?) due to your statements I noted above.
    It clearly did not in my case, and I'll state again, like any scientist would, that my results are not extrapolatable to conditions beyond what I tested.
    It is unreasonable and of no use to draw the whole of my post record out of context into this argument. Can we agree to limit the discussion to posts in this thread? I wasted 10 minutes looking and relooking for the quotes you posted... in this thread... and took a search 99% of MTBR posters are unaware of to discover your source.

    Quote Originally Posted by InertiaMan View Post
    So enough with the nitpicking, and back to the interesting stuff, since we both agree "it depends" . . . but I'd be interested in further study/discussion to see what it depends upon.
    amen (as ironic as that is)... I'm on the same page.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  25. #50
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    Quote Originally Posted by meltingfeather View Post
    taking posts from historical threads completely out of context is seemingly intentionally misleading and complicating.

    Arguments you take out of context are hardly relevant... and hack tactics. Buck the tilt and let's talk about what's interesting, not your juvenile emotional reactions to to something I said in another thread/context ages ago.

    It is unreasonable and of no use to draw the whole of my post record out of context into this argument. Can we agree to limit the discussion to posts in this thread? I wasted 10 minutes looking and relooking for the quotes you posted... in this thread... and took a search 99% of MTBR posters are unaware of to discover your source.
    Finding the origin of quotes is easy: just click on the little blue double arrow at the top of the quote, and it will take you there.

    I'm hardly drawing on "the whole of your post record" or taking you out of context. Both of the brief quotes I referenced are from an isolated portion of a thread where you invited folks to post data to this thread. You connected the threads on April 4th, I posted the data you requested the following day, and now I'm a juvenile/out-of-context/hack for remembering it?

    At any rate, since we're now on the same page, lets get back to science. Have you got some rim/tire combos to measure and expand our data set?

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