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  1. #1
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    Tire Pressure and Spoke Tension

    In case you want to know what happens when you put a 700x28 commuter tire on your Crest 29er rim and pump it to 85 psi for use on the road and a trainer...
    The figure shows drive-side tension on a rear wheel in six different scenarios: at four different tire pressures declining from 85 psi to 0 psi, one with the bead off, and after readjustment.
    The "readjusted" tension line is just about how the wheel left my hands the first time... not that long ago, and right on the 100 kgf mark. Now it has a little more variation. I asked Stan's what they thought and they said increase tension. I'm not sure this isn't going to happen again fairly quickly.
    The most intersting thing to me was to see that the tension stayed about the same (the middle shape is actually four lines), even dropping from 85 psi to zero, until the bead came off.
    The tire is a Specialized All Conditions Armadillo 700x28.
    Attached Thumbnails Attached Thumbnails Tire Pressure and Spoke Tension-crest-29er-pressurization.jpg  

    Last edited by meltingfeather; 03-27-2012 at 12:19 PM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by meltingfeather View Post
    In case you want to know what happens when you put a 700x28 commuter tire on your Crest 29er rim and pump it to 85 psi for use on the road and a trainer...
    The figure shows drive-side tension on a rear wheel in six different scenarios: at four different tire pressures declining from 85 psi to 0 psi, one with the bead off, and after readjustment.
    The "readjusted" tension line is just about how the wheel left my hands the first time... not that long ago, and right on the 100 kgf mark. Now it has a little more variation. I asked Stan's what they thought and they said increase tension. I'm not sure this isn't going to happen again fairly quickly.
    It was intersting to me to see that the tension stayed about the same until the bead came off.
    The tire is a Specialized All Conditions Armadillo 700x28.
    What's different about road wheels? Shouldn't this happen with those as well, considering they are run at over 100psi?
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    Quote Originally Posted by Buzzaro View Post
    What's different about road wheels? Shouldn't this happen with those as well, considering they are run at over 100psi?
    The interesting thing to me is that the bead seating, not the tire pressure, seemed to be the cause of the lion's share of the detensioning.
    This fits with anecdotal evidence of some folks having issues with Stan's tubeless road rims dropping tension, assuming they have a similar bead design.
    So... a typical road clincher with a 622mm BSD would not experience the same detensioning because the tire bead doesn't fit as tightly on it... meaning the rim doesn't get compressed, or not nearly as much.
    This wheel had been ridden wobbly for a bit (not sure how long), which is why I think the tension was no longer uniform.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    I have a set of Stans road rims that eventually got some Maxxis tubeless tires on them. Shortly after the rear wheel wouldn't stay true. I am running a set of Crests on another road bike with 28mm tires and they have been solid so far.

    I understand the data but I don't know what to conclude. Should such a wheelset built to run road tires be retensioned? How much of load can a wheel carry if its spokes are detensioned by half as appears here?

    Also, would the type of spoke used effect these results?

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    Quote Originally Posted by craigsj View Post
    I have a set of Stans road rims that eventually got some Maxxis tubeless tires on them. Shortly after the rear wheel wouldn't stay true. I am running a set of Crests on another road bike with 28mm tires and they have been solid so far.
    I've heard some similar reports about road tubeless, to which Stan's has recommended raising tension. I think that variability in tire beads may play a role here, as it does in mounting tubeless or tubeless ready mountain tires on Stan's rims.
    Quote Originally Posted by craigsj View Post
    I understand the data but I don't know what to conclude. Should such a wheelset built to run road tires be retensioned?
    I'm facing that quandry myself. I don't want it to happen again, and my options seem to be: 1) tell the customer he shouldn't do what he's doing, and 2) jack the tension up on the Crest, neither of which I really want to do. I did bump the tension up a bit, but I wonder if it's pissing in the wind by looking at scale of what happens.
    After I retensioned the wheel to an average of 106kgf I re-inflated the tire to 65 psi and the average tension dropped to 80 kgf, which is better than the 58-and-all-over-the-place it came in at. I didn't go through total stress relief because I knew I was going to try this out, but after I remounted the tire, inflated to 65 psi, and pulled the tire back off, the tension was again all over the place. I've attached that figure. Based on my inability to dial the tension uniformity to what I typically do with a new wheel, I think the rim is warped from being ridden wobbly. Two NDS spokes had zero tension when it came in.
    Quote Originally Posted by craigsj View Post
    How much of load can a wheel carry if its spokes are detensioned by half as appears here?
    Not sure... I'd assume about half, which is apparently less than what the wheel is subject to. I've built quite a few Crest 29er wheelsets, even for guys significantly heavier than this rider, and never had this issue.
    Quote Originally Posted by craigsj View Post
    Also, would the type of spoke used effect these results?
    It's built with Revos. I'd think the phenomenon would be even more pronounced with a less elastic spoke.
    Attached Thumbnails Attached Thumbnails Tire Pressure and Spoke Tension-pressurizing-crest-after-readjustment.jpg  

    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Thanks, MF. Very interesting.

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    Quote Originally Posted by meltingfeather View Post
    The interesting thing to me is that the bead seating, not the tire pressure, seemed to be the cause of the lion's share of the detensioning.
    This fits with anecdotal evidence of some folks having issues with Stan's tubeless road rims dropping tension, assuming they have a similar bead design.
    So... a typical road clincher with a 622mm BSD would not experience the same detensioning because the tire bead doesn't fit as tightly on it... meaning the rim doesn't get compressed, or not nearly as much.
    This wheel had been ridden wobbly for a bit (not sure how long), which is why I think the tension was no longer uniform.
    Did this detensioning affect the radial or lateral true of the wheel? Have you tried any other tires on the wheel? Not insinuating your data is erroneous, just trying to isolate the cause.
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    Quote Originally Posted by Buzzaro View Post
    Did this detensioning affect the radial or lateral true of the wheel? Have you tried any other tires on the wheel?
    Yes... that's why the rider brought it back to me. It was out of true pretty badly until I fixed it.
    I don't recall specifically, but I don't think it went significantly out of true when I re-inflated the tire to 65 psi after fixing the wheel, even though it skewed the tension. Don't quote me on that, though. I went over the wheel again thoroughly after doing that.
    Quote Originally Posted by Buzzaro View Post
    Not insinuating your data is erroneous, just trying to isolate the cause.
    Not taken that way... I'd be stoked if you're able to see or think of something I missed. That's why I posted.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    For what it is worth, I just built a set of Pacenti tl28's (a lightweight 26" rim about 390 grams each) with Wheelsmith DB14 spokes and DT Swiss 240s hubs, and these wheels have done the same thing. Tension was right at 100kgf (recommended) in the truing stand. After a ride the rear rim dish was off center and had a couple of loose spokes (NDS). Took the tire off (Continental Trail King 2.2), re-tensioned everything, re-installed the tire (32 psi)...then I noticed that dish was off-again. Checked tension and the DS had fallen about 15-20% and some of the NDS spokes were so loose that my park tension meter wouldn't even register a tension (off the 'chart'...the TM would show a number like '4'). It happened after the tire was installed and inflated, and the effect was more pronounced on the rear than the front. I didn't take notes/data points as MF, but I was so stumped on what to do that I have just been riding a different set of wheels and bouncing the same ideas as above around in my head (ride it with loose spokes is asking for trouble, so more tension, tension with a tire on the rim, maybe split the difference). The guy who taught me to build wheels suggested bumping the tension up on the rear to close to the recommended tension with the tire on the rim and inflated. But I haven't decided what to do. I want to see what is the effect of using a different tire. I wonder if the tires make the difference? Maybe a different manufacturer? Or a different bead design (UST vs 'tube' bead)? I'm a relative novice compared to many of the highly experienced wheel builders here, so I don't have much to add, other than my observations at this moment. I'll try to report back after trying some other tires.
    Last edited by jason300b; 03-27-2012 at 10:27 PM.

  10. #10
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    bump for a calculation of bead tension due to mounting. It's hoops stress from spoke de-tension plus rim circumferential compression. Come on, you know you want to do it.

    It's no surprise that psi doesn't affect spoke tension. Think of the force of air pressure on a rim. One part pushing radially inward against the spoke bed. An equal cross section pulls radially outwards via the bead hooks.

    As to whether you should increase the spoke tension - that depends on what the limit of spoke tension is. Usually, as Jobst Brandt points out, it's when you stress relieve a wheel and it goes loopy. Same as when 4slomo finds that the rim gets increasingly sensitive to spoke adjustments. It's when the rim is starting to get near instability. In the case of Stan's rims, I though the tension limit was due to lack of spoke eyelets?

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    I had the same thing with my Podium MMX rear. Built the wheel to 100kgf with less than 5% variance. Fitted a Race King Supersonic 2.2 and within half an hour of riding had to stop and redish/retension the wheel. Spokes were loose everywhere. The wheel was so sloppy that it felt like I had a flat tyre.

    Redid the wheel with the tyre off, nice even 100kgf all round, fitted tyre and within half an hour had the same thing happen. WTF? Posted on mtbr and kdiddy mentioned the Alpha 240s problem.

    Redid the wheel again, then mounted the tyre and inflated it. DS tension dropped to between 70kgf and 80kgf. NDS tension went down too (can't remember by how much). The wheel did not go out of true.

    I then brought the wheel up to final tension (100kgf) with the tyre on and inflated to 28psi. Since then, the wheel has been bombproof. No loose spokes and runs true, I've done around 1500km on it.

    Perhaps there are just some tyre/rim combos or even batches of a particular tyre that have extremely tight (or perhaps strong) beads.

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    I had another idea. Maybe on the rims this is happening to, the joint is loose. Perhaps their diameter is changing slightly when the tire is mounted. I mean a diameter change is the likely cause either way, but this could be the culprit. A 1mm excess at the joint could be overlooked, especially with rim strips or tape. This would decrease the finish diameter by about .3mm or so. That might be enough to throw the tensions all off.
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    Quote Originally Posted by TigWorld View Post
    I then brought the wheel up to final tension (100kgf) with the tyre on and inflated to 28psi. Since then, the wheel has been bombproof. No loose spokes and runs true, I've done around 1500km on it.
    Do you change tires very often? Any issues? I'm assuming your Podiums are now at ~120kgf w/out the tire mounted, right?

    Quote Originally Posted by TigWorld View Post
    Perhaps there are just some tyre/rim combos or even batches of a particular tyre that have extremely tight (or perhaps strong) beads.
    This is what I'm thinking... probably a combination of the two factors.
    Quote Originally Posted by pvd
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    Quote Originally Posted by beanbag View Post
    bump for a calculation of bead tension due to mounting. It's hoops stress from spoke de-tension plus rim circumferential compression. Come on, you know you want to do it.
    I'm pretty sure spoke tension and circumferential compression are directly related, not additive.
    Quote Originally Posted by beanbag View Post
    It's no surprise that psi doesn't affect spoke tension. Think of the force of air pressure on a rim. One part pushing radially inward against the spoke bed. An equal cross section pulls radially outwards via the bead hooks.
    It remains surprising to me, and I don't think this argument is plausible for two reasons: 1) the bead is supporting itself in large part (i.e., the bead hook is not the only thing holding it on), and 2) I don't believe the "bead hooks," if you can even call them that, on a Crest would be capable of providing much support.
    Quote Originally Posted by beanbag View Post
    As to whether you should increase the spoke tension - that depends on what the limit of spoke tension is. Usually, as Jobst Brandt points out, it's when you stress relieve a wheel and it goes loopy. Same as when 4slomo finds that the rim gets increasingly sensitive to spoke adjustments. It's when the rim is starting to get near instability.
    Probably going this route, or the-tension-with-tire-on route.
    Quote Originally Posted by beanbag View Post
    In the case of Stan's rims, I though the tension limit was due to lack of spoke eyelets?
    I'm thinking it's more due to the light weight.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by Buzzaro View Post
    I had another idea. Maybe on the rims this is happening to, the joint is loose. Perhaps their diameter is changing slightly when the tire is mounted. I mean a diameter change is the likely cause either way, but this could be the culprit. A 1mm excess at the joint could be overlooked, especially with rim strips or tape. This would decrease the finish diameter by about .3mm or so. That might be enough to throw the tensions all off.
    Spitballing....
    Not a bad thought, though I'm pretty sure the joint in this case is tight.
    After I broke the bead and was adjusting the tension, I spent a few minutes chasing a "click" in the rim, thinking that the joint pin had dislodged, only to find out the presta valve in the tube was flopping around.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by meltingfeather View Post
    It remains surprising to me, and I don't think this argument is plausible for two reasons: 1) the bead is supporting itself in large part (i.e., the bead hook is not the only thing holding it on), and 2) I don't believe the "bead hooks," if you can even call them that, on a Crest would be capable of providing much support.
    I wasn't sure of his perspective either. When you consider that all the elements in the structure are elastic to some extent, I don't think the result is so easily predictable.

    MF, do you have an idea how much compression of the rim is required to see the net reduction in tension you are measuring? I wish I could be of more help here, but I find this really interesting.

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    I too experienced this phenomenon when I first mounted tubeless road tires onto my Alpha rims. There was a considerable loss of spoke tension (I'm not sure of the amount- I don't own a spoke tensiometer.) I then tried a regular, kevlar beaded clincher road tire at the same pressure and the result was nowhere near the same amount of spoke tension loss. It was evident to me that the nearly inelastic carbon fiber bead of the tubeless tire was compressing the rim; more so than just the air pressure alone. I simply retensioned the rims with the tires mounted and inflated on the rims. That was almost a year ago, and I'm still running the Alpha wheelset with no problems and no need for further adjustments. (Although I might lower the spoke tension if I ever switch back to regular clinchers. That's probably not likely, though.)

    So it stands to reason that any tight fitting beads can reduce the spoke tension of a rim; particularly lightweight aluminum or scandium alloy rims. BTW, I don't believe there is any 'upward' force exerted on the bead hook of a rim by a bead that's also exerting a compressive force on the rim.

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    Interesting

    Quote Originally Posted by meltingfeather View Post
    Probably going this route, or the-tension-with-tire-on route.

    I'm thinking it's more due to the light weight.
    Guessing it has to be the light design/open profile. . would love to see your chart comparing these profiles

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    Quote Originally Posted by meltingfeather View Post
    I'm pretty sure spoke tension and circumferential compression are directly related, not additive.

    Yes, they are directly related, AND they are additive for hoop stress calculation.

    It remains surprising to me, and I don't think this argument is plausible for two reasons: 1) the bead is supporting itself in large part (i.e., the bead hook is not the only thing holding it on), and 2) I don't believe the "bead hooks," if you can even call them that, on a Crest would be capable of providing much support.

    In the same vein, the air pressure pulls up on the bead, causing it to compress on the spoke bed by less.


    I'm thinking it's more due to the light weight.

    That sounds like engineer-speak to me. "The part wasn't too weak - it was too light."
    ...

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    Quote Originally Posted by beanbag View Post
    Yes, they are directly related, AND they are additive for hoop stress calculation.
    OK... maybe I misunderstood... as I see it, bead tension in the tire is going to come from tire pressure and rim compression, the latter being directly related to the change in tension.

    Quote Originally Posted by beanbag View Post
    In the same vein, the air pressure pulls up on the bead, causing it to compress on the spoke bed by less.
    I see now what you're getting at... I thought you were saying the bead pulls on the rim, which I don't think happens, but it's materially the same affect as compressing less.

    Quote Originally Posted by beanbag View Post
    I'm thinking it's more due to the light weight.

    That sounds like engineer-speak to me. "The part wasn't too weak - it was too light."
    Could be... I have been know to do that on occasion... I just don't think it's due to the lack of eyelets.
    Quote Originally Posted by pvd
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    Quote Originally Posted by bholwell View Post
    I too experienced this phenomenon when I first mounted tubeless road tires onto my Alpha rims. There was a considerable loss of spoke tension (I'm not sure of the amount- I don't own a spoke tensiometer.) I then tried a regular, kevlar beaded clincher road tire at the same pressure and the result was nowhere near the same amount of spoke tension loss. It was evident to me that the nearly inelastic carbon fiber bead of the tubeless tire was compressing the rim; more so than just the air pressure alone. I simply retensioned the rims with the tires mounted and inflated on the rims. That was almost a year ago, and I'm still running the Alpha wheelset with no problems and no need for further adjustments. (Although I might lower the spoke tension if I ever switch back to regular clinchers. That's probably not likely, though.)
    Your point about dropping the tension back down is particularly interesting. Raising tension would be a much easier decision if this wheel did not see use both with the road tire for training and with tubetype mountain tires for trail riding. He changes pretty frequently between the two.
    Quote Originally Posted by bholwell View Post
    So it stands to reason that any tight fitting beads can reduce the spoke tension of a rim; particularly lightweight aluminum or scandium alloy rims. BTW, I don't believe there is any 'upward' force exerted on the bead hook of a rim by a bead that's also exerting a compressive force on the rim.
    I agree.
    Quote Originally Posted by pvd
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    Quote Originally Posted by meltingfeather View Post
    Do you change tires very often? Any issues? I'm assuming your Podiums are now at ~120kgf w/out the tire mounted, right?
    I have changed rear tyres - now using a Race King 2.2 Racesport setup tubeless which has slightly thicker side walls than the supersonic version (used with a tube) which originally gave me the problems. I just measured the spoke tension and DS is right around 100kgf with the Racesport version as well. I assume the tension would be ~120kgf without a tyre on but I haven't measured it.

    Interestingly, at the valve hole I've got the overlap of the Stans tape. It's 3 layers thick for the spokes either side of the valve hole and two layers thick everywhere else. This should create extra deflection by the bead for those two spokes, but those spokes do not seem to have lost any tension. 1 extra layer of tape seems inconsequential.

    It would be interesting to know whether the extra tension (sans tyres) will damage the spoke holes.

    It seems for these weight weenie rims that spoke tension really needs to be dialled in with the intended tyre in place.

    Meltingfeather - your stroke of genius was to measure with bead seated and no pressure. The fact that inflation pressure makes only a small difference to spoke tension makes me a little more comfortable on setting the spoke tension with the tyre seated esp. tubeless. In the event of a flat, the bead will still be in place containing the spoke tension.

    120kgf without a tyre on may not be a problem as you can't ride on it without a tyre.

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    Quote Originally Posted by craigsj View Post
    MF, do you have an idea how much compression of the rim is required to see the net reduction in tension you are measuring?
    By my estimate a ~1.0mm reduction in circumference (a 0.30mm reduction in diameter) would give the ~20kgf tension drop I'm seeing.
    Quote Originally Posted by pvd
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    I recently ran in to the same issue building a set of Alpha 340s for a friend. I initially built the wheels to 120 kgf, and once we got on to building up the rest of the bike, I noticed the spokes being very soggy, and measured them at 70 kgf with the tire (and tube, not tubeless) at about 110psi. The front, radially laced wheel dropped from about 100 kgf to something below what the Park tension chart would give me a deflection conversion for (I believe 54 kgf was the lowest listed conversion)

    I had him ride the bike home and back a couple times to get out any possible kinks and then had him bring me the bike to retension the wheels. Though I did not put a tensiometer on the spokes while doing so, we slowly let out air pressure while plucking the spokes, and there was a distinct change in pitch as the tire deflated.

    I jacked the spoke tension up to 135 kgf in the rear this time around, making sure to keep an eye on any weird occurances in the rim due to the high tension, but it seemed fine. When I inflated the tire again this time around, the tensioned dropped only to 110 kgf, half the difference that occured after the initial build.

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    Thanks for all the above info and ideas.

    I too have just build up a set of Crest 29ers and got a nice even tension at 95 +/- 7%. On fitting a super tight Racing ralph this had dropped to 50!

    I tried another tire (Ignitor) that i could mount by hand and found the tesion had dropped but by a slightly less amount.
    I then re tensioned the wheel with tire on. Yet to ride.

    Last year i had a new Crest/ Hope Hoop that after a crash in it's 1st race had an unrepairable taco, it was also running a RR that was not easy to get on. I now wonder if loss of spoke tension could have contributed to the wrecked wheel??

    I also see in a lot of reviews of light wheelsets that the reviewer complains of loose spokes after a short ride. Perhaps the spokes were loose after fitting tire before the bike was ridden (or got worse because of loss of spoke tension).

    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?

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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.

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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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    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.

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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.

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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.
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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.
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  32. #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.

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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.

  34. #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.

  35. #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.

  36. #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.

  37. #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.

  38. #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.

  39. #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.

  40. #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

  41. #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...

  42. #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.
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  43. #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.

  44. #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

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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.
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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!

  47. #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.

  48. #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.

  49. #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.
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  50. #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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    Quote Originally Posted by meltingfeather View Post
    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.
    If you have a wheel and you change the air pressure in the tire and the spoke tension changes
    then meltingfeather I ask you, what other force is responsible for the change in spoke tension?

    please... get some books on physics and learn how a wheel/tire actually works

    unlike you, who says sorry you are "wrong", with no further explanation

    I provided simple clear "facts" to back up that statement
    if you don't like that bad luck, this is to for the other intelligent forum readers...

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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 probably saw your "don't have original data" post in an email update and didn't look back for follow up "unoriginal" data... Understandable I think, now that I'm familiarizing myself with year-old dialogue again.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    [QUOTE=Muchas;11119813]
    Quote Originally Posted by InertiaMan View Post
    :


    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
    from my observation, more internal rim width will increase on the amount of spoke de-tensioning from tire air pressure, due to increase of the area of the rim the air pressure is acting on

    what I also found is that after tire de-inflation you are left with the bead pressure
    measurable on the spoke tension gauge, immediately after you unseat the bead the spoke tension drops back to initial

    unseating the bead on the Enve 26Am rim dropped the spoke tensions by about 10kgf/spoke
    hard to believe it would be this high a value, as it was not hard to do (unseated the bead by hand)

    as you pump tire pressure you will overcome this bead pressure as the outer tire also pulls the bead away from the rim

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    Tire Pressure and Spoke Tension

    Quote Originally Posted by WaXed64 View Post
    If you have a wheel and you change the air pressure in the tire and the spoke tension changes
    then meltingfeather I ask you, what other force is responsible for the change in spoke tension?

    please... get some books on physics and learn how a wheel/tire actually works

    unlike you, who says sorry you are "wrong", with no further explanation

    I provided simple clear "facts" to back up that statement
    if you don't like that bad luck, this is to for the other intelligent forum readers...
    It's unfortunate that you bring infantile emotional rhetoric to a mostly valuable thread. Clean up your diaper and regroup.
    Limiting the discussion to the relevant (this thread) context so we can all easily be on the same page, I did not say that pressure does not contribute.
    I can not ignore the fact that the data demonstrated that it did not in my case; if you'd like to take that up analyze my measurements to support your position.
    I said you are wrong because my results and numerous others clearly show you are. Pressure is not the sole responsible mechanism as you proclaimed.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Tire Pressure and Spoke Tension

    Quote Originally Posted by InertiaMan View Post
    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.
    Thanks for the tip, coach. It doesn't make out of context cherry picks any more relevant.

    Quote Originally Posted by InertiaMan View Post
    I'm hardly drawing on "the whole of your post record" or taking you out of context.
    Sorry to point out the painfully obvious, but grabbing a single sentence from another thread/conversation and bringing it here without context is the definition of "out of context"... pretty straightforward.

    Quote Originally Posted by InertiaMan View Post
    At any rate, since we're now on the same page, lets get back to science.
    Thank god... no but I'll take some measurements and post this weekend.
    Do you have any measurements on Stan's rims, which have the enlarged BSD hypothesized to cause this phenomenon?
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by meltingfeather View Post
    It's unfortunate that you bring infantile emotional rhetoric to a mostly valuable thread. Clean up your diaper and regroup.
    Limiting the discussion to the relevant (this thread) context so we can all easily be on the same page, I did not say that pressure does not contribute.
    I can not ignore the fact that the data demonstrated that it did not in my case; if you'd like to take that up analyze my measurements to support your position.
    I said you are wrong because my results and numerous others clearly show you are. Pressure is not the sole responsible mechanism as you proclaimed.
    you can cut the derogatory comments please
    what other mechanism is responsible then? please meltingfeather fill us in on this valuable information you have

  57. #57
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    u can look at post 37

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    Tire Pressure and Spoke Tension

    Quote Originally Posted by WaXed64 View Post
    you can cut the derogatory comments please
    Agreed.
    Quote Originally Posted by WaXed64 View Post
    what other mechanism is responsible then? please meltingfeather fill us in on this valuable information you have
    I'm going to look past the sarcasm/snark, and answer this question directly.
    First, did you read the thread? From your first post through this one it seems very much like you haven't or you wouldn't be asking the question "what's the mechanism" all smugly and sarcastically when that mechanism is the subject of 90% of the thread. You might understand my initial response better if you read the thread.
    Second, it clearly says throughout, and as supported by my data, that the compression of the rim due to Stan's design of interference fit between BSD and tire bead was responsible in my case, which makes your proclamation that pressure is responsible based on reading one post irresponsible (for not bothering to read the thread) and... wrong.
    Maybe the tension drop from the rim compression by the tire bead was large enough to mask all pressure effects... it must have been, since I saw no effects of pressure over a very wide range.
    IM's results clearly show pressure effects, so, once again, my conclusion is, "it depends"... on circumstances, and each can clearly play a dominant role.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Half the conflict on this thread is probably because we're mixing two similar-but-different topics: a) what explains the weird observations of the Crest wheel in post #1, and b) what can be generally said about bike wheel spoke de-tensioning in response to tire mounting/airing (especially the case of MTB tubeless wheels). This thread started with (a) but has defacto shifted to (b) for better or worse.

    MF, your wheel example has the unique role of being the origin of this thread, for which I'm grateful. However, unless I missed an example, it is also the ONLY wheel which has exhibited virtually no de-tensioning due to air pressure. Every other wheel we have data for showed measurable de-tension due to air pressure. So I'm thinking it may not be the most representative example to discuss topic (b) above.

    First, its a Crest, an extremely light rim which would presumably be more vulnerable to possible "rim structure" issues that may/may-not be in play here. Secondly, the original data you posted was collected on an admittedly compromised wheel with spoke tensions far below normal.

    The second set of data you posted (measured on the re-tensioned wheel) helped some, but unfortunately only includes the 65psi and bead-off cases, and no intermediate pressure scenarios, or the all-important low-pressure/bead-set scenario. And the fact its after-inflation state didn't revert to its before-inflation state indicates some atypical variables may be involved.

    Don't misjudge this as criticism. The data is what it is, and its interesting. I'm just highlighting some of the unique elements of the example.

    Is it possible to fill in this data gap a bit?

    I would be highly interested to see measurements taken on a new/solid/tensioned Crest build, so we can compare to the data from post #1. Perhaps it will be very similar, and we can confirm that there is a fairly unique response of Crest rims to pressure/bead interaction. Or perhaps the data will be different (more similar to the non-Stans rims in my data, showing some measurable de-tensioning with air pressure) and we will learn that the wheel that inspired this thread was an anomaly in the larger picture, perhaps due to its compromised integrity and relatively "weak" rim structure.

    Anyone with a solid Crest wheel and a tensionmeter?

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    Interesting thread.

    Wouldn't it be really easy to figure out if Derby was on to something? Excuse my rim model number ignorance if there is already data I missed above, but has anyone tried measuring changes on a triple box x-section, or single wall vs a regular double wall as Derby pictured?

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    Quote Originally Posted by Zowie View Post
    Wouldn't it be really easy to figure out if Derby was on to something? Excuse my rim model number ignorance if there is already data I missed above, but has anyone tried measuring changes on a triple box x-section, or single wall vs a regular double wall as Derby pictured?
    No data in this thread for triple box or single wall. I could get some triple box data from an i23 I suppose, but it may force me to find a compressor to re-seat the bead.

    A straightforward experiment to partially test Derby's hypothesis (which is specific to Stans Crest) would be to take a series of rim width measurements with a digital caliper at various inflation pressures. If the width is invariable, it arguably disproves Derby's explanation, since he clearly expects the top edge of the rim to move outward. If width IS changing consistently, then it would be consistent with Derby's hypothesis (though not proof of it . . . in theory you could have the rim wall expand without the pivoting/rising of the spoke bed).

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    Quote Originally Posted by InertiaMan View Post
    Half the conflict on this thread is probably because we're mixing two similar-but-different topics: a) what explains the weird observations of the Crest wheel in post #1, and b) what can be generally said about bike wheel spoke de-tensioning in response to tire mounting/airing (especially the case of MTB tubeless wheels). This thread started with (a) but has defacto shifted to (b) for better or worse.
    Two different topics indeed. My problem, and the one experienced by others with Stan's rims who have posted, was a wheel that could not maintain enough tension to be durable... and what to do about that.
    It really doesn't matter to me whether air pressure drops my tension some if it's still enough tension to keep the wheel stable. Sort of a, "mildly interesting but of little practical use or importance" (to me) type of thing.

    Quote Originally Posted by InertiaMan View Post
    MF, your wheel example has the unique role of being the origin of this thread, for which I'm grateful. However, unless I missed an example, it is also the ONLY wheel which has exhibited virtually no de-tensioning due to air pressure. Every other wheel we have data for showed measurable de-tension due to air pressure. So I'm thinking it may not be the most representative example to discuss topic (b) above.

    First, its a Crest, an extremely light rim which would presumably be more vulnerable to possible "rim structure" issues that may/may-not be in play here. Secondly, the original data you posted was collected on an admittedly compromised wheel with spoke tensions far below normal.
    The Crest is a very representative example of rims people have had this problem with. In terms of the larger "b" discussion, maybe not, but like I said above, even a measurable and theoretically predictable drop in tension from pressure is not something I care about unless it is a problem. It's not surprising that it would happen and it makes sense. I expressed surprise at my lack of observation of pressure-related tension drop in one of my first posts.

    Quote Originally Posted by InertiaMan View Post
    I would be highly interested to see measurements taken on a new/solid/tensioned Crest build, so we can compare to the data from post #1. Perhaps it will be very similar, and we can confirm that there is a fairly unique response of Crest rims to pressure/bead interaction. Or perhaps the data will be different (more similar to the non-Stans rims in my data, showing some measurable de-tensioning with air pressure) and we will learn that the wheel that inspired this thread was an anomaly in the larger picture, perhaps due to its compromised integrity and relatively "weak" rim structure.
    A huge variable is going to be the actual tire (even beyond make and model) used, since the interference of the fit is a critical determinant of the drop, and it varies, even within tires of the same make, model & production run.

    Quote Originally Posted by InertiaMan View Post
    Anyone with a solid Crest wheel and a tensionmeter?
    The retensioned Crest I measured and reported on has been in service for over two years without issue.
    I didn't repeat the pressure variation for the retensioned wheel because I had already determined that pressure was minor if contributing at all and it seemed like a waste of time at that point. I was and remain relatively uninterested in the "b" topic.
    I'm not meaning to be dismissive, just demonstrate my perspective.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by WaXed64 View Post
    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
    Waxed64,

    Can you do another measurement of this wheel, with low/no pressure but the bead still seated?

    I'm curious how Enve compare to LB and Stans in that tire state.

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    Quote Originally Posted by meltingfeather View Post
    Two different topics indeed, one with a practical application/problem to solve, and one that seems more about theoretical musings with little practical application.
    I guess I disagree about the practical benefits of topic (b). This thread has had a practical influence on my wheelbuilding, even on non-Stan's rims. I was surprised to learn that we have spoke tension differences of 20-30kgF between bare wheel and the same wheel with tubeless tires installed at typical operating pressures. The scale of that tension reduction is on par with the optimal tension window on a given wheel (100-120kgF for example). My practical takeaway, especially for tight tubeless tire/wheels, is to push bare-wheel tensions toward the high side of recommended to ensure that the wheel remains in a sufficiently high-tensioned state during actual use with a tire installed. In the past, I was more conservative with the tensions, often aiming for middle of the range. Net effect, my tubeless builds are now tensioned 10kgF higher, or more, than in the past.

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    Quote Originally Posted by InertiaMan View Post
    I guess I disagree about the practical benefits of topic (b).
    Well I'm glad it came up then.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    I have another rim/tire combo datapoint which is pretty surprising.

    Rim: 32H LB 35mm hookless 29er with 14g DB spokes
    Tire: Michelin Wild Grip'r 29x2.25 installed tubeless

    Spoke tension on the brake side (front wheel) was 110kgF before tire install. With tire installed and pumped to 25 PSI, the spoke tension dropped to 85-88 kgF. With air pressure then released to zero, but beads still seated, tension returned to 110kgF.

    That's a pretty significant drop in tension, and it is apparently due only to air pressure. Seems to behave differently than the LB 30mm hooked rim, perhaps due to a different bead shoulder dimension (my LB 30mm numbers at top of thread were with a Bontrager tubeless rim strip installed).

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    Quote Originally Posted by InertiaMan View Post
    I have another rim/tire combo datapoint which is pretty surprising.

    Rim: 32H LB 35mm hookless 29er with 14g DB spokes
    Tire: Michelin Wild Grip'r 29x2.25 installed tubeless

    Spoke tension on the brake side (front wheel) was 110kgF before tire install. With tire installed and pumped to 25 PSI, the spoke tension dropped to 85-88 kgF. With air pressure then released to zero, but beads still seated, tension returned to 110kgF.

    That's a pretty significant drop in tension, and it is apparently due only to air pressure. Seems to behave differently than the LB 30mm hooked rim, perhaps due to a different bead shoulder dimension (my LB 30mm numbers at top of thread were with a Bontrager tubeless rim strip installed).
    That is interesting.
    Thanks for posting up the data point.
    As with most things, it seems like there are many factors at play and no rule that can be stated regarding spoke tension as relates to tire pressure and bead seating.
    "It depends" is about as good as it gets.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by InertiaMan View Post
    Waxed64,

    Can you do another measurement of this wheel, with low/no pressure but the bead still seated?

    I'm curious how Enve compare to LB and Stans in that tire state.

    from memory the ENVE with no air pressure spoke tension went back up to 105kgf (bead still seated) and then back up to 117kgf after bead unseated
    tires were schwalbe TLR 2.25 (so bead seat probably not as tight as UST)
    My thinking is basically the tighter the bead on the rim the more effect of spoke tension reduction it will create, however tire pressure will push on the rim bed and apply opposite force on the tire to pull the bead pressure off the rim (tire pressure also forces the bead up onto the bead to start with)

    composites have very good tensile strength, however a spoked wheel is under a compression load

    I guess the more compressive rigidity a rim has, the less will be the effect of spoke detensioning from tire pressure

    In all respects the ENVE AM suffers a hell lot more spoke tension variations than the Alu ZTR Flow rims I have.... very unimpressed

    what I have also noted is that temperature also had a measurable effect on the ENVE wheel spoke tensions ie. when temp goes down the spoke tensions also drop further... ( I put this down to the carbon composite rim contracting with drop in temperature)
    the spokes shpould also contract but I guess it must not be at the same rate
    on the ENVE AM I measured around 10kgf lower going from 25degC down to 15 degC ....

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    Quote Originally Posted by meltingfeather View Post
    The retensioned Crest I measured and reported on has been in service for over two years without issue.
    to clarify did you re-tension with the tyre still fitted and inflated?

    I have a similar issue with the crest that seems to be tight TLR bead rather than pressure related.
    What exactly is a rigid hard tail?

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    Quote Originally Posted by WaXed64 View Post
    what I have also noted is that temperature also had a measurable effect on the ENVE wheel spoke tensions ie. when temp goes down the spoke tensions also drop further... ( I put this down to the carbon composite rim contracting with drop in temperature)
    the spokes shpould also contract but I guess it must not be at the same rate
    Many plastics have a heat expansion rate ten times larger than steel. Your observation makes perfect sense.

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    Quote Originally Posted by Stuart B View Post
    to clarify did you re-tension with the tyre still fitted and inflated?
    No.

    Quote Originally Posted by Stuart B View Post
    I have a similar issue with the crest that seems to be tight TLR bead rather than pressure related.
    I raised the tension to an average of 106 kgf and the wheel has not been back (though the guy moved to Colorado).
    I also suspect the rim has now been replaced... the guy rides a LOT.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Re: Tire Pressure and Spoke Tension

    Quote Originally Posted by meltingfeather View Post
    No.


    I raised the tension to an average of 106 kgf and the wheel has not been back (though the guy moved to Colorado).
    I also suspect the rim has now been replaced... the guy rides a LOT.
    OK cheers .


    sent from my phone so apologies for any typos
    What exactly is a rigid hard tail?

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    Quote Originally Posted by Saul Lumikko View Post
    Many plastics have a heat expansion rate ten times larger than steel. Your observation makes perfect sense.
    Carbon/epoxy composite have up to 10x less thermal expansion rate than steel:

    Mechanical Properties of Carbon Fibre Composite Materials

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    I just unseated my tyre and checked tension as it was pretty much as set before mounting the tyre. So I just upped the tension a bit a re-dished to try and account for the change in dish after the tyre is mounted.

    While pumping up and re-seating the bead I watched my tension gauge, initially it went down with pressure as the bead seated, each time the bead popped the tension went down suddenly. I then let all the air out and the tension remained where it was....so I believe in my case it is the incredibly tight bead. Tight enough I think I am going to buy some new tyre levers!

    the upside is they are the easiest tyre I have had to inflaste with a track pump! not sure its worth the trade off for spoke tension though.

    maybe I should have gone for the arch ex, but the crest were 30% off
    What exactly is a rigid hard tail?

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    Leonard Zinn discusses this topic here:
    http://velonews.competitor.com/2011/...tension_198452

    Tire pressure does indeed reduce wheel spoke tension. Perhaps not all rim/spoke/hub/lace pattern/tire equally, but it does. I don't understand why Meltingfether would challenge this pretty well-established fact.

    So here's my question. Why not run up final tension on a road wheelset - especially those with more dish and/or aluminum nipples and/or zero-offset rim holes (which cause even more nipple friction) - with tires at full inflation - or even overinflated?

    I know when I'm reaching optimal drive-side tension, nipple friction gets very high. Yes, I use lubrication and/or thread lock on both thread and rim interfaces. I've only stripped a few nipples in the last several years, so it isn't like I'm experiencing nipple failure on a regular basis. But man, those nipples sure get hard to turn! Seems that instead of pushing nipples to their maximum applying so much torque, just install tires, inflate to 20 to 40 psi over tire's printed maximum* so you can achieve high final tension much easier. Plus, it gives the hands a break when building multiple wheel pairs.

    I realize that final radial truing will be difficult to impossible to achieve with the tire installed. At least the lion's share of nipple tightening will be done more easily. Once optimal tire-on tension is achieved, remove tire and conduct final radial and lateral true.

    I have not tried this. Nor have I researched this idea much online. But I thought I'd poke my head in on this thread to ask if any of the wheel builders are doing this as part of their building procedure.

    When thinking back to a personal rear wheel build, I now realize tire pressure spoke detensioning was responsible for NDS spoke loosening. I didn't utilize a spoke tensionmeter at the time and just accepted the fact that 9+ speed rear wheels had so much dish, loose NDS spokes were hard to avoid.

    Seems like utilizing tires would be a way to achieve high tension without killing nipples and one's hands during builds.

    *Tire max pressure rating is determined by inflating a tire properly on an industry standard rim and inflating it until it pops off. The pressure at which it pops off is divided by 2 and that's the tire's max pressure. So going 20 to 40 psi over a tire's max. pressure rating is usually going nowhere near blow-off pressure (assuming an industry standard rim or equivalent is used).

  76. #76
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    Tire Pressure and Spoke Tension

    Quote Originally Posted by TandemBear View Post
    Tire pressure does indeed reduce wheel spoke tension. Perhaps not all rim/spoke/hub/lace pattern/tire equally, but it does. I don't understand why Meltingfether would challenge this pretty well-established fact.
    I didn't. It would help if you read the thread.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  77. #77
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    Quote Originally Posted by meltingfeather View Post
    I didn't. It would help if you read the thread.
    I guess I either perused it too quickly or missed the first page. The post I saw of yours seemed to challenge this. Sorry to have missed the intent of your comment.

    Either way, thanks for providing some good discussion on the issue. I'll give the thread more attention when I have a moment to do so.

  78. #78
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    Quote Originally Posted by TandemBear View Post
    I guess I either perused it too quickly or missed the first page. The post I saw of yours seemed to challenge this. Sorry to have missed the intent of your comment.

    Either way, thanks for providing some good discussion on the issue. I'll give the thread more attention when I have a moment to do so.
    No worries.

    Through this discussion it became apparent to me that both tire pressure and bead seating can and do play roles and either one can be dominant, depending on circumstances. I was actually surprised by the fact that tire pressure did not seem to play a role under my particular set of circumstances, as my first post indicates.

    It seems like most people want to take their experience and use it to theorize some universal law. Unfortunately (for them) reality, like Homey, don't play dat.
    Last edited by meltingfeather; 01-07-2015 at 05:17 PM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  79. #79
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    I'll add my data to this thread, use it as you will. My rear tire's sealant needed to be refreshed, so I took the opportunity to check tensions and re-true.

    Chris King ISO rear hub, sapim straight spokes, brass nipples, stans arch rim, 26". Maxis Ardent EXO 2.1 tire. The bead didn't sit incredibly tight on the rim, it popped off fairly easily once deflated, but it didn't fall off on it's own either.

    https://docs.google.com/spreadsheets...it?usp=sharing

    I took the average of 4 random spokes for each set of meausrements. in hindsight I should have done all, or used the same 4 each time
    My bike MCA kinda climbs like a billy-goat. WOO WOO!

  80. #80
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    I'm getting a much bigger drop in tension with my Light Bicycle carbon rims, DT spokes, and WTB Cross Boss tire. I'm worried that if I raise the tension enough to be at an acceptable level with the tire on, it'll be too high with the tire off. The rim has a published max of 180kgf and I'm already at as much as 167 on the drive side with the tire off.

    14-53kgf, 15-58kgf, 16-64kgf, 17-70kgf, 18-77kgf, 19-85kgf, 20-94kgf, 21-105kgf, 22-117kgf, 23-131kgf, 24-148kgf, 25-167kgf.

    Some of them lost half their tension! The first DS spoke for example. That's 148 down to 70kgf.

    Drive side

    24 -> 17
    25 -> 20
    25 -> 18
    25 -> 19
    24 -> 16
    25 -> 19
    24 -> 18
    25 -> 20
    24 -> 17
    24 -> 19
    24 -> 20
    24 -> 20
    25 -> 21
    24 -> 19
    24 -> 18
    25 -> 21

    Non drive side

    19 -> 14
    21 -> 18
    19 -> 12
    19 -> 12
    20 -> 13
    21 -> 16
    20 -> 15
    19 -> 15
    19 -> 16
    19 -> 15
    20 -> 15
    21 -> 17
    20 -> 15
    21 -> 16
    20 -> 15
    21 -> 18

  81. #81
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    Quote Originally Posted by Alias530 View Post
    I'm getting a much bigger drop in tension with my Light Bicycle carbon rims, DT spokes, and WTB Cross Boss tire.
    What's the comparison here?
    Seated to unseated tire?
    Pressured to flat but still seated?
    Pressured to flat and unseated?
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  82. #82
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    Quote Originally Posted by meltingfeather View Post
    What's the comparison here?
    Seated to unseated tire?
    Pressured to flat but still seated?
    Pressured to flat and unseated?
    This is comparing to bare wheel to 40psi/seated rim bead (tubeless).

    This is a 35mm tire so 40psi is not that much.

    I don't know what to do now...

    I had the wheels built for me, kept having NDS spokes go slack, checked tension and I was at 95kgf DS/70kgf NDS and determined that to be too low so I tried to fix it and ended up starting from scratch. Then I got the wheel up to 150kgf on the DS and thought I was golden but as soon as I put the tire on I'm right back to where I started. I thought the wheel builder did a bad job but I am coming up with the same result.

  83. #83
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    Spoke tensions in the range of 150-160kgF are pretty much categorically too high, regardless of components used, especially on a 32H rim. Tensions above 130kgF are relatively rare. 120 or less is a more typical target for drive side tension.

    What model of DT spokes are you using? What model LB rim?

  84. #84
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    Quote Originally Posted by InertiaMan View Post
    Spoke tensions in the range of 150-160kgF are pretty much categorically too high, regardless of components used, especially on a 32H rim. Tensions above 130kgF are relatively rare. 120 or less is a more typical target for drive side tension.

    What model of DT spokes are you using? What model LB rim?
    DT Comp spokes and the 29er XC rim (27mm outer/22mm inner diameter) with extra layers of carbon to reach about 410g (normally 365g if I remember right).

    With the tire on some of the NDS spokes are below 50kgf... that's way too low isn't it? I still haven't gotten a consistent answer as to whether "max" and "recommended" tensions are with or without the tire on. I'm seeing a bigger gap than most apparently do, to the point that my "with tire" tensions are unusably low.

  85. #85
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    I checked your tension values on the Park cross reference table and confirmed you are reading it correctly. Presumably you are also placing the tensiometer only in the butted section of the spokes when reading. So no obvious "errors" to explain things.

    One thing I suggest you try is another tire, simply for another datapoint. The Cross Boss is designed as a tubeless cross tire, which would logically be targeted at substantially narrower rims typically used in that application. In addition, road tubeless tires are normally designed to be even tighter at the bead than MTB tires due to the higher pressures normally encountered. So if we assume that WTB designed these tires for common road/cross wheels and used a nominal bead diameter that was (relatively) small/tight, then your current rim/tire combo is sort of a worst case scenario for this tension-loss-under-tire-pressure scenario. In other words, my hypothesis is that your tire bead is tighter than anyone else on this thread that has taken sample measurements, so your before/after tire tension drops are alarmingly higher.

    Edit PS: You should also take a tension reading (a) with the tire mounted and at pressure, and (b) with tire deflated but bead still seated. If the deflated-but-seated tensions are nearly as low as the inflated tensions, then you'll know this is primarily a bead diameter issue.

    As for tension targets, you can ignore the max tension from the LB website. If anything, that is a failure tension in their testing, or some statistical threshold preceding failure My recommendation would be to shoot for 130kgF on DS without a tire. Spoke pull though is not unheard of on these rims, so I'd be hesitant to recommend higher.

    A typical no-tire tension target is 110-120kgF on the DS and >80kgF on the NDS. Unfortunately on these rims (and others), it can be difficult/impossible to get the NDS spokes > 80kgF while keeping the DS below 120. And even harder to keep the NDS spokes sufficiently high AFTER a tire is mounted. Get the spoke tensions as consistent as humanly possible, and perhaps the NDS side will be >80kgF.

  86. #86
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    The Cross Boss sidewall says the max pressure is 65psi if I remember right, which is about what a mountain bike tire usually quotes as max. The bead was tight but not any tighter than a normal tubeless mountain bike tire.

    I just checked the front wheel (same rim/spoke type but 28 spokes/bigger tubeless cyclocross tire) and the disc side spokes were at 85kgf and non-disc was at 64kgf.

    The rear wheel drive side spokes average around 95kgf and NDS average around 64kgf but some so low there's no spot on the conversion chart. I was losing spoke tension in the rear when the non drive side was at 70kgf. I guess I can try another tire or locktite the NDS threads?

    Prior to the tire I had the NDS around 90kgf and 150kgf on the DS.

    Is it possible that the spokes are too tight and that contributes to the tension drop with the tire? Is there any way that dropping the tension would result in a lower drop when I add the tire?

  87. #87
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    Quote Originally Posted by Mac_Aravan View Post
    Carbon/epoxy composite have up to 10x less thermal expansion rate than steel:

    Mechanical Properties of Carbon Fibre Composite Materials
    Yeah but if you look at UD carbon (unidirectional, that seems to be the norm these days) you will see that in one direction is actually has negative thermal expansion but in the other direction it has roughly 3x higher thermal expansion compared to steel.

    In the same direction it also happens to have 1/20 the stiffness (youngs mod) of the steel listed,
    1/20 ultimate tensile strength, and 1/4 ultimate compressive strength.

    All this could very well explain the behaviour of spokes going soft when the wheels get colder with carbon wheels.

    That is if I'm reading the table correctly, but I think I am.
    Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.

    Quote Originally Posted by iheartbicycles View Post
    Specialized sucks ass.

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    So pleased I found this thread which I’ve just read right through, and special thanks to meltingfeather and InertiaMan for their inputs. My experience with Schwalbe Hans Dampf and RockRazor mounted on Stans Arch 650B rims run tubeless…

    Just built up my first ever wheelset using Roger Mussons excellent book and determining spoke tension by pitch – using some 26” Crest wheels as a reference. Wheels were straight and true but doubts about tension got the better of me so splashed out on a Park Tensionmeter just to be sure!

    Checked front wheel disc side and the tensions were way below the 125KgF recommended on the notubes website, averaging out around 100KgF, with the NDS of course considerably lower. But this was with the tires now mounted and inflated (at this point I had no idea the tires had an effect on spoke tension).

    I adjusted the tension to ballpark 125KgF throughout, then off with the tire to check radial and lateral trueness, tweaked these in then checked tension again – 150KgF average! The penny dropped – tires in some way had an effect on tension. A couple more hours with the tire off again getting the tensions back to where they probably were in the first place when originally tensioned using pitch, 125 KgF with no tire fitted.

    On to the back wheel and this time I checked the Drive Side tension with tires inflated to around 25PSI (95KgF average), tires deflated (same), and bead unseated (125KgF).

    So in my experience with my set-up the tire is dropping tension by around 25-30KgF, and it is the bead not the tire pressure that seems to be causing this. I noticed somewhere on the web than Stans recommended tension used to be 100KgF but is now upped to 125KgF, and I wonder if this is why, because a tire mounted on their rims reduces tension so drastically?

    For now I’ve decided to leave the wheels as they are and keep an eye on the spoke tensions once the bike is finished and actually gets ridden. That is around 100KgF with tires on (which equates to 125KgF with tires off and is now Stans recommended tension)

    For info NDS tension on the rear wheel with tire mounted is considerably lower at only about 60KgF average.

  89. #89
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    Nice post and observations.

    However, given your options, I think you should opt for the higher tensions. You want the recommended spoke tension for real-world situations. That is, appropriate tensions when you're riding, not when the wheel's in the truing stand with the tires off.

    However, if the manufacturer has anticipated the resulting tension loss when tires are mounted, then you'd want to hit their posted value in the truing stand.

    It would be worthwhile to confirm with the rim/wheel manufacturers if their listed tensions are for real-world usage, or tension during building, prior to tire installation.

    Thanks again.

  90. #90
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    PS I just corresponded with Stans to ask for clarification. I'll keep an eye on my inbox and let you know if I hear from them.

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    I lost quite a bit of tension with my Light Bicycle rims. They said (and the Park Tensionmeter user manual) says that tension should be without a tire. Tire pressure and type play such a big role it seems like you'd want tension WITH a tire.

    I eventually gave up on mine and changed to a different tire. I would have to run such high tension without a tire to get it high enough with a tire that I'd crack the rim if I ever had a blowout. So, new tire it was.

  92. #92
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    Thanks TandemBear, I await Stans response with interest.

    One option might be to split the difference and take the truing stand tension up to say 135KgF and therefore the real world tension up to about 110KgF...This would negate any worries about the tension being too high and at the same time feeling more confident that the real world tension is high enough to support the wheel.

    Lets see if Stans reply first though as I don't relish removing the tires and tinkering a third time on this wheelset!

  93. #93
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    OK, Peter at Stan's got right back to me, which was nice since it was almost quitting time on their end of the country.

    Spoke tensions are given for bare wheels. They assume spoke tension will decrease with tires, so don't worry about it.

    I Stan(d) corrected!

    Nice to have that issue cleared up!

    PS Anyone ride the new Flow Trail at Soquel Demonstration Forest yet? Official grand opening this Saturday, but I can't make it. Can't wait to get back down there to ride - it's been WAY long. Will ride it on the half bike the first time, but hoping to hit it on the tandem, too!!!

    Demo Flow Trail of Soquel Demonstration State Forest now open - Mtbr.com

  94. #94
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    I had built a bunch of wheels and never had this problem, so I never checked for it.
    Until last year...
    I built up a pair of 35mm Velocity Blunts for my own bike. Mounted up tires (tubeless) and went for a 20 mile ride. In the middle of my ride, my bike started to feel all loose and weird. I checked my tire, figuring it was soft and it was not. Then I noticed all of my spokes were loose on my rear wheel.
    When I got home, I took the tire off and checked the wheel out. tensions were low, but not like with the tire mounted, so I mounted the tire back up and retensioned the spokes with the tire mounted. Wheel has been fine since.
    Then I realized I had just laced a set of Flows for a friend's bike build I was doing, so I mounted his tires and checked tension... Same thing. So I tensioned his with the tires on. He's been on that bike about a year now with no problems.
    This has been with Geax Saguaros on all three of these wheels. I recently built a 26" Flow and mounted up a Specialized rear tire and no change in tension.
    I guess you should always just check.
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  95. #95
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    As I recently considered the soon to be available Schwalbe Procore system, it made me wonder how the wheels are going to handle the increased pressure.

    Consider that Schwable recommends inflating the inner chamber to 60-90psi. That's WAY higher than any typical MTB tire setup. It scares me to think what that may do to spoke tensions, especially on wide rims. I searched online and found a couple similar comments from readers on forums elsewhere, but no response from Schwalbe about this aspect of the Procore system.

    I can imagine the spoke tension getting reduced 30-40kgF if subjected to 75psi across a 28mm internal width rim. Hard for me to imagine how to compensate for that. If you tension the wheel higher to compensate, you're looking at 150kgF+ on the rim/spoke/nipple when tires aren't mounted.

    I was excited to try the Procore setup, but this has me concerned.

  96. #96
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    Quote Originally Posted by InertiaMan View Post
    I was excited to try the Procore setup, but this has me concerned.
    I'm curious to see this as well.
    As we have seen, sometimes tire pressure affects spoke tension and sometimes it does not. Because ProCore is a pressure-containing bladder as opposed to a tube in a tire, it may and IME probably will exert less force on the rim than a tube inflated to the same pressure.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  97. #97
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    Quote Originally Posted by meltingfeather View Post
    I'm curious to see this as well.
    As we have seen, sometimes tire pressure affects spoke tension and sometimes it does not. Because ProCore is a pressure-containing bladder as opposed to a tube in a tire, it may and IME probably will exert less force on the rim than a tube inflated to the same pressure.
    I do not have a ProCore system...but it appears to me that the solution is roughly a tube in a tire. That tire may have a different bead and appears to be around 70mm b2b but it looks like a tire casing without tread. I think it's an interesting question just how different the loads are on the rim.
    Last edited by craigsj; 08-09-2015 at 04:53 AM.

  98. #98
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    Quote Originally Posted by craigsj View Post
    I do not have a ProCore system...but it appears to me that the solution is roughly a tube in a tire. That tire may have a different bead and appears to be around 110mm b2b but it looks like a tire casing without tread. I think it's an interesting question just how different the loads are on the rim.
    You're right... I was mistaken about the design.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  99. #99
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    Just sharing my data. I recently built a rear wheel with an arch ex 29 rim. Measured the tensions w/o a tire, with tire at 40 psi and with tire at 0 psi but mounted on the rim. I build the wheel a little bit over the tension spec to account for tension drop. Tire used was a fairly old maxxis icon.

    No tire DS: 135 kgf (26)
    Tire 40 psi DS: 103 kgf (23.5)
    Tire mounted 0 psi DS: 120kgf (25)

    *(park tool tm-1 unit)

    Cheers

  100. #100
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    I think rim/tire combo matters a lot. My Rovals with Maxxis tires hardly drop, but my Light Bicycle mountain bike rims with tight cyclocross tires on them lower a lot.

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