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The article briefly mentioned the undesirable side effect of the continuing trend towards "wider and lighter" tubeless ready road rims as loss of wheel longevity and durability.

I wish they had elaborated and analyzed further what is really happening when rim makers merely push the envelope making rims wider while maintaining or even reducing the rim weight without reengineering the structural profile and reinforcement of the rim.
I am referring to the continuous thinning of the alloy extrusion while maintaining the same structural profile (U-shaped shell with intermediate support connecting the two sides) rims were made when rim widths were shorter, weights were heavier and there were no road tubeless at 100 psi.

From the wheelbuilder's prospective I see the side effect of these thinner extrusion rims to be severe loss of spoke tension when the tire is first inflated or even fitted if its tubeless. The manufacturer prescribed tensioning value of 120 kgf has remained unchanged through this "wider and lighter'" rim evolution but so have the laws of physics prescribing a certain minimum tension required for the NDS spokes to keep the wheel tight as it loads and unloads. In the past a 5 to 10 kgf drop in tension was expected when the tire was first put on and inflated, now reductions in the range of 20 to 35 kgf are not uncommon for these "wider and lighter" rims. This means that if you tension the DS spokes at the max value of 120kgf you could end up below 90 kgf when the tire is first put on. This, simply, is not enough tension to keep the NDS spokes tensioned within their elastic region. Slacking of the spokes occurs under use and the spoke soon thereafter breaks.

A common reaction to this dilemma is to increase the DS tension. I have done it, as a lot of other builders have. However, at least empirically, it is shown that this is not the answer either. Rim cracks develop at around the nipple as the thinner extrusion is subjected to the stresses caused by the influence of the thinner extrusion reacting to the forces imposed by the tire inflation/bead pressure as the rim lips rotate outwards and the rim internal edge elongates from this movement as well as the increased spoke tension. The end result is a much shorter rim life as the material gives out at the spoke holes and cracks are formed. Evidents of this are abundant throughout the internet in forums such as ours.

IMO, further engineering is needed to reexamine the structural integrity of the rim under these newer conditions and come up with a newer reinforcing layout. Until I see evidence of such developments I will refrain from building any more wheels with internal bead spacing significantly over 17mm and weight below 470grams or so for mid-depth extrusions, especially for riders over the 180 lbs mid-range mark looking for a non-racing specific wheel.
 

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Until I see evidence of such developments I will refrain from building any more wheels with internal bead spacing significantly over 17mm and weight below 470grams or so for mid-depth extrusions, especially for riders over the 180 lbs mid-range mark looking for a non-racing specific wheel.
I would guess this has to do more with design issues rather than strictly being a weight issue. I recently built up some wheels with Kinlin XR31T hoops which are widely regarded as being very stout and durable and certainly not feather weight rims (they weighed in at 480g ish each). Yet even these lost 30kgf+ of tension when I mounted some tubeless tires on them.

As far as needing to add extra tension to compensate for this, I don't necessarily think it's a big deal. My rear wheel had a final DS tension of 140kgf which translated to ~110kgf with the tire mounted. The wheel takes the stress that's going to potentially cause cracks when out on the road with the tire mounted, not in the truing stand.

However, I could see an issue with all this where somebody switches between running tubeless and non tubeless tires. If you compensate by over tensioning the wheels, then you run the risk of getting rim cracks when running normal clinchers. Conversely if you don't compensate the tension, then when running tubeless you risk breaking spokes on the NDS side- or at least living with noodley feeling wheels. Since I ride tubeless 100% of the time, the choice was a simple one to make. But if your a high volume custom wheel maker who doesn't really know what your client's habits are, I'm not sure sure which way you go?
 

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Couple of thoughts here.

The dynamic that happens alongside the pressure drop is the rim moving towards the drive side. It stands completely to reason that this accounts for the majority of the pressure drop, if not quite all of it, instead of a circumferential reduction in the rim. My first "a-ha" on this came when I measured the non-drive drop to be less than equivalent to the tension ratio of the drive and non-drive spokes (non-drives didn't drop as much).

Lately, as I've been building more offset rims, I notice a bit of tension drop but no lateral displacement. So it's clearly not all displacement to the drive side that's driving the tension loss, but it's a lot of it.

Cooskull's measurement of the XR31T isn't typical of my measurements with them, but my build check is a relatively loose fitting non-tubeless tire which then gets pumped to 100 psi. See below.

This phenomenon is highly variable based on tires. And tires themselves are variable. A new Conti 4000S is a fairly snug fit on many rims, but 1000 miles in (or after 4' in the dryer - which is a trick that WAY pre-dates tubeless rims, btw) they aren't nearly so snug. A Schwalbe One isn't as tight as a Schwalbe Pro One, and neither is quite as tight after some use as it is new.

The thought that this phenomenon is more prevalent among lighter rims isn't at all consistent with my experience. Pacenti SL23v2 is a rim that proved to push the envelope on weight, but didn't have a big pressure drop. A HED Belgium+, not as deep and ~ 40g more, suffers more tension drop than a Pacenti. And Pacenti (even though v2 wasn't nearly as tight a fit as v1) is a tighter tire fit than either HED B+ or Kinlin XR31T.

A spoke thread is 2.0mm x 56 TPI (yeah, TPI). Pressure drops that I see on drive side are typically equivalent to between 1/4 and 1/2 turn on the drive side, so equivalent to about a .004" or so reduction in rim diameter if my math is right. But again, there's clearly an element of lateral displacement that happens.

I think most people pay wildly too much tension to drive side tension. You need to make sure you have at least the minimum acceptable tension on the NON-DRIVE. That's really all you care about. I shoot to have 60kgf on the non-drive side before a tire goes on. Evidentially, this more or less eliminates non-drive spoke breakage from them going slack.
 

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I think most people pay wildly too much tension to drive side tension. You need to make sure you have at least the minimum acceptable tension on the NON-DRIVE. That's really all you care about. I shoot to have 60kgf on the non-drive side before a tire goes on. Evidentially, this more or less eliminates non-drive spoke breakage from them going slack.
Shooting for 60kgf on the NDS is pretty good but dont you find that only very few hubs have flange offsets spaced accordingly to result to a tension ratio of 50% without going over 120kgf on the DS?
I find most 11s hubs have tension ratios below the 50% mark which means that in order to have 60kgf at the NDS, the DS tension would be in excess of 120kgf based on TR x DS kgf = NDS kgf. (Simplified formula w/o consideration for spoke length but close enough to within a couple of kgf).
Examples:
WI T-11 48%
CK R-45 50%
DT 240 52%
Tune 150 49%
BHS UL190 43%
BHS SL210 45%
9000/6800 45%

Then when the tire is fitted on the rim, if the DS tension drops, the NDS drops proportionally and the 60kgf could become 40kgf on a 45% TR hub which is arguably too low to be reliable without other measures such as locking, etc.

Incidentally, I find your statement about the particular combination of rim-tire significantly affecting the tension drop spot on with my observations. However I also find that the variances between different combinations to be too extensive to derive a definitive conclusion for other than the particular combination. I found certain rims, like the HED C2 (not the B+), to be less prone to this and thus my short term decision to remain with the older stuff until we have more data to better assess the shortcomings.
Needless to repeat that the above is not as significant for a racing specific wheel as is for a general use wheel where a lesser degree of performance is supposed to be compensated with higher durability.
 

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The thought that this phenomenon is more prevalent among lighter rims isn't at all consistent with my experience. Pacenti SL23v2 is a rim that proved to push the envelope on weight, but didn't have a big pressure drop. A HED Belgium+, not as deep and ~ 40g more, suffers more tension drop than a Pacenti. And Pacenti (even though v2 wasn't nearly as tight a fit as v1) is a tighter tire fit than either HED B+ or Kinlin XR31T.

A spoke thread is 2.0mm x 56 TPI (yeah, TPI). Pressure drops that I see on drive side are typically equivalent to between 1/4 and 1/2 turn on the drive side, so equivalent to about a .004" or so reduction in rim diameter if my math is right. But again, there's clearly an element of lateral displacement that happens.
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Just saw a series of articles published by Wheel Fanatyc on tension drop in his website. This one offers some insight to the forces at play causing the elongation of the extrusion, or "shortening of the rim" as Ric calls it. Link : Kgf v. Psi, part 1 - Wheel Fanatyk

His example shows a rim elongation of 1mm, your example showed an elongation of 0.1mm (0.004"). I think both are possible depending on rim and tire used. Elongation of 1mm, however, is pretty significant in causing the spoke tension to drastically reduce. One of his suggestions is also to consider adding mass to the rim or at least don't take any more out without reconfiguring how to best support the rim structure from severely deforming when under tire pressure.
 

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I haven't seen the thing you linked (currently in airport, I'll spare you all my TSA screed) but a 1mm reduction in circumference would be catastrophic. Certainly WAY more than I've ever seen. That would over a full one turn drop (56tpi ~ 22tpcm/2.2tpmm, half of that bc spoke ~ radius not diameter). Even a Stan's Iron Cross with a Hutchinson tubeless cx tire (world's worst combo for tension drop) doesn't see that.

Maybe some day I'll build a jig to measure and confirm or refute this 1mm claim, but until then I'm comfortable that 55 on the non-drive side, pre tire install, works great. That happens at about 120kgf drive side with every hub we use (powertaps may be a tiny bit worse).

DT gets the ratio they do bc the flanges are really close (and I've never gotten notably better ratio on DT in practice), and either the 2% difference between WI and CK falls within a margin of error or the very high diameter of the CK non-drive flange (50mm, iirc, same as drive side) screws with the calculation you have.
 

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Does the tension drop affect carbon rims to the same extent? Especially deep section carbon wheels seem like they would be much more resistant to the deformation that causes reduced spoke tension.
 

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I haven't seen the thing you linked (currently in airport, I'll spare you all my TSA screed) but a 1mm reduction in circumference would be catastrophic. Certainly WAY more than I've ever seen. That would over a full one turn drop (56tpi ~ 22tpcm/2.2tpmm, half of that bc spoke ~ radius not diameter). Even a Stan's Iron Cross with a Hutchinson tubeless cx tire (world's worst combo for tension drop) doesn't see that.

Maybe some day I'll build a jig to measure and confirm or refute this 1mm claim, but until then I'm comfortable that 55 on the non-drive side, pre tire install, works great. That happens at about 120kgf drive side with every hub we use (powertaps may be a tiny bit worse).

DT gets the ratio they do bc the flanges are really close (and I've never gotten notably better ratio on DT in practice), and either the 2% difference between WI and CK falls within a margin of error or the very high diameter of the CK non-drive flange (50mm, iirc, same as drive side) screws with the calculation you have.
I dont have any means of actually measuring the rim elongation either. Maybe my best would be a spreadsheet to calculate the theoretically expected value but that's about it.
I have seen,however, drops in tension as much as 35 kgf; what this equates to rim elongation I am not sure.

Have a safe flight!
 
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