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Tech & Wearables

Technical FAQ: Road tubeless reliability, squealing carbon rims

Recent standardizations in tubeless wheels and tires have changed Lennard Zinn's mind on tubeless.

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Have a question for Lennard? Please email us to be included in Technical FAQ.

Dear Lennard,

A few years ago, you published this post about the potential issues/horrors with road tubeless. I’ll admit it kind of put me off on the whole idea of tubeless for the road, as opposed to gravel and MBing, where it’s a clear winner.

What is your thinking these days with regard to road tubeless, especially now that we’ve got a lot of road tubeless guinea pigs, aka World Tour racers. My two sets of wheels are Tubeless Ready, not true tubeless, which I suspect is also true of the World Tour riders. What has me more interested than before is that I am now running 32mm tires on my one set of rims (DT Swiss R470), at 55/65 F/R pressures, which feels like it’s getting close to what I would consider a safe pressure for Tubeless, which is around 50 psi.


Dear Steve,

My thinking has indeed changed on this. On August 1, 2022 (effective January 1, 2023), the ISO (International Standards Organization, which has standards for every product) working group for bicycle tires and rims adopted standardized metric dimensions of bike tires and rims, and its international members universally agreed to them. This was a first, hard though that may be to believe. The ISO standard 5775-1 & 5775-2 to be released January 2023 will be the first true Tire & Rim standard, and, finally, ETRTO (European Tire and Rim Technical Organization, an older organization specifically for all wheeled vehicles made up primarily of automotive tire companies) standards will match those of ISO. ISO has many bike standards (frames, forks, bars, stems, saddles, etc.) but never had a standard for product interaction before this one. ISO also clarified maximum tire pressure for straight-sided rims (i.e., non-hook-bead rims) and width tolerances for tires, dependent on tire width.

Before this, there was a gray area, and rim manufacturers could, for instance, label a rim as 700C that did not have a bead-seat diameter of 622mm. There is no longer a gray area — 700C means a rim, under spoke tension, will have a bead seat that measures 622+/-0.5mm. It is the responsibility of the tire manufacturer to make their tires fit this rim size. Tire bead diameter is harder to measure than rim diameter, and the tire manufacturer builds in the amount of expected stretch of the tire bead.

I believe that the failures of road tubeless tires highlighted in that 2019 post would not have happened, had the tires fit perfectly on the rims. Until that ISO agreement a couple of months ago, there was nothing to prevent manufacturers from making it a bit of the wild west with regard to sizing. Some rim manufacturers intentionally varied from the 622mm standard 700C bead-seat diameter, as that was part of their philosophy of how best to fit tubeless tires. However, the tire always gets blamed if it is either too tight to mount without bursting blood vessels or breaking tire levers, and it also gets blamed if it blows off of the rim. But if the rim diameter is not consistent from brand to brand, then tire makers will make different sizing decisions in order to best fit on all rims.

The problem in the past was a group of American wheel companies intentionally making their wheels 623.0 to 623.5mm bead-seat diameter under spoke tension. Tire manufacturers were trying to fit wheels being built to two different standards — an impossible task with tubeless while maintaining safety. Tire manufacturers either needed to make the bike shops (and consumers) happy by making their tires easier to mount (and risk a potentially fatal blow-off) or making them the correct size (for a 622mm BSD) and getting a bad reputation as being too tight. Continental may have suffered the most from this issue; I have regularly heard complaints over the years from readers about their Contis fitting too tightly.

Other fit issues resulted from central rim channels too narrow for both beads to drop into, making mounting a pain, and from wheel companies promoting using too narrow of tires on wide rims for aerodynamic reasons, making for inadequate tire retention.

I can’t tell you how many times I have had conversations with tire companies about their tires being super hard to mount and being told that they actually are adhering to the standards, and it’s the rim that is the issue. I believe that this recent ISO agreement will result in much more consistent tire fit and consequently more rider safety on tubeless road tires. Of course, there are still many, many thousands of those oversized “tubeless ready” wheels around, so it will take a while for this standardization to really take hold.

― Lennard

Dear Lennard,

I recently bought a pair of Campy Bora WTO 45 2-way fit rim brake wheels. At the time of this writing I, have over 2000 miles on them and am running them as clinchers with Continental 5000 tires. Since day one, the rear wheel, when I brake, makes a blood-curdling squeal. First like an injured animal, then morphing into a sound like a screaming child. Very embarrassing.

I have Chorus Skeleton brakes circa 2013 on the frame. With the red Campy brake pads that came with the wheels, the front brake functioned properly right away. Over the past summer months, I have tried several things to stop the noise: the toe-in brake pad technique at least a dozen times; cleaned and lubed brake parts; centered the brakes and adjusted the cable tension. Typically, I do my own work, but out of desperation I want to a local shop. Sadly, Campy has lost so much market share, none of the nearby shops have any experience with the components, so that turned out be a futile exercise as well.

Would you recommend different pads? Could the back wheel be slightly out of true? Could a small misalignment cause the squealing? Do I need a brake upgrade? Are the 2013 Chorus brakes not robust enough to handle the wider 19 mm Bora inner rim width, causing the squeal?

― Erv

Dear Erv,

I doubt it’s misalignment, and I’m sure you’ve cleaned those rims with various solvents and sanded the pads (do so, if you have not). I doubt the brake caliper itself is the issue, since the front one doesn’t squeal, although I suppose if you have a brakeset with a dual-pivot front caliper and a single-pivot rear one, then I would not be able to make the “they are identical” argument.

I recommend that you try different brake pads. In my experience, I could almost always get squealing carbon rims to stop squealing if I tried enough carbon-specific brake pads. There are (or were, before disc brakes became ubiquitous on road and cyclocross bikes) umpteen different approaches to carbon brake pads, from straight cork ones to all sorts of different compounds. The manufacturer’s recommended pads often weren’t the ones that finally quieted the brakes down.

― Lennard

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder and purveyor of non-custom huge bikes , a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”

He holds a bachelor’s in physics from Colorado College. 

Follow @lennardzinn