Technical FAQ
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Technical FAQ: Specialized Turbo 2Bliss tire blowoff

In this week's Technical FAQ, a reader wonders why his Specialized S-Works Turbo 2Bliss blew off his Hunt Aero 30 wheels during a ride. Lennard believes the answer lies in the reader's crochet-type rims.

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Dear Lennard,
I recently replaced my Schwalbe Pro Ones on Hunt Aero 30 wheels with Specialized S-Works Turbo 2Bliss ready tires of the same size. After 115 miles, while leisurely negotiating a curve, my rear tire blew completely off the rim and wrapped around the cassette.

The blowoff caused people in front of me to think we were being shot at and the people behind me to think there was an explosion at an adjacent factory. The resulting crash broke my hip and has shaken my confidence in tubeless tires.

I see where on recent posts, Colan and Chip had similar experiences with Specialized 2Bliss tires. My question is: Do you think this is a tubeless problem, a Specialized 2Bliss problem, or are Colan, Chip and I just not living right? I have read so much conflicting information on hooked vs hookless rims and tire bead materials that I seriously don’t know what to believe. Do you have any advice that might help me get comfortable with tubeless again?

Both the Schwalbes and the Specializeds were 28s (700 X 28C), and both sets of tires were run tubeless. The Specialized website only shows the S-Works Turbo 2bliss in a 28.

I emailed Specialized and asked if the Roval C38 disc wheelset (21 mm internal width) was compatible with the 28mm S-Works Turbo 2Bliss ready tire. I also inquired if they had been tested. Nathan from Specialized replied that they were compatible and had been thoroughly tested.

— Kenny

Dear Kenny,
I requested a response from Specialized in early November, and the response just came in the form of this tech bulletin, which only addresses a single size (700 X 28C) of the Specialized S-Works Turbo 2Bliss-ready tire, stating that it is only rated for tubeless use on a crochet-type (the bulletin spells it “crotchet”) rim of up to 17mm maximum inner width.

The bulletin further shows that that tire can be used with an inner tube on crochet-type rims between 17mm and 21mm in inner width and that it is not to be used at all on hookless rims or on rims wider than 21mm internally.

Note that crochet-type rims are also called hook-bead rims; the cross section of the rim wall resembles a crochet hook, hence the name. And note that Specialized has said that no tubeless tire should be inflated to over 80psi on any hookless rim.

Your Hunt Aero 30 wheels have crochet-type rims with a 21.3mm internal rim width, which is outside of the size range, even for use with an inner tube, of an S-Works Turbo 700x28c 2Bliss-ready tire.

Chip’s Giant SLR-1 rims seem to have had 17mm inner width.

Colan blew a 25mm Continental GP5000 TL off of his front wheel and both 25mm Specialized tubeless tires off of his front and rear wheels. He said that his “tubeless specific Hed Ardennes wheels are from 2017 and the Plus model.” These have crochet-style (hook-bead) rims with a 21mm inner width.

I suspect that the 21mm inner rim width is implicated in your and Colan’s exploded tires. Chip’s, however, should have been within safe limits, and Colan’s Specialized tires were 25mm, not the 28mm size addressed in Specialized’s bulletin.

According to Specialized tire engineering director Oliver Kiesel, “The only affected tire is this SW Turbo 2bliss ready in 700×28.

We didn’t (have) any other tubeless ready road tire in the market causing this blow off issues on wider rims. It is an individual case for exactly the mentioned SKU. The new Turbo RapidAir tires are differently designed, especially the bead design with a much higher safety standard, even on wider modern rims.”

So, while this new Specialized bulletin explains your crash, it doesn’t really explain those of Colan and Chip. I’m also waiting to hear from Continental about Colan’s crash with the GP5000 TLs.
― Lennard

Dear Lennard,
I currently own an old but highly upgraded Trek 7000 from the 90’s with a threaded headset that I use as my “city slicker”. Recently I picked up a Fuji FC 770 Carbon alloy fork with MTB sizing (1 1/8”) out of a dumpster. The carbon fork is an integrated type with a tapered tube and what looks to be a 2″ crown. I understand the fork cannot be integrated into the current frame; however, is there a way to install an external cup/bearings that would allow the use of the new fork into the old type head tube? I would expect that this may be quite the research project and would not ask that you do it for me. I am asking for any information and/or contacts you may have that would get closer to an answer.
— Reed

Dear Reed,
I don’t think there is any way you can do that.

I believe that your Trek 7000 mountain bike must have a 1-1/8” steering tube. That means that it most likely has an internal head tube diameter of 34mm. The fork you found in the dumpster, having a tapered steerer for a mountain bike, must be 1.5” at the base of the steerer and 1-1/8” at the top. Since 1.5 inches is equal to 38.1mm, there is no way that steering tube will fit inside of your 34mm I.D. head tube.

If you use the headset fit finder from either Chris King and input these dimensions, you can see what I mean.

And the more pressing question is, why are you even considering using, and trusting your life to, a carbon fork that you found in a dumpster?
― Lennard


Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), 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