Today's title has been written as a question in many outlets on many occasions, I've just removed the question mark.
Tubeless cross tires have been a bit of a black art so far. Incantations, incense, chicken bones - they've all been used in the name of getting and keeping a secure tire/rim interface, preventing the dreaded and catastrophic burp. Having used tubeless mountain bike tires for half a decade without so much as a hint of a burp, with all manner of different tires tubeless ready and not (more often not), I'm tempted to say that people maybe thought cx tubeless would follow that arc and be easy. Not so. The interwebs overflow with sad tales of "it was working so well and then..."
If you've been following along for a while, you know that this is my personal white whale, to some degree. To be blunt, I hate gluing tires, I think owning and dealing with an armful of wheel sets in order to have a range of treads sucks, I still see a ton of rolled tires every weekend, and tubulars are expensive as f. Tubed clinchers require too high of a tire pressure to ride right. Properly functioning tubeless offers the best potential to the racer who has to deal with his/her own stuff, full stop.
So what gives me such confidence to remove the question mark? Multiple things, most of which fall under the blanket of conjecture since we don't know and can't isolate which elements make the difference. One or more of them is doing the trick, though.
The primary suspect is better beads. Stronger, lower stretch, often carbon-cored, and with better shapes. Burps happen at the bead, and a more secure bead means better burp resistance. There are small but noticeable differences between clincher and tubeless versions of tires, as well as small weight differences. The more secure bead is worth its weight, and then some, and the differences are usually fairly small in any case. Among the tubeless ready tires we've tried, all have inflated with just a floor pump, all have competently held air without sealant (but you definitely want to use it), and none have yet burped.
A second suspect is wider bead seat width. I can't find the link just now, but last year I read this thing that very convincingly showed how a wider bead seat width reduced the leverage that the tire was able to exert over the bead. Combined with tubeless ready tires, Grails, SL25s, and SL23s are all kicking ass, and all are 20+mm wide.
I don't think the rims tape or strip has much to do with it once the tire's inflated. In fact, I think that a lot of tape buildup could give you a good inflation and a false sense of security. We use Tesa tape, which is available cheaply at U-Line and is similar to/the same as what other people sell as tubeless tape. It applies easily and works perfectly.
Here are some of the tires and brands that we've found to be solid so far, and we can recommend them without reservation. This is NOT an evaluation of their treads - that is an entirely other kettle of fish.
1. Kenda tires with SCT designation
2. Maxxis Mud Wrestler (their other tires are not tubeless ready)
3. Hutchinson tubeless ready models (I'll be using these this year)
4. Specialized tubeless ready models
These are the tires that we've found not to work well:
1. Clement. No one can wait until they launch their tubeless, which they've announced they will. Until then, we don't recommend them. Neither do they.
2. Kenda models without SCT designation
3. Michelin. I know, the Mud2 was a popular tubeless choice. Was. Things got better.
4. Anything with a tan sidewall.
This is a tire that mystifies me by how well it's working:
1. Challenge Grifo clincher (not open tubular - clincher). It's worked really well for a ton of hot laps so far. Nothing about this tire should work as well as it has so far.