Tubeless tires suck (in my opinion) for the following reasons.
- They leak air. You either put goop in there which reduces your weight savings or you pump them up all the time. This might be due to my first set being Panaracer Fire XC Pro UST which really suck, you could see the goop coming out all over the tire it was like a sieve. Kenda have been better, but the goop got between the layers and made a tire tumor that killed the tire (they replaced it, but lectured me not to use goop in tires, even though my Hutchinson New Python's came with goop!).
- Flats on trails, you end up not wanting to fix flats on trails and trying to hobble home on really low tires. If you use goop, putting in a tube on the trail is really messy and when you come to take that tube out when you get home it's ruined and goopy. Even if you don't use goop it's still going to be a pain taking out that valve stem and trying desperately not to lose it since you won't have a spare. It's always going to take longer than just swapping out a tube.
- Setting the tire. I have an air compressor and I've still had to give up on a Kenda UST tire being tubeless since I still can't get it to sit right on my tires. They have raised writing on the side that lets air escape too much for them to clip onto the rim as they come out of the inner ridge. It's always crap shoot as to whether it's going to be easy, or an hour trying to put a new tire on.
- Pinch flats. I got a pinch flat in my Hutchinson New Python UST from the railway tracks by Rincon, the tire is pretty much toast now. $50 wasted and I only rode about 60 miles on them. I'm not even sure I can use them with a tube (but I'm likely to try).
- Cost. tubeless tires cost at the very least $25 usually $35 to $50. I can get a lot of really nice tubed tires for $20 (plus $3/tube of course!).
- Valve stem bending. If the valve in my UST rim gets bent by a pump I need to get a new one, which is going to be a pain since no one stocks them.
- I don't run low pressure anyway. I run 40psi in my tires, tubed or tubeless, it's a nice round number that's easy to hit on the pump dial and I'm used to how my bike rides at that pressure. Any less pressure and I would seriously worry about damaging my rims, making them useless for all tubeless tires.
- Tire choice. There's so much more choice in tubed tires than tubeless. for the race at Laguna Seca I was looking for a semi-slick <= 2.0" tire and it took ages to find the Python UST. there are a gazillion tubed tires I could run.
- Talcum powder. I like to put talcum powder in between my inner tube and tire, I miss the smell when I'm changing a tire on the trail.
- Building tubeless wheels is kinda weird. I have Mavic 819 disc tubeless, I think, you screw a nipple holder into the rim, it's clever, lots of revolving weight and lots of nooks and crannies to get dirt in I'll never clean out.
That's all I can think of, I'm sure you can easily come up with 10 explanations of why all my reasons are wrong.
Here's a nice rebuttal from JohnG.
I think one's experience with UST tires largely depends on three factors:
- The rockiness of the terrain you ride
- The tires you use
- Your weight
USTs make the most sense if you are riding sharp rocks on a regular basis. In the Bay Area, such trails don't exist (with a few exceptions). But up here in the Sierra, we have trails that are nothing but rocks. For a 200+ lbs guy like me, tubed tires are a pain because I pinch flat so frequently on the technical trails I love to ride. After riding USTs for 3-4 years now, I won't be going back to tubed tires again.
You might also be interested in what James has to say over at Lactic Acid Threshold.