Originally Posted by
cyccommute
I would agree that the sealant is different. Slime doesn't need to be replenished while most of the tubeless sealants I've heard about have to be refreshed and/or replaced every few months (3 to 6 seems to be the interval). Stan's, for example, tends to dry out over that time frame. The real question you have to ask is where does it go? The bicycle tire is a sealed system that is (mostly) impervious to liquids. If you were to fill your bike tires with water, you would still have water in them 6 months later. That's what makes tires such a good home for mosquitoes.
It took me a while to figure out where that liquid was going and it all has to do with the solvent used in tubeless tire sealants. Slime uses glycerol as the solvent while the tubeless sealants are mostly propylene glycol. The propylene glycol has a fair amount of solubility in the rubber of the tire and penetrates it. However, propylene glycol doesn't have much in the way of vapor pressure so any that ends up in the rubber stays there. Some will be ablated away with the tire rubber but, for the most part, it dissolves into the tire and stays there.
Glycerol doesn't do that so it doesn't need the constant refreshing.
Interesting. Thanks for the explanation.
Originally Posted by
cyccommute
I think you are underestimating the amount of sealant in the tires and slightly overestimating the weight of a standard tube. According to the Stan's tire installation instructions, a tire should have 1.5 to 2 cups of sealant per tire. That's 12 to 16 oz of fluid per wheel.
Stan's say 2-3 ounces per tire on the bottle and that is what I used.
The weight I listed was for a standard weight brand new 29er MTB tube that I had on hand. A quick check shows that other brands are in that ball park for standard weight 29er tubes in the 2.1-2.4" range. Some a little more and some a little less.
Originally Posted by
cyccommute
There's also the issue of the sealant dissolving into the tire. If you put in 12 to 16 oz of liquid and 90% of it goes into the tire and stays there and then you add another 12 to 16 oz of sealant, that adds up to a couple of pounds of weight after only a few months. And, as I'm not sure how much propylene glycol the tire can hold before it starts moving out of the tire due to rubber ablation, I can't say how much weight is added the next time you have to refresh the sealant.
First, as I said the bottle says 2-3 ounces and the Stan's web site says:
"How much sealant should I use?
For a standard 2.0” mountain bike tire, we recommend 2 ounces of sealant. You may want to use 3 or more ounces in larger mountain bike tires or for the initial setup in tires that you find difficult to seal. For road and cyclocross tires we also recommend 2 ounces."
Also my assumption was that much of the weight doesn't dissolve into the tire. My thought was that much of it was lost to leakage. It hadn't occurred to me that it all stayed with the tire, but even if you are correct we are talking 2-3 fluid ounces
not 12-16 ounces as you mentioned. Not sure where you got that figure, but everything I read from Stan's said 2-3 (fluid) ounces.
I figure a good bit of that 2-3 ounces must have escaped since I undoubtedly have had a dozen or even dozens of thorns that self sealed and I'd expect that a tiny bit is lost each time there is a puncture. I'd further guess that there is a bit of leakage at the bead with low-ish pressures and rock and root impacts.
Originally Posted by
cyccommute
The whole "refreshing sealant" thing is probably what bothers me about tubeless the most. Personally, I don't what the headache of having to do that on a regular basis.
Headache? I didn't find it to be. It is a matter of sucking up 2 ounces in the Stan's syringe, attaching it to the valve stem, and depressing the plunger. It does mean deflating the tire, but the whole process is easy, not messy, and takes a few minutes. Doing that once or twice a year is a just not that much trouble, especially when I would otherwise have been patching tubes often during that period.
Originally Posted by
cyccommute
I don't have tubeless and probably never will go that route. But I have been involved in trying to mount them and I see the paid mechanics at my local co-op when one comes in. Nobody really want to mess with them. It's kind of a toss up between which is more onerous: brake bleeds or tubeless install. I'd almost say they'd rather do a brake bleed and nobody wants to do that one.
Maybe it was because I used some very compatible tires and wheels, but it was a complete non issue for my tires. I have read that it can be a real pain, but it was really easy, easier than installing a tire with a tube where you need to take care not to pinch the tube. My results may not be typical, but I assure you it was completely painless and has remained so even when I needed to remove a tire to change a spoke nipple.
Originally Posted by
cyccommute
The tire that give us all so much trouble was one that had an o-ring kind of bead on it. The "o-ring" was pressed into a channel around the rim and it was next to impossible to break free. We ended up having to use Park Tool's long metal tire levers and had to use them the entire way around the tire on both sides to pry the o-ring out. It was no easier to get the tire to seat either. It was one of the more challenging things I've ever been asked to do and that is saying a lot considering what kinds of problems we see every day at the co-op.
Sounds like a pain.