The SO rides tubeless tyres and uses a sealant in them, it works reasonably well but it is not foolproof. He does ride them at a lower pressure than a normal tyre set up, he is about 14 stone (quick maths: 196 pounds) and I think he runs them about the 40/45psi mark. Making the probably fairly accurate assumption that you are significantly lighter than this then I would have thought you should have no problems riding lower than 40 psi if you want to. I run a normal tubed tyre set up and run my front tyre, Panaracer Fire XC Pros at 30 psi with no problems (I'm about 140 pounds).
The So uses them as a general tail tyre rather than a race tyre however he has single handedly put everyone in our riding group off using tubeless tyres, ever. He probably doesn't really get any more flats than before but the hassle of fixing them in the wilds when the sealant doesn't quite work is magnified (very messy and they can be a b*gger to seat on the rims) and they are usually fixed by putting a tube in them anyway. I'm not convinced they are a great idea for long rides (especially anywhere near thorns). As for racing, I have a feeling that they are best used here but I have no direct experience of them in that context.



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