Mavic cosmic carbone ultimate tubulars! Thoughts?

Not sure about these Mavics, but my experience with Tubs has been very positive.

Overall they seem less prone to punctures than clinchers in my limited experience.. This is a good job because puncturing on the road with a tub is a bit more of an operation than that required for clincher repair. If you're very concerned about it, sealant (preemptive use or applied after puncturing on the fly) will cover most punctures, as it would in a clincher, once re-inflated and spun a few times it's worked for me, though I don't routinely use it.

For longer rides I tend to take an entire spare tub, pre-glued which goes on fairly easily. Note that the only time I've punctured has been in very wet conditions and in all honestly I shouldn't have been using them!

The drawback comes to repairing them - which is possible, but will take some skill with a needle and thread. The next time I puncture a new, expensive tub, I'll be going down this route, but wouldn't bother with one that's on it's last legs..

As for the benefits, for summer use - I'd say go for it, be open minded. There's some beautiful-rolling supple tyres out there from vittoria and veloflex, the weight is very low at the rim and the process to glue on is quite enjoyable, as you perfect the art!

It's the only way to really take advantage of deep, aerodynamic rims whilst avoiding the safety concerns (overheating in carbon clinchers) and weight penalty you might otherwise get. For reference, my tubs are sub 1200g and 46mm deep and ride beautifully.