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The only downside I’ve found to inserts for more xc/ marathon use is in the back on a hardtail it makes the back wheel Bob (or bounce) over small bumps making it hard to get power down- I assume I was smashing through the small volume of air in my tyres and bouncing off the insert repeatedly. Not a reason not to use them but I’d maybe take it out if I did that race again
Tallboy-
That's a really good point about air volume, and I wonder if there are some similarities to air suspension and tokens/spacers. It seems everyone that chucks loads of tokens into an air fork say the small bump is good, then suddenly there's a wall of progression. With a tyre and insert, there's no damping, so no wonder it bounces back hard and starts oscillating
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Introducing more progression via (effectively) adding volume spacers is something that Rimpact talks about on their site IIRC.
I’ve not ridden my hard tail without an insert so can’t really comment, my only frame of reference is riding the same trails on full FS and (no surprise) I can stay seated and spin through chop on that which gets you out of the saddle on the HT.
TooTallTim
Dammit
Obviously I'm not a marathon rider, so not qualified on that front. I do use tyres, though.
I think I'd have "to win the race you have to finish the race" running through my mind, and I'd discount XC tyres and go for trail tyres, with inserts front and rear with a decent amount of sealant.
I used to run Schwalbe but found that they puncture a lot more than the Maxxis (and Michelin) I run now, although I will say that on only one occasion was the puncture unable to be immediately sealed by the Stans swilling around inside the tyre.
I think people pick the wrong primary reason for inserts - yes they can and do save your carbon rims when you are going through a rock-garden, but they also give you much more grip because you can run a lower pressure than you could otherwise due to the risk of e.g. rolling the tyre in a fast corner. They also bring damping to what is otherwise an air-spring damped only by the sidewalls, which for a downhill casing is significant - not so much on a lightweight trail tyre.
If you're tired, it's dark and the ground is choppy you're going to appreciate the bike tracking neatly and not ricocheting around between the rocks.
Finally, and I've done this once, you can ride on the insert until the sealant gets the better of the puncture, then pump the tyre up again to the correct pressure.