Taking my mtb on a plane in a couple of weeks time (for the first time). From what I understand, I need to deflate the tyres but what pressure can you get away with? I am running tubeless so don’t want them to be fully flat if at all possible,

The whole deflating thing is nonsense. The hold is pressurised.

If it depressurises an extra 15psi relative in your tyres is the least of your worries.

No. Just leave them as they are.

Haven’t done any math on this because I’m not at uni doing mech eng any more and even then it was far too hard for my brain.
But, MTB tyres.. I wouldn’t bother deflating at all tbh.

Just tell them you’ve done it if asked. The difference in pressure between sea level and 38,000ft is 10PSi, u less your tyres are actually solid, you won’t have a problem

You don’t need to do anything. The hold is pressurised to the same altitude as the cabin (circa 10,000ft depending on aircraft type).

Maximum pressure differential on a 737 is about 8psi off the top of my head. Im pretty sure your tyres will be fine can cope with 8psi more in them (relative) that whatever they are ow without exploding.

That is exactly the answer I was hoping for – thanks!

I always do, but a 29″ wheel with a large tyre is quite a tight fit in my box so I have to…

I’ve never done it out of choice but the other year coming back from Canada when they checked inside my bike bag I was asked to partially deflate my tyres, I let about half the air out each and they seemed happy about that.

As above, its bobbins, just say yes if they ask, they just need to tick that box

Ask them what happens to the airplanes tyres when they’re retracted back into the airplane, and that you’ll do the same. 737 tyres are at something like 200 psi

Leave them inflated to protect your rims while the baggage handlers try their best to crush them.

Is the plane on a conveyor belt?

The correct answer, when asked at check in is that yes, of course you have deflated the tyres.

The actual answer is to quietly roll your eyes at the tickbox questions and then get on with life.

Possibly not the place to give a lecture on physics though. The check in staff won’t care but they do have the power to make life very awkward. Be nice to them! 🙂