I thought about this in the Alps recently.
I've been to the USA and walked through Telluride at about 9100 feet and even walking left me feeling the thin air, not out of breath, but definately breathing harder. You can feel the thin air. But in Morzine and Chatel I didn't notice it at all, even riding. Maybe it did have an effect I didn't notice, but what sort of altitude has an effect on your performance? Just wondering, like… 🙂

Isn't Morzine only at about 3000ft though, so you wouldn't really expect to feel much of an effect.
/Edit just re-read your question properly. Ignore my response 🙂

Isn't Morzine only at about 3000ft though, so you wouldn't really expect to feel much of an effect.

Well yes, that's what I would have thought, but I've seen others mention it, which is why I was wondering. 🙂
Just idle interest really, and more fun posting here than googling it! 😉

Pic Blanc at 3,300m I noticed the altitude but then you don't normally ride at that height in the Alps. Makes the start of the Mega hard if you have to run (ok ok walk)

1st ride on 2nd day in the US in Crested Butte. 8,924 ft (2,720 m)

Hey this is alright. No real affect of altitude.
I'll just sprint up this (very) short climb.

On my knees unable to breath :0)

By the end of the holiday in Fruita I didn't notice (although it is a reasonable amount lower than CB) Elevation[4] 4,514 ft (1,376 m)

edit – corrected the heights and I guess as I wasn't going uphill at Pic Blanc the effect felt less than CB. Fruita is quite low in comparison.

By the end of the holiday in Fruita I didn't notice (although it is a reasonable amount lower than CB)

Ohh you lucky git! 🙂 That's where I wanna go next. You got any nice pics for me to drool over? 😀

Fruita and CB are a must if your going. Although I understand Joes ridge is not what it was in 2004. Too much use and to much rain.

Kessel run

Joes ridge

From mountaineering I guess I first noticed around 8000 ft and became obvious around 10 000 ft. How long do you spend riding at that height?

You also acclimatise fairly quickly. a couple of weeks in Bolivia at 10 000ft and I didn't notice when we went up to 15000 ft

Seems fair enough TJ. I guess it could be different for everyone though?

@ Tom's pics –

**dribble**
😀

A couple of years ago I climbed (riding and pushing) up to the top of Monte Chaberton (3100m) from Cesana (1300m) in one go, without particularly noticing the effects of altitude.

But the height was gained so slowly (nearly 4 hours) that I probably gradually acclimatised on the way up. Jumping out of a chairlift and then attempting to hammer it straight away might have been a different story!