I have some RS Revelations … so if I reduce the travel, presumable the air pressure inside the spring goes up ?

Or is the air pressure in the fork independent of the length of travel …?
Or have I got this all wrong?

you are totally wrong 🙂

Ok the pressure stay constant no matter what length is chosen?
So that must mean you lose some travel?

No, you remove or add spacers to the shaft of the air spring so that it can extend/compress less/more. That reduces/increases the travel. You do this with the fork empty of all air, because you have to physically remove the air spring shaft from the upper chamber to do it. You then put it all back together and pump it up to the same sort of pressures you had before you removed or added the spacer.

Running a fork with the same length air spring sagged by removing air doesn’t affect travel , as the fork can still move between the same points. It will ride lower due to the sag, but the total available travel from unweighted to fully compressed isn’t affected.

Does that answer your question?

So I have some revs, U-turns. Variable between 140 and 110 mm of travel.

I run them normally at 140 with about 20% sag. On climbing hills , I drop them down to 115 ish. So if the spring is an air spring at this stage it must be getting compressed -or how else the travel alter??
Hence they must get stiffer as you drop the travel !

Help, it really doesn’t matter but it is doing my head in!

nope, the whole spring assembly drops further into the lowers on talas type forks.

It’s voodoo magic. The sag and air pressures stay the same whatever travel you select!!

Ok, now I know it is Voodoo Magic, I can relax !!

Thanks all