Originally Posted by Crx_In_Motion
yes nitrogen is more dense then air......hellium is less dense and "lighter" i guess you would say.....But IMO why would u want "lighter tires"..... also hellium is'nt flamable , it is an oxidizer though. and yes hellium does expand, as with all other gasses if heated.
~jake
helium is inert, it is NOT an oxidizer, it doesn't react with anything (hence why it is an inert gas)
to answer the original question:
it doesn't matter WHAT gas you put in your tire, they will all have the same compressibility. at the pressures used in a tire gases behave nearly ideally anyway.