Try hydrogen. Its lighter (fractionally), cheaper, and you'll get some extra "push" when they explode :!: :shock: 
Since either of these gasses are so "light weight" there would be a _small_ weight savings. Although I can't imagine that even in an Insight you could "see" it on the MPG meter.
The biggest practical problem with helium is it being so light it will permeate the tire several times faster than air. _And_ that its pressure is much more temperature sensitive. I'd venture a guess (without consulting the old college Chemistry book) that you'd have to stop more than once during tire "warm-up" to reset the pressure
The reason high performance cars use nitrogen is its more stable temperature characteristics. With the potential for high speed comes even greater heating and increasing tire pressure. Pure Nitrogen (not the common 80% variety = air) expands less under these extreme conditions therefore keeping the tire within pressure norms when its needed most, extreme high speed.
Let me know how the hydrogen experiment improves your MPG. <VBG>
HTH!
Since either of these gasses are so "light weight" there would be a _small_ weight savings. Although I can't imagine that even in an Insight you could "see" it on the MPG meter.
The biggest practical problem with helium is it being so light it will permeate the tire several times faster than air. _And_ that its pressure is much more temperature sensitive. I'd venture a guess (without consulting the old college Chemistry book) that you'd have to stop more than once during tire "warm-up" to reset the pressure
The reason high performance cars use nitrogen is its more stable temperature characteristics. With the potential for high speed comes even greater heating and increasing tire pressure. Pure Nitrogen (not the common 80% variety = air) expands less under these extreme conditions therefore keeping the tire within pressure norms when its needed most, extreme high speed.
Let me know how the hydrogen experiment improves your MPG. <VBG>
HTH!
