Using Helium in Tires

So... I have this idea that just came to my mind when I saw a helium balloon recently and here's what I was thinking.

Since helium balloon fly upwards because atmospheric air is denser than helium, does pumping helium into the bicycle tire makes the bicycle lighter?

 Since I do triathlon, weight of bicycle does matter for long distance cycling so this idea came into me. It might have sound ridiculous but there is no harm finding out more about it right? So the questions start coming into my mind

• Is there anybody who have already tried putting Helium into the tire?
• Apparently there is a lot of forums when you just googled "helium in tire", and the answer is yes. There are people as crazy as me to think of such a thing.

• So what are the results (based on internet answers)?

1. Helium is lighter than atmospheric air so it does help to save about 12-16g off the bicycle weight
2. Helium molecules are smaller than atmospheric air (mainly Nitrogen and Oxygen) so it will escape from the butyl tube more quickly
3. Other gases (Hydrogen, Carbon Dioxide and Nitrogen) has been used in tire as well
4. Many race vehicles prefer to use nitrogen filled tires for racing 

• Based on the information online and being a Sport Science graduate, this is what I think:

• The pressure of a tire is about 150 PSI. Volume of gas also remained constant in the tire since the tire has a fixed shape. Using pV=nRT (Assuming temperature is the same for both atmospheric air and helium), the number of moles for each gas will be the same if they were to be filled in the tube. Since, Helium is lighter in weight, there will definitely be a save in weight on the bicycle
• Size of Nitrogen and Oxygen molecule are about 10 Angstrom whereas size of Helium molecule is less than 1 Angstrom. Butyl rubber is porous so no doubt Helium will leak out much faster than Nitrogen and Oxygen. Also, Nitrogen molecule is bigger than Oxygen molecule despite the molecular mass, so Nitrogen is a preferred gas which answer to No. 4 above as well.
• Like Helium, the small Hydrogen molecules will leak out of the butyl rubber in no time. Also, Hydrogen is a very reactive so it will be too risky to use it in a tire. Similar for Carbon Dioxide, the molecules are rather small so leaking is a problem too. Carbon Dioxide is commonly used as a refill cartridge for quick refill during races. The Nitrogen, on the other hand, is rather stable and not reactive to temperature, so it can be used in tires
• As mention in  the above 2 points, nitrogen is very stable and less likely to leak, it is a preferred gas than atmospheric air. Looking at the molecular mass, atmospheric air also contain a significant amount of Oxygen which is heavier than Nitrogen. A Nitrogen filled tire will be lighter, even though the difference might be negligible.

• So after all these findings, what are the implications?

1. The use of Helium does reduce a significant weight of a bicycle during the race. A mere 12-16g difference of weight might not seems a lot but let me show you how much 1 gram is worth in cycling. Let's take Shimano chain as an example. CN-6800 chain weighs 253g while CN-7900 weighs 252g and the price difference is about USD10.00 on Amazon. 
2. Helium is more commonly found in party shops rather than bicycle shops. On top of that, the rate they charge for inflating a standard size balloon is about SGD5.00. Is it worth it to spend such money to inflate tires when atmospheric air is free to take?
3. Although Helium is good for weight reduction, the inability to stay in the tube pose a problem. What I have not find out is what is the rate of Helium leaking out of the tube. Can it last for a 100km or just 10km ride? Is there any material that can be used as tube to slow down the leakage of Helium? If there is such a material, will be material be too heavy which might end up negating the benefits of Helium?

Personally, after all these research, I find Helium is not feasible to fill up a tire. Despite the cut in weight, there are too many concerns for using Helium. I will not use it since that few grams doesn't really matter to me. I am not an elite cyclist anyway. I will just stick with my atmospheric air. It is good enough for me and it's FREE!