This is a really interesting topic and it pops every now and then experiments on the other gasses like nitrogen have been conducted and it is used in all kinds of tires but helium is somewhat of an oddball and as kids we learned that helium is lighter than air that makes it more fascinating to use it in an actual bike and see what happens.
If you are here for the short answer then.
Helium can be used in bikes but since its molecular structure is so small that it even leaks from balloons, tubes or tubeless tires will not hold it for long, in case we somehow isolate helium inside tires it will make little difference in weight and experience
helium is lighter than air and nitrogen but the difference is very small if we take these gasses on a larger scale the numbers or not very different the difference you would make if you put weight in perspective is around 10 grams you can lose more weight than that if you clean dirt off your bike.
How long tires will stay inflated when filled with helium :
Normal tube tire tubes are made of butyl rubber and they are porous although every tire and tube is porous since there is a gap between the molecules and heliums molecules are much smaller than that and it would escape the tube just like it does with a balloon.
But it won’t just go poof and leak out all the helium at once it would need plenty of time before it goes completely flat for example normal balloons (thin layer of latex) would completely lose helium in 10-20 minutes while other balloons(like thick latex layered balloons used for birthday parties) would lose helium in about 5-6 hours and comparing that with the tube which is made of butyl
butyl is less porous than latex meaning it will take longer for a tube tire to lose helium completely by the comparison that I made above it would take around 8-10 hours for the tubes to go completely flat (just an estimate)
as for the single-ply tubeless tires it would take even longer so yeah the possibility of you filling it in your tires and having fun with them before they go completely flat is there, especially in the case of double-ply UST tubeless tires used in mountain bikes add in the sealant and the duration would increase more but the overall timing would still be less than 24 hours.
Would filling your tires with helium give you any kind of benefit to weight :
and adding the fact that you would need more helium to maintain that tire pressure removes any advantage.
Did you know that : In 1976 track cycling events for olympics (Not UCI) were held indoor and the west german team rode to victory with tires filled with helium source
Dont take this into as something viable because the internal lining that you would have to do just to keep helium inside in your tires would just level that weight difference and may even exceed that
but on the other note there are already tubeless tires (not tubeless ready) and they hold off air quite well even without a sealant.
It’s an interesting thought that since helium is lighter than air wouldn’t it somehow lift the tire and maybe give you an edge? well, the thought is viable but in reality, we are struck by many other factors.
Like if you calculate how much helium is required to lift a person with the weight of 60 kg in the air is around 5000 balloons or 57k liters of helium that’s a lot and add in the bike weight and that number is insane (the values come from an online calculator source)
but let’s suppose we need enough to negate the weight of your body and the bike weight the amount of helium you would still need is much more than what a normal tire can contain whether it is a mountain bike tire or a road bike tire and the constant air loss that we would need to compensate would be a large number.
and the last I checked a liter of liquid helium costs around 3-15 $ across the world and maybe in some cases a lot higher than that.
So depending on these numbers the value that you would get from adding helium to your tires wouldn’t do much but on the other hand, we still haven’t talked about how would it feel to ride on helium-filled tires because normal tires constantly contract and they act as somewhat of a suspension and helium being lighter the effects could be different.
But how would the experience be if the weight is out of the equation since helium is lighter and it should act or feel differently so did some research on that as well and here are all the different qualities that helium has an air lacks and how they act on tires.
How would pure helium-filled tires would feel :
As I mentioned above helium in tires would not make a difference in weight (the difference it might make is negligible) but looking from the perspective of riding the tires with helium wouldn’t change either.
The reason for that is that helium would act the same way as normal air (which has main components such as oxygen and nitrogen and other gases). when inside tires whether it be helium or air or any other gas the only difference that they create is heat conduction nothing more.
when the tires start rolling air travels in the tires for example when you hit a rock if the tires of the bike pinch for an instant the air gets compressed and stored in other areas so air is constantly on the move inside the tires and dissipates heat and helps in keeping the tires cool as well.
In the case of any gas inside a tire, the differences they would make would be the heat reduction and tire pressure (in some cases it becomes more uniform like nitrogen). Meaning if you fill your tires at 2 bar pressure there will be very minimal difference in the pressure whereas when you run your bike at high speed and especially in cars the tires would heat up fast and air would expand and increase the buoyancy of the gas molecules and that in turn increase the tire pressure
but it’s not an eternal phenomenon the molecules when they cool down will come back to their original speed and you might even notice some decrease in air pressure after that.
I did an article on Nitrogen in bike tires | Myths and Educational perspective Explained well if you had like to read more about that as well
Would helium keep the tires cooler than air :
yes, helium would keep the tires cooler than nitrogen and oxygen if they can be properly trapped inside the tires.
Helium has better heat dissipation qualities than other gasses like nitrogen and oxygen because its molecules are smaller than those gasses they would conduct heat easier and dissipate it in the same sense as well.
So yeah helium would keep the tires cooler and act as a better gas to be filled in tires and if you fill helium in your tires the pressure should keep uniform as well better than nitrogen because of its heat dissipation.
Will helium damage tires :
As helium’s molecules are so small that they can leak through the tires more so in case of conventional tires, tubeless-ready tires, and tube tires while some other exceptions like pure ust tubeless tires or double ply(casing) tires and latex tubes which can hold air fairly well and are not as porous as other tires, while it’s not proven by any experiment but we usually see bubbles in tire casing that happens due to air slipping in the side walls of the tires
So I think that helium might damage the tires if used for a long time because if air can slip under the sidewalls of the tires then helium’s molecules are much smaller than that and it should be easily able to slip in the sidewalls
So to some extent, I believe that it can damage the tires but as far as experiment conduction goes and you want to try it I dont think it will damage tires right away but if used for long periods I do think that it can damage the tires.
Is helium expensive :
One of the reasons that you dont see people conducting experiments with helium in their tires is that pure helium is not readily available the helium used in balloons is not pure its mixture of air and helium.
and pure helium costs around 20-100$/liter in liquid form based on locations around the world and you may or may not be able to find it in at least any stores
So this is one of the reasons as well that you dont see many people use helium and experiment with it.
You can use helium in your tires for long-term use I wouldn’t advise it and you won’t get any weight benefit from it either even if you get it’s very very small almost negligible and as I have explained you might not get the advantages that you think you might.
And if you want to load on your bike better try balloons because there is no way bike tires can hold that much amount of helium in them.