# Thread: crazy idea! Pressurized bike frame to decrease weight and increase stiffness

1. ## crazy idea! Pressurized bike frame to decrease weight and increase stiffness

I thought about this idea today and could not get it out of my mind. My idea is to pressurize a bike frame with helium to lighten and stiffen a bike.I think you would be able to build a frame lighter and keep it as stiff or stiffer because of the air pressure. I thought about it today when i tried to crush a sealed pop can and couldn't get it to budge. Then I opened it and could bend and crush it really easily. So...would this work or would it crash and burn. I think it would be really useful for hard tails rear ends that way you can make them stiffer or compliant by adding more pressure or decreasing pressure.

2. gas compresses liquid doesn't. ie: if you drop a full gallon of piss 10ft in front of a car going 70mph the container explodes. if the container is half full. the air inside compresses and theirs no explosion.

3. By adding gas, and then compressing it enough to actually influence the frame's stiffness, you're making the bike heavier.

Not to mention you'd have to reinforce the frame (add material) in order to make it able to withstand internal pressure of any real amount.

4. adding helium may reduce the overall weight, but would not reduce the mass, which is the real goal. less mass = less force required to accelerate it. we just use weight because it can be directly measured simply, and is a familiar concept.

adding helium would also be a negligible difference in weight, which would be offset by sealing the frame and compressing enough to stiffen the frame.

also, helium is EXTREMELY expensive, sending your \$/gm saved through the roof.

quick experiment, weigh a wheel with a flat tire, then pump it up to 50psi and weigh again, whats the difference? I'd wager it's <5g. replacing such a small, volume of air with He would likely save you less than that 5g difference. blimps use huge volumes of gas for a very small cargo space. granted they are lighter than air as a unit, but that still takes a massive volume.

5. pressurizing a thin walled cylinder prevents the sides from buckling. This is what you see in the popcan. With buckling, once it starts it really isn't very controllable, structurally speaking. So, I don't think having various pressures to vary the stiffness would really work.

Also, a pop can has, essentially, water in it. Water is far more stiff than any gas would be.

All that said, I remember a rocket at NASA in Huntsville, AL that was pressurized for increased structural performance. It had this noisy air compressor that was kicking on and off to keep it pumped up. I remember the sign on it said if pressure was lost the side would buckle and the rocket body would collapse under it's own weight. It also was the only one like that there so I have to assume it was a sub-optimal design.

6. This has been done with a road bike frame. There was an internal rubber bladder that youbfill up. This allowed the frame to be made a lot thinner (lighter) then normal. But if it wasnt filled up it wasnt strong enough to ride or somthing like that.

7. My sarcasm detector may not be working properly, but you may want to check the date on that article.

8. Originally Posted by kidd
gas compresses liquid doesn't. ie: if you drop a full gallon of piss 10ft in front of a car going 70mph the container explodes. if the container is half full. the air inside compresses and theirs no explosion.
Excellent point, but am I the only one wondering why he chose piss for the liquid?

9. Lol good eye. I was wondering why there wasnt any pics of it.

10. Originally Posted by shupack
adding helium may reduce the overall weight, but would not reduce the mass, which is the real goal. less mass = less force required to accelerate it. we just use weight because it can be directly measured simply, and is a familiar concept.
Not exactly, because the force required to accelerate a bike also depends on attrition forces, and the helium will add an upward component that decreases them. Add a big balloon of helium and your bike will be easier to accelerate (unless there is some contrary wind). This however only until it leaves ground, and then you would have a hard time moving unless you install a propeller connected to your cranks.

11. Originally Posted by Davide
Add a big balloon of helium and your bike will be easier to accelerate (unless there is some contrary wind).
So... you can accelerate faster with a large balloon (parachute) attached to your bike? I'm learning something new here every day!

12. Syntace did this with their trials frame many years ago.
Syntace Trials Frame - Bike Pictures - Trials-Forum

13. Originally Posted by J.B. Weld
So... you can accelerate faster with a large balloon (parachute) attached to your bike? I'm learning something new here every day!
Keep reading, it is a never ending source of knowledge. You might even acquire a sense of humor!

14. Originally Posted by t-ruh
I thought about this idea today and could not get it out of my mind. My idea is to pressurize a bike frame with helium to lighten and stiffen a bike.I think you would be able to build a frame lighter and keep it as stiff or stiffer because of the air pressure. I thought about it today when i tried to crush a sealed pop can and couldn't get it to budge. Then I opened it and could bend and crush it really easily. So...would this work or would it crash and burn. I think it would be really useful for hard tails rear ends that way you can make them stiffer or compliant by adding more pressure or decreasing pressure.
Chuck a few bearings in there and you've just described a full suspension bike.

15. "to lighten and stiffen a bike"....??

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