So you've bought the ultimate carbon fibre bicycle frame? Still too heavy? Simply attach a vacuum pump and evacuate the tubes, saving the weight of the air inside!
-- aglet, Jun 02 2006

finflazo went one better Lighter_20than_20air_20bike
[fridge duck, Jun 02 2006]

Bikenotrh say it will soon be feasable http://www.bikenort...inmail/200404/3.php
With [finznlo's] hbi gone, this is a last trace of the subject on the web [pashute, Mar 31 2008]

Weight is the measurement of the effects of atmospheric pressure and gravity exerted on points in contact (either directly or indirectly) with the earth. Evacuating the air from the inside of the bike frame will not make it lighter. The local atmospheric pressure is still exerting pressure on the frame as a whole from the outside. Simply displacing the small amount of air that fills the cavities of the fram would have an inconsequential effect anyway. And if you've seen a way to bend the laws of gravity by generating a void of atmospheric air, I'd like the paperwork on my desk in the morning.

Lighter-than-air custard would be a good fill, though.
-- Letsbuildafort, Jun 02 2006


will evacuating weaken the tubes? Maybe, but it might make them stronger.
-- sninctown, Jun 02 2006


Probably. Carbon fiber has an exceedingly high strength with loads exerted along its lateral axis. It doesn't handle shearing-loads well at all.
-- Letsbuildafort, Jun 02 2006


Yes, it would be a teeny bit lighter, briefly, until it got smushed flat. How much lighter?
-- Heathera, Jun 02 2006


Bad idea. Tubes can be made stronger by pressurizing them--think of balloons, for instance. Putting a vacuum in a tube is going to make much more prone to collapse. As soon as it gets dented, it progressively fails to a flat ribbon, thanks to the greater pressure on the outside.

Fishbone for thinking that nobody ever thought of this. Some things are not being done because they don't work.
-- baconbrain, Jun 02 2006


I once saw the calculation of the weight decrease achieved by pumping the tyres with Helium instead of air. It equalled approximatley the weight of a speck of mud. You'd get a better weight advantage from running your chain without any lube (albeit not for very long) or having a shave before riding (before you ask - this includes the ladies).
-- Karnuvap, Sep 11 2007


Actually I think there is a possibility that it would get stronger in the same way that a concrete bridge is stronger when it has steel reinforcement under tension. The tube would be weaker to crushing forces but possibly have more resistance to bending.

This theory could be tested with 2 strip lights. Suspend weights from one until it breaks. Then suspend slightly less weight from the other. Then drill a hole in the end to equalise the pressure and see if it is now stronger or weaker.
-- marklar, Sep 11 2007


Be sure to drill the hole in the end cap, or you will be weakening the tube.
-- Galbinus_Caeli, Sep 11 2007


possibly the other way round would be better: make the tube wall much thinner and pressurize it with air.
-- loonquawl, Sep 11 2007


Hey LetsBuildAFort: What? Pressure and weight are quite unrelated. And how is the earth involved? You seem to be laboring under some sort of misapprehension.

This will indeed make the bike slightly lower in mass, and this will be detectable on a sensitive enough scale.

The benefit will likely befar more than canceled out by the need to properly seal the tubes, though.

// bend the laws of gravity by generating a void of atmospheric air// Ummm... vacuum chamber? But how is gravity involved?
-- GutPunchLullabies, Sep 11 2007


The extra metal and valve to seal the bike would far outweigh the air taken out of the bike
-- F_R_O_G, Sep 12 2007


This would be roughly the same as pouring out a teaspoon of water from your water bottle.
-- ldischler, Mar 31 2008



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