No compressors? No problems!

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  • #2
Merlin3189
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I first saw this years ago on a documentary about driving in Iceland. They lower the tyre pressures to get more traction in soft snow.
We’d already dropped the tyre pressures of our highly modified Toyota pickups from 30psi to just 3psi, flattening their sidewalls until their footprints were more than twice their normal width and three times their normal length.
The vehicles have on-board compressors for reinflation, but the squidgy tyres can get pulled off their rims, making reinflation difficult. (At least, that was true then: perhaps they've developed ways of preventing that now, since the above, more recent article, makes no mention of this.) A squirt of petrol (I think) and the tyre went back on with a bang, as in your video. I can't remember how they lit it, but rather them than me.
 
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  • #3
256bits
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They don't show the tire deflating after the gas cools.
 
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  • #4
Borek
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Same trick was shown in Top Gear's Polar Special.
 
  • #5
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They don't show the tire deflating after the gas cools.
This is just to pop the tyre onto the bead. Once there, you can inflate it with a small on-board compressor.
 
  • #6
256bits
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This is just to pop the tyre onto the bead. Once there, you can inflate it with a small on-board compressor.
Quite right.
Just a couple of weeks ago I beaded a tire with brute force ( hammer and a thin shim for one bead , and compressed air by pushing down on the rim for the opposite bead ), rather than using the explosive technique.
 
  • #7

So the thread title is a bit misleading because, if you have no compressor, you do have a problem.
 
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  • #8
256bits
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I don't even want that done on on my tires at all, except in an emergency to bead the tire.
Scary stuff.

The pressure within the tire due to explosion can go up to 8bar ( 120 psi ), ( depends on the actual fuel -air ratio ) but probably not since some of the gas would escape ( not sure how much in the milli-second combustion ) - even 5 bar ( 75 psi ) is double the rating for most car tires.

After the tire is set and cooling, the pressure within can drop to 2 or 3 psi, or even to a negative guage pressure.
One combustion product is H2O, which can condense to a liquid.
Example:
Ethanol Stoichiometric C2H6O + 3 O2 + 12N2 → 2 CO2 + 3H2O + 12N2
--> a 1/16 increase in volume ( approx 1 psi )
Condensing of the H20
--> a 2/ 16 decrease in volume ( approx a 2psi negative pressure )

Non stoichiometric , excess fuel most likely, would give different results, probably in favour of a positive pressure for volatile fuels.
 
  • #9
Baluncore
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I have used the technique with different spray packs, many times on truck tyres.
Only once has it ripped the sidewall clean off the bead, and that was an old dry tyre.

I keep a long piezo lighter for a gas stove to ignite the spray.
It is an evil technique. Use it only when necessary.
Stand well clear, to the side. Take care.
 

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