Airing up from the spare

[DiddyZook]

I saw this done years ago but have not seen it since or any reference to it.

I used to wheel with a guy who rather than having a compressor or air tank etc, would over fill his spare (he actually had two spares) then for the trip home after having aired down at the start of the "offroad" part of a days wheeling, he had a length of hose with an inflator on the end. He attached the other end of the hose to the spare and would re-inflate his tyres. This was so simple.

I have often thought about doing something similar. Is there such a thing available or was this a home made invention?

I never asked how much he had to put in the spare etc, i imagine it wuld have to be a lot as it would always have to be at a higher pressure in order to inflate the others.

Can anyone shed any more light on this?

[Shadow]

Wouldnt be hard to make one, need a regular tyre inflator, a bit of hose, and a clip-on shrader connector on the other end instead of a compressor.

The maths.

There is an inverse relationship between pressure and volume, so a tyre at 14psi guage (=28psi real) has twice as much air as a tyre at 0psi guage(14psi real).

At 0 psi on your guage there is actually 14psi, as a guage only measure relative pressure, not absolute pressure, and at near sea-level there is 1 atmosphere of pressure which is approximately 14psi.

A tyre at 32psi has 1.4375 times as much air as a tyre at 18psi.

So say you have to air up 4 tyres from 18psi to 32psi, you need 3 times as much air in your spare, which equals 112.5psi guage (26.5 real).

Say you air down to 10psi, and back up to 32, spare needs 200psi.

If you had two spares, 18psi to 32psi, your spares would need to be running 86psi.

So it really depends on what pressure you want to air down to. If you go 18 to 32 and have 2 spares its doable, but if you have 1 spare and want to go from 10 to 32, then your buggered.

[r0ck_m0nkey]

I saw this done years ago but have not seen it since or any reference to it.

I think you might find that the reason people don't do it these days is because buying a 12v portable compressor isn't an expensive option anymore like it once was.

[DamTriton]

Wouldnt be hard to make one, need a regular tyre inflator, a bit of hose, and a clip-on shrader connector on the other end instead of a compressor.

The maths.

There is an inverse relationship between pressure and volume, so a tyre at 14psi guage (=28psi real) has twice as much air as a tyre at 0psi guage(14psi real).

At 0 psi on your guage there is actually 14psi, as a guage only measure relative pressure, not absolute pressure, and at near sea-level there is 1 atmosphere of pressure which is approximately 14psi.

A tyre at 32psi has 1.4375 times as much air as a tyre at 18psi.

So say you have to air up 4 tyres from 18psi to 32psi, you need 3 times as much air in your spare, which equals 112.5psi guage (26.5 real).

Say you air down to 10psi, and back up to 32, spare needs 200psi.

If you had two spares, 18psi to 32psi, your spares would need to be running 86psi.

So it really depends on what pressure you want to air down to. If you go 18 to 32 and have 2 spares its doable, but if you have 1 spare and want to go from 10 to 32, then your buggered.

Although having ANY tyre at 200 psi would be a worry....even 85 would scare the crap out of me if I was anywhere near it. Far to dangerous to even contemplate.

Remember that you have to find someone with a 200psi compressor to begin with.

Perhaps the fact that no one does it now says enough in itself

[Jeff80]

Wouldnt be hard to make one, need a regular tyre inflator, a bit of hose, and a clip-on shrader connector on the other end instead of a compressor.

The maths.

There is an inverse relationship between pressure and volume, so a tyre at 14psi guage (=28psi real) has twice as much air as a tyre at 0psi guage(14psi real).

At 0 psi on your guage there is actually 14psi, as a guage only measure relative pressure, not absolute pressure, and at near sea-level there is 1 atmosphere of pressure which is approximately 14psi.

A tyre at 32psi has 1.4375 times as much air as a tyre at 18psi.

So say you have to air up 4 tyres from 18psi to 32psi, you need 3 times as much air in your spare, which equals 112.5psi guage (26.5 real).

Say you air down to 10psi, and back up to 32, spare needs 200psi.

If you had two spares, 18psi to 32psi, your spares would need to be running 86psi.

So it really depends on what pressure you want to air down to. If you go 18 to 32 and have 2 spares its doable, but if you have 1 spare and want to go from 10 to 32, then your buggered.

Although having ANY tyre at 200 psi would be a worry....even 85 would scare the crap out of me if I was anywhere near it. Far to dangerous to even contemplate.

Remember that you have to find someone with a 200psi compressor to begin with.

Perhaps the fact that no one does it now says enough in itself

And you will only get approx half the air out, IE: one tire at 0PSI and a spare at 20 PSI, it will stop pushing air in to the flat tire at 10PSI as it will then be of equal pressure in each.

Hope this makes sense...

[Shadow]

Wouldnt be hard to make one, need a regular tyre inflator, a bit of hose, and a clip-on shrader connector on the other end instead of a compressor.

The maths.

There is an inverse relationship between pressure and volume, so a tyre at 14psi guage (=28psi real) has twice as much air as a tyre at 0psi guage(14psi real).

At 0 psi on your guage there is actually 14psi, as a guage only measure relative pressure, not absolute pressure, and at near sea-level there is 1 atmosphere of pressure which is approximately 14psi.

A tyre at 32psi has 1.4375 times as much air as a tyre at 18psi.

So say you have to air up 4 tyres from 18psi to 32psi, you need 3 times as much air in your spare, which equals 112.5psi guage (26.5 real).

Say you air down to 10psi, and back up to 32, spare needs 200psi.

If you had two spares, 18psi to 32psi, your spares would need to be running 86psi.

So it really depends on what pressure you want to air down to. If you go 18 to 32 and have 2 spares its doable, but if you have 1 spare and want to go from 10 to 32, then your buggered.

Although having ANY tyre at 200 psi would be a worry....even 85 would scare the crap out of me if I was anywhere near it. Far to dangerous to even contemplate.

Remember that you have to find someone with a 200psi compressor to begin with.

Perhaps the fact that no one does it now says enough in itself

And you will only get approx half the air out, IE: one tire at 0PSI and a spare at 20 PSI, it will stop pushing air in to the flat tire at 10PSI as it will then be of equal pressure in each.

Hope this makes sense...

I dont think 85 psi is anything to be worried about, most trucks run up to 100psi. Perhaps a tyre guy can chime in here, but i would expect when seating a bead you run some pretty high pressures.

[high n mighty]

I remember watching an episode of the leyland brothers and they put 100psi into a tyre for the same purpose. I wouldn't even contemplate it

[v840]

why not just fit an airtank?
They are pretty cheap from truck wreckers, or an old scuba tank, and can easily be fitted under most 4wds. Not much additional weight and probably alot safer.

[Shadow]

why not just fit an airtank?
They are pretty cheap from truck wreckers, or an old scuba tank, and can easily be fitted under most 4wds. Not much additional weight and probably alot safer.

yeh i was thinking this too,

problem is a 33x12.5x15 inch tyre holds about 45litres of air.

So if you had a 45litre tank, youd need to have 112.5psi tank pressure.

with a 10 or 20 lite tank youd need about 200-300psi.

so i guess its just easier to get a compressor.

[DamTriton]

Wouldnt be hard to make one, need a regular tyre inflator, a bit of hose, and a clip-on shrader connector on the other end instead of a compressor.

The maths.

There is an inverse relationship between pressure and volume, so a tyre at 14psi guage (=28psi real) has twice as much air as a tyre at 0psi guage(14psi real).

At 0 psi on your guage there is actually 14psi, as a guage only measure relative pressure, not absolute pressure, and at near sea-level there is 1 atmosphere of pressure which is approximately 14psi.

A tyre at 32psi has 1.4375 times as much air as a tyre at 18psi.

So say you have to air up 4 tyres from 18psi to 32psi, you need 3 times as much air in your spare, which equals 112.5psi guage (26.5 real).

Say you air down to 10psi, and back up to 32, spare needs 200psi.

If you had two spares, 18psi to 32psi, your spares would need to be running 86psi.

So it really depends on what pressure you want to air down to. If you go 18 to 32 and have 2 spares its doable, but if you have 1 spare and want to go from 10 to 32, then your buggered.

Although having ANY tyre at 200 psi would be a worry....even 85 would scare the crap out of me if I was anywhere near it. Far to dangerous to even contemplate.

Remember that you have to find someone with a 200psi compressor to begin with.

Perhaps the fact that no one does it now says enough in itself

And you will only get approx half the air out, IE: one tire at 0PSI and a spare at 20 PSI, it will stop pushing air in to the flat tire at 10PSI as it will then be of equal pressure in each.

Hope this makes sense...

I dont think 85 psi is anything to be worried about, most trucks run up to 100psi. Perhaps a tyre guy can chime in here, but i would expect when seating a bead you run some pretty high pressures.

Truck tyres designed for it, yes, but most light truck/passenger vehicle tyres have a maximum inflation pressure (stated on the sidewall) of about 50 psi.

[MKPatrolGuy]

Wouldnt be hard to make one, need a regular tyre inflator, a bit of hose, and a clip-on shrader connector on the other end instead of a compressor.

The maths.

There is an inverse relationship between pressure and volume, so a tyre at 14psi guage (=28psi real) has twice as much air as a tyre at 0psi guage(14psi real).

At 0 psi on your guage there is actually 14psi, as a guage only measure relative pressure, not absolute pressure, and at near sea-level there is 1 atmosphere of pressure which is approximately 14psi.

A tyre at 32psi has 1.4375 times as much air as a tyre at 18psi.

So say you have to air up 4 tyres from 18psi to 32psi, you need 3 times as much air in your spare, which equals 112.5psi guage (26.5 real).

Say you air down to 10psi, and back up to 32, spare needs 200psi.

If you had two spares, 18psi to 32psi, your spares would need to be running 86psi.

So it really depends on what pressure you want to air down to. If you go 18 to 32 and have 2 spares its doable, but if you have 1 spare and want to go from 10 to 32, then your buggered.

Although having ANY tyre at 200 psi would be a worry....even 85 would scare the crap out of me if I was anywhere near it. Far to dangerous to even contemplate.

Remember that you have to find someone with a 200psi compressor to begin with.

Perhaps the fact that no one does it now says enough in itself

And you will only get approx half the air out, IE: one tire at 0PSI and a spare at 20 PSI, it will stop pushing air in to the flat tire at 10PSI as it will then be of equal pressure in each.

Hope this makes sense...

I dont think 85 psi is anything to be worried about, most trucks run up to 100psi. Perhaps a tyre guy can chime in here, but i would expect when seating a bead you run some pretty high pressures.

Truck tyres designed for it, yes, but most light truck/passenger vehicle tyres have a maximum inflation pressure (stated on the sidewall) of about 50 psi.

My 35 BFG Muds have a max inflation pressure of 35psi. No way I would be putting 85-100psi in it

[Shadow]

Wouldnt be hard to make one, need a regular tyre inflator, a bit of hose, and a clip-on shrader connector on the other end instead of a compressor.

The maths.

There is an inverse relationship between pressure and volume, so a tyre at 14psi guage (=28psi real) has twice as much air as a tyre at 0psi guage(14psi real).

At 0 psi on your guage there is actually 14psi, as a guage only measure relative pressure, not absolute pressure, and at near sea-level there is 1 atmosphere of pressure which is approximately 14psi.

A tyre at 32psi has 1.4375 times as much air as a tyre at 18psi.

So say you have to air up 4 tyres from 18psi to 32psi, you need 3 times as much air in your spare, which equals 112.5psi guage (26.5 real).

Say you air down to 10psi, and back up to 32, spare needs 200psi.

If you had two spares, 18psi to 32psi, your spares would need to be running 86psi.

So it really depends on what pressure you want to air down to. If you go 18 to 32 and have 2 spares its doable, but if you have 1 spare and want to go from 10 to 32, then your buggered.

Although having ANY tyre at 200 psi would be a worry....even 85 would scare the crap out of me if I was anywhere near it. Far to dangerous to even contemplate.

Remember that you have to find someone with a 200psi compressor to begin with.

Perhaps the fact that no one does it now says enough in itself

And you will only get approx half the air out, IE: one tire at 0PSI and a spare at 20 PSI, it will stop pushing air in to the flat tire at 10PSI as it will then be of equal pressure in each.

Hope this makes sense...

I dont think 85 psi is anything to be worried about, most trucks run up to 100psi. Perhaps a tyre guy can chime in here, but i would expect when seating a bead you run some pretty high pressures.

Truck tyres designed for it, yes, but most light truck/passenger vehicle tyres have a maximum inflation pressure (stated on the sidewall) of about 50 psi.

I believe its a maximum operating pressure, not a maximum inflation pressure.

[chops]

I dont think 85 psi is anything to be worried about, most trucks run up to 100psi. Perhaps a tyre guy can chime in here, but i would expect when seating a bead you run some pretty high pressures.

remove the valve core if you want to seat the bead easier..can add a bit of dish washing liquid or something similar (that wont do damage to the rubber) to help the bead pop over the rim

trucks run any pressue from 65 psi right up to 120.. all depends on the tyre size, as well as the load carried.. 600/650/750r16 anything from 60-80.. 8.25r16 90-100psi and for the big buggers (11r22.5 / 295/80r22.5) etc see between 100 and 120

anything over 50psi I'd be wanting to put it in a safety cage before inflating any further..

[cloughy]

Wouldnt be hard to make one, need a regular tyre inflator, a bit of hose, and a clip-on shrader connector on the other end instead of a compressor.

The maths.

There is an inverse relationship between pressure and volume, so a tyre at 14psi guage (=28psi real) has twice as much air as a tyre at 0psi guage(14psi real).

At 0 psi on your guage there is actually 14psi, as a guage only measure relative pressure, not absolute pressure, and at near sea-level there is 1 atmosphere of pressure which is approximately 14psi.

A tyre at 32psi has 1.4375 times as much air as a tyre at 18psi.

So say you have to air up 4 tyres from 18psi to 32psi, you need 3 times as much air in your spare, which equals 112.5psi guage (26.5 real).

Say you air down to 10psi, and back up to 32, spare needs 200psi.

If you had two spares, 18psi to 32psi, your spares would need to be running 86psi.

So it really depends on what pressure you want to air down to. If you go 18 to 32 and have 2 spares its doable, but if you have 1 spare and want to go from 10 to 32, then your buggered.

Although having ANY tyre at 200 psi would be a worry....even 85 would scare the crap out of me if I was anywhere near it. Far to dangerous to even contemplate.

Remember that you have to find someone with a 200psi compressor to begin with.

Perhaps the fact that no one does it now says enough in itself

And you will only get approx half the air out, IE: one tire at 0PSI and a spare at 20 PSI, it will stop pushing air in to the flat tire at 10PSI as it will then be of equal pressure in each.

Hope this makes sense...

I dont think 85 psi is anything to be worried about, most trucks run up to 100psi. Perhaps a tyre guy can chime in here, but i would expect when seating a bead you run some pretty high pressures.

Nah, see when seating a bead, you need a large VOLUME of air, not pressure, whilst the bead is seating your loosing air at a rapid rate, and not building pressure, until the bead is seated then pressurising begins

[chops]

I believe its a maximum operating pressure, not a maximum inflation pressure.

max pressure for max load

[bazzle]

You CAN use a HAND pump to seat a bead.

Just use an old pushbike inner tube between tyre bead and rim lip to seal the gap. Pull out as tyre seals up.

Bazzle

[Jeff80]

You CAN use a HAND pump to seat a bead.

Just use an old pushbike inner tube between tyre bead and rim lip to seal the gap. Pull out as tyre seals up.

Bazzle

OR

http://www.fugly.com/videos/5855/fix-yo ... -fire.html

[patzuki]

I use this method to pump up my sierra tyres, works great, but I normally reinflate from 10 to about 20psi for highway pressures. I made it up for about 30$ and carry it with me cause I was frustrated with the reliability of my ARB compressor.

[up2nogood]

Be careful overinflating tyres, this has killed people before.

[bazzle]

Alot safer doing this.

http://www.offroader.com.au/content/con ... r-tank.cfm

Bazzle

[Witchdoctor]

Give up on the slow stuff & get a CO2 inflation system, will do all the things you need it to do in no time.

Davo

[mick80]

Nah, see when seating a bead, you need a large VOLUME of air, not pressure, whilst the bead is seating your loosing air at a rapid rate, and not building pressure, until the bead is seated then pressurising begins[/quote]
i popped a 35 inch claw off the bead bias i reseated it with a bushranger comresser i was amazed it never went down
cheers mick

[bluemq]

I believe its a maximum operating pressure, not a maximum inflation pressure.

max pressure for max load

big difference in max load when the tyre is cold & there is no weight on it

as apposed to being run at 110km/hr and holding 2 tonne of 4wd.

i would imagine 85psi when its being used as a spare is not that big a deal