Any chance of attaching a foot pump to a completely flat tyre (apparently let down) and managing to pump it up?
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As long as the bead is still sealed to the wheel and the tyre has not been punctured the only problem should be aching legs. Difficult to tell if the sidewall has been damaged by the weight of the car though.
Edited by Old Navy on 06/04/2009 at 20:44
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Yes, i cant see why it would be a problem, its going to be mighty tiring on your legs though !
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If the tyre has been let down make sure the valve core has not been removed.
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>>make sure the valve core has not been removed...
Thanks yes. Top of list to check...
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You could try squirting lighter fluid into tyre and putting a match to it !! or starting fluid or butane gas www.youtube.com/watch?v=Gmdo2T_g5FE&NR=1
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Do you know anyone with one of those electric-plug-into-the-fag-lighter-socket jobbies ?
Borrow one of those and lean on car drinking tea while observing progress. Excercise is like fine wine, too much is bad for you...............
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The CC3 comes with a can of goo and an accessory socket compressor, but no jack, or wheelbrace, come to that.
So presumably, the little compressor is deemed able to pump up a flat tyre while it's on the car.
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I've done that. Thought I was going to die...
JH
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Do you have one really muscular leg and one sort of normal one now ?
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New years day in about 1998. Came out to the car, inserted sprog into child seat and thought that was more of a bend down than usual. Got in drivers seat and notice lower view - all four tyres had been let down in the night (as had all my neighbours).
Oh how I laughed as I pumped all four up with my single barrel footpump. The son and heir just sat there giggling at me.
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It might be easier to jack it up to pump it up (so its off the ground) otherwise you'll have to "lift" the car with your pumping. My plan B would be to take it off and ask someone for a lift toa grage wih an air-line.
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This is madness! The tyre would be pumped up in the time it would take to jack up and remove the wheel. The weight of the car adds an insignificant percentage to the total effort.
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Forget the toy inflators that the high st accessory shop sells, as for a foot pump...perlease..
This will inflate tyre from flat in less than a minute, one of my best buys
tinyurl.com/5go4ys
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My first thought was that there's much more energy involved in pressurising the air in the tyre than in lifting the car. This corresponds to not seeing a large pressure difference between measuring a tyre pressure with the wheel on or off the ground.
Here's a vague calc about the subject;
mean_radius=(15*25.4e-3/2)+(195e-3*(65/100)/2); CSA=195e-3*(195e-3*(65/100)); Vol_air=CSA*2*pi*mean_radius; p1=101325; p2=p1+(2*p1); Q=p2*Vol_air*log(p2/p1)
Q =
1.3166e+004
W=(1000/4)*9.81*(195e-3*(65/100))
W =
310.8544
Q/W
ans =
42.3553
This shows that there's something 40 odd times more energy in the pressurised air than in lifting a quarter of the car by the sidewall height. i.e., it's probably not worth getting the jack out!
The assumptions are
196/65/R15 tyres
2 Bar inflation pressure
the cross section can be considered square 195mm x 195mm x 65/100
and the biggie (I'm the first to confess thermodynamics isn't my strongest subject!)
Q=p2*Vol_air*log(p2/p1)
This assumes isothermal compression. Yes, the air is temporarily heated during compression the foot pump, but, all that heat is given away to the metal rim of the wheel once the air is inside, and so, the start and end state of the gas is only discernible by its pressure.
In practice, owing to the losses in the pump, both Q and W as given are idealised and will significantly underestimate the amount of work that you would actually have to expend - but, the ratios would remain substantially unchanged.
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Does that mean it's quite hard then ?
;-)
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No, it means its a piece of cake to pump up a tyre from flat with a footpump, and it's all a big fuss about nothing.
Edited by Dynamic Dave on 07/04/2009 at 01:35
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Keep Crunching, Numbers. Ill use my electric pump.
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>>Here's a vague calc about the subject;
>>
Well on my calculations I am glad I have low profile tyres to pump up. At last an advantage in having them.
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Ah I can see where I went wrong though.
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recall myself and a friend rescuing some morons who'd taken their soft-roader onto a beach, and were stranded.
Sand-ladders, flatten tyres, lots of digging (not by us - by them - we just stood and directed), and then we lent them a pump to reinflate their tyres afterwards.
I asked my friend WHY he'd leant them a pump, when his Landrover had a built-in compressor.
"They'll %@#$%-well learn their lesson this way, won't they?" was his reply...
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It took me 500 strokes of a single barrel footpump to raise the pressure from 32 psi to 46 psi. Using that information, someone (!) will probably be able to calcuate how many strokes it would take to increase the pressure from 0 psi to 32 psi.
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What's this on- a tractor rear wheel? On an ordinary tyre with an ordinary pump it takes about 10 strokes to raise the pressure just over 1 psi, when it's about 30 psi
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On an ordinary tyre with an ordinary pump it takes about 10 strokes to raise the pressure just over 1 psi when it's about 30 psi
The number of strokes needed to raise the pressure by each successive 1 psi increases as the pressure increases.
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Another thing you would need to be aware of is that if the car had been sitting on the deflated tyre for some time, ie overnight, the tread pattern would probably have developed a flat section. Therefore when you pumped up the tyre and drove off, you might have felt a "lumpy"sensation - if there is such a technical explanation - from that wheel.
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Like driving on thrupenny bits (NOT the cockney connotation).
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I once did a simple experiment to answer a question here. A tyre off the car measured 0.5 psi lower than when the car was sitting on it. Therefore NC is right - it's insignificant.
Pumping by foot from flat is not too difficult. It is very important though to let the pump come right up each time. If you only let it rise say 75% you save a bit on leg muscle but waste a lot of your effort because you are not compressing the air enough and getting a full charge.
Slow full strokes are much more effective than quick short ones.
If you are like me you will find it virtually impossible to pump with the "wrong" foot.
Final tip: spit into the connector and twiddle it a bit when connecting. A tiny air leak is the last thing you need.
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How long did it take ?
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How long did it take ?
5 minutes perhaps. Less time than trying to remember where I left the electric plug-in thing, and they are pretty slow anyway.
Years ago I once changed 4 LandRover tyres using screwdrivers as makeshift levers, and pumped them up by foot, all because the dealer offered them at a discount because his tyre machine was out of order. That was hard work.
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I just posted about the T Max electric pump that I bought last year. A seriously effective piece of equipment that would probably inflate a flat in 2 mins.
For some reason my post disappeared into the ether.
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At my age I had to try it -- The long slow strokes seemed to work better - took much longer to get out of breath.
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Still got a Schrader engine pump somewhere but no use on catalyst equipped cars(or diesels).
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I recall a story of an engine apparently badly pinking.
When the head was later removed a piston crown was found in effect shot peened.
The cause was using a tyre inflator that you screwed in to replace a plug.
Unfortunately the little ball bearing that was surposed to operate as a valve got sucked into the combustion chamber hence the pinking sound as it hopped around.
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I used to wonder about the compressed air/petrol mixture being pumped into the tyres. It ought to have made for some spectacular "blowouts", but apparently never does.
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One of the better tyre fit companies in the North East uses a special gas to inflate tyres.
I think they do that because crummy old fresh air causes corrosion to alloys.
Not sure what the gas is, might be nitrogen, or nitrogen mixed with something else.
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Not sure what the gas is, might be nitrogen ...
I would guess nitrogen, or possibly CO2 (now there's a way to reduce global warming) - more likely N2. Anything else (other than air) would be too expensive, or flammable.
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