The hose steals 2 PSI

her husband doesn't comprehend the difference between static pressure and dynamic pressure. friction loss only affects dynamic pressure. he also knows nothing about reading treadwear.

now if there was a significant altitude change - by which I mean hundreds of feet considering it is air we are talking about - there would be some pressure loss.

In Germany, the gauging office checks gas pumps and air pumps of fuel stations regularly. So if you use the air pump, the reading is as official as it can be.

The "Myth" is, that people belief that the hose steals air so the preset is wrong and you get less air pressure with the long hose.

I had forgotten to mention that I had heard that one pretty often.

Originally, the common tool to check/inflate your tire was this:


It's an air tank with a gauge and two buttons (+/-) which hangs on the air outlet of the gas stations compressor to refill. You pick it up and take it to your wheels. Convenient and worked well. But more and more of those become stolen.

Then they came up with a wall mounted version which started the myth because those had to have a really long hose. You connect it to your wheel, walk back and dial in the pressure with the +/- buttons.

When you connect the hose to the wheel, a lot of air rushes into the hose decreasing the tire pressure significantly. E.g. you have dialed in the correct pressure, e.g. 2.0 bar, disconnect the hose with a loud hiss and then reconnect, the gauge will read 1.8 bar or less (~3 PSI less) because the hose really steals pressure when connecting. The problem is that the loud hissing sound appears when disconnecting the hose so people think the hose will steal the air out of the tire in this moment and not when connecting it before the pressure is dialed in.

So people wrongly belief they must compensate this loss by dialing in extra pressure.

Some gas stations came up with an "Air Column" to reduce the length of the hose,


which is much more user friendly since you don't need to pull the hose all the way around your vehicle and then coiling up the dirty hose to put it back into the wall cradle. And the more modern versions like in the picture have a preset, just dial in the pressure you need, connect the hose and wait until the thing beeps, then move to the next wheel.

But there are still many people who think the hose will steal air and need to add more air to the wheel to compensate.

Yesterdays encounter was at a modern "Air Column" but one with an extra long hose because they had only one of those for 4 service spots.

Interesting.

On its own this might be a little, well, threadbare - in so far that there doesn't seem a great deal of potential testing or expansion.

However, what about 'Forecourt Fables'? As in a number of smaller car/tire/gas station myths they could look at in conjunction with this? For example the idea that 'super unleaded'/high octane gasoline will really improve performance of the average car, or what happens if you fill your diesel car with gasoline?

Ideas?

There are several myths, especially about the gas pumps.

The Mythbusters could visit random gas stations and compare their bill with what they actually get. They could also check the accuracy of the air pumps as well.

Most gas pumps use a star of little piston pumps with a crank in the middle. Each piston injects a specific amount of gas into the hose with the nozzle. To adjust the pump, the slack of individual pistons can be set greater or tighter. This usually isn't done evenly.
So when you only pump little amounts each time like the myth for saving weight as fuel says, the chances to stop after "short" pistons adds up and you get less fuel than pumping the same amount all in once and top up your gas tank.

Each piston creates an impulse for the counter. Cell phones might be able to add extra impulses to the counter. Another good reason not to use a cell phone while pumping gas. According to the federal German gauging office, this works for supermarket scales for sure! They registered up to 50% higher readings when a cell phone is "talking" close to the scale.

What other good reason is there? Good being defined as not busted by the MB's

I know cell phones can't ignite gas vapors as static discharge has been shown to do, but what about a lit cigarette? I've seen a number of people, usually women for some reason, filling up while puffing on a cigarette. Even holding it in the same hand as the gas nozzle while taking it out of the car. I can't imagine someone being that stupid but they are. I even asked one woman that was filling up next to me to please put out the cigarette. All she did was call me an unrepeatable name and kept right on puffing.

Don't think you can do that on most pumps anymore. With all of the pumps I've used, as soon as the pressure in the hose drops, the nozzle will no longer stay open. You may get a few drops but that's about it.

Air pumps, ££ paid-for coin operated ones.

Anyone yet managed to get all round and do all four corners on your 20p?.. or whatever coin it takes where you are....?..

I suspect a conspiracy to steal an extra 20p, as you cant just check three tyres can you?...
Someone has timed the average it takes to do 4 tyres and subtracted a quarter of that on the time allotted to 20p.

You are not allowed to show footage of the gas stations without the companies permission, or unless an investigation has/had been carried out to confirm wrong-doing. Otherwise the show would be sued.