cool air for inflating tires - Fuel Economy, Hypermiling, EcoModding News and Forum

NiHaoMike · 06-22-2009, 10:17 PM

The next time you inflate your tires, take a note of how hot the air compressor gets. That happens because air heats up when it is compressed. If you don't have an air cooler (which can just be a long length of hose), you'll be inflating your tires with hot air, which will then decrease in pressure when it cools down, which means the tires would be underinflated.

Therefore, either let the air sit for a while in the tank to let it cool down before inflating or use an air cooler to ensure you're really getting the correct pressure in your tires. Another benefit is that some of the moisture would be condensed out of the air as it cools, prolonging the life of the tires and reducing pressure variations as they warm up.

I actually have an idea for making an air cooler out of 1/4" copper tubing, a fan, and a compressed air condensation catch can.

hamsterpower · 06-22-2009, 10:25 PM

I prefer to use a bicycle pump. its a great work out, uses no electricity, and might be more accurate.

no really, I'm not kidding.

NiHaoMike · 06-22-2009, 11:40 PM

One of my plans is to use an inverter to run my air compressor from a hybrid bicycle. (The compressor uses a universal motor so it should work just fine with a simple square wave inverter.) The charge can then simply be regened back the next time I ride the bicycle.

hyperyaris · 06-22-2009, 11:46 PM

Air heats as it compresses, but cools as it expands. It cools down in the tire as it expands.

NiHaoMike · 06-23-2009, 12:31 AM

Not so because the absolute pressure in the tire is about 4 times the barometric pressure (for 44PSI tires). And the energy that went into compressing the air must go somewhere.

hyperyaris · 06-23-2009, 01:15 AM

Quote:

Originally Posted by NiHaoMike

Not so because the absolute pressure in the tire is about 4 times the barometric pressure (for 44PSI tires). And the energy that went into compressing the air must go somewhere.

I stand corrected. I was assuming a completely airless tire. My mistake.

CapriRacer · 06-23-2009, 08:52 AM

Uh ...... Mmmmmm.......

The problem: The compressor heats the air
The solution: In line heat exchanger?

Wouldn't it be easier to over inflate by a couple of psi, let the tire cool, then bleed it down?

Daox · 06-23-2009, 09:24 AM

I'd say its probably easiest to just check your pressure once a month. You shouldn't be loosing any sizable amount of pressure in that short of a time period.

Ryland · 06-23-2009, 10:34 AM

this is why good compressors have fins on the line before the air goes in to the tank, but the tank is also a big steel heat sink so really you are putting cold air in the tire unless you have been using the compressor alot and it's hot, hand pumps also heat the air, it's the compression that does it.

tjts1 · 06-23-2009, 10:55 AM

Quote:

Originally Posted by NiHaoMike

The next time you inflate your tires, take a note of how hot the air compressor gets. That happens because air heats up when it is compressed. If you don't have an air cooler (which can just be a long length of hose), you'll be inflating your tires with hot air, which will then decrease in pressure when it cools down, which means the tires would be underinflated.

This is bad advice. Your tires will get hot anyway while you're driving. Following the above procedure, your tires will be over inflated in real world driving. I know a lot of people around here like to overinflate anyway but you at least want to have an accurate idea of the pressure in your tires when the car is moving.

If you are over inflating your tires, always check the pressure right after driving on the highway. This will tell you the peak pressure in your tires.