With the cost of gas going crazy, all the experts recommend that one of the best things we can do to increase the gas mileage of our autos, is to be sure that our tire pressure is filled to the auto maker specifications. As someone always trying to get the most out of a gallon of gas, I check my tire pressure regularly, but my problem is that auto makers and tire manufacturers always publish “COLD” tire pressure specs for their tires!
Ok , so I check my tires in my driveway before I leave the house (cold tires), but I then have to drive to the gas station to put air in them (unfortunately I don’t have an air compressor sitting around in my garage), but after I drive to the gas station I now have WARM air in my tires and now have no idea to what pressure I need to fill my tires!!!
Is there an easy formula to convert “COLD” tire pressure to “WARM” tire pressure so I don’t have to sit around the gas station waiting for my tires to cool down before I can put the proper amount of air in them??!!
How far is the gas station? Unless you’re traveling at high speed for more than a few miles to get there, the temperature of your tires (and the air within) won’t change appreciably. Worst case, fill your tires two or three PSI over the placard rating at the gas station, and then check your pressure the next morning in your driveway.
Good advice to get a hand or foot tire pump. Actually, you can get a small portable electric pump (either AC or rerchargable battery) for not all that much. Then, you can take it with you on trips.
Besides which, air pumps as gas stations are notoriously inaccurate. If you do use 'em, don’t rely on their readout, use your own pressure gage. Maybe you do.
You can also buy a small compressor that plugs into your dash. I had to stop at a gas station for air recently, first time in years. It was 75 cents, so I decided to check all four tires, just to get my money’s worth. The thing shut off before I could get to all 4. I’d guess it ran for 3 to 4 minutes.
Ah, go get a quality tire pressure gauge. Never trust pressure gauges at gas stations or connected to air pumps. Then either adjust the pressure at home with your own pump. Or measure just before you go to the gas station for air, and once there, measure again before and while filling with air.
Places like Pep Boys sell small portable air tanks that you can fill at the service station and then use to inflate tires. The problem with them is they lose top off capacity very quickly. Harbor Freight used to sell kits to convert old refrigerant tanks into porta tanks, but the legality of doing that under DOT regs is dicey. The one I made up 20 years ago still works well, though.
Would it be better to have slightly overinflated tires than slightly underinflated?
Let’s define “slightly” as no more than 2 psi and have “better” include all aspects of tire existence; gas mileage, tire wear, braking distance, safety and so forth.
There are “notoriously inaccurate” because the traditional design with the metal plunger-type gauge had that gauge located at the business end of the air hose, and it was forever being run over or dropped onto concrete.
The new, computerised units have no measuring equipment on the end of the hose - it all takes place back at the main pump. I think those should be fine.
That’s a difficult question to answer due to the variables involved. And do you mean under/over inflated with respect to the recommended pressure, or the maximum on the tire sidewall? If it’s with respect to the recommended pressure, then I’d say that slightly over inflating will be better off overall. If it’s with respect to the maximum allowable pressure, then err on the side of under inflating, obviously.
Some people under inflate their tires slightly in the belief that it will give a greater contact patch and help with cornering, braking, etc. The truth is, it depends on the tire, the car, the road, and the surface. In some cases under inflating can give you poorer handling due to the geometry change of the tire, and even poorer braking for the same reason.
Folks (in general) should just worry most about keeping the tires at the recommended pressures, not so much about trying to super-optimize things. The problem is not the diligent people who are +/- 2 psi from their optimal setting, it’s the enormous number of people out there driving on 10 psi with tires intended for 35 psi. When I worked at the auto shop back in the 80’s, one of my many gofer jobs (since I was the more junior mechanic) was to check and air up customers tires. And it was rare - very rare - that more than one tire on a car was within 5 psi of the recommended pressure. The number of times I saw tires at 10 psi or less was appalling. On one car I saw less than 5 psi on several tires, and I wondered how on earth the bead could still have a seal with pressure that low.
Then again, given how many people had their cars towed in because they ran it dry of oil…I guess it’s no surprise.
Nah-still got all the factory standard bits. I don’t use it (the converted refrigerant tank) frequently any more, as I can get about 300’ from the shop door with air line, and also have old, removed from service (but still current in hydrostatic test) 2200 PSI SCBA cylinders with appropriate regulator. Top off a whole lotta tires with one of them.
If its keeping you up at night some tire dealerships can fill your tires with Nitrogen now, which supposedly doesn’t change pressure with temp nearly as much as air (Indy cars use it). Costs money though…
Is that really true? Remember that good old N[sub]2[/sub] makes up almost 79% or ordinary atmosphere, and after that, O[sub]2[/sub] makes up the next near 21%. Perhaps one of our resident chemists will comment on the coefficient of expansion for Oxygen v that of Nitrogen.
If you wanted to use it, industrial dry nitrogen isn’t expensive. Once you’ve purchased the cylinder and regulator, that is. I think they charged $15 for a tank swap last time.
While this company appears to sell air tanks and thus isn’t necessarily neutral, the info on this page appears credible to me. It supports the Cecil’s take on it.
