Car Tire Inflation


#1

Hi All!

I recently purchased a 2017 Mazda CX-5 Grand Touring. I love the SUV. Anyway, I live in the Midwest, and today it is 27 degrees. I checked my tires air pressure, and they were all at about 33PSI (sticker inside the door says 35psI). As a result, I put 36psi into all 4 tires. Now, I am wondering if I should put a little more in since the tires will probably lose 1-2 pounds when it and the temperature gets colder.

Wha would you all suggest? Do you overfill in the winter? I don’t want to fill so much that the ride is super bumpy, but I want to make sure I am good.

I would appreciate all of your thoughts.

Thanks!


#2

You are fine, relax .


#3

Don’t overfill. If it gets much colder, check again and adjust if needed. No big issue if your a couple of psi off either way.


#4

If “Midwest” means “Minnesota area,” then you’ll want to recheck it probably next Monday when the temps are supposed to drop into the negative-teens overnight, which would be about a 40 degree change, meaning your tires might lose up to 8 pounds. But over the next few days, you’re fine with what you’ve already done.


#5

Yeah if it gets below zero, you can check them again but otherwise no big deal. If you don’t have your own compressor though, you need to be careful with those service station air hoses. They contain a lot of water and can freeze the valve on the tire if you use them when its ten below. Plus a lot of them get frozen up when it gets that cold when you need them most. I always add a little more air and then purge the valve a little to push any water out to get down to the correct pressure.


#6

The tires will heat up as you drive too.


#7

You have too much air in them already. Cold is 68F or 20C. The tires lose about 1 psi for every 10F below 68 so at 27, you should have had about 31 psi. The lower pressure at these lower temps helps heat the tire up to a more normal temperature as you drive it and the warmer tire will have better traction.


#8

No, tires should be inflated to the specified pressure at the current conditions, not at some ‘standard’ conditions. That would be impossible for people to do. 35 psi if it’s 100 out, 35 psi if it’s 10 out.


#9

This is incorrect. “Cold” is the coldest temperature that the tire will be used at, which is usually the temperature first thing in the morning.


#10

I don’t overfill in winter, but I check the pressure often when temperatures drop in fall and winter and top off the tires as needed. I have a little inflator in the garage, so this is easy to do.

On the other hand, I do overfill my spare tire, knowing that I can drop the pressure at roadside if necessary.


#11

You have already done what was needed. Smart.


#12

It’s good to put no more than 3lbs more in the winter or summer, for better mileage, but it can gradually wear out the tires. Instead of checking your tires, try checking gas mileage with every fill-up. If the mileage goes under, check each tire’s psi.But I also notice better tires
keep the air in longer.


#13

That just does not make sense at all. If one fill up has nothing but highway miles at a reasonable speed and the next one is all city stop and go there will be a big difference in MPG and tire pressure will have nothing to do with it.


#14

Cold means ambient temperature, whether that’s 0 or 100 degrees F. Warm means the temperature the tires reach while driving. No matter what the starting temperature is, the temperature rise while driving will be nearly the same and so the pressure rise will be nearly the same.


#15

So many things can affect your gas mileage, temperature, elevation, headwinds, the temperature at which the gas you buy is dispensed at, and even the calibration of the gas pumps where you buy gas.
If the gas coming out of the hose is real warm, you are getting gypped. If the gas coming out of the hose is ice cold, don’t top off your tank because it may run over when you park in the sun and the gas heats up.
This variation in volume is why aircraft engine specific fuel consumption is rated at pounds per horsepower-hour and not gallons per horsepower-hour.


#16

Being the cynical person I am when it comes to mechanics,(not sure why, but maybe it’s bc they have a reputation of ripping people off that know nothing about cars.
I agree 100% . They’ve never had someone thank them, never got their own hands dirty, but like to tell everybody else. Especially during the Christmas season.


#17

I am going to try to fill in some of the gaps.

The inflation pressure of a tire will vary according to the ambient temperature. For a passenger car, it’s close to 1 psi for every 10°F (For other types of tires that use higher pressures, 3% for every 10°F).

So if you are setting the pressure in winter, it is important estimate how cold it is going to get before the next time you check.

So why is inflation pressure important? Heat generation. Needless to say, this isn’t as critical in winter as it is during the summer. - AND - people tend to drive much slower when it’s really cold (Cars don’t like the really cold weather much, either!) Besides, it’s a real pain to check tire pressure when it’s cold.

So I think a practical approach is in order. Measure and correct the pressure when it’s warm - say 50°F. Target for 0°F as the lowest temperature (5 psi over) and don’t worry about it when the temperature gets sub zero. Correct the pressure when it gets warm in the spring. (note: if like me, you live somewhere that doesn’t get to zero very much, then pick an appropriate low temperature as your target.)

Lastly, tire wear is NOT greatly affected by inflation pressure. There are other things that have a greater effect - alignment, for example. Being off 5 psi for the winter is not going to cause a major tire wear problem.


#18

The nice thing about your CX-5 is that it does not use individual sensors in each tire for the TPMS system. It uses the ABS sensors to monitor tire rotation for any changes in the speed of each wheel. It works pretty well, in my experience as a Mazda owner, and has the advantage of not getting persnickety about small changes in pressure in all four wheels as a result of temperature changes. Just keep the pressures equal and as close to the 35 PSI recommended as you can. If you are at 33 to 37 PSI (cold) in all four wheels I think you will be just fine.

I personally raise my tire pressures one or two pounds in the winter since we tend to get days that are close to zero degrees and I usually check and fill my tires when it is above freezing (32 degrees for you non-science folks).


#19

Not the best statement on a forum that has many very good mechanics and some that own their own shops.


#20

I got a lot of replies saying that the cold pressure is ambient at that time. How do you know that? Has any tire manufacturer ever actually tested this or is this something that has just been passed down without question?

I have contacted Michelin through their web site and asked them these questions and I will let you know what they answer.

The reason that I ask this is that I have worked with a lot of engineers over the years and they don’t ask these questions, they just go by what they were taught. To an engineer, ambient temperature is either 0C or 20C, its never the current temperature. So I would not be surprised to find that they have never tested tires for optimum pressure and any other temperature other than one of the two standard temperatures.