Hot tire pressure

[Patman]

I’m wondering how many people here are like me and pay attention to what the hot tire pressure is, as well as the cold. Manufacturers always tell us to set the pressure when cold but they never really give a recommendation for the hot pressure. But yet that is an important factor as well. In colder weather the hot pressure doesn’t change as much compared to the cold pressure so I have always factored that into my mind and then I set the cold pressure higher than the recommended pressure just to compensate. As an example my Civic has a recommendation of 32 psi and when I use that in the summer I will see the hot pressure at around 37 after a highway drive. But in the cooler weather that hot pressure might only be 34 psi. So to compensate, I like to set the cold pressure to 35 during those months. I think one of the smaller factors as to why people report getting lower MPG in cold weather is because the hot tire pressure in their cars isn’t quite high enough.

Am I alone in my overthinking about this or are there more of us out there than I thought?

 

[Rand]

What is the mechanism for less pressure rise when it's cold outside, it should be about the same. Unless you are in heavy snow etc.

 

[eljefino]

I would "need" TPMS with actual data on the dash, not an idiot light. I don't check my pressure hot because I know it's "wrong."

I set my winter tire pressure for the coldest possible day, so I use the ten degrees F per PSI rule and, at freezing, go 3 PSI above placard. This allows me to ignore my car at zero-F. I once checked tire pressure at the start of a cold snap, not before, and a chunk of ice from humidity inside the tire locked the valve slightly open. Tire deflated overnight. I've since been ridiculed here for changing to low-humidity winter air, LOL.

 

[Lubener]

I only pay attention to the recommended cold tire pressure. Warm tire pressures often do not even exceed the maximum pressure listed on the sidewall.

 

[FowVay]

I drove from Atlanta to Charlotte this past summer when the temps were in the mid-to-upper 90's. I noticed quite a few vehicles on the side of the highway during my drive.

I set my tire pressure to 33 PSI on my Nissan Frontier since that's what the placard on the door specifies and that was my cold starting pressure. When I arrived at my destination and after the vehicle had sat for well over 2 hours, I checked the pressure before heading back to Atlanta. I saw pressures of between 40 - 42 PSI in the tires after sitting. That tells me that the pressure on that drive got well over the maximum bead seating inflation number of 40 PSI.

I believe these high temperatures is what led to many vehicles being stranded with flat tires on the highway. I never gave it much thought but this was an eye opener for me.

 

[BigCahuna]

I've seen new car dealers will put Nitrogen in your new cars tires for a greatly inflated price. (little pun there), The only reason I can see for using it is, it's more stable in cold weather, meaning the pressure won't drop much. Years ago I worked for a company that refilled fire extinguishers. And we used nitrogen for a few reasons. First it's a inert gas, and secondly the pressure wouldn't drop in the units that were always in a cold unheated environment. If moisture in your home compressor might be a concern, places like Harbor Freight have inline air dryers to remove moisture. That would be helpful if you have dampness in your compressor line.And if you use your compressor for spray painting.,,

 

[Patman]

What is the mechanism for less pressure rise when it's cold outside, it should be about the same. Unless you are in heavy snow etc.

Hotter weather and hotter pavement means that the tire temperature goes up more.

 

[Marcozi]

The reason why the car manufacturer and the tire manufacturer don't set a hot temp is because conditions vary widely. If you're driving across a desert with the outside temp at 120*F the tire temps are going to be much higher than if were driving through slushy roads with an outside temp of 35*F.

 

[Hermann]

I’m wondering how many people here are like me and pay attention to what the hot tire pressure is, as well as the cold. Manufacturers always tell us to set the pressure when cold but they never really give a recommendation for the hot pressure. But yet that is an important factor as well. In colder weather the hot pressure doesn’t change as much compared to the cold pressure so I have always factored that into my mind and then I set the cold pressure higher than the recommended pressure just to compensate. As an example my Civic has a recommendation of 32 psi and when I use that in the summer I will see the hot pressure at around 37 after a highway drive. But in the cooler weather that hot pressure might only be 34 psi. So to compensate, I like to set the cold pressure to 35 during those months. I think one of the smaller factors as to why people report getting lower MPG in cold weather is because the hot tire pressure in their cars isn’t quite high enough.

Am I alone in my overthinking about this or are there more of us out there than I thought?

Every so often I will check the psi when hot running down the road. In the summer on a interstate trip, after a half hour of so the pressure will rise about 5 psi. 37 psi increasing to the low 40's psi. Winter is only 2 or 3 psi higher on the interstate and takes longer to get the rise in pressure. For years I always have my tires "overinflated" in the winter.

Thanks for making me think about my winter mileage holding up better than some folks.

 

[930.engineering]

Manufacturers always tell us to set the pressure when cold but they never really give a recommendation for the hot pressure.

For a reason. The pressures when hot vary widely depending on several circumstances.
To watch pressures when hot would unambiguously overwhelm the average driver by far.
It's clearly smarter to suggest only check and set tire pressures when cold.

Am I alone in my overthinking about this or are there more of us out there than I thought?

Perhaps you're not alone, but you're clearly overthinking. Definitely.

Setting tire pressures when hot pertains to race tracks and autocrossing or off-road trips etc..
.

 

[mightymousetech]

When you check the tire pressure on a newer BMW in the iDrive, it will give you recommended pressures based on ambient conditions if the sensors are asleep, or tire temperature when the sensors have woken up by driving. Recommended pressures will be the same as door jamb pressures at about 20C.

 

[ARCOgraphite]

Hotter weather and hotter pavement means that the tire temperature goes up more.

Interesting exercise. Tires are heated by mechanical action (distortion stress and strain) when rolling and direct sun radiation. Tires may be heated or cooled by pavement contact and aggressively by the fluid (ambient air) they are working in. Consider the environment a "heat exchanger".

 

[ARCOgraphite]

I don't like high tire pressure in snow/slush/ ice driving. I imagine one would not want a convex tread profile on the road surface. Getting the balance right can be tricky and is, of course, vehicle, load and tire dependent

And, Sorry for being late to the party and chiming in out of the blue

 

[Ranger83]

When I competed, used a Pyrometer to check tire temp across the tread and adjusted accordingly.

Competing with a motorcycle, the front warmed up a few degrees but the rear heated up a lot. Pressure increase might be 10-12psi.

Saint Todd tested gages and found many of them inaccurate. Just ordered a Jaco Digital.

 

[someonesomewhere]

Just ordered a Jaco Digital.

Love mine, got the one with the hose. It always matches what my Milwaukee M18 inflator (also recommend, got mine last year BF for 'free' with a dual-battery kit) says, so I don't use it as often as I should. But it's nice to have in the car if I get caught out needing air and don't have the inflator with me (or the batt is dead).

An aside, add quick release fittings to your portable inflators. Game changing vs the lever-lock style or screw-on. Threaded style for the Milwaukee (can't bring myself to cut the hose lol): https://a.co/d/d8uAdie $6ish for 2.

They also have barbed options for the kind with crimped on lever-lock fittings (like most cheaper inflators. Cut the hose, zip ties for clamps, works great on a cheap one we got from Amazon a few years back. The cheap end on that one actually laid my thumb open, which is how this upgrade cycle started. Got a refund for the inflator (returnless refund), so I fixed it. Lol

Anyway. Happy Thanksgiving y'all!

 

[earthbound]

When I competed, used a Pyrometer to check tire temp across the tread and adjusted accordingly.

Competing with a motorcycle, the front warmed up a few degrees but the rear heated up a lot. Pressure increase might be 10-12psi.

Saint Todd tested gages and found many of them inaccurate. Just ordered a Jaco Digital.

Yep just bought that jaco, it's fantastic....

 

[barryh]

What I read into the OP's post is a recognition that the pressure that matters is the running pressure or hot pressure.

While accepting all the reasons why manufacturers have to stipulate pressures when cold I can also recognise the point made that the differential between cold and hot pressures will inevitably be smaller in the winter than in the summer and that must lead to lower winter running pressures.

It gets more complicated, I'm wondering if slightly lower winter pressures are such a bad thing. Is what we really want to achieve not a particular tyre running pressure but a running temperature i.e. not so hot that the tyre fails but hot enough to enhance grip while still supporting the load placed on the tyre. Higher pressures reduce the cold to hot differential and lower pressures increase the differential. I doubt there is a perfect outcome in the winter to this relationship but I appreciate the OP's thoughts.

 

[Patman]

The reason why the car manufacturer and the tire manufacturer don't set a hot temp is because conditions vary widely. If you're driving across a desert with the outside temp at 120*F the tire temps are going to be much higher than if were driving through slushy roads with an outside temp of 35*F.

True. I do realize that it’s complicated for a manufacturer to give a hot pressure because there are more variables. But I also think that it might be a good idea if owner’s manuals would mention that it’s a good idea to run 2-3 more psi in sub freezing weather. At the same time, I wonder what percentage of owners ever even check their tire pressure on a regular basis. Most pressures probably only get checked when they go to a quick lube place for an oil change (and even then I bet half of those places don’t do it either)

 

[Marcozi]

True. I do realize that it’s complicated for a manufacturer to give a hot pressure because there are more variables. But I also think that it might be a good idea if owner’s manuals would mention that it’s a good idea to run 2-3 more psi in sub freezing weather. At the same time, I wonder what percentage of owners ever even check their tire pressure on a regular basis. Most pressures probably only get checked when they go to a quick lube place for an oil change (and even then I bet half of those places don’t do it either)

Tire pressure decreases about 1psi for every 10F degree decrease in temperature. I check my pressures every other Monday.

 

[ARCOgraphite]

My little Mahindra Group offshore built Ford suv has a readout on the small center DIC display showing inflation pressure at each of the four corners. When I change tire pressure, this readout has matched my pencil gauge within a half of a psi - so I trust it.

I might just double check this "agreement" in the spring. Being a former MC commuter on good weather days, I religiously check tire pressure and appearance before each outing. Yep he's an antique now (not mine but similar/same)