Tire inflation, what temperature is "cold"
- Thread starter Wayne
- Start date
ctechbob
Well-known member
You sucked me in Wayne. Something I'd never really thought about other than to make sure the car had the pressures checked in the garage before driving or any sun hitting them. Sent me down a rabbit hole and danged if someone didn't write a really nerdy sounding wikipedia article about it:
en.wikipedia.org
and
Ok, I've read more about that than I needed to tonight.
Cold inflation pressure - Wikipedia
and
Ok, I've read more about that than I needed to tonight.
Azjeff
Active member
Apparently cold means not heated up by being driven and could be 30f or 90f ambient. Good question for Capriracer. For my vehicles it's garage temp in the morning. For trailer it's temp in the morning before being driven and before the sunlight hits the tires. To be full on OCD you'd want to check and adjust when you get much temperature variance from when you last checked. How much I don't know. I do know I get nervous when I set the trailer tires to the recommended 65psi which happens to be max in the morning at 60f and later in the day when it's 95f and the TPMS is saying high 70s. I've backed my starting psi back to 55 psi and still have a large cushion of load capacity and brought the max psi down. Somewhere I found a calculator that shows load rating at different psi but can't find it right now.
Why do trailers just call for max psi for the recommended tire?
I PM's Capriracer.
Why do trailers just call for max psi for the recommended tire?
I PM's Capriracer.
MSCH
Well-known member
for lack of a better explanation Cold tire pressure is measured at ambient temp after vehicle has been parked overnight or for a good period of time.
makes no sense to go full OCD on tire pressures... the fudge factor is built into them.. to allow for heating up when driving or to allow for the fact climate and temp changes affect the devices...
so best method is to just check them befor eheading out and not to overthink it.
for instance its pretty much a rule of thumb that you gain or lose 1 psi for every 10 degre F change in temp...
for instance I just went to NC... I had set all my tires to 110 psi before we left FL. it was down around freezing in NC, I check the tires and they were 105 106... did I add air? hell no.. I'm going back to Fl and I know the pressure will probably come up to 110.
another one is all tires lose between 1 to 2% of their pressure per month, due to permeability of air thru rubber..so no matter what you do or how OCD you are they always change pressure over time..
makes no sense to go full OCD on tire pressures... the fudge factor is built into them.. to allow for heating up when driving or to allow for the fact climate and temp changes affect the devices...
so best method is to just check them befor eheading out and not to overthink it.
for instance its pretty much a rule of thumb that you gain or lose 1 psi for every 10 degre F change in temp...
for instance I just went to NC... I had set all my tires to 110 psi before we left FL. it was down around freezing in NC, I check the tires and they were 105 106... did I add air? hell no.. I'm going back to Fl and I know the pressure will probably come up to 110.
another one is all tires lose between 1 to 2% of their pressure per month, due to permeability of air thru rubber..so no matter what you do or how OCD you are they always change pressure over time..
MSCH
Well-known member
from what I understand trailers tires and axles are sized according to the max vehicle weight of the trailer.. so the MAX pressure setting is where those tires would be if the trailer was at its GVR.
Azjeff
Active member
My tire load index of 107 gives me max tire capacity of 8600 lbs at 65 psi and the trailer GVWR is 6700. My tongue weight is around 700 so practical in use GVWR is 6000. I don't think I need 2600 lbs of safety capacity.
MSCH
Well-known member
makes you wonder if the trailer has the correct tires on it.. because they generally don't give you extra, they go bare minimum. assuming it is a tandem axle, basic math is GVWR of trailer divided by 5 ( pin weight plus 4 tires) should get you in the ballpark of the load on each point. if what you are saying is true of the current tire you could always use a load pressure chart for that tire and adjust the pressure downwards and if you really want to go full bore OCD get the trailer weighed and adjust accordingly... . this chart is from Toyo but they dont have ST tires listed. https://www.toyotires.com/media/pxcjubjs/application_of_load_inflation_tables_20200723.pdf
MSCH
Well-known member
another chart for ST tires https://www.yournexttire.com/trailer-load-inflation-chart/
@CapriRacer is a tire engineer. Let's see what the tire industry thinks "cold" is.
CapriRacer
New member
Hi Guys!
AzJeff asked me a question through another website and mentioned he wanted to post on this one. So I decided to cut out the middleman (no offense, Jeff) and join. So here is what I wrote in case you didn't catch it above:
We tire folk use the term "Cold" when we really mean "at ambient conditions". That means both temperature and pressure. It's just that atmospheric pressure doesn't vary much, but temperature does!
While it may seem that ambient temperature would be important, it's that pressure buildup is more important. Put another way, even though the starting temperature/pressure is important, starting pressure is way, way more important!
Yes, everyone is aware that if you set a tire's pressure at 40°F, at 90°F it will be higher. (about 5 psi for passenger car tires) But tire pressure affects the spring rate and temperature doesn't much. And spring rate is very important for vehicle handling, so that's what we go with.
You may ask what's someone supposed to do - adjust the pressure every day?
A bit of over-inflation doesn't affect things very much. A bit of under-inflation isn't as good, but close. So if just check the pressures once in a while, it will be OK. It's just you want to avoid substantial under-inflation!
****************************************************************************************************************
Expanding on that a bit, we use the term "hot" to mean fully up to operating conditions - so one way to look at "cold" is where it starts.
AzJeff asked me a question through another website and mentioned he wanted to post on this one. So I decided to cut out the middleman (no offense, Jeff) and join. So here is what I wrote in case you didn't catch it above:
We tire folk use the term "Cold" when we really mean "at ambient conditions". That means both temperature and pressure. It's just that atmospheric pressure doesn't vary much, but temperature does!
While it may seem that ambient temperature would be important, it's that pressure buildup is more important. Put another way, even though the starting temperature/pressure is important, starting pressure is way, way more important!
Yes, everyone is aware that if you set a tire's pressure at 40°F, at 90°F it will be higher. (about 5 psi for passenger car tires) But tire pressure affects the spring rate and temperature doesn't much. And spring rate is very important for vehicle handling, so that's what we go with.
You may ask what's someone supposed to do - adjust the pressure every day?
A bit of over-inflation doesn't affect things very much. A bit of under-inflation isn't as good, but close. So if just check the pressures once in a while, it will be OK. It's just you want to avoid substantial under-inflation!
****************************************************************************************************************
Expanding on that a bit, we use the term "hot" to mean fully up to operating conditions - so one way to look at "cold" is where it starts.
MSCH
Well-known member
I'm pretty sure it is static air temp after being stationary for a suitable period, say overnite or 8 hours..dont know what the industry exactly specifies it as but I'm pretty sure it is along the lines of my statement.. they don't try to be too specific just because Cold is going to vary by climate but there isn't any real necessity in defining it other than that.. otherwise you'd have to change your air pressure every time the weather changed.
good luck on even getting most people to check the air in the tires once inawhile. it is one of the most ignored things on a vehicle, which is probably why the Feds mandated the fuggin TPMS crap on new vehicles..
personally think people over think it in much the same manner the guys on BITOG way over analyze mundane items such as oil level.. I'm sure you've seen the guy on Bitog worrying about a 1/4" discrpeancy on a dipstick reading.. then you have someone like me who just checks it if it sat overnite and not going to Add anything until it goes below the Add mark.. knowing it isn't all that critical or necessary to be accurate to the tenth of an inch.
CapriRacer
New member
It's sort of because they generally put the minimum tire on the trailer, but that isn't the whole truth.
Ya' see, the travel trailer industry kind of came under scrutiny from NHTSA, the government agency that regulates vehicles, and they pointed out how marginal that was, so many manufacturers who couldn't put a larger tire on, went up in Load Range.
Anyway, if you have any questions, just ask!!
Azjeff
Active member
Calls for 205/75-15 load D which is what is on it. 2149 load rating @ 65 psi. Somewhere I found a chart that shows capacity at lower pressures. I could go to 45 psi and still have margin at GVWR and we never pull that heavy.
CapriRacer
New member
You want to be careful here. You have to account for front-to-rear and side-to-side weight variation! Many travel trailer manufacturers didn't do a good job in this area!
ls1mike
Active member
I love the Carlisles radial trail HD. I went D's as well. Cold to me is prior to movement. Not after driving.
ctechbob
Well-known member
Yea, I think they're a pretty good value, even though mine were made in China, still more comfortable with those than the CastlRocks that came on the trailer. Those things started wearing weird after the first couple trips, and I'd made 100% sure they were set at 65#. I think that may have been too high, but I wasn't taking any chances given the amount of interstate towing we do. They started wearing right down the middle like they were an old bias ply and they were over-inflated.
Ohh well, the Carlisle's (Or Calstar as they are now) have been perfect for me. I too set them at 65# before the sun comes up or many hours after it sets. TPMS shows them creep up to about 70 on long trips though, I just assume they take that in to account when they tell you what to run.
ls1mike
Active member
I have tpms as well, on longer hit trips I will see 70 as well.
MSCH
Well-known member
pretty hard to find a trailer tire that isn't made in China..