What exactly does cold pressure mean?

I help maintain a Ford E350 used for a vanpool.
The door panel spec says that the rear tires require 80 psi.
The sidewall specs on the rear tires say that the maximum pressure is
80 psi.
So, what does cold pressure mean exactly?
If I check the tires on a cold morning (say 35 degrees) I will end up
putting in a few extra pounds more that I would at 70 degrees. But I
bet the operating temperature of a tire is largely independent of
whether the ambient temperature is 35 or 70.
Reply to
Tom Adams
The difference in pressure between 35F and 70F is no more than about 3-4 psi.
The "cold" pressure to be that which is measured on a tire which is has not been heated by road use. It is the ambiental temperature whether it is 35F or 70F.
Reply to
hls
Seems like that 3-4 psi would lead to a higher operating temperature and pressure when you got up to speed and fully warmed up the tire. Correct?
Are you saying that should be ignored even when you are operating at the maximum pressure specified on the tire wall?
Reply to
Tom Adams

Seems like that 3-4 psi would lead to a higher operating temperature and pressure when you got up to speed and fully warmed up the tire. Correct?
Are you saying that should be ignored even when you are operating at the maximum pressure specified on the tire wall?
I didnt say you should ignore anything. If the tire is specified at 80 psi max COLD, then that is what it means. The pressure will rise as the tire heats up, but then that is not a cold pressure reading.
If you are going to be on the highway, then you can stop and measure the hot pressure when you fuel. You can reduce them to 80PSI if you tire says 80psi maximum pressure.
Reply to
hls
Tom Adams wrote in news:2438871f-28ff-443d-ab57- snipped-for-privacy@z17g2000prz.googlegroups.com:
Ambient temperature, or estimated middle of an ambient range.
I'm wondering if those tires are correct for the vehicle. Seems to me that you ought to be running tires with a max pressure of more like 100 psi, to allow for seasonal changes in ambient.
Are these truck tires (LT instead of P)?
That's correct. You're supposed to adjust the cold temperatures regularly, as ambient changes with the seasons, adding or bleeding-off as needed.
Roughly, every 10F in ambient temperature changes tire pressures by 1 psi, up and down. Since ambient won't ever be exactly the same all the time, you guess the average ambient temperature range for your time of year in your area, then set cold-pressure tire pressures for the middle of that range.
Suppose ambient tends to be between 20F and 40F. You'd set the pressures to be 80 psi at 30F. At 20F, you're 1 psi underinflated, and at 40F, you're 1 psi overinflated.
If you happened to check the pressures when the ambient was at its high of 40, you would need to make sure the tire read 81 psi, so that it would be 80 when ambient dropped to 30, or 79 when it dropped to 20.
Probably is, but it's still starting from that cold-pressure setting. And an underinflated tire is going to generate a lot more heat at 90F than it would at 20F, even with the same number of psi underinflation.
Reply to
Tegger
That is essentially what I told him.. Maybe he is a little slow to get up to temperature.
Reply to
hls
That is great IF the tires on the van are the same ones that came from the factory. Otherwise it's basically crap.
And what does the chart for that tire say the operating pressure should be given the load you carry? If your not driving around at the GVW all day then you probably also don't need the maximum pressure.
Cold pressure means NO drive time on the tire. What it reads after the van has sat long enough for the tires to reach ambient air temperature. So you come out in the AM, Start the engine so it warms up and check the tire air pressure. (Don't forget to check the spare)
That is why you check the pressure at whatever the "normal" temp is for the given season. So if you normally see 35-40 degrees during the winter check it at 37 degrees. The small amount of change won't make much difference.
Same in the spring and summer. If the "normal" temps are around 80 degrees then check it at that temp.
Reply to
Steve W.
well, it might be crap for the tire, but it's not for the van's stability. you certainly don't want the pressure to be less than that if it's loaded - and vanpools usually are.
Reply to
jim beam
No it is crap all around. That number is based on the OEM tire and GVW. It is only valid for the same tire.
Say I buy the same van, Say it comes OEM with a 245 75 16. So I decide to replace the tires with something like a 265 35 20 (or whatever fits in the rubber band sizes). Does the tire pressure apply? NOPE.
Noww if the tire is the same ply rating, same type of construction and same size as OEM then it could be used as a guide IF those tires are rated the same way.
Reply to
Steve W.
don't be ridiculous - nobody's going to be monkeying about with non-stock wheels on an f350 carpool.
same pressures apply - see above.
Reply to
jim beam
Does the door panel actually say 80 psi is the REQUIRED pressure? Or is it the maximum pressure with the recommended pressure something closer to 60 psi?
Reply to
John S.
.
If I set them to 80 cold, then they are around 84 after highway driving.
Reply to
Tom Adams
I think I will thicken the plot a bit.
We recently had a bumpy feel in the steering wheel. The mechanics found a "broken belt" in the left rear (probably just a separated belt, but I did not get to eyeball it). Since then I have been trying to figure out any possible causal factors. None of the van drivers recall hitting a pothole at high speed.
I had been checking the tires in the morning before the van was driven, noting the pressure differential, and then adjusting the pressure later in the day using the differentials.
I plan to start checking pressure at something closer to average ambient, rather than the morning temperature. That will probably knock a pound or two off the maximum pressure when the van is in operation.
This van has also has something called Rollgard
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I would call Rollgard a spring stiffener but "Rollgard is not a spring stiffener" seems to be Rollgard's defacto motto ;-)
I personally think Rollgard is a sick joke. There is no testing data. I read that they tried to get NHTSA to test it but were declined. All they have are testimonial letters on their web site, some of which are laughable. One says Rollgard shortens the turning radius! Rollgard makes drivers feel better because they detect less sway in turns, I think. I don't know if that translates into more or less safety.
Anyway, I now have a theory that Rollgard is a tire belt breaker. Makes sense that it would increase the forces on a tire on the bumpy rural roads that we drive on part of our route.
Also, I think putting Rollgard on a vehicle makes it harder to sue Ford in the case of a rollover. But this is a conversion van anyway, so that might also make it harder.
I think these vans have about average safety overall because of the size advantage, but they are one of most (if not he most) rollover- prone vehicles still made. I think Ford may be paying up for rollovers since they lost a suit a few years ago that left the judge foaming at the mouth at Ford's practices.
Equipping a E350 with Rollgard probably makes it harder to extract money from Ford in the case of a rollover or other design-related failure.
And, left rear blowouts often lead to fatal rollovers in the E350.
BTW, the NHTSA says to use the door panel pressure. 80 psi in the rear tires is probably about right when the van in close to fully loaded:
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erPiece.pdf
I don't think the van has sub-standard tires, but I will double-check that.
Reply to
Tom Adams
I will double-check, but I think the tires are within specs. And, I think the orginal tires had an 80 psi limit. Our van pool drove 2 2009 models during 2010 and all the tires had that rating. They were not perfectly new, but I am assuming that the conversion van company and the State of NC did not switch out the tires that Ford put on these vans. I have not found a 15-passenger van with tires with a higher rating.
I think the real problem is that the Ford E350 passenger van has a flawed design.
Reply to
Tom Adams
It's the recommended presssure in the rear tires. The recommended pressure in the front tires is 60 psi.
The Ford E350 is a weird vehicle.
Reply to
Tom Adams
the reason it's not a "spring stiffener" is that the two moving arms on each end allow it to float. but that also means the thing is doing absolutely nothing unless one of those ends bottoms against something. bottom line, you're just carrying extra weight and potentially rubbing fatigue initiation points into your real springs - i'd get rid of it immediately.
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all tires are /not/ created equal. get the best quality tires for this thing - you have multiple lives at stake - especially if you have a rear blowout and this thing becomes unstable and rolls. commuter vans are terrible in the rollover stability department.
Reply to
jim beam
it's also cheap, nasty and built by frod. the exploder fiasco shows frod will simply disregard safety if there's money to be made.
Reply to
jim beam
you don't need a higher rating - just one that doesn't fall apart /at/ that rating. what do michelin offer in your size?
well, it's a design that doesn't safely address the inevitability of tire failure, that's for sure. best fit tires with the lowest possible failure rate.
Reply to
jim beam
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Read the web site. Regardless of what they call it that is nothing more than a helper spring. BUT it looks like it's a composite type so it likely doesn't have a lot of power.
ALL vans and large vehicles are top heavy, They are ALL prone to roll over if they are not driven properly. The main reason why all of these vehicles are rolling over has to do with a lack of respect of the operator for the vehicles limits.
Take a Jeep CJ. You can take them off road and darn near climb trees and they won't roll over. Side hills are not a problem IF YOU GO SLOw. When they came out they were popular with drivers who had used them in combat and who respected they way they handled. The next generation was raised with them and were taught how they should be driven, BUT they didn't buy a lot of them when the older ones started failing. They wanted B I G G E R vehicles and moved to large cars and wagons. Their kids didn't get taught on narrow wheelbase vehicles, they were taught on huge land yachts that wouldn't roll over unless you were really stupid. So those kids and their parents more or less forgot how to deal with the smaller vehicles. So did their kids. Then 4X4s became popular again. What happens? These folks who had never though about vehicle dynamics bought up a ton of Jeeps, Small SUVs, Vans and figured that they could drive them just like they did the cars they had before. WRONG. They are not meant to be driven down a twisty road at 60 mph and tossed into corners like a car.
End result, They roll over. Then these folks complain about it and the media (who were raised the same way) think that the problem is in the vehicles design. The truth is that most of the people who roll vehicles shouldn't be driving that type of vehicle in the first place.
But since pointing a finger at the person and saying "You're an idiot for driving that way" is no longer an acceptable thing to do and personal responsibility is a forgotten concept, it's so much easier to say "It's (name company with money) fault, they made (insert product being used by an idiot here)"
Think about this one. Everyone makes fun of the stickers that say things like "Do not use in the shower/bath" stuck on a hair drier or curling iron that is wall powered. Many look at that and say DUH! Who would be dumb enough to do that, it's just common sense. That sticker wouldn't be there if that didn't happen at some point and a Judge and jury decided that the company that made it was at fault for not warning the user about that very danger!!!
Go take a look at the visor warning tags that have to be on every 4X4 and SUV now. The ones that warn you that these vehicles handle different and that you have to be careful. Care to guess why they are there?
How about that maximum pressure warning on those tires. Think it is there because the maker got sued at one time because Billy Bob decided that 80 PSI just wasn't enough and tried to put 120 PSI in them "Like a REAL TRUCK TIRE"
Reply to
Steve W.
7-
Michelin is probably a good suggestion. There is a van that parks near the one I drive that has Michelin's. The tires on that van are rated at 80 psi max, BTW.
However, I don't think I could get the transit authority to change their tire buying policies. I could suggest that.
The NHTSA puts out advisories on these vans, but they have never recommended higher standards for tires. They do have a recommendation for replacing older tires even when they have tread, but that was not the problem on our 2009 van.
Reply to
Tom Adams

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