PS. The tire busters wouldn’t see liquid unless the tire valve were down and sprayed out the water.
In any other position, as the tire begins to be dismounted, the valve releases the pressure of the compressed air, and the water evaporates, as the dew point inside the tire changes with pressure.
Water condenses in the compressor tank (high pressure, most of the water condenses there). Once that air then goes to the lower-pressure tire it doesn’t have any tendency to condense. Anyway, that effect has nothing to do with your problem, it would apply to all tires.
So fact is your 55 series tire has about the same volume as a 70 series tire. Your pressure loss is not because of the tire profile.
I could see water condensing in a tire using a tankless compressor on a 75 deg 100% humidity day and the temperature then drops to, say, 50 deg.
@texases wrong. compress the air while humid. send it into the tire where it is still in high pressure (about 3 atm). then let it cool 30 degrees F.
liquid water.
Nope, compress the air into a tank, knock out most of the water. Move the (saturated) air to a lower pressure, relative humidity decreases. I’d be surprised if cooling that dry air would knock out much water. Insignificant in terms of pressure. Here’s a plot that show how it works:
Compress saturated 70F air to 87 psi, you knock out over 80% of the water. Cool it down to 30F, it’s still not saturated, nothing drops out. Even if it did, saturated air is only 1% - 2% water, so the air pressure change would be negligible.
But you’re missing the IMPORTANT point - all tires would be equally affected, it’s not the reason for your tire pressure changes.
I have a 1949 Frigidaire refrigerator in my shop that has has been operating for many years without fail. I am amazed since over the years I have had to replace 3 refrigetators in the kitchen due to various failures. Obviously they were doing something better 65 years ago. Change for the sake of change, technological or otherwise, isn’t necessarily an improvement. If the tire monitoring system were a $200 option how many buyers would opt to leave it off? Likewise a great many other techinical “snake oils.” But it again comes back to the economy pushing long term financing as an incentive to spend more than we can really afford by spending money we haven’t yet earned. We can get all the car we think we deserve financed for 84 months while trading in a car that is upside down financially. WOW. Life is good???
There was an auto parts store in Arizona that kept the soft drinks it sold in a 30’s era GE refrigerator. My nephews called it the “robot fridge” because of it’s monitor top. It had been running since the owner’s father plugged it in way back then. I don’t know how many times that I offered to buy it on the spot but the offer was always refused. He stocked it with bottled soft drinks because he refused to sell the canned or plastic bottle drinks. I have to admit…sometimes I visited the store just to buy a bottled Pepsi. I’m sure that I wasn’t alone in doing so.
Melott said: “Dear Engineer,
Yes, there may be more flex in a higher profile tire. However, the force is the product of pressure times area…”
Sorry, but that is not true, but it is a commonly held fallacy. I explore that area and cite some studies here:
http://www.barrystiretech.com/airortire.html
“… Second, are you saying that the tire is more permeable to water vapor than to air? That’s possible, but I would need to see evidence. Note, absence of water vapor is one of the claims made for the use of nitrogen. What goes out can go in; if you are right it’s useless to try to put dry gas into a tire…”
I think the idea that gas can enter a pressurized tire is difficult for people to grasp. The idea that oxygen and water vapor permeate through the rubber matrix - oxygen going into a 100% nitrogen filled tire and water vapor going out of a 100% saturated air mixture - is so counter intuitive that most folks don’t believe it happens.
“…Second, are you saying that the tire is more permeable to water vapor than to air? That’s possible, but I would need to see evidence. Note, absence of water vapor is one of the claims made for the use of nitrogen. What goes out can go in; if you are right it’s useless to try to put dry gas into a tire…”
Of course, but you are aware that tires are inflated to something less than what the tank is - otherwise air wouldn’t flow into the tire. The air in the tank is saturated, but when it is pumped into a tire at lesser pressure, it is less than saturated. I did the calculation once and the temperature would have to drop to around zero for some water to condense out - and if that happened, the tire would be put of balance due to the frozen puddle of water. Sorry, but that just isn’t an occurrence that is being reported.
"…PS. The tire busters wouldn’t see liquid unless the tire valve were down and sprayed out the water.
In any other position, as the tire begins to be dismounted, the valve releases the pressure of the compressed air, and the water evaporates, as the dew point inside the tire changes with pressure.
First, the water doesn’t evaporate that fast. In the minute it takes to release the pressure and dismount the tire, you would think SOME tire busters would have reported instances of water puddling in tires - and they don’t.
Look at it the other way: They use a liquid lube that contains water in the mounting process and it is still there well after the tire has been mounted. If the water doesn’t completely evaporate then, it won’t completely evaporate in dismounting.
Some people are missing several important points: "But you’re missing the IMPORTANT point - all tires would be equally affected, it’s not the reason for your tire pressure changes."
UH, in my OP, I said all 4 tires were affected equally. One important point is to take into account what was already said.
Regarding force, area, etc: Your posts seem to imply that all tires should be run-flat tires. I don’t believe they are. The paper you cite is a conference proceedings by a student. In the 5 years since, it has never been published in a journal, has it? At least you don’t cite anything. Anyone in “science” wants to get his stuff published in a journal–if it can be.
Your comments on saturation don’t seem to take into account changes in saturation with temperature. And you argued against something I didn’t say: I do not have a problem with diffusion into or out of a tire. However, it must be very slow, almost negligible, or tires would lose pressure rapidly. Diffusion will be more rapid away from the region of high pressure–because it is denser, not because of the pressure.
Etc, etc.
so…
why the switch to these low profile tires anyway?
On my part, it’s what came with the car. Some models are even lower (50).
Globally, I write it off as a marketing ploy, like tailfins.
@melott - One more time: All tires, regardless of profile and size, would be affected equally by any water condensation-caused reduction in pressure, and they’re not, so that’s not the cause of your particular problem.
Your tire inflation problem has nothing to do with them being 55 series tires.
Water vapor permeating the tire itself? Nonsense. The liner is butyl rubber:
"A synthetic rubber, or elastomer, butyl rubber is impermeable to air and used in many applications requiring an airtight rubber. Polyisobutylene and butyl rubber are used in the manufacture of adhesives, agricultural chemicals, fiber optic compounds, ball bladders, caulks and sealants, cling film, electrical fluids, lubricants (2 cycle engine oil), paper and pulp, personal care products, pigment concentrates, for rubber and polymer modification, for protecting and sealing certain equipment for use in areas where chemical weapons are present, as a gasoline/diesel fuel additive, and even in chewing gum. The first major application of butyl rubber was tire inner tubes. This remains an important segment of its market even today.
Butyl rubber and halogenated rubber are used for the innerliner that holds the air in the tire."
If a water vapor molecule could go through the tire liner, so would the other gases which are much smaller. It would be loosing air at a rapid pace. Leaks occur at the tire to wheel interface, the valve or through porous metal defects in the wheel itself.
If you fill your tires with air from a compressor that does not have a water separator on it, water is going into your tires, albeit in small quantities. That vapor is not escaping through the tire itself nor is the atmospheric water vapor entering your tire through the tire carcass…
@TwinTurbo, that was my point. Although a water molecule is a wee bit smaller than an oxygen or nitrogen molecule, the difference is not that great.
You’re right, I should be more specific. When it comes to permeability, I believe the shape is as important than the size. A water molecule is shaped like a V and an oxygen molecule is larger but shaped like a dumbell. Regardless, I agree not that significant, good point…
My guess is you can likely reduce to a 16" wheel if you are luckly at most a 65 profile. Check out tirerack.com to see what winter wheels fit.
Remember vehicles have significantly better brakes due to larger disks so your wheel has clear that.
Let’s be clear, air does diffuse out of a tire through the rubber.
Well, at least we have figured out what the problem is.
"I write it off as a marketing ploy…"
I hear you. Damned if you do, damned if you don’t. Though many cars need larger rims given recent brake design and requirements and handling goals, there is still a range where “looks” and consumer appeal take over. Without offending anyone, "women dress for other women and cars are designed as much for eye candy and not entirely for performance for boys and their toys. "
So yes, big wheels are like tail fins in many respects. Different then tail fins, I see them not changing in the too distant future. My 4Runner came with 17 inch rims 11 years ago with 265/65/17 tires which at the time, I thought was way too big given what the car was to be used for. Now I have a car…a little “dinky” car that comes with 19inch rims in some models. The tail fins are getting bigger. We’ll have to repave the roads and fill the potholes with a lot more regularity then we do now !
Yes, 15 inch wheels are so very gauche.