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Old 05-06-2015, 10:01 AM   #43
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jadatis, I think you should get out into the real world more often.

The whole point of tyre manufacturers going to so much trouble to come up with set-and-forget recommended tyre pressure for a given wheel loading is that all normal driving conditions are allowed for without allowing the operating conditions to get into an area where safety is compromised.

Just dwelling on water and partial pressures for a second. Once there is no liquid water left (which is just about always unless you actually add a cupful of water to the tyre) the resulting mixture of gases - N2, O2, CO2, H20 and a little bit of other gases, closely obey the gas laws. Trick will be to discount the effects of any non-rigidity of the rubber tyre when checking how closely the gas law is followed.
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Old 05-06-2015, 11:03 AM   #44
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This tire pressure thing is some kind of hobby of mine, I also get into the real world.

But now looking back WDW ( topicstarter) has not reacted again.
He started a pretty open question , to wich in time many parts have been answered.

Thats the advantage of the internet and fora, that you can get things explained.
Then the long story's I make is to let people understand how it works.
Once you understand, you can forget most of it and use the outcome.

About the reserves there are.
I calculated aproximately that if you calculate a pressure for a sertain load , there is a range in the loads in wich tire is save and comfort and gripp acceptable.
Lets put it in an example. Mind the exact values are discussable.
calcuating load for say 1000 kg/lbs or whatever Lets state outcome is 40 psi. Asuming Q speedrated tire for max speed of 160km/99m/h.

Then if the real load is below 850 discomfort for persons and animal begins.
Below 800 screws tremble loose from woodwork of TT and real glasses can break.
If you then drive realy 99m/h you dont have to be affraid,the tire gets to warm so the rubber hardens and damage in next bendings of rubber, so deflections.
This with all the reserves the tire maker build in.
If you drive about 65m/h maximum at real weight 1200 the tire wont get to warm so damage.
At 50m/h even at weight of 1400 the tires wont damage.

Knowing this, you can fill up the tire with a calculated pressure with the formula that is to laws of nature the right one ( and thats not the American used formula in pressure/loadcapacity lists), and then if loads gets a bit more , or pressure drops a little , or load is misyudged a bit to low , or pressure reading is a bit inacurate, etc etc. you still wont damage your tires.
Then you dont have to manically monitor your pressure that much.

But this means that you have to determine the pressure using as accurate data as you can get.
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Old 05-06-2015, 12:36 PM   #45
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In fact I do say that. When going from freesing point of water is zero degrees C/32degrees F to boiling point of water 100degr C/212degr F the humidity water 100% is rising partial pressure of water from 0.00611 bar = 0.09 psi to 1.0134 bar=14.7 psi , so rising of pressure only by the more watergas in tire=14.61 psi,

snip
Well for me tire engineering was and is a Profession not a hobby.

If your contained air temperature is 212F you have more to worry about than a few psi as the rubber structure in all probability is being permanently and irreparably damaged.
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Old 05-07-2015, 04:05 AM   #46
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I agree that when realy 212 degrees inside gas temp, you have more to worry about then that temp.
In Europe there are in Austria , France and Zwitserland some descendings from the mountains with about 10 to 12% for longer distances.

I rode with motorhome a few and max speed was going down 40 to 50 km= about 25 to 32 miles/h . Could not prefent to use the brakes at times, but dont think my inside tire temps gotten above 70 degr C/??F.

But read already about plastic wheelnutcovers that went melting because of the high temp of rimm.
Also braking oil that went cooking with airbubbles so sponchy brakes.

At that lower speed the wheels make lesse cycles a second , and together with the lesse deflection of tire, most likely that less heat is produced by the tire, that critical spots dont get to hot.

A man from a Dutch tire maker told me that tires are "baked"at 170 degr C/about 300degr F, to give the rubber the right amount of sulfur bridges to make it flexible.
At to high temp of rubber , and my estimation is above 130degrC/??F it already begins. more sulfur bridges form and the rubber gets to hard so not flexible anymore, and damages in next bendings so deflections.

So its possible that at 212degr F /100degr C inside tire temp, the rubber does not reach the 130 degr C/??F.
This because that less energy is produced in the rubber, because of the lesser cycles the tire make at lower speed , together with the lesser deflection even when dry air, but beter wet air.

So what you write about structure already sertainly damaged at that temp , can still be happening, but with wet air mayby yust not. Or mayby even with dry air yust not happening.
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Old 05-07-2015, 10:22 AM   #47
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Originally Posted by jadatis View Post
I agree that when realy 212 degrees inside gas temp, you have more to worry about then that temp.
In Europe there are in Austria , France and Zwitserland some descendings from the mountains with about 10 to 12% for longer distances.

I rode with motorhome a few and max speed was going down 40 to 50 km= about 25 to 32 miles/h . Could not prefent to use the brakes at times, but dont think my inside tire temps gotten above 70 degr C/??F.

But read already about plastic wheelnutcovers that went melting because of the high temp of rimm.
Also braking oil that went cooking with airbubbles so sponchy brakes.

At that lower speed the wheels make lesse cycles a second , and together with the lesse deflection of tire, most likely that less heat is produced by the tire, that critical spots dont get to hot.

A man from a Dutch tire maker told me that tires are "baked"at 170 degr C/about 300degr F, to give the rubber the right amount of sulfur bridges to make it flexible.
At to high temp of rubber , and my estimation is above 130degrC/??F it already begins. more sulfur bridges form and the rubber gets to hard so not flexible anymore, and damages in next bendings so deflections.

So its possible that at 212degr F /100degr C inside tire temp, the rubber does not reach the 130 degr C/??F.
This because that less energy is produced in the rubber, because of the lesser cycles the tire make at lower speed , together with the lesser deflection even when dry air, but beter wet air.

So what you write about structure already sertainly damaged at that temp , can still be happening, but with wet air mayby yust not. Or mayby even with dry air yust not happening.
Well this is where we see how dangerous a little knowledge on a complex topic can be.

1. Melting of plastic lug nut covers is probably due to high brake heat. The rim at the hub may well be over 212F but there will be much cooling (due to air circulation) of the steel or aluminum before the edge of the wheel where it contacts the tire.

2. Yes tire curing temperatures can be over 300F BUT this is done to initiate the chemical reaction and the time is controlled to the second as curing for too long will damage the sulfur bonds. In fact the tire is removed from the press before all the curing is complete as the heat is still moving through the tire structure to the thickest parts which complete their cure (chemical bonding) last. Once a tire is cured exposure to much over 200 can result in destruction of the sulfer bonds (called reversion)

3. Soft or spongy brakes from gas bubbles in brake fluid is due to the water moisture boiling and turning to steam in the fluid. If you bother to read the info on a can of brake fluid you should see a statement for the "dry" boiling temperature and "Wet" temperature with the dry temperature being much higher (+100 to +150F). Also you should know that by "wet" it does not mean you can see water in the brake fluid but that the fluid has absorbed a small percentage (3.7%)of moisture.

4. Your recommendation to actually add water to the tire air chamber is not to my knowledge supported by any tire manufacturer or wheel manufacturer or any regulatory agency that deals with tires. I have no idea why you feel, as just a hobbyist feel your concepts are better than all the tire engineers in the world.

IMO If people wish to follow your advice than I would only ask that if they ever have any problems with their tires that they contact you for warranty adjustment.
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Old 05-07-2015, 12:10 PM   #48
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Tire pressure deviation

As usual we have a bunch of engineers making simple things complicated. It is simple when it is hot the pressure goes up...when it is cold it goes down......the dryer the air the less it will vary. The rest is a big waist of time.
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Old 05-07-2015, 07:54 PM   #49
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As usual we have a bunch of engineers making simple things complicated. It is simple when it is hot the pressure goes up...when it is cold it goes down......the dryer the air the less it will vary. The rest is a big waist of time.

Sorry about taking up space here I do try and keep things simple but to often I read incorrect or in-accurate information from non-engineers.

I doubt that anyone would accept . "no, you are wrong" as a sufficient reply.

But if a number of you want that brief answer I am willing to oblige.
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