Partly Loaded for Tire Pressure Purposes
03-22-2018, 01:35 PM
#31
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I provided an answer (possibly even a correct one) to the question of why there is only one Porsche-recommended pressure for snow tires: given a specific single tire size the snow tires seem to have a lower load index.
I don’t know what you are trying to point out with your post in relation to the question. That there’s a big safety margin in the specs?
I don’t know what you are trying to point out with your post in relation to the question. That there’s a big safety margin in the specs?
03-22-2018, 01:49 PM
#32
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Here’s an article that begins to describe how load index is related to maximum speed (at the bottom.)
TL;DR
https://www.tirerack.com/winter/tech...jsp?techid=72&
TL;DR
Originally Posted by The Article Below
...rated load capacity of the tire is reduced in 5% increments for every additional 10 km/h...
03-22-2018, 01:53 PM
#33
Burning Brakes
I provided an answer (possibly even a correct one) to the question of why there is only one Porsche-recommended pressure for snow tires: given a specific single tire size the snow tires seem to have a lower load index.
I don’t know what you are trying to point out with your post in relation to the question. That there’s a big safety margin in the specs?
31/36 psi F/R partly loaded and
31/42 psi F/R fully loaded.
I guess the second setting is for when you somehow have shoehorned two 150-pounders into the rear seats.
03-22-2018, 02:07 PM
#34
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Yeah. I see now that I glossed-over full/part-load pressures when I wrote only ‘one pressure.’ In the context of the question ‘one’ meant ‘standard’ pressures.
If Porsche had snow comfort pressures then we’d have 8 total: 4 for summer and 4 for winter :P
Two adults. Frunk and rear seats/shelf packed to the gills with the heaviest clothing and vacation accoutrements you can find with the intention of not unloading before hitting the Silver State Classic in the 180mph class. All set.
If Porsche had snow comfort pressures then we’d have 8 total: 4 for summer and 4 for winter :P
I guess the second setting is for when you somehow have shoehorned two 150-pounders into the rear seats.
03-22-2018, 04:46 PM
#35
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If anyone (besides me) wants to geek-out on this:
http://dawsengineering.com/linked_fi...ducedloads.pdf
http://www.barrystiretech.com/index.html
https://static1.1.sqspcdn.com/static...+inflation.pdf
https://toyo-arhxo0vh6d1oh9i0c.stack...s_20170203.pdf
http://dawsengineering.com/linked_fi...ducedloads.pdf
http://www.barrystiretech.com/index.html
https://static1.1.sqspcdn.com/static...+inflation.pdf
https://toyo-arhxo0vh6d1oh9i0c.stack...s_20170203.pdf
03-22-2018, 07:26 PM
#36
Burning Brakes
Not so much the frunk, as the front pressure doesn't change between part load and full load.
03-23-2018, 11:42 AM
#37
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I guess the a$$-heavy 911s front tires are less load-constrained than the rear. So, front pressure is lawyer-dictated to ensure understeer.
Regardless, I think we’ve beaten the OP’s horse into glue here.
06-23-2019, 06:53 PM
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In motorsports, a lot of teams use nitrogen, because it's safer, ie- non flammable, and they don't want to have mutiple systems running gear, torque guns, and etc, so they just run nitrogen.
Nitrogen fill also offers benfits to cars that see long periods of winter hibernation (4-5 months or more). Again, the air tends to be dryer.
06-23-2019, 07:02 PM
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What LexVan said. Moisture is the enemy. A nitrogen tank, depending upon quality, will have almost no water in it. Compressed air with the 'atmosphere' (Nitrogen, Oxygen, Carbon Dioxide) as the source will have tons of water in it unless there's a really good dryer on the output side.
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Class5Kayaker (06-24-2019)
06-24-2019, 06:17 AM
#41
The water in normal air can only give marginal cold pressure difference. And when hot inside tire ( can be even 100degr C/212 degr F. incidentally) it gives an extra pressure rising that gives lesser deflection so lesser heat-production of the rubber.
So then its even an advantage. At that 100 degr C. the partial pressure of water-gas, can maximally be 1013mb/14.7 psi, but then its an advantage because that gives lesser deflection, ( so also even worse grip).
Liquid water has about 1/1000 of volume then water as gas, so can be neglected for the pressure, and as put in tire its pretty clean , so wont give rust to metal rimms or oxidation to light-metal rimms.
When a tire-fitter gets the old tire of the rimm, seldomly rust or oxidation is seen on the part of rimm inside the tire.
Water also cools down the inside air a bit better then other gasses.
The pressure loss in time is also often exaggerated to even 5 times as much for oxygen then Nitrogen.
In real it is 3 times as fast, but because 20% oxygen and 80% nitrogen still more nitrogen leave the tire by diffusion then oxygen.
And when oxygen leaves the tire the partial pressure of oxygen sooner comes closer to that of the outside air, so diffusion gets less.
up to a point where in and outside oxygen partial pressure is the same, then the same amount of oxygen is going in as out, and no oxygen loss anymore.
So in long time the oxygen percentage will work its way to a fixed percentage depending on the measured over-pressure in tire.
1.013bar/14.7 psi > 10%, 3 bar/44psi > 5% , 4 bar/59psi > 4%.
If you manage to fill the tire with 100% nitrogen, the loss of nitrogen in time is a bit compensated because the partial pressure of oxygen is more outside tire then inside, so to the law of Dalton, the oxygen diffuses into the tire , against the high total over-pressure .
So pressure loss in time is also a selling argument of nitrogen filling that is exaggerated, and I would not spend the extra money on.
Then nowadays , the Nitrogen is not anymore filled with a bottle of 200 bar/ 2900 psi, in with practically no water% , but with a pistol that filters the oxygen out, so probably still water, and no 100% Nitrogen, probbably 95%, wich even brings back the effect of nitrogen filling,
And even filled on the empty tire, with 14.7 psi pressure outside air filled . This goes for N2 from a bottle and with the pistol filled.
So then its even an advantage. At that 100 degr C. the partial pressure of water-gas, can maximally be 1013mb/14.7 psi, but then its an advantage because that gives lesser deflection, ( so also even worse grip).
Liquid water has about 1/1000 of volume then water as gas, so can be neglected for the pressure, and as put in tire its pretty clean , so wont give rust to metal rimms or oxidation to light-metal rimms.
When a tire-fitter gets the old tire of the rimm, seldomly rust or oxidation is seen on the part of rimm inside the tire.
Water also cools down the inside air a bit better then other gasses.
The pressure loss in time is also often exaggerated to even 5 times as much for oxygen then Nitrogen.
In real it is 3 times as fast, but because 20% oxygen and 80% nitrogen still more nitrogen leave the tire by diffusion then oxygen.
And when oxygen leaves the tire the partial pressure of oxygen sooner comes closer to that of the outside air, so diffusion gets less.
up to a point where in and outside oxygen partial pressure is the same, then the same amount of oxygen is going in as out, and no oxygen loss anymore.
So in long time the oxygen percentage will work its way to a fixed percentage depending on the measured over-pressure in tire.
1.013bar/14.7 psi > 10%, 3 bar/44psi > 5% , 4 bar/59psi > 4%.
If you manage to fill the tire with 100% nitrogen, the loss of nitrogen in time is a bit compensated because the partial pressure of oxygen is more outside tire then inside, so to the law of Dalton, the oxygen diffuses into the tire , against the high total over-pressure .
So pressure loss in time is also a selling argument of nitrogen filling that is exaggerated, and I would not spend the extra money on.
Then nowadays , the Nitrogen is not anymore filled with a bottle of 200 bar/ 2900 psi, in with practically no water% , but with a pistol that filters the oxygen out, so probably still water, and no 100% Nitrogen, probbably 95%, wich even brings back the effect of nitrogen filling,
And even filled on the empty tire, with 14.7 psi pressure outside air filled . This goes for N2 from a bottle and with the pistol filled.
Last edited by jadatis; 06-24-2019 at 06:33 AM.