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Old 12-12-2013, 07:54 AM   #15
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Thanks Sky_Boss for your usage explanation. I don't have a tire monitor system yet but it is in the financial plans, also the duel psi balancing system.

When I read all of the data about tire failure it is always blamed upon low pressure that causes heat. All of the explanations and pictures I have seen of over inflated tires show center tread excessive wear and talk of harsh ride.

With your usage of your monitors I see you reducing the psi and, as you stated, keeping the ride comfortable. I don't see a problem with heat failure in this scenario.

What do you do when going from a high altitude and warm temps to a lower one and cooler temps? Do you add air as needed to match the upper alarm limit? (My head is starting to hurt!)
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Old 12-12-2013, 08:53 AM   #16
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Quote:
Originally Posted by jerichorick View Post
...

What do you do when going from a high altitude and warm temps to a lower one and cooler temps? Do you add air as needed to match the upper alarm limit? (My head is starting to hurt!)
To be honest...haven't had that yet. So my thoughtful, careful answer is that the most likely answer is a qualified yes under the assumption I was working with "hot" tires. As long as I am at my upper pressure limits and temps are all looking the same, that would appear to ME to be the safest hedge.

Keep in mind that the assumption of higher temps at higher altitudes is probably not realistic. You would probably transition from high altitude and cooler temps to lower altitudes with warmer temps most of the time. The rise in temps might help offset the the affects of "thicker" air as you go lower.

I don't use the Crossfire system http://http://www.dualdynamics.com/crossfires/ but I haven't ruled it out in the future either. I'm normally for any safety system but I just don't like the looks of it. Never the less, I think the concept is excellent. the biggest trick is to have a stable load on the duals because you have to order the system to a specific PSI rating. So...I think for us MH users we would have to have either a pretty good guess of what weights the drive wheels will run at or enough history to know what we need.
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Old 12-12-2013, 08:55 AM   #17
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Originally Posted by jadatis View Post
...
Will include a picture of my pressurecalcationwithtemp spreadsheet , that i used in another topic with that 24 degrees, to show what it can chanche.

Do you have a link to that spreadsheet? If not I would be pleased if you would email it to me. I'm just anal enough to appreciate its workings.
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Old 12-12-2013, 10:44 AM   #18
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At 30 degree drop in temperature and 3000 feet drop in elevation there would be a 5.4 psi drop in tire pressure using 100 psi as the example:

100 psi - 2% = 98 psi
(for each 10 degrees of temperature change there will be a 2% increase/decrease
pressure
98 psi minus 2% = 96.04 psi
96.04 psi minus 2% = 94.12

For every 1000 feet of elevation there will be a 0.48 increase/decrease in pressure. As elevation decreases, pressure increases.

At sea level the 94.12 psi would have gain 1.44 psi and the tire pressure would be 95.56 psi

The only time that you would have a problem is if your have set your pressure in your tires for the exact load rating. That is, if your front tires are loaded (Michelin 275/80R22.5 LRG) at 5510 pounds the exact pressure to support that load is 95 psi.

Let's apply the "Fudge Factor." Set the air pressure of the same tire and load to 100 psi and it supports 5780 lbs. You have a fudge factor of 355 pounds in case you or the dw gains some weight on your trip, or you pick up a lot of souvenirs and put them in the front of the coach.

You also have a "Fudge Factor" of 5 psi so a drop from 100 psi to 95.56 psi is still within the minimum pressure to support 5155 lbs.

Check the tire before each trip (day), yes. Add or remove air to meet a minimum requirment - not necessary unless the minimum and maximum are exceeded.

The inverse is true. At 100 psi and increase in temp/altitude
100 psi plus 2% = 102 psi
102 psi plus 2% = 104.04 psi
104.04 psi plus 2% = 106.12 psi
Minus the elevation change of 1.44 decrease = 104.68 psi
A 4.68 psi increase in pressure and still within the chart limits for the tire.

Some references:

Michelin Tire Manual

Good Year Tire Manual

Make sure that the tire manual used is for the tires being checked. Do not use a different manufacturer's tire manual.

There is a user on this forum, Tireman9 (Roger Marble) that has a vest experience in the tire world. Give his TIRE BLOG a reading.
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Old 12-12-2013, 12:59 PM   #19
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Quote:
Originally Posted by Sky_Boss View Post
Do you have a link to that spreadsheet? If not I would be pleased if you would email it to me. I'm just anal enough to appreciate its workings.
Yes I have a link to a map on my public map of skydrive that belongs to my hotmail.com adress with the same username as in this forum ( so combine yourselfes , spamm robots cant this way).

https://skydrive.live.com/?cid=a526e...E092E6DC%21793

First download a spreadsheet and then open it in Excell or Open Office CALC on your computer. Download by RIGHTCLICKING and then choose DOWNLOAD . Other means go wrong like leftclicking or open in web-app . Open in Excell when right clicked also dont do, to complicated and asks to log in with your hotmail-adress and password.

From this motorhome calculator map you can navigate my complete public map like in a forum , 3/4 th of it is about tire-pressure.
In that map take the "pressurecalculationwithtemp"spreadsheet, but the newest motorhome calculator is also handy.

But with my spreadsheet you can also chanche the ambient pressure , yust have to calculate it yourselfes from the hight with the system Waine M gave.
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Old 12-12-2013, 03:58 PM   #20
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Talking

Dang! And I just fill them up till the bulge goes away - kidding!
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Old 12-13-2013, 07:41 AM   #21
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With this information I am wondering just how many of us are tooling down the road ignorant to the fact that we are sitting on time bombs because our tires are far out of psi spec. I know I need to be more diligent about daily checking. I recently bought a small compressor that seems to deliver better air than my coach air chuck. On this coach Freightliner in Gaffney, SC (the factory) recommends 110 psi all around after weighing the rig. I also have to find a way to convince DW that the 'stuff' she keeps bring on board is truly overloading the rig. She just moved her favorite plates from the house to the coach: ceramic and very heavy!
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Old 12-16-2013, 03:31 AM   #22
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Quote:
Originally Posted by Wayne M View Post
At 30 degree in temperature and 3000 feet drop in elevation there would be a 5.4 psi drop in tire pressure using 100 psi as the example:

100 psi - 2% = 98 psi
(for each 10 degrees of temperature change there will be a 2% increase/decrease
pressure
98 psi minus 2% = 96.04 psi
96.04 psi minus 2% = 94.12

For every 1000 feet of elevation there will be a 0.48 increase/decrease in pressure. As elevation decreases, pressure increases.

At sea level the 94.12 psi would have gain 1.44 psi and the tire pressure would be 95.56 psi


You also have a "Fudge Factor" of 5 psi so a drop from 100 psi to 95.56 psi is still within the minimum pressure to support 5155 lbs.

Check the tire before each trip (day), yes. Add or remove air to meet a minimum requirment - not necessary unless the minimum and maximum are exceeded.

The inverse is true. At 100 psi and increase in temp/altitude
100 psi plus 2% = 102 psi
102 psi plus 2% = 104.04 psi
104.04 psi plus 2% = 106.12 psi
Minus the elevation change of 1.44 decrease = 104.68 psi
A 4.68 psi increase in pressure and still within the chart limits for the tire.

Make sure that the tire manual used is for the tires being checked. Do not use a different manufacturer's tire manual.

.
Shotened the quote a little .
But what you write about pressure drop when going higher is only for outside the tire. Also at sea level the overpressure you measure of a tire is lower then at 3000 feet. The amount of air in the tire stays the same , but the pressure outside the tire goes down at 3000 ft, so the overpressure you measure is higher at 3000 ft then at sea level.
For that reason the pressure difference measured is marginal, and can go to 14,5 psi/1bar higher when in space.

But its better to use my made pressure loadcapacity lists, for wich you only need to read the maximum load and AT wich pressure from the sidewall.
The lists used in America are made with a formula that leads to to much deflection in the lower loads/pressure combinations.

In my lists where you can navigate to from my former given link, I also give higher pressure then the pressure needed for the maximum load, as given on sidewall or belonging to the Loadkind ( C- to H-load) . This is not the maximum pressure of a tire, as is only given on P-tires/standard load and XL/reinforced/Extraload tires .
Even stiffer TRA system allowes 10 psi above maxloadpressure for LT tires and 20 psi for truck tires ( when may you call it a truck-tire?).

Goal must be that in the worst case scenario the tire gets a deflection that it is allowed for the conditions. Then if the deflection gets less because of higher pressure at higher temperature or because of higher grounds ( that 3000ft fi) it still is save and up to a point still comfortable and good grip.
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Old 12-16-2013, 08:59 PM   #23
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Whatever course you take, keep in mind the RMA-Rubber Manufacturers Association says over 90% of all tire failures are the result of under-inflation/overloading. Those tire pressure/load charts display the minimum acceptable tire pressure, not necessarily the optimum.
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Old 12-20-2013, 08:44 PM   #24
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I think the posters here are taking this air pressure thing too seriously...like the man says, fill your tires when it's cold (even -14) to the COLD pressure recommendation and when you pull in for the night in warmer weather, THEN set your tires for the actual driving temperature. 5 or even 10 lbs is not going to make your tires fail...!
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Old 12-26-2013, 08:33 AM   #25
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Whew!...

This seems to be getting complicated, let me assume something for a moment, the real danger in under inflated tires is heat build up do to excess tire movement, flex in sidewall and heat build up in tread. Assuming again, I properly inflate my (cold) tires at 70 degree ambient temps in the afternoon and leave the next morning for a trip with air temp at 25 degrees (happens here all the time!!), if I check all tires that morning and find that they are at same psi, meaning none are losing air, then can't I assume I can safely proceed, and that when the ambient air temp later in day is going to be 70 degrees again I will be at proper pressure. Point being that when I pull out at 5:30 AM when temp is 25 degrees, the tires are not very likely to suffer heat damage with 2-3 lower psi than at 75 degrees, because the air temp is 25 degrees. My point is the cooler temps to some degree have to compensate for the lower pressure by keeping the tire cooler. Otherwise I would be putting in or removing air every departure unless the temp is exactly the same every time.

As mentioned below, "fudge factors" can easily compensate for these differences anyway. i.e. I have my tires inflated for actual weights plus about 200 lbs.
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Old 12-26-2013, 08:36 AM   #26
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I think you are right

Quote:
Originally Posted by Ramzfan View Post
I think the posters here are taking this air pressure thing too seriously...like the man says, fill your tires when it's cold (even -14) to the COLD pressure recommendation and when you pull in for the night in warmer weather, THEN set your tires for the actual driving temperature. 5 or even 10 lbs is not going to make your tires fail...!
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Old 12-26-2013, 10:07 AM   #27
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Quote:
Originally Posted by Ramzfan View Post
I think the posters here are taking this air pressure thing too seriously...like the man says, fill your tires when it's cold (even -14) to the COLD pressure recommendation and when you pull in for the night in warmer weather, THEN set your tires for the actual driving temperature. 5 or even 10 lbs is not going to make your tires fail...!
I agree with Ramzfan. I really don't think that over the road truckers are constantly changing the tire pressures going from north to south. Most truckers I've seen just hit the tires with a club to insure they're not flat and then drive..non-stop! I'm not saying neglect your tires. I'm only saying check them when they're cold, adjust if necessary, and drive (as long as they are less than 7 years old). Worry about about something worth while, like finding a good BBQ restaurant along the way...Just saying..

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