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Old 04-30-2017, 09:26 PM   #11
talk2cpu
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5er tires at 80# when cold always
Is that at 40 F ambient (morning with no sun) or 75 F ambient also morning with no sun? It is a 4 to 5 pound difference. Also a 40 morning and up to 90 in the afternoon, could it cause an over inflated condition.

I am not going to fire up the generator and compressor every time a weather front moves through. If the tires were good yesterday and have not lost any air, they should be good today. Next week, a different story, I will adjust if needed.
Tom
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Old 05-01-2017, 04:19 AM   #12
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Originally Posted by talk2cpu View Post
Is that at 40 F ambient (morning with no sun) or 75 F ambient also morning with no sun? It is a 4 to 5 pound difference. Also a 40 morning and up to 90 in the afternoon, could it cause an over inflated condition.

I am not going to fire up the generator and compressor every time a weather front moves through. If the tires were good yesterday and have not lost any air, they should be good today. Next week, a different story, I will adjust if needed.
Tom
Also depends on the altitude. Wherever you're at, first thing before starting out, tires as cold as they're likely to be that day, 80 psi.

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Old 05-01-2017, 04:45 AM   #13
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Originally Posted by talk2cpu View Post
Is that at 40 F ambient (morning with no sun) or 75 F ambient also morning with no sun? It is a 4 to 5 pound difference. Also a 40 morning and up to 90 in the afternoon, could it cause an over inflated condition.

I am not going to fire up the generator and compressor every time a weather front moves through. If the tires were good yesterday and have not lost any air, they should be good today. Next week, a different story, I will adjust if needed.
Tom
When there big temperature swings, like the example you stated, (a 40 degree morning) and then it gets up to say 90 degrees in the afternoon, yes, that could cause an overinflation situation.
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Old 05-01-2017, 08:22 AM   #14
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When there big temperature swings, like the example you stated, (a 40 degree morning) and then it gets up to say 90 degrees in the afternoon, yes, that could cause an overinflation situation.
The new 2018 generic Keystone Owner's Manual recommends attending to your tire pressures anytime you suspect they may need adjustment and to do it as soon as you can get a valid cold reading.
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Old 05-01-2017, 08:41 AM   #15
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So we need to retrofit some HUMVEE autoinflation systems to our campers....
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Old 05-01-2017, 10:17 AM   #16
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Good one, Jeepshots. Maybe a continuous monitoring system, but what about at night, when you're sleeping??? Wouldn't that run down the battery and wouldn't the compressor wake up the baby? We've got enough "phantom drains" on the battery system already, adding more without having "solar and lunar charging" (that wouldn't be efficient use of that "night-time light).... OK, I know, and it was said "tongue in cheek".....

Now, Not directed at Jeepshots, but intended as a general comment, the reality is that even a "first semester engineering student" is taught that environmental conditions are always "engineered into the system". What that means is that the ambient temperature (cold inflation pressure) is expected to rise with use. That environmental rise, caused by tread friction, heat, loading, sidewall motion and a host of other "not usually considered" conditions is factored into the "operating pressure rise" of the tire. Every tire manufacturer considers this when designing a new tire for the market and it's a part of the testing process during pre-production tests and is followed closely after the tire is released to the public.

Every tire manufacturer has considered and accommodated the ambient/operational/environmental pressure increase in the design concept of the tires that are on any RV. Most tire manufacturers, somewhere in their literature have instructions that follow these guidelines:

1. Check tire pressure and adjust the "cold inflation" (which means before the trailer is towed, not before the sun hits the tire)
2. Do not bleed air from a tire that has been towed to "lower it to the recommended max pressure".
3. Do not adjust for altitude or temperature in a hot tire. A tire is considered "cold" after it has cooled for approximately 3 or 4 hours.
4. Expect about a 1 PSI increase for every additional 10 degrees F and about a 1 PSI decrease for every 10 degrees that the temperature falls. Understand that the latter, temperature decreases are more dangerous than the increases because underinflation leads to more potential for tire damage than slight overinflation (which is already factored into the tire design).
5. Monitoring tire pressure does not mean adjusting tire pressure as it will be constantly changing based on the above factors, all of which are a part of the design elements of the tire and are fully compensated for in the tire construction.

My thoughts, for what they're worth, tire pressure is something to consider and to stay "ahead of" but it's not "rocket science" and it doesn't require an extra-ordinary amount of time and thought during use. Just adjust pressure before the tires are "sun soaked" and monitor them frequently during use. No need to "overthink it and make it impossible to do".....
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Old 05-01-2017, 10:45 AM   #17
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OK, here's a thought I've had a time or two. The way my trailer sits in my yard one side gets sun most of the day and the other side never gets sun. The sun side tires are usually a few to several psi higher than the non-sun side. I have to go out around 6AM to check them if I want to avoid the sun heating the tires, usually not on my schedule. Otherwise I have to wait for the sun to go behind the trees 600 yards away and then wait for the tires to cool, which could be after dark. So if I air both sides to max sidewall psi when one side is hotter/higher than the other, pull out of my driveway, go down the road a bit, and the sun is in my face, behind me or it's shady, the once sun side tires are now several psi higher than the non-sun side tires because neither are "sun side" now. So now the once sun side tires have cooled off since I pulled out of the driveway and are now several psi "underinflated". Do I stop and put a few more psi in them???
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Old 05-01-2017, 10:58 AM   #18
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Or you might just put a piece of cardboard in front of the tires on the sunny side while having your "adult beverage" before bedtime and check the pressure after your second cup of coffee the next morning???
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Old 05-01-2017, 11:06 AM   #19
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Or just run these...
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Old 05-01-2017, 11:18 AM   #20
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I probably tend to "over-think" tire pressure sometimes, partially because I'm somewhat anal about those kind of things, and partially because I spend a good deal of time getting precisely the correct air pressure settings for my track/racing motorcycle. The rear tire that I use is incredibly sensitive to the proper air pressure and if overinflated even 1 - 1.5 psi, it will start hot tearing and I will destroy a $200 tire in a matter of a day. I own a calibrated air pressure gauge that is guaranteed to be accurate to one half of one percent all the way to 60 psi. I also own a probe type pyrometer and take hot tire temperatures as soon as I exit the track, along with pressure readings

I just need to let that thought process go when it comes to trailer tires where a pound or two difference really isn't a big deal in the scheme of things.
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