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Old 07-09-2019, 01:05 AM   #1
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Tire Pressures... what is correct

I sat the other day with a "sundowner" and a couple of friends and we started talking tire pressures. I know what I have read, I have heard from the usual "experts" about inflation.

My situation, I have the monitoring system. I have got the proper weight of my typical load out. Right now in Arizona, it is bloody hot.

So... cold door pressures? Someone chime in who is not shooting from the hip.

Thanks
Rick
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Old 07-09-2019, 02:07 AM   #2
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Within 6 hours pf stopping travel the temperature of tires will decrease to ambient or close enough. Doesn't matter what the ambient pressure is as long as you don't exceed the max pressure on the tire and do not go below the minimum you have figured based on your loading. That means as you go up in altitude you may need to lower the tire pressure to ambient (temperature and pressure altitude). Coming back down the mountain you may need to add some air. As it gets colder, you will have to add air and let a little out in the heat. It is the volume of air in the tire that holds the coach up not the sidewall of the tire. The object is to keep as little air as is safe in the tire to soften the ride and promote even tire wear. If you are traveling, then is is best to check the engine oil and the tire pressure every morning. If you are not moving, then who cares what the oil level is in the engine or the pressure in the tires (unless the tire is going flat).
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Old 07-09-2019, 02:33 AM   #3
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It doesn't matter what the experts on the internet say, I always go with the tire manufacturers inflation tables. You have the weight of your rig, you have the actual tire data, just look it up.
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Old 07-11-2019, 01:18 AM   #4
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Set the cold inflation pressure based on your weights. The tire chart gives the minimum inflation pressure for that weight. Do not reduce pressure in your tires due to heat buildup while driving.
https://www.michelinb2b.com/wps/b2bc...s_Brochure.pdf
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Old 07-11-2019, 03:25 AM   #5
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I check tire pressures early in morning. Same as I do with racecar, before sun hits them. Along with setting pressure I look for variance between tires. On the road I will feel all Rv/trailer tires for temperature. If I feel something out of order, will check with temp gun. A failing tire will usually start getting hotter than others under same load/conditions. My base pressure is set from axle weight charts after going to scale.
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Old 07-14-2019, 07:15 PM   #6
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Originally Posted by Hooligan2 View Post
Set the cold inflation pressure based on your weights. The tire chart gives the minimum inflation pressure for that weight. Do not reduce pressure in your tires due to heat buildup while driving.
https://www.michelinb2b.com/wps/b2bc...s_Brochure.pdf
Exactly. many think the psig on the sidewall is the max whereas it is truly the minimum for the max weight

If your tires are running hot you are probably over loaded or under inflated
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Old 07-14-2019, 07:57 PM   #7
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Thanks to all. I am pretty happy now with the advice. For me... I will adjust pressures first starting with the base and then adjusting to the current conditions, altitude, temp, and road conditions which is also fed from the tire monitors. On my last 180 mile test trip, I got 10.6 mpg by adjusting pressures based on conditions and used a control on the left side which I went with base pressures. Sorry but that is all wet. If you can adjust on the fly you will be better off IMHO. 7 psi and about 8 degrees of temp. Of course I honor the side will info. The tire manufactures tables are great... but they are like the Weather Channel... they sell it.. As Steven Crowder says... "prove me wrong"

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Old 07-15-2019, 06:12 PM   #8
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If you have changed tires the pressures may have changed. You really would need to go over truck scales and get the weight of your rig for front and rear, and then one side.

From that you can look at the tire literature, which will say for xxx lbs in a dual position you need xxx psi, and so forth.

Its best to do this with the rig as loaded as it can (all tanks full, toad attached, etc). If not, you can add some weight on to what the scales says.
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Old 07-15-2019, 10:45 PM   #9
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Originally Posted by PS Cruisign View Post
Thanks to all. I am pretty happy now with the advice. For me... I will adjust pressures first starting with the base and then adjusting to the current conditions, altitude, temp, and road conditions which is also fed from the tire monitors. On my last 180 mile test trip, I got 10.6 mpg by adjusting pressures based on conditions and used a control on the left side which I went with base pressures. Sorry but that is all wet. If you can adjust on the fly you will be better off IMHO. 7 psi and about 8 degrees of temp. Of course I honor the side will info. The tire manufactures tables are great... but they are like the Weather Channel... they sell it.. As Steven Crowder says... "prove me wrong"

Cheers
You're traveling north on I15 thru southern Utah. Hot July day and the driver's side tires are at 10 psi high then the passenger side because of the afternoon sun on that side. Do you reduce the driver's side or increase the passenger side and adjust everything again at 3 AM?

You boondocked for a couple of days at Horseshoe Meadow Equestrian Camp Lone Pine, CA (10,000+ feet). Had a great time. Next stop in 305 miles is Pismo Beach at sea level. When do you adjust pressure for the altitude change and if so what do you adjust the pressure too? And do you adjust again at 3AM once everything cools down?

Spent a couple of day outside of Cleveland Ohio but now you're making a speed run to Charleston SC. A cold front moved in off the Lake overnight and it's 50 degrees. 6 hours later you hit the Shenandoah Valley and it's 70 degrees. What do you adjust the pressure too? 5 more hours down the road and Charleston SC is 90. What should the new pressure be? 3 AM it's below 60. Strange weather day. Do you adjust again?
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Old 07-15-2019, 11:11 PM   #10
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Originally Posted by Sweetbriar View Post
You're traveling north on I15 thru southern Utah. Hot July day and the driver's side tires are at 10 psi high then the passenger side because of the afternoon sun on that side. Do you reduce the driver's side or increase the passenger side and adjust everything again at 3 AM?

You boondocked for a couple of days at Horseshoe Meadow Equestrian Camp Lone Pine, CA (10,000+ feet). Had a great time. Next stop in 305 miles is Pismo Beach at sea level. When do you adjust pressure for the altitude change and if so what do you adjust the pressure too? And do you adjust again at 3AM once everything cools down?

Spent a couple of day outside of Cleveland Ohio but now you're making a speed run to Charleston SC. A cold front moved in off the Lake overnight and it's 50 degrees. 6 hours later you hit the Shenandoah Valley and it's 70 degrees. What do you adjust the pressure too? 5 more hours down the road and Charleston SC is 90. What should the new pressure be? 3 AM it's below 60. Strange weather day. Do you adjust again?
That was an absolutely awesome post. Sure it makes one think. The only thought is I am not up at 3 am. LOL. Let me chew on your thoughts a bit. I think I might need one of those stools so I can sit while adjusting tire pressures!

Cheers
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Old 07-15-2019, 11:36 PM   #11
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My answers based on my tire rules. These are mine, you are welcome to have your own opinion.

#1. No you do not adjust tire pressures when hot. (rule A)

#2. 10,000 feet to sea level would be a 10psi change. If you had set tire pressures at 10k you would want to inflate the tire an extra 10psi before you left. However as long as tire pressures never went below the psi required for the weight on your tires, you are fine. (rule B)

#3. If you do not rest during all that time, and tire pressures were set in 50 degree air, you are fine. If you do rest see rule D of tires.

Rules of tires.
A. Only adjust tire pressures on a cold tire.
B. If a tire has less air than in needs at any point in time, adjust the air to its proper psi. This is not considered adjusting.
C. PSI is a function of load and tire design. Understand your weight and the load carrying vs PSI settings of your tires.
D. Always check and adjust tire pressure at the start of driving.
E. A slightly over pressure tire is much safer than a slightly under pressure tire.
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Old 07-15-2019, 11:40 PM   #12
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Originally Posted by PS Cruisign View Post
That was an absolutely awesome post. Sure it makes one think. The only thought is I am not up at 3 am. LOL. Let me chew on your thoughts a bit. I think I might need one of those stools so I can sit while adjusting tire pressures!

Cheers
I keep a 5 gallon bucket with lid in my RV for a million and 1 things. Tire pressure checking is one of them
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Old 07-15-2019, 11:42 PM   #13
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Im just wondering why in lets say NASCAR, they adjust pressures with every tire change....

Not trying to be overboard here at all. Im just saying... Apr67, you eluded to changing tire pressures. Fine.. cold.. fine.

I just think a plug and play recipe off the side of the tires is maybe not the ultimate answer.

I dont want to have a blow out at 70 but my experiment I just did was a mile per gallon better than just going with cold pressures.

Cheers

Will get some more data when it is not a billion degrees in Arizona.,
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Old 07-16-2019, 12:30 AM   #14
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Also, what is the point of a monitoring system...?

Besides knowing I have a tire deflating...

After 30 minutes, rear tires are at 125 degrees and 119 psi. That was cold pressures of 110 at the start of the day. Hmmmmm


Should I adjust because its 200 miles to go in the same climate?

Still listening...
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Old 07-16-2019, 12:56 AM   #15
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Wow... you guys are really over thinking this thing! Set the pressures when cold and fuggetaboutit. I checked my tire pressures 3 times while on our winter trip to Phoenix, AZ from Wenatchee, WA. We were gone 8 weeks, never adjusted them once. And, no TPMS system either.
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Old 07-16-2019, 01:47 AM   #16
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Originally Posted by PS Cruisign View Post
Also, what is the point of a monitoring system...?

Besides knowing I have a tire deflating...

After 30 minutes, rear tires are at 125 degrees and 119 psi. That was cold pressures of 110 at the start of the day. Hmmmmm


Should I adjust because its 200 miles to go in the same climate?

Still listening...
Do you really not know the purpose of a TPMS? Or are you just trolling?
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Old 07-16-2019, 01:49 AM   #17
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Im just wondering why in lets say NASCAR, they adjust pressures with every tire change....
When I raced we had a starting pressure for tires at a given temp. 1 degree + or - for every 10 degree change in ambient starting pressure. After that we read the tires when we came of the track and attempted to get the temp from the inner, middle and outer part of the tire tread as similar as possible. However we were never worried about a blow out due to low pressure, handling would be useless well before that is an issue.
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Old 07-16-2019, 01:51 AM   #18
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Originally Posted by PS Cruisign View Post
Also, what is the point of a monitoring system...?

Besides knowing I have a tire deflating...

After 30 minutes, rear tires are at 125 degrees and 119 psi. That was cold pressures of 110 at the start of the day. Hmmmmm


Should I adjust because its 200 miles to go in the same climate?

Still listening...
Nope, you should not. Tire companies tell you what the COLD pressure required to hold the load is, they do not tell you the hot. As long as you are below the maximum pressure for the tire (which isn't the sidewall max) and temperature, you are fine.
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Old 07-16-2019, 05:00 AM   #19
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The tire pressure gospel according to Goodyear.

https://www.goodyearrvtires.com/pdfs...care-guide.pdf

Page 5 is where the most important data starts.
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Old 07-16-2019, 11:49 AM   #20
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Originally Posted by PS Cruisign View Post
That was an absolutely awesome post. Sure it makes one think. The only thought is I am not up at 3 am. LOL. Let me chew on your thoughts a bit. I think I might need one of those stools so I can sit while adjusting tire pressures!

Cheers
The thing is you're constantly chasing a number attempting to achieve multiple conflicting goals. You can set for a comfortable ride but your compromise mileage or you can reduce for fear over over inflating but when temperature cools you'll be under inflated or,,,,. The problem is changing pressure on a hot tire will cause other problems later, specifically where the pressure will end up once the tire and air cools down, at 3AM.

Use the TPMS to monitor (the M in the name). Easy to do a quite check in the morning and ensure the numbers all look good, above minimum. On the road you're looking for consistency. Pressures and temps are rising about the same percentage. There will be some variation and you just need to get a feel for your configuration and how everything settles in once warmed up. Pressure are going to go up due to heat but as long as you started out at the correct pressure you should be OK. There are many years of engineering, mistakes, improvements and research getting you down the road. You can either trust it or head on out on your own. Just keep in mind if you make a mistake the results can be ugly.

And of my scenarios -
1. Hot Side - leave them alone. They will balance back out once cool.
2. Altitude Change - Pressures will be above minimum when you arrive at Pismo due to heat but you probably get a 3AM low pressure alarm IF you reduced pressure while up on the mountain. It's about a 10 PSI change.
3. Air Temp Changes - Much the same as the altitude change. Above minimum while on the move but below once cold.

Tires are pretty amazing considering what we put them thru and the service they provide even after the abuse. But there are limits and a big preventable tire killer is low pressure for the load regardless of is the tire is rolling or sitting still. As long as the pressure is above the limit for the load at any given moment you'll be OK. Be it 3AM sound asleep in the campsite or high noon at 60 MPH crossing the bottom of Death Valley in July.
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