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Old 07-11-2015, 08:24 PM   #15
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Get each position weight and set the tire pressure to the heaviest wheel per axle. The place card is for max load with original tires.

Also, if you don't have a TPMS get one.

Rick Y
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Old 07-12-2015, 10:57 AM   #16
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I have a 2003 Newmar Kountry Star, 40ft. I have always inflated my tire @ 105# front and rear. Never had a tire problem. I believe some people run 105 in the stear and 90 on the duals. But as others have stated check the placard
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Old 07-12-2015, 02:53 PM   #17
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When I was an otr truck driver we set all tires at 90 psi. Our max weight per tandem. "8 tires" was 34,000 lbs". Our max weight on our front was 12,000 lbs. Never had any problems running 90 psi. Tire pressure increases as tires get hot.
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Old 07-14-2015, 07:56 AM   #18
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Please allow my to confuse you a bit more. If you are only able to get axle weights and not individual wheel weights, it's much safer to take 55% of the axle rate to establish the individual wheel weight rather than just dividing by "2". Rarely are coaches loaded evenly so one side is going to be heavier than the other. The 55% rule is a good way to compensate for weight differential between driver and passenger side.
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Old 07-14-2015, 08:51 AM   #19
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Please allow my to confuse you a bit more. If you are only able to get axle weights and not individual wheel weights, it's much safer to take 55% of the axle rate to establish the individual wheel weight rather than just dividing by "2". Rarely are coaches loaded evenly so one side is going to be heavier than the other. The 55% rule is a good way to compensate for weight differential between driver and passenger side.
This is how I got where I am with inflation:
Scale weights ready to travel: Front 6,280 Rear 12,460 (can't get individual weights so I too use the 55% fudge factor)

Front: 6,280X.55=3,454 Chart pressure for singles is 80PSI-3,640, 85PSI-3,740 and 90PSI-3,890 I run front at 85 for margin of safety of about 8-10% on top of the 5% addition for axle weight distribution.

Rear: 12,460X.55=6,853/2=3,427 Chart pressure for duals is 80PSI-3,415, 85PSI-3,515 and 90PSI-3,655 I run rear at 90, again for margin of about 8-10% and the 5%

I feel "comfortable" with this system, and religiously check tires cold on every departure. No worries so far, and ride is WAY better than when I picked it up at 125PSI all around!

Actually using the actual axle weights and chart, the minimum pressure or 80PSI would be adequate all around, i.e. 2X3,640=7,280 which is well over the 6,280 front axle weight and 3,415X4=13,660 is well over my rear axle weight of 12,460. So anything over the minimum pressure on these tires would be safe, I am looking for combination of safe and comfortable ride.
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Old 07-14-2015, 09:51 AM   #20
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Quote:
Originally Posted by koda59 View Post
When I was an otr truck driver we set all tires at 90 psi. Our max weight per tandem. "8 tires" was 34,000 lbs". Our max weight on our front was 12,000 lbs. Never had any problems running 90 psi. Tire pressure increases as tires get hot.
I have to admit Koda, this thread and others related to tire pressure has to be the most confusing discussions we ever dive into.

I too relate to my OTR experience the take all the confusion out of how I deal with load and balance issues.

(95-110) in single wheels, (95) in dulles. Never a wear, heat, or ride issue. I'm running 22.5 LP's so that may not work out very well for those running the 19" wheels.
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Old 07-14-2015, 12:20 PM   #21
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My placard shows the following:
MY GVWR is 20,700
My Front GAWR is 7,500 cold 85 PSI
My Rear GAWR is 13,500 cold 85 PSI

As long as I am at or under my GVWR 20,700 and at or under 7,500 Front GAWR and at or under my rear GAWR 13,500 it is safe just to maintain the cold 85 PSI at all times???

You would never exceed this since those are your max weights and cold psi. The only time your cold psi could go lower is if you are under the GVWR weight and under each GAWR's.

Is this a correct assumption or am I still missing something??
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Old 07-14-2015, 01:06 PM   #22
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I exceed my recommended pressures by ~10psi both front and back. I am still under the maximum pressure the tire can take. The coach rides good and I think with the higher pressures it is more stable and has less rolling resistance. Tire wear is excellent, I have ~45K on my front tires and they look like new.

Last August I had to install new TPMS sensors so I took the time to check all my pressures. I keep my TPMS on all the time and my pressures have remained the same as when I sent them ~11 months ago (when the ambient temp is the same).
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Old 07-15-2015, 07:21 AM   #23
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I exceed my recommended pressures by ~10psi both front and back. I am still under the maximum pressure the tire can take. The coach rides good and I think with the higher pressures it is more stable and has less rolling resistance. Tire wear is excellent, I have ~45K on my front tires and they look like new.

Last August I had to install new TPMS sensors so I took the time to check all my pressures. I keep my TPMS on all the time and my pressures have remained the same as when I sent them ~11 months ago (when the ambient temp is the same).

That's the difference between calculated pressures based on the tire chart's recommendations, and actual usage wear, handling, and ride comfort.

I would continue to do just as you have since you've found that sweet spot for lack of a better word.

It's worked that way successfully for years for those who have found how to adjust their equipment to their needs.

Remember, underinflation is a tire killer, over inflation turns your ride into the Flintstone mobile. Reading your tires and paying attention to what they are telling you, you will never go wrong.
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Old 07-15-2015, 09:42 AM   #24
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Just a reminder to all about keeping your tire pressure consistent over time. One factor to consider is moisture in the air you use. I have added a dryer to my compressor line to ensure I have dry charge air. This will help reduce the effect of the normal expansion of the air do to driving.

Here is a simple rule of thumb to take all the confusion and mystery out of this procedure. Know the weight of each wheel. (Your responsibility to find a scale that will give your this information.) Adjust the pressure according to the heavier wheel per axle to the load/pressure chart for your tire. Always check your tires cold and shaded before each trip or before your roll out on your next leg of a trip. NEVER let air out of a hot, travel expanded, tire.

Happy trails is to do our part to avoid a blowout. I know. I did not succeed. UGH!

Many of them,
Rick Y
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Old 07-15-2015, 10:18 AM   #25
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Ok, after one rear blowout and one left front blowout I use extreme caution in setting my tire pressures.

After these two blowouts I purchased a TPMS system and after 10000 miles or so of traveling I have concerns.

Depending on the morning temps, my tire pressures may increase by 15 psi in each tire while traveling. Depends on conditions.

I have listened to safety lectures that tell me the MFGR takes this into consideration so always set pressures cold. But I still worry about high "road pressures" since I have seen no charts or studies from anyone about Road or Highway pressures.

I wish they would also publish Maximum tire pressures under hot road conditions.
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Old 07-15-2015, 10:38 AM   #26
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Originally Posted by jerichorick View Post
Get each position weight and set the tire pressure to the heaviest wheel per axle. The place card is for max load with original tires.
Also, if you don't have a TPMS get one.
Rick Y
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I agree
However a TPMS is of no use when initially determining the necessary/correct/safest pressures for tires.
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Old 07-15-2015, 09:13 PM   #27
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I had the same confusion as a lot of fellow users here so I went to my local big truck/MH tire shop and asked them.

They said they put the minimum cold PSI in the tires that are on the tire itself.
Reason, they said, is because some trucks/MH don't use the same tires that came with the rig new. The tire PSI chart in the coach, they said, was for the brand, size, weight, etc., tires that came originally with the coach.

So I have been running the mimimum cold PSI in my goodyear 22.5 tires front and back and the rig handles great. Already put over 2,000 miles on that tire pressure and the rig handles well over good and very bad roads.

If you cannot get a weight per axle, then go to your local big tire store, not a walmart or Pep boys, but one store that goes out at 2:00 AM to replace tires on 18 wheelers or MH that brake down on the road. They can get you in the right PSI.
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Old 07-16-2015, 11:14 AM   #28
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Ok, after one rear blowout and one left front blowout I use extreme caution in setting my tire pressures.

After these two blowouts I purchased a TPMS system and after 10000 miles or so of traveling I have concerns.

Depending on the morning temps, my tire pressures may increase by 15 psi in each tire while traveling. Depends on conditions.

I have listened to safety lectures that tell me the MFGR takes this into consideration so always set pressures cold. But I still worry about high "road pressures" since I have seen no charts or studies from anyone about Road or Highway pressures.

I wish they would also publish Maximum tire pressures under hot road conditions.
I am with you on this one. I have also been told that the tires are designed around max hot (rolling) pressure. Because of this very thought I have replaced my front tires with a higher rating tire. I was running at the MAX COLD of 110#. This is what my tires required for the load of my axle. The new tires are rated at 120# and I am still running the 110# per their chart. This little extra head room makes me feel safer. I am using pure logic and emotion on this one. When the rolling pressure goes to 125# I am now only 5# over the cold max.

As far as the TPMS goes, consider this. If you have a tire that is falling, what warning do you now have without this system installed? I, too, had a front blowout. No warning something was going wrong with the tire because I didn't have a TMPS installed.

The TMPS is only a friendly reminder and a theft alarm as such. You can't stop the happening from happening but you can be warned something is not right.

I do not trust my TPMS for anything else but a warning system. When I charge my tires I use a digital gauge and set each tire as it requires. The monitor does not always reflect the correct set values but it is a good bench mark. My tires pressure and temperature will rise differently for each axle and even position. Sun heating a side can make a difference. But, with that said, if all of the readings stay steady I feel comfortable that I have no pending tire problems. If the pressure in one tire changes drastically in a short span of time it is a warning that the coach MUST be gotten off the road ASAP. Slowing down my give a little time before the blowout happens, but not much.

For those who have never had a blowout on a RV, the damage is massive, especially in the front. I had $17,000 worth of damage on my last coach when I lost a front tire. I wish I had the TPMS then. I don't know if it would have predicted this failure or not but, as it is, I will never know.

Happy and safe trails all,

Rick Y
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