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Old 10-20-2019, 03:14 PM   #1
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Tire pressure..Again!!!!!!

2019 Discovery. Michelin xline energy Z. Im exactly 5,600lbs on both front tire weights and exactly 10,100lbs on both back duallys. Chart says i can run 90psi on all 6 tires. Seems alittle low for me. I got them all at about 107-110 well below the 120psi max for the tires. What does everyone think?
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Old 10-20-2019, 03:25 PM   #2
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Your tire chart was prepared by tire engineers who conducted numerous tests before publishing the info and are probably very accurate.

If you weighed your coach when it was full (black, gray, water, fuel, food, clothes, pots/pans/dishes etc, people any trinkets you take with you etc) then the posted weight and PSI charts are correct.
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Old 10-20-2019, 03:30 PM   #3
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Post #2 is spot on, I run my fronts at 87 and rears at 102,
based on accurate weight from scale, and I added 5 pounds
as a cushion.
Over inflated tires cause poor tire wear and a harsh ride.
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Old 10-20-2019, 03:41 PM   #4
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I run the 90 psi from the chart, plus an extra 5 psi because I don't want to fiddle with tire pressures every day. Or even every week or two.


Why do you think you know more about the appropriate pressure than the tire engineers who built the chart?
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Old 10-20-2019, 06:49 PM   #5
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I set mine by the manufacturers specifications. I have a 2004 Winnebago Sightseer and it calls for 80 psi all around and that is what I use. The tire spec does not know what the tire is being used on, it just tells you what the max pressure for that tire is without regard for the application.
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Old 10-20-2019, 08:31 PM   #6
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If it were my coach and the pressure chart says 90 psi I would run 100 just for a little Cush.
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Old 10-20-2019, 08:53 PM   #7
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I run 10 over what the chart recommended MINIMUM pressure is. Then if I have one that slowly loses air, I have plenty of time to correct before damage is done. Here's what Goodyear has to say on their RV tire website: "When minimum inflation pressure requirements are not met, tire durability and optimum operating conditions are compromised. Tire inflation pressure should always meet at least (my emphasis) the minimum guidelines for vehicle weight." Their charts are to be considered minimum pressure recommendations as tested by their experts. They also warn against overinflation, over the tires psi rating or over the rim psi rating. If you are between those numbers, you're golden!
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Old 10-21-2019, 08:44 AM   #8
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Got it. Is 100psi too much then. Juat as a cushion?
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Old 10-21-2019, 09:18 AM   #9
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Cushion i guess is relative to an extent i guess. I have a similar coach (Expedition). My weights versus the charts put me at the absolute minimum inflation of 85 psi (that is regardless of weights thetires should never see a lower pressure). Like an earlier poster, i run mine at 5 psi over (ie 90 psi), because that seems to mostly compensate for pressure variation due to early morning temperatures. I most definitely see a reduction in handling/ride at higher pressures, so i keep them as close as possible to that load curve rating.

(Aside, early on i ran the tires at the sidewall rating of 120. Handling was TERRIBLE)
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Old 10-21-2019, 10:24 AM   #10
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We have a different coach than you but same principal at work. Our manufacturer charts call for 80psi Cold inflation for our weight. I run 88psi all the way around to compensate for temp variance and a little cushion. I also look at my tire wear pattern every couple of thousand miles or so to check for even wear.

BTW...I set my TPMS low alarm @ 80psi.

If you or anybody is interested, here's a great link to just about any tire question you may have.
http://www.rvtiresafety.net
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Old 10-21-2019, 10:24 AM   #11
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100 is fine but again, make absolutely sure your fully loaded weights correspond to the weight chart.
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Old 10-21-2019, 11:27 AM   #12
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Quote:
Originally Posted by Gary RVRoamer View Post
I
Why do you think you know more about the appropriate pressure than the tire engineers who built the chart?
I know I donít know more than Goodyear so I asked them. Background: The psi from the placard says 92 which has no correlation to published axle weights. Ford manual says for my chassis to run 95 as I have the 7,500lb front axle. I weighed my unit and looked those weights up in the Goodyear tire chart which allows low to mid 80ís.

I emailed Goodyear about the discrepancies and the response they provided strongly suggested I use the placard weight as the minimum, and also stated that they have seen the best overall performance for my chassis is attained at 95 psi.

I fully understand why people can get so confused...
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Old 10-21-2019, 11:40 AM   #13
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The placard is provided by the coach builder per federal law. Since they don't know what your coach really weighs, they have to assume worse case (loaded to axle max) and set psi accordingly.


There is no "discrepancy" - just a different perspective being presented. The Goodyear chart gives the minimum pressure required for the stated load-weight. It's the same chart the coach builder used to determine the psi for the placard. GY won't "recommend" that you use any particular value - it's up to you to choose the weight range that matches your actual loading. The coach builder assumed some weights to be used and looked up the psi in the GY table. You have actual weights, so came out at a different entry in the chart.
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Old 10-21-2019, 11:28 PM   #14
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I find that the different tire makers, the chassis makers and all other charts to be so confusing you can't get a positive answer.

When I was investigating what psi to run my tires at, the advise ranged from 80 to 115.

I weighed front & back tires with what I considered to be the maximum just to be safe.

It was so confusing I took the average and went with it; 110 on front & 100 on rear.

Oddly thing was when I had to have a mobile tire service man come to fix a slow leak in a valve stem, he said he always puts in 100 psi no matter the size or weight of an RV. He said if I wanted to alter it, that was up to me and when I asked for some advice, he would stick to his 100 psi and said that he believed any alteration in tire pressure deteriorated the strength of the tire.

He also said he had been in the business for over 30 years......hmmmmmmm
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