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Old 09-16-2020, 11:47 AM   #1
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My Last Tire Question-Hopefully

New Ventana 4002 with tag that weights 37,000 lbs according to scale. The front tires are Michelin 305/70 R22.5 and have 125 lbs of air in them cold. Air temp is 90 degrees here. Before I take off on our first trip back to VA from FL towing a 7500 lb. pickup should I let 5 lbs out of the front tires? The sidewall shows max weight with 120lbs cold. The rear tires are all 85lbs. Thanks
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Old 09-16-2020, 11:59 AM   #2
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No set COLD pressure to what the sticker says for all tires. Dont worry about them heating up during the day.
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Old 09-16-2020, 12:44 PM   #3
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The "cold" pressure is set first thing in the morning before driving the MH, regardless of what the outside temp is.
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Old 09-16-2020, 12:54 PM   #4
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I would drop them to at least 120psi, before you start driving.
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Old 09-16-2020, 01:56 PM   #5
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I guess I will check them early in the AM. The dealer said they were set to 120lb in the front and 80lb in the rear before I took delivery.They were 125 and 85 lbs respectively today at 11:00 am when the air temp outside was high 80's. The coach is under cover. Am I being too anal over this?
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Old 09-16-2020, 02:18 PM   #6
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Yup, if its under cover, your not going anywhere, why check the tire pressure ?
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Old 09-16-2020, 04:08 PM   #7
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What does the placard near the driver's seat state what pressures to use? If the dealer did not get a four position weight or even axle weights, how would he know what the pressures should be? An accepted practice is to inflate to the placard pressures till you get a four corner weight. Then set according to the load inflation chart for the tire. As mentioned, the pressures are checked and set in the cool morning before the tire has rolled a mile.
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Old 09-16-2020, 05:00 PM   #8
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The only way to get the correct tire pressure it to weigh the coach and set the tire pressure to the tire manufactures recommended pressure for the weight . Four corner weighing is most accurate but a CAT scale at the truck stop will give you the axle weights and you can go up 5 to 10 lb. from there as a safety factor . Also set all tires on the same axle to the same pressure .
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Old 09-16-2020, 05:22 PM   #9
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Per the Michelin tire guide, 120 psi is max for a load of 7380 (single tire application). (https://www.michelinrvtires.com/refe...tion-tables/#/)

So the answer is probably. 125 is a lot of air and your ride will suffer depending on how far overinflated you are. Once you get loaded and weighed, go back to the guide and adjust accordingly. For comparison I run 110 in my 43' tag axle Beaver with similar loading. I have different brand tires, but seldom does one brand vary that much from others for similar tire sizes.

I weigh at least once per season at a closed weigh station along the way. Many states leave the scales on when closed. Look for a 0 (zero) on the readout sign. That indicates the scales are still on. Drive front axle on, write down weight, have the better half get out and watch when the front and drive axle are on the pad, write down weight. Drive forward until tag axle and toad are on, write down. Then pull forward so that only toad is on, and write down that number. It's not as accurate as a true 4 corner weighing but it'll get you close.
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Old 09-16-2020, 05:49 PM   #10
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Quote:
Originally Posted by twinboat View Post
Yup, if its under cover, your not going anywhere, why check the tire pressure ?
Helpful. Thanks
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Old 09-16-2020, 05:54 PM   #11
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Originally Posted by bucks2 View Post
Per the Michelin tire guide, 120 psi is max for a load of 7380 (single tire application). (https://www.michelinrvtires.com/refe...tion-tables/#/)

So the answer is probably. 125 is a lot of air and your ride will suffer depending on how far overinflated you are. Once you get loaded and weighed, go back to the guide and adjust accordingly. For comparison I run 110 in my 43' tag axle Beaver with similar loading. I have different brand tires, but seldom does one brand vary that much from others for similar tire sizes.

I weigh at least once per season at a closed weigh station along the way. Many states leave the scales on when closed. Look for a 0 (zero) on the readout sign. That indicates the scales are still on. Drive front axle on, write down weight, have the better half get out and watch when the front and drive axle are on the pad, write down weight. Drive forward until tag axle and toad are on, write down. Then pull forward so that only toad is on, and write down that number. It's not as accurate as a true 4 corner weighing but it'll get you close.
That is good info there for a newbie. Thanks to all!
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Old 09-16-2020, 06:10 PM   #12
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5 psi on a tire that runs 120 psi is only 4% of the total. So I'd tend to agree that you're being anal when you're considering that. Modern big rig tires are very robust in construction and can handle a lot of abuse....which is usually caused by underinflation. Underinflation is not recommended of course.

I'd suggest you run the rears higher then the 85 psi you're mentioning...that seems a bit low. Or was that for the tag axle?

Note that lower pressures give you a better ride and manufacturers tend to like that so often suggest lower pressures, but the flexing of the sidewalls because of that can cause early tire aging or even failure especially if it's too low. The lower pressures can cause early tire wear as well.

I keep my 22.5's pressures pretty high for the weight, up over 100 psi. My RV only weighs 26,000 lbs. Tires give me a long life though at those higher pressures I've been using for years and the ride is very smooth and comfortable. Which I think is probably normal for a modern RV with air bags even at higher tire pressures. JMO.
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Old 09-16-2020, 06:44 PM   #13
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I'm sure getting your weight at a closed highway scale is a workable option, I just don't like not knowing if it is going to be closed or not if I were to choose to drive to one. Personally, I'd rather just go to any CAT Scale and use the CAT Scale Weigh My Truck App to get my weight, with a copy of the weight certificate emailed to me. Yeah, it costs $13, but getting your accurate axle weights is a pretty important task. There is a very good YouTube tutorial video that shows you everything you need to know set up your account and get your RV weighed without having to speak with anybody or get out of your coach. URL is: https://youtu.be/L4RR_BX8-Gs. CAT Scales are everywhere, and typically not in use based on my experience with them over the last few years. For me, for the few bucks it costs, it's well worth it.
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Old 09-17-2020, 03:51 AM   #14
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Quote:
Originally Posted by Crasher View Post
What does the placard near the driver's seat state what pressures to use? If the dealer did not get a four position weight or even axle weights, how would he know what the pressures should be? An accepted practice is to inflate to the placard pressures till you get a four corner weight. Then set according to the load inflation chart for the tire. As mentioned, the pressures are checked and set in the cool morning before the tire has rolled a mile.
The placard states 120lbs. for front and 85lbs for drive and tag.
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