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Topic: Tire Inflation (Read 2146 times) previous topic - next topic

Re: Tire Inflation

Reply #20 –
Here's what Michelin says is the minimum pressure to inflate their tires to:

Load & Inflation Tables | Michelin Truck

Find your installed size/model tire in the chart and inflate the tires to the pressure in the table corresponding to your axle weights (divide the axle by 2 and each tire to this pressure depending on single or dual loading)...cold, full fuel, full water, empty gray/black tanks.  Tire pressures will increase with temperature changes, especially after driving, so don't EVER let air out of a warm tire as the tire (and wheel) is engineered to take much more pressure than the cold ratings.  It's that simple.  If the ride is rough, deal with it...the ride will never be car-like, but it's close.

Also, a TPMS is mandatory for my peace of mind...this includes the towed and tag.  Woody out.

Re: Tire Inflation

Reply #21 –
Dan, I would listen to wolf10.  He has more knowledge and experience than any of us on this forum.  He is extremely cautious before making a recommendation.  We are not trying to criticize you or the advice you've been given.  We just want you to question the advice you've been given, do more research, and make your own researched and educated choice. No problem sending me a personal message if you would rather discuss it that way.

As an example, to compare mine (97 U295 40') to yours (96 U295 36'), I load my rv heavy, near the axle limits rated by the FT plate at 10,500 front 19,500 rear.  So off the Toyo chart, I use 105 in the front, 90 in the rear.  This gives me a tire capacity of 10,740 in the front, 19,540 for the rear duals.  Using your Uniroyle chart for your RS20 275x80x22.5, 90 lbs all the way around would give you 10,740 front capacity and 19,540 rear capacity respectively.  Do you not see the error your tire store made, as wolf10 pointed out? You are 20 lbs overinflated all the way around from the maximum carrying capacity of your rv!  I disagree with your tire dealer and agree with the Uniroyal tire inflation book.

Having been in the industry when rv mfgs, leading tire dealers, and rv dealers went to recommending the max inflation pressure printed on the sidewall, sometimes ignoring axle capacity, rv loaded weights, etc., they made steering sometimes horrible, and the ride sometimes horrible. I questioned the tire dealers, the service department, the supplier of tires to CC and Monaco, and the rv manufacturers Country Coach and Monaco.  All responces came back to avoid lawsuits, after advice from their legal departments.

Note, this change in recommendations did not come from the engineering or service departments,  but from the legal department.

In other words, I was told too often owners raise the weight they are carrying, they do not check the pressure before travel, etc.  These three Industries wanted to avoid being involved in a suit involving underinflated tires.

After that I had a truck tire gauge in my desk as well as the correct tire manufacturers inflation guide.  I had the good fortune to have a a free state run truck scale a few miles away.

To solve customer issues before, and after the sale, I'd visit these scales with the appropriate mfg tire inflation guide.  Many an owner said they could not believe the difference.  Telling them would not do it, it would take an hour and a half or two, the benefits were extreme.

If your trying to be cautious, and on the safe side, weigh each side of each axle when you are at full load, and then add 5 lbs of air for that little extra weight you might add.  I carry two tire gauges that read the same, and a blown up copy of my Toyo inflation pressures. 

As I said earlier; "I've attached the Uniroyal commercial tire inflation book. For 275-80-22.5, 110 lbs., that takes you to 22,750 on your rear axle, (check your plate, it is probably only 19,500) and 12,350 on the front axle, (which is probably only rated at 10,500). So it appears you are overinflated by 20 lbs. The pressure you've been recomended is too high, so I would at least weigh sometime when fully loaded and check with Uniroyal book for your tire size or at least do not overinflate beyond your axle capacity."

Both the Uniroyal and Michelin Guides recommend the same inflation pressure, 90 lbs, for your tire size,  to get the above tire load capacities.

Re: Tire Inflation

Reply #22 –
As jack just posted I did the exact same thing hundreds of times. Don't believe us.  Do it your way.  Unsafe as the tire "crowns"

Research my water test I posted here a while ago to demostrate to lack of edge loading overinflated tires cause.

Mine are 97 and 87 on "h" rated 7610 max load Michelin's. 

No other tire is past 7160 so their pressure will be higher.

Otherwise I would be almost 10 pounds higher per axle and lose the great ride on our bad roads.

Re: Tire Inflation

Reply #23 –
Yes Wolfe & Bob & Jack. . I appreciate the info for sure.  The Michelin tire table doesn't really help with Uniroyal Rs20 tires. Uniroyal states 120 is max with a full load. I weighed my coach without water or groceries, etc etc. True empty except cargo area full. 27,500 total. I did not weigh axles separate yet. I'll play with 100 to 110 when loaded and weigh it again. This has been my winter project and only drove it over the winter on nice days and empty. I also pull a 20 foot cargo trailer weighing in at 4500lbs.
Thanks for the info. I'll call Uniroyal direct and ask them as well. This is my 6th RV in 25 years and never had a blowout running max or 10 psi less than max on the RV's or trailers. Colorado has horrible roads because of our last 3 Governors. You must be aired up to survive the potholes, ruts and drop-offs.
I'll post the Uniroyal info when I get it
Thanks for all the input. I really do appreciate the opinions. That's what makes a forum work. Knowledge is good, to much is dangerous as the old saying goes

Re: Tire Inflation

Reply #24 –
Try running your coach through water then out to dry white concrete at an arc.  As the tire prints dry out stop and go back and look at the contact patch.  Adjust pressure.  Try it again. 

Re: Tire Inflation

Reply #25 –
Quote from: dans96u295ft –
This is my 6th RV in 25 years and never had a blowout running max or 10 psi less than max on the RV's or trailers.

OK, that could mean that your previous RV's speced tires that had less safety reserve and did require at or close to full PSI to support their actual weight. Don't know without facts on both tires and weights.

That COULD be true with your Foretravel, but without 4 wheel position weights (best) or at least axle weights, all of us (and you) are having to express an opinion rather than base PSI on FACTS.

BTW, excellent plan to contact Uniroyal and have them e-mail you or give you a link to the inflation table for your tires.  They spent a lot of $$ and research to develop the table.  Take advantage of it.

Re: Tire Inflation

Reply #26 –
Quote from: dans96u295ft –
I weighed my coach without water or groceries, etc etc. True empty except cargo area full. 27,500 total. I did not weigh axles separate yet. I'll play with 100 to 110 when loaded and weigh it again. This has been my winter project and only drove it over the winter on nice days and empty. I also pull a 20 foot cargo trailer weighing in at 4500lbs.
Thanks for the info. I'll call Uniroyal direct.....

90 lbs all the way around, by the attached Uniroyal tire inflation guide takes you to the 30,000 GVWR of your rv.  That is 10,500 front, 19,500 rear.

From my earlier post: "As an example, to compare mine to yours, I load my rv heavy, near the axle limits rated by the FT plate at 10,500 front 19,500 rear.  So off the Toyo chart, I use 105 in the front, 90 in the rear.  This gives me a tire capacity of 10,740 in the front, 19,540 for the rear duals.  Using the Uniroyal chart for your RS20 275x80x22.5, 90 lbs all the way around would give you 10,740 front capacity and 19,540 rear capacity respectively........"

Re: Tire Inflation

Reply #27 –
Our bad roads here in so cal required the highest capacity tires made so we could lower the correct pressure per the load to have the best possible ride quality.  Then add the Koni fsd's

Fixed. 

If you have good roads then you can skip most of this as the differences may not be apparent until you hit bad roads.

Just saying.  We had a need that had to be addressed,  you may not.

Re: Tire Inflation

Reply #28 –
Ok. Called Uniroyal-Michelin and they want fully loaded corner weights on all 4 to determine psi as some have stated. They recommend if you don't know it, max to 120 psi to be on the safe side. When I get it fully loaded and ready to use, I'll call them back with corner weights and report back at their recommendations
 

Re: Tire Inflation

Reply #29 –
Quote from: dans96u295ft –
Ok. Called Uniroyal-Michelin and they want fully loaded corner weights on all 4 to determine psi as some have stated. They recommend if you don't know it, max to 120 psi to be on the safe side. When I get it fully loaded and ready to use, I'll call them back with corner weights and report back at their recommendations

Until you can load and weigh, just take the maximum weight rating of the axles and either call them or use the following pdf file. That would be the GVWR (Gross Vehicle Weight Rating) axle ratings that are on your federal FT weight sticker by the drivers seat.  Might be 10,500 up front and 19,500 on rear axle till you can weigh. So corners would be 5,250 lbs up front and 9,750 lbs on duals in the rear.

Off the following Uniroyal data book for your RS20's, 275x80x22.5, that would be 90 lbs all around to carry 10,740 on the front axle and 19,540 on the rear axle.

If you believe the rv is not loaded evenly, add 5-10 lbs to each tire, until you can load and weigh properly.