Confusion re. correct tire pressure

[jadatis]

The braketestbank often has weighing possibility in it.

[wolfe10]

Originally Posted by LETMGROW

How does the tire store check the weight? Do they have scales?

In a word, they DON'T!


Unless you tell them correct PSI for your coach, they will either go with PSI on the tire sidewall (more likely) or the PSI on the GVWR sticker (better).

[mlpeloquin]

Originally Posted by LETMGROW

How does the tire store check the weight? Do they have scales?

They do not go by the side wall max psi. They use the PSI on the GVWR sticker. That sticker list the minimum psi at max weight your RV should weigh. Same with your car. Look up the maximum weight your car is rated at, look up the load/pressure chart for your tires, and you will fine that the psi on the door sticker is for that weight. Can you put less psi in the tires, yes if the weight is less then the maximum weight rating.

[Ray,IN]

Every tire mfgr. that publishes a load/inflation chart also within their literature states to never run less air pressure than listed on the Federal Tire Placard.
Michelin, Goodyear, Firestone, etc all have that statement in their air pressure literature, all you gotta do is read.

[Shall36]

Originally Posted by Ray,IN

Every tire mfgr. that publishes a load/inflation chart also within their literature states to never run less air pressure than listed on the Federal Tire Placard.
Michelin, Goodyear, Firestone, etc all have that statement in their air pressure literature, all you gotta do is read.

I had never heard this so I downloaded the Michelin XRV tire manual. Page 4 talks about proper inflation depending on vehicle weight. They do reference the placard in the vehicle but paragraph 8 on page 4 says to weigh the RV and determine proper inflation. Maybe I’m reading this incorrectly but it seems like the literature says to weigh and determine pressure and not to automatically use what’s on the placard.

https://dcadprod.azureedge.net/b2b-e...-april2023.pdf

[Crasher]

I have also read to inflate to the placard. That is a safe pressure to use for anyone that does not want to take the time to get to the best ride, and best tire wear. However, with a motorhome, tread wear and longevity is of little concern, as most tire will age out before wear out. The ride difference is quite often negligible, so for the average person, the placard pressure is the easiest to use and is safe.

[Ray,IN]

Originally Posted by Shall36

I had never heard this so I downloaded the Michelin XRV tire manual. Page 4 talks about proper inflation depending on vehicle weight. They do reference the placard in the vehicle but paragraph 8 on page 4 says to weigh the RV and determine proper inflation. Maybe I’m reading this incorrectly but it seems like the literature says to weigh and determine pressure and not to automatically use what’s on the placard.

https://dcadprod.azureedge.net/b2b-e...-april2023.pdf

Michelin tire pressure statement.

Here is the Goodyear statement under the paragraph "Tire Loading".

The Rubber Manufacturers Assn. says on pg 13 to never set tire pressure below the Mfgrs recommendation on the Federal Tire Placard.

[Shall36]

Didn’t read all of the referenced materials but the Michelin statement seems specific to passenger vehicles. For example, it specifically reference pressures referenced on the door jam placard. The Michelin XRV tire manual provides very different information. The Rubber Manufacturers document is specific to passenger car and lighT Truck tires. Car manufacturers specify tire pressures to accommodate load and achieve specific vehicle handling characteristics.

Maybe there’s a trucking industry expert on the board who knows differently but heavy truck tires are designed to be run at a pressure based on weight. There’s a large variety of weights a truck tire may see across applications.

The notion that RVs should use placard weights when actual weights are not know is good but it presumes that the rig is not overweight. Higher than needed pressures can cause an awe full ride especially on gassers like the F53. Even 5psi can make a big difference in ride quality.

[Chuckge]

The only thing I would add is be aware of tire pressure increases during your trip. During a recent trip running 400~ miles a day my tire pressures increased from morning cold pressure of 82 to afternoon tire pressures of 96 while the air temperature was 76-80 degrees.
If you start out to high by the end of your days travels you may max out your tires capacity with no room for safety.

[wolfe10]

Originally Posted by Chuckge

The only thing I would add is be aware of tire pressure increases during your trip. During a recent trip running 400~ miles a day my tire pressures increased from morning cold pressure of 82 to afternoon tire pressures of 96 while the air temperature was 76-80 degrees.
If you start out to high by the end of your days travels you may max out your tires capacity with no room for safety.

Sorry, that is incorrect.


The "max" PSI (actually what is on the sidewall is the PSI needed to carry the max load) is defined by all tire manufacturers as "at ambient temperature before driving/exposure to outside heat sources such as in the sun".


The tire engineers KNOW that as tire temperature rises PSI will rise. That has been taken into consideration when the engineers prepared the inflation tables.

[RVStitchy]

Originally Posted by propchef

The only accurate way to know the proper inflation is to measure the temperature of the tires after they get hot. Track guys have known this for years.

I have raced cars and have an RV. Race car tires are different from the sidewall construction of most RV tires. The rules are different.

[Crasher]

Originally Posted by Chuckge

The only thing I would add is be aware of tire pressure increases during your trip. During a recent trip running 400~ miles a day my tire pressures increased from morning cold pressure of 82 to afternoon tire pressures of 96 while the air temperature was 76-80 degrees.
If you start out to high by the end of your days travels you may max out your tires capacity with no room for safety.

In addition to what Brett said, I contacted Michelin years ago to know what was the max pressure the tire should see. Their response was that if the tire had at least the minimum to carry the load, a 15% up to 20% increase in pressure from rolling resistance was normal. My steer tires started @ 120 psi (maximum cold psi) for the load they carried. On a 100 degree day they would increase to 144 psi. Part of that increase (7.2 psi) was a 30 degree increase in ambient temperature during the day and the rest was rolling resistance. All perfectly normal according to Michelin.

[CntryCoachRV]

Originally Posted by propchef

The only accurate way to know the proper inflation is to measure the temperature of the tires after they get hot. Track guys have known this for years.

That does not apply to Rv tires, you measure the tires pressure before you drive, which means ambient temperature also know as cold temperature then you check inflation against inflation table on tire manufacturers web site. Use the weight of your Rv, 4 corner weight is most accurate. It’s a simple task that far too many try to make complicated by entering what you just entered. Hope he ignores that.

[Mikesrq]

Originally Posted by ckwcw

We have a Winnebago Intent 31P 2018; Tires: Goodyear (original) G70 RU 245/70R19.5; Cold 110. Miles: ~12,000.
Weight Ratings: GCWR 23,000 lbs; GVWR 18,000 lbs.; GAWR-Front 7,000 lbs. Plate next to driver door: 82 PSI. An RV mechanic said it's best to run at 90-100 psi. Another RV Mechanic recommends 90-92.
(We tow our 2014 Honda CRV, if that makes any difference)
What tire pressure should it be when cold? TIA

You have a more important issue. The age of your tires.

The rule of thumb for changing your RV tires is around 3-5 years. The consensus from RV owners leans to the 5-year end of that estimate, but I'm sure this group will weigh in.

You can check the DOT number (generally located on the inside sidewall near the rim. The letters “DOT” are followed by eight to thirteen letters and/or numbers that identify where the tire was manufactured, tire size and the manufacturer’s code, along with the week and year the tire was manufactured.

DOT (Department of Transportation)
Tire manufacturer / plant code
Tire size code
Tire manufacturer
Week and Month of Manufacture

For example: DOT AF WD9E 0517 05 indicates the tire was manufactured in the 5th week of the year 2017.

Sorry to say that mileage and treadwear are rarely indicators of the need for tire replacement on RVs or travel trailers. The rubber and other tire materials age out before they wear out.

Mike Rado
Sarasota, Florida
2011 Winnebago Access 31'