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Topic: Tire pressure question - without scales (Read 4814 times) previous topic - next topic

Re: Tire pressure question - without scales

Reply #20 –
I was looking at Barry's spreadsheet  and seeing the rear axle being overloaded. I have never weighed our and wondering if mine is overloaded also 

Re: Tire pressure question - without scales

Reply #21 –
We got our coach 4-corner weighed at Escapees in Livingston, TX.  Found out we are slightly overweight on our front axel, and 900 pounds over the total GVWR.  We weighed with full water and fuel tanks, and 1/2 tank of propane.  The tech suggested we could travel with less fresh water on board to reduce overall weight.  We have since adopted that procedure.  We also upgraded from the old G rated tires we had, to new H rated tires.  This gave us some additional safety factor in the tire load department.  I figure (hope) the axle ratings are probably pretty conservative, and our placarded GVWR looks suspiciously low to me...especially when compared to the same model year U300:

Foretravel Vehicle Weight

Regardless of what method a driver uses to set tire pressures, getting 4-corner weighed is a interesting exercise.  Like most other reports, our side-to-side balance was fairly close.  I guess Foretravel got that part of the engineering right!

Hanging At Camp FOT

Re: Tire pressure question - without scales

Reply #22 –
Whenever I hear those stories about coaches being overweight, I think of that scene in 'The Long Long Trailer' where Desi discovers Lucy's rock collection!  ;)

Re: Tire pressure question - without scales

Reply #23 –
If you don't know! Go with Max pressure on side wall of tire.  Example g rated 110psi

Re: Tire pressure question - without scales

Reply #24 –
When I didn't know, I went tire FT placard pressures plus five psi. Still under sidewall Max.

Re: Tire pressure question - without scales

Reply #25 –
Quote from: Gary and Kathy –
If you don't know! Go with Max pressure on side wall of tire.  Example g rated 110psi
Just remember that for truck tires (the ones on our motorhomes) the sidewall pressure is the MINIMUM pressure for the maximum load. The maximum pressure for the tire is higher than the sidewall pressure.

Re: Tire pressure question - without scales

Reply #26 –
Easy to download specs these days. Here's our Michelins:

Re: Tire pressure question - without scales

Reply #27 –
Quote from: D.J. Osborn –
Just remember that for truck tires (the ones on our motorhomes) the sidewall pressure is the MINIMUM pressure for the maximum load. The maximum pressure for the tire is higher than the sidewall pressure.
With all due respect, for Michelin tires, the sidewall pressure on the tire is the maximum pressure for the tire. I have no idea about other makes of tires. For Michelin tires, the max load for the tire and the maximum PSI are stamped on the tire. Michelin tire inflation charts also show the maximum load and inflation pressure for the tire.

Re: Tire pressure question - without scales

Reply #28 –
Actually D.J. is correct, though we may be getting into a bit of semantics here.

The sidewall/inflation charts state MAX load and the PSI needed to carry that load.

If less than max load, it does not require that PSI.

But, adding air above that on the side wall will not increase carrying capacity.

And, all tire PSI's are for cold (before driving at current ambient temperatures).

Re: Tire pressure question - without scales

Reply #29 –
The subject of tires and "optimum" (cold) inflation pressure always generates interesting discussions here.  I haven't been around all that long, and I have witnessed a few.  See first link below for one example.  It seems to me that among our Forum members, there are two schools of thought.

One group thinks you should weigh your coach, as accurately as possible (4 corner?) and then set tire (cold) pressures according to load charts and recommendations published by the tire manufacturer.  Following this method, if the weight of the coach changes dramatically, then the (cold) tire pressures might require adjustment to compensate.

The other group thinks you should just pick some "safe" (cold) tire pressure, up to and including the pressure embossed on the sidewall, and run that pressure all the time.  "Safe" means a (cold) pressure that would always be at or above the pressure required to support the coach GVWR.  This pressure (for OEM tires) is generally displayed on the placard affixed to the wall next to the driver seat.

Every coach owner needs to think about tire pressure. and decide for themselves which approach is best.  The second link below is the opinions of some truck people who choose to take actual load weight into consideration when setting (cold) tire pressures.  Take it for what it is worth.

Uniroyal Tires

The Magic Number - Maintenance - Trucking Info

Re: Tire pressure question - without scales

Reply #30 –
Quote from: Chuck & Jeannie –
One group thinks you should weigh your coach, as accurately as possible (4 corner?) and then set each individual tire (cold) pressure in according to load charts published by the tire manufacturer. 


One correction-- all tires on an axle should be at the same PSI based on the heavier wheel position.

Said another way, even if left is 1000 pounds lighter than right, they both have the same PSI based on the heavier/right side.
From: http://www.michelinb2b.com/wps/b2bcontent/PDF/RV_Tires_Brochure.pdf

MICHELIN® RV Tires  HOW TO USE THE ACTUAL RV WEIGHT INFORMATION WITH THE TIRE DATA LOAD CHART

"Let's consider an RV running on 275/80R22.5 MICHELIN® X® LINE™ ENERGY Z LRG tires, with actual corner weights of 5,400 lbs. on the left front tire, 5,175 lbs. on the right front tire, 8,500 lbs. For control of the RV, it is critical that the tire pressures be the same across an axle. Therefore, we must "overinflate" the right front tire and the left rear duals. Checking the load/inflation table below shows that a cold tire pressure of 95 psi will support 5,510 lbs. on a single front tire."

Re: Tire pressure question - without scales

Reply #31 –
Quote from: wolfe10 –
Actually D.J. is correct, though we may be getting into a bit of semantics here.

The sidewall/inflation charts state MAX load and the PSI needed to carry that load.

If less than max load, it does not require that PSI.

But, adding air above that on the side wall will not increase carrying capacity.

And, all tire PSI's are for cold (before driving at current ambient temperatures).
I do not know how to post a link, so I am going to have to make a quote. At Michelinrvtires.com, Tires, Tires 101, how to read a sidewall, it states, "USA Regulation, Max. Load Per Tire, Single and Dual, Kg. and Lbs., Max pressure per tire, Single and Dual, Kpa. and PSI."  Also, the Michelin Tire Inflation chart states, "Maximum Load and Pressure On Sidewall". In the English language the Maximum is an adjective and it applies to both the Load and Pressure. In other words, it reads Maximum Load and Maximum Pressure. I am reading all of this to say that the PSI stamped on the sidewall is the MINIMUM to support the load and the MAXIMUM pressure for the tire.

Re: Tire pressure question - without scales

Reply #32 –
Quote from: Chuck & Jeannie –
I agree with Brett - the exact definition of the pressure on the tire sidewall is subject to semantic interpretation.

Also, you have to be careful to specify what type of tire in this discussion.  Some tires are designed to be run at (cold) inflation pressures above the pressure embossed on the sidewall.  Which can just add more confusion to the discussion.  See 3rd paragraph in link below:

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=196
Please read paragraph four in that link. Where it talks about the tires maximum inflation pressure.

Re: Tire pressure question - without scales

Reply #33 –
Quote from: ltg –
Please read paragraph four in that link. Where it talks about the tires maximum inflation pressure.
Yes, you are correct.  I misread the 3rd paragraph.  I got "sidewall max pressure" and "pressure required for maximum load" confused.

NEVER MIND!

(Went back and deleted my post - it was not beneficial to the discussion)

Re: Tire pressure question - without scales

Reply #34 –
Everyone would do well to download and then completely readl Michelin's Truck Tire Service Manual and their Recreational Vehicle Tire Guide. They make it clear that truck tires are built to different requirements than are passenger tires. Truck tires are specifically built for heavy-duty service and (unlike passenger tires) the sidewal pressure is the MINIMUM pressure for the maximum load. Under certain conditions the pressure can--and should-- be set higher than the sidewall minimum for the maximum load. Our tires will serve us well if we fully understand them, but may disappoint us if we make incorrect assumptions.

Re: Tire pressure question - without scales

Reply #35 –
Quote from: ltg –
Please read paragraph four in that link. Where it talks about the tires maximum inflation pressure.
Please understand the difference between passenger tires and truck tires and the fact that they are built to entirely different requirements. Understand that different rules apply to them. Go to Michelin's truck tire Website and download their truck tire service manual.

Re: Tire pressure question - without scales

Reply #36 –
Quote from: D.J. Osborn –
Everyone would do well to download and then completely readl Michelin's Truck Tire Service Manual and their Recreational Vehicle Tire Guide. They make it clear that truck tires are built to different requirements than are passenger tires. Truck tires are specifically built for heavy-duty service and (unlike passenger tires) the sidewal pressure is the MINIMUM pressure for the maximum load. Under certain conditions the pressure can--and should-- be set higher than the sidewall minimum for the maximum load. Our tires will serve us well if we fully understand them, but may disappoint us if we make incorrect assumptions.
Again, with all due respect, the sidewall pressure is the MINIMUM pressure for the maximum load and the MAXIMUM PRESSURE for the tire. There is an exception: if you are checking the tires when they are hot, you may add up to a certain amount to compensate when they are hot. Please read the following link.
How to Read a Sidewall | Michelin Truck.
Max Load, Max Pressure, Max speed.

Re: Tire pressure question - without scales

Reply #37 –
Quote from: ltg –
Again, with all due respect, the sidewall pressure is the MINIMUM pressure for the maximum load and the MAXIMUM PRESSURE for the tire. There is an exception: if you are checking the tires when they are hot, you may add up to a certain amount to compensate when they are hot. Please read the following link.
How to Read a Sidewall | Michelin Truck.
Max Load, Max Pressure, Max speed.
Please take the time to read the entire Michelin Truck Tire Service Manual. After you do you will understand that for truck tires the sidewall pressure is the minimum pressure required for the maximum load. Online graphics are onteresting--bit don't necessarily accurately represent to information in pfficial documents.

Please take the time to read a passenger tire sidewall and compare it to a truck tire sidewall. The passenger tire will read "maximum load" and "maximum pressure" while the truck tire will read "maximum load xxxx lbs @ yyy psi cold." The truck tire sidewall does NOT" read "maximum pressure."

Re: Tire pressure question - without scales

Reply #38 –
Quote from: D.J. Osborn –
Please take the time to read the entire Michelin Truck Tire Service Manual. "
Ok, I read it. You are saying that because Michelin said that in the unusual situation when a trucker has a steer tire on an axel that has reached the maximum load  for the tire, and is having unusual wear issues, the trucker can increase the pressure from 110  psi to 120 psi, that there is no maximum pressure for the tire. So, a forum member that has tires that have maxed out on the load, can add 5, 10, 15 psi as a safety factor. Like is sometimes recommended on the forum when the tires are not maxed out on load. And, when forum members have not yet weighed their coach, they can add 5 or 10 psi above what is on the placard just as another safety amount. Say the placard says 110 psi, they can put 120 psi and be OK.

Re: Tire pressure question - without scales

Reply #39 –
Quote from: ltg –
Ok, I read it. You are saying that because Michelin said that in the unusual situation when a trucker has a steer tire on an axel that has reached the maximum load  for the tire, and is having unusual wear issues, the trucker can increase the pressure from 110  psi to 120 psi, that there is no maximum pressure for the tire. So, a forum member that has tires that have maxed out on the load, can add 5, 10, 15 psi as a safety factor. Like is sometimes recommended on the forum when the tires are not maxed out on load. And, when forum members have not yet weighed their coach, they can add 5 or 10 psi above what is on the placard just as another safety amount. Say the placard says 110 psi, they can put 120 psi and be OK.
The short answer is that you finally have the right idea. However, for Michelin truck tires you would need to study their Truck Tire Safety Manual and the load/inflation table for the tire's specific size and load range to learn exactly how much additional pressure can and should be added under certain specific conditions. Most other truck tire manufacturers follow the Tire and Rim Association (TRA) guidelines and those are similar--but not identical--to Michelin's recommendations. Therefore, it's essential to get the detailed information for whatever tire you are running.