Tire pressure/load questions based on scale weight

[FastEagle]

Originally Posted by chs

We just returned (early) from our trip and drove roughly 700 miles. I had the 70 in the front and 75 in the rear. Worked fine. much smoother ride than the 75F & 80R pressures. No rise in temps or excess pressures. It's not much pressure difference, but it did seem to make a nice difference without going to extremes.

FYI, like I said before, When lowering the air pressure in tires (especially when trying out things) you need to watch temps go up more than pressures. OEM TPMS's do not do that.

IMO there is no valid reason to lower vehicle tire inflation pressures below what has been recommended by the vehicle manufacturer. The entire tire industry supports that opinion for OE tires because none will recommend anything below what has been recommended.

[nodine]

Originally Posted by FastEagle

IMO there is no valid reason to lower vehicle tire inflation pressures below what has been recommended by the vehicle manufacturer. The entire tire industry supports that opinion for OE tires because none will recommend anything below what has been recommended.

In my opinion they are covering their butts. A tire will perform best when the tire pressure is per the manufacturers tire pressure tables. That means the pressure is based on the load. If the owner knows what the weight on each tire position is they can safely use the manufactures tables. Most owners don't know beans about the weight on their tires and do not closely monitor tire pressure. Beside that they carry everything under the sun and then pick up more at grandma's house. That is why the vehicle manufacturer puts those stickers on the door with the pressure's at the maximum axle load.

[Kid Gloves]

Originally Posted by FastEagle

IMO there is no valid reason to lower vehicle tire inflation pressures below what has been recommended by the vehicle manufacturer. The entire tire industry supports that opinion for OE tires because none will recommend anything below what has been recommended.

Not true. They publish load and inflation tables for owners to determine the correct pressures for their vehicle. Not all vehicles operate at their GVWR.

For our fully loaded coach weight, the recommended front tire pressure is 95psi. At the FAWR the recommended pressure is 120psi. The owners manual has a load and inflation table and the tire manufacturer provides a load and inflation table, neither recommends 120psi, based on the load.

Tag-axle coaches rarely approach their RAWR’s. My pickup truck has LR-E tires. Recommended pressures and loads, per tire, range from 35-80psi and 1910-3415lbs, respectively. Sometimes the rear axle supports 2600lbs, sometimes it supports 6000lbs. I don’t run around with 75-80psi in the rear tires unless I intend to carry a full load.

For many Class B and C rigs, which typically operate near GVWR, it may be acceptable to inflate to the placard recommendations. It is also possible to make a more informed decision.

[FastEagle]

The following information is from various RV tire maintenance manuals/PDFs. All are verifiable.

Under no circumstances should the tire inflation pressure be reduced below that stated on the vehicle’s tire information (certification) placard to achieve improvements in ride comfort. If you do not know where the tire information placard is, contact your vehicle manufacturer for its location and tire inflation recommendation. For RVs, the certification label is usually placed on the wall or bulkhead to the left of the driver’s position.

If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure.

Inflation pressure recommendations may also be determined based on the tire manufacturer’s specifications, which define the amount of inflation pressure necessary to carry a given load. These inflation pressures may differ from those found on the vehicle tire placard or certification label. However, never use inflation pressures lower than specified by the vehicle tire placard, certification label or owner’s manual. Nor should inflation pressure exceed the maximum pressure molded on the tire sidewall.

[rd36mnm]

Originally Posted by FastEagle

The following information is from various RV tire maintenance manuals/PDFs. All are verifiable.

Under no circumstances should the tire inflation pressure be reduced below that stated on the vehicle’s tire information (certification) placard to achieve improvements in ride comfort. If you do not know where the tire information placard is, contact your vehicle manufacturer for its location and tire inflation recommendation. For RVs, the certification label is usually placed on the wall or bulkhead to the left of the driver’s position.

If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure.

Inflation pressure recommendations may also be determined based on the tire manufacturer’s specifications, which define the amount of inflation pressure necessary to carry a given load. These inflation pressures may differ from those found on the vehicle tire placard or certification label.Howeve r, never use inflation pressures lower than specified by the vehicle tire placard, certification label or owner’s manual. Nor should inflation pressure exceed the maximum pressure molded on the tire sidewall.

Ok, I am totally confused. You say inflation pressure recommendations may also be determined based on the tire manufacturer’s specifications, which for my weight is 50 front/80 rear.Then you say never use inflation pressures lower than specified by the vehicle tire placard, certification label or owner’s manual. My placard on the door reads 75 front/80 rear.

This statement is totally contradicting to me.

[kedanie]

FastEagle will never tell you what he thinks. He will always quote some other source so that you can’t blame him. He is in love with government documents and will go on and on. Your best choice is to ignore him and let him post all his nonsense.

You are doing the right thing in getting weighed and adjusting pressures according to the tire manufacturer’s weight charts.

Carry on!

Keith

[Kid Gloves]

Michelin recommends setting tire pressure based on axle loads. Likewise, Roger Marble, aka:Tireman9, also recommends setting tire pressure based on loads on his rvtiresafety.net site.

[sibe]

some of us have older rigs, maybe 25, 20 or 10 years old, same tires .. Tires have stayed the same and tires have changed,,
What was recomended on my older C by chassis then the rv manf tag is a tad different and then my new michelins on back are even different..
So I tend to lean towards my tires and there specs and the wieghts on my axles.. not that hard to look at max loads and then some easy adjustments that make sense.. Then I drive it, watch the wear and ride quality / handling.. +/- 5 psi is ok IMO.. dang I started in AM at 37 degrees and was at 97 by end of day.. I aint messing witha couple PSI .. geez..

[Gordon Dewald]

Tire pressures matched to the load carried is very important IMO. Leads to the best of ride, tire contact for traction and braking as well as better mileage and tire life.

[ArtJoyce]

I would plan to adding 10 psi to what ever you calulate.

Rear, you added the 155cc and hitch.? Would that not have a fulcrum and lever effect? The rear axle as the fulcrum the weight hitch and 155cc trying to lift the front wheels with the lever on the rear axle fulcrum? Add more weight to the rear axle then the weight of the hitch and 155. It has a multiplier based on the lever length. At the same time you remove the muiplyed weight off the front. So the longer the distance is from the rear axle to the hitch the more weigh you have of the rear axle.

Give me a long enough lever and I could lift the world. Who said that,?

[Kid Gloves]

Originally Posted by sibe

some of us have older rigs, maybe 25, 20 or 10 years old, same tires .. Tires have stayed the same and tires have changed,,
What was recomended on my older C by chassis then the rv manf tag is a tad different and then my new michelins on back are even different..
So I tend to lean towards my tires and there specs and the wieghts on my axles.. not that hard to look at max loads and then some easy adjustments that make sense.. Then I drive it, watch the wear and ride quality / handling.. +/- 5 psi is ok IMO.. dang I started in AM at 37 degrees and was at 97 by end of day.. I aint messing witha couple PSI .. geez..

You’re all over the map with your wisdom.

First, the age of the coach is irrelevant. The axle ratings and GVWR haven’t changed.
Second, 5psi below the recommended minimum pressure is not “ok”.
Third, yes, know your axle weights and inflate to the tire manufacturers recommended pressure based on those loads.
Fourth, the temperature at the end of the day is irrelevant. The tires were probably warmer than 97 while you were driving. Expect pressure to increase 10-20% above the cold setting while on the road. Check the pressure in the morning on your next travel day.

[rd36mnm]

When I started this thread I surely did not expect this much discussion. It has been very interesting . I have decided to follow the suggestions of this article. I find it made the most sense to me.
https://www.rvtravel.com/rv-tire-saf...terms-rvt-963/

[Kid Gloves]

Originally Posted by rd36mnm

When I started this thread I surely did not expect this much discussion. It has been very interesting . I have decided to follow the suggestions of this article. I find it made the most sense to me.
https://www.rvtravel.com/rv-tire-saf...terms-rvt-963/

Tire pressure can be an explosive subject. You’ve found a good source for information. It’s really quite simple for the consumer. Some folks just like to make a meal out of it.

[FastEagle]

Originally Posted by rd36mnm

When I started this thread I surely did not expect this much discussion. It has been very interesting . I have decided to follow the suggestions of this article. I find it made the most sense to me.
https://www.rvtravel.com/rv-tire-saf...terms-rvt-963/

Roger provides loads of great tire information. However, he lacks a little in the interpretation of DOT minimum rules, regulations and standards.

It is printed everywhere that the correct inflation pressures for OE tires has been set by the vehicle manufacturer and displayed on the vehicle federal certification label, vehicle owner's manual and tire load placard.

That allows for optional pressure from what has been recommended to sidewall max.

NHTSA has an interpretations desk. You can request one. The answer will be the same, OE tire pressures on the vehicle certification label is MINIMUM.

What happens to load capacity reserves when tires are inflated to the load carried?

The trucking industry uses that method. The results can be found on any major highway in the country.