Tire Inflation Questions

[GizmosMom]

(I did a search about "tires" on this forum and there were 270 pages that came up so I thought it best to just ask my question directly)

I just read a post on this forum from someone who had a rough ride in their Class C.

We also have a Class C and at times the ride is rough. We have inflatable shocks. WE set them at 50-60 pounds.

Someone posted an answer to the original poster stating that maybe his tires were inflated too much.

I told my husband about this and he said he inflates our tires to 80 pounds. We have Michelin tires and they recommend 85. He likes to follow the manufacturers recommendations.

So our question is: If we go lower will we do any damage to our tires?

[Mich_F]

Unless you have something other the stock tire size that came on your motorhome, I doubt that Michelin recommends 85 psi for tires that have a maximum 80 psi for maximum load rating stamped on the sidewalls.
Your vehicle should have a sticker on the door or door post where the MH manufacturer recommended front and rear tire pressures, which are probably 75# for the front tires and 80# for the rear tires, based on the vehicle being loaded to the front and rear axle max load ratings.

[Grit_dog]

Some of these responses are like the guy (another thread about tire pressure......go figure) a couple days ago who said that as temperature increases, he also increases his cold psi. And the tires supposedly had more than enough air for the load to begin with.

Some folks level of understanding should not allow them to pilot large trucks and trailers.

[Grit_dog]

Optimistic Paranoid wrote:

aftermath wrote:
Grit Dog said: "Grossly over inflated ties ( for the load, even if within max sidewall psi) can be almost as dangerous as under inflated tires in some (maybe different) situations."

I don't agree with this. Inflating a tire beyond what is needed to meet weight carrying needs is not a dangerous thing to do. It will most likely cause the tire to wear faster, but that is it. When the manufacturer prints the maximum carrying capacity of a tire at the maximum pressure listed it means that the tire is safe for this weight and pressure. If you have less weight than the max but you still air it up to max you are not doing anything dangerous.

When a tire is properly inflated, it's tread is making maximum contact with the road surface.

When a tire is overinflated, only the center of the tread is making contact with the road. Less square inches of contact means less traction. Less traction means longer stopping distance when you brake. It also means that steering will be less than optimal even on dry roads, and much, much worse on wet ones.

I'd call that dangerous.

You're right. Aftermath mustn't drive in rain or snow or ever need to make a panic stop or accelerate hard from a stop. Over inflated tires lose a large % of their available traction......but hey they match the door sticker....lol.

[Grit_dog]

jplante4 wrote:

Grit dog wrote:
This may be good info for a little car tire with max 32psi or whatever rating, but it is NOT a 1 size fits all is correct recommendation. Period. Grossly over inflated ties ( for the load, even if within max sidewall psi) can be almost as dangerous as under inflated tires in some (maybe different) situations.

Also remember that car tires are over inflated by default to up the gas mileage to meet CAFE requirements. The door sticker amounts to government propaganda and should be viewed with that in mind.

Hard part is explaining that to the door sticker readers that believe if a mfg put it there, it is gospel. Same folks afraid of penalty by law if they remove the tag from their bedroom pillows!

[Cummins12V98]

"I told my husband about this and he said he inflates our tires to 80 pounds. We have Michelin tires and they recommend 85"

I would look at the sidewall of the tires. I am willing to bet they say 80psi "MAX". If so ask your husband why he is over inflating the tires.

[jplante4]

Grit dog wrote:
This may be good info for a little car tire with max 32psi or whatever rating, but it is NOT a 1 size fits all is correct recommendation. Period. Grossly over inflated ties ( for the load, even if within max sidewall psi) can be almost as dangerous as under inflated tires in some (maybe different) situations.

Also remember that car tires are over inflated by default to up the gas mileage to meet CAFE requirements. The door sticker amounts to government propaganda and should be viewed with that in mind.

[Slownsy]

No but I believe that is why most advice to go over by 5lb to compensate for any side weight difference.
Frank.

[Optimistic_Para]

wa8yxm wrote:

One a SCALE. one capable of weighing JUST that wheel. not it's mate across the RV or Tow Vehicle.

Speaking of that, does anyone know if the CAT scale people will let you drive just one side of your rig across the scales, and then get a second weight with the other side? Anyone tried that?

[wa8yxm]

OPtimistic said it.. Proper inflation = Full tread engagment = Maximum control = Longest tire life

To find proper tire inflation you need two things

One a SCALE. one capable of weighing JUST that wheel. not it's mate across the RV or Tow Vehicle.

Two. A chart in your case from Mitchlin.

I like to add 5 PSI to what M says .

[Optimistic_Para]

aftermath wrote:
Grit Dog said: "Grossly over inflated ties ( for the load, even if within max sidewall psi) can be almost as dangerous as under inflated tires in some (maybe different) situations."

I don't agree with this. Inflating a tire beyond what is needed to meet weight carrying needs is not a dangerous thing to do. It will most likely cause the tire to wear faster, but that is it. When the manufacturer prints the maximum carrying capacity of a tire at the maximum pressure listed it means that the tire is safe for this weight and pressure. If you have less weight than the max but you still air it up to max you are not doing anything dangerous.

When a tire is properly inflated, it's tread is making maximum contact with the road surface.

When a tire is overinflated, only the center of the tread is making contact with the road. Less square inches of contact means less traction. Less traction means longer stopping distance when you brake. It also means that steering will be less than optimal even on dry roads, and much, much worse on wet ones.

I'd call that dangerous.

[aftermath]

Grit Dog said: "Grossly over inflated ties ( for the load, even if within max sidewall psi) can be almost as dangerous as under inflated tires in some (maybe different) situations."

I don't agree with this. Inflating a tire beyond what is needed to meet weight carrying needs is not a dangerous thing to do. It will most likely cause the tire to wear faster, but that is it. When the manufacturer prints the maximum carrying capacity of a tire at the maximum pressure listed it means that the tire is safe for this weight and pressure. If you have less weight than the max but you still air it up to max you are not doing anything dangerous.

Trailer tires are different from those you put on a motorhome. I agree with those who say, weight the vehicle and then pay attention to the weight capacity of your tires. If you don't want to run them at max pressure just make sure that you know the weight capacities at the lower pressures. There are lots of charts out there that will help you decide on a safe pressure.

[copeland343]

That is a lot of PSI in the Airbags. Why so much?

[Grit_dog]

GizmosMom wrote:


We also have a Class C and at times the ride is rough. We have inflatable shocks. WE set them at 50-60 pounds.

Someone posted an answer to the original poster stating that maybe his tires were inflated too much.

What would cause you to need 60psi in airbags in addition to the spring suspension? Sounds like alot of extra weight, improper use of airbags, or ICBW and the camper is designed to need a significant amount of suspension help even within normal loading.
Assuming it's the first one, then you may need to keep your tires at 80psi if you're packing a bunch of extra weight.
If it's the 2nd one then you need to look at how/why you're deciding to put that much air in a basically new camper.
If it's the last, then I stand corrected.
Regarding tires, you need to have some semblance of what it weighs and then air the tires down accordingly if it's alot lighter than what you're aired up for.

[Grit_dog]

CALandLIN wrote:

GizmosMom wrote:
Thanks, everyone. Very informative answers.

I made a mistake...we have air bags, not shocks.

Will get the rig weighed at the beginning of our next trip and go from there.

I have always loved this forum and the people who help me/us!

I only write about tire inflation pressures from the way they are supposed to be inflated and in accordance with tire industry standards.

Bypassing normal automotive tire industry standards and inflating your tires to the load carried is a procedure supported by FMCSA. Those are commercial standards and are not applicable with FMVSS which gives us all the recommended cold inflation pressures found in the vehicle owner’s manual, vehicle manufacturers -final stage - certification label and on the vehicle load and tire placard.

The recommended cold inflation pressures provide by your vehicle’s manufacturer are considered the minimum safe operating pressures for your vehicle. WRONG!

The U.S. Tire Manufacturing Association (USTMA) will not recommend inflating your tires below the recommended cold inflation pressures displayed on your vehicle’s certification label. NOT A GOOD RECCOMENDATION!

You can find all you need to know about proper tire inflation for your RV starting on page 42 of the reference in the “Click Here!“ tab below.


Click Here!

That's great and it's a good beginners document to understanding "tires", however they are still virtually wrong on p10-11 on inflation pressures and pretty much contradict themselves between 2 paragraphs.
Now I know where the "must fill your tires up to the sticker on the door psi" folks get it from. That book says to. It also says to maintain proper pressure in your tires for max performance, tire life, etc.
This may be good info for a little car tire with max 32psi or whatever rating, but it is NOT a 1 size fits all is correct recommendation. Period. Grossly over inflated ties ( for the load, even if within max sidewall psi) can be almost as dangerous as under inflated tires in some (maybe different) situations.

This is not debatable, it's physics, dynamics and mechanics of materials.