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?

[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.

[2oldman]

GizmosMom wrote:
(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)

You can narrow it down with a subsequent search for 'inflation'. When you see your 270 pages of results, you'll see a box up top labeled 'Search Within Results.' Enter 'inflation' ( or pressure, or whatever) there and see what happens.

[CALandLIN]

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.

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.

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!

[time2roll]

Assuming the tire is stock oem size and load range.... the driver's door sticker will give minimum pressure to meet the required GVWR. The sidewall of the tire will give the maximum cold inflation pressure. These give the upper and lower limits to play with to improve ride and handling to your taste.

Scale weight will confirm that you are not over the GVWR or axle gross weights.

If you go to the chart to get minimum pressure I recommend always being 5 psi over the minimum on the chart. Not to exceed the sidewall max.

[GizmosMom]

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!

[BarryG20]

If you are wanting to lower your inflation only do so after having weighed the rig ready to travel. Then find the load inflation table for your tires (if I am not mistaken the load tables are the same regardless of brand just make sure you are looking at the correct size and load rating and whether single or dual. I personally use the tables and air accordingly. Some want to use inflation as stated on the rv manufacturers sticker, some want to use the max inflation on the tire sidewall, some want to follow the load inflation tables and some do whatever they want, don't care and drive until their tires are toast without a care in the world. I wont say any are wrong. "I" will say that "I" feel the load inflation tables are the ultimate resource for tire pressure. First and foremost they are designed around a standard that the tire manufacturers recognize and follow. Who knows more about their own tires than the manufacturer. No one, not the rv manufacturer and not the government mandated stickers, not the rv dealer, not the local mechanic nor Billy Bobs best friends ex sister inlaw who used to work at a tire store 40 years ago for a summer. The rv manufacturer doesn't know anything about tires they buy them and put them on though they may very well have looked at the load inflation table to come up with the number on their sticker but that number is based on max GVW of the unit and may be totally appropriate for the unit and it may be overly high that depends on the unit and how much cargo/stuff you carry. I know on my trailer the original tires were barely adequate for the load and they did ride at max psi as they needed it. When I changed tires I went up a load range and gained significant capacity. I was able to lower the air pressure from max 80psi to 60psi which was actually 5lbs less than the previous tires which had a max of 65psi. I am still well within the tire capacity based on the unit weight. I know I looked at some trailers that had 4k of cargo capacity I usually have about 1200lbs including water. Why do I need to inflate my tires to max capacity if I am not using max capacity? I dont but someone else might carry 3500lbs of cargo in the same trailer and need that max capacity. The rv manufactures psi recs are based on gvw to cover their arses which is forced upon them by two things our litigious society and the government. The government does not trust the average citizen to be able to figure out the correct course of action in this case. They know few people pay any attention to their tires and I dont disagree with that. If you were to go to the Federal Register and read the law about TPMS systems you would find that the only reason for it is the government does not trust the average consumer to properly inflate and monitor the tire pressure, it says that very thing in very plain english more than once in the Federal register.

Long winded way of saying don't do anything until you weigh the unit axles or even better a 4 corner weight to find out what capacity is needed(even with 4 corner weigh all tires on same axles should be at same psi using heavier side as the base). Then go from there whether you stick with the rv sticker, tire sidewall max pressure, the load inflation tables or your own ideas of what is right at least you started out with knowing what the real load is going to be on the tires.

[Isaac-1]

downtheroad, Personally I don't see a big hassle to spend an extra $10 and 5 minutes of time after fueling up at a truck stop while on a trip and therefore loaded for travel to get a CAT scale weight, how else would you know if you are overloaded and exceeding your GVWR?

[time2roll]

Exactly what is the tire size? What does the door sticker say?

Air shocks? I think you would do better with air bags or helper springs or a new spring pack if the suspension seems to be sagging.

[downtheroad]

Ideally what Isaac-1 posted above is correct....but way too much hassle and realistically not possible on a day to day basis....

thus...again, keep it simple and air them to the max and get on down the road.

[Isaac-1]

You should inflate your tire to the recomended pressure for your loaded weight, this is best done with 4 corner weighing, though if that is not available many people use axle weights from CAT scales at truck stops (the charge to get a CAT scale weight is about $10), also many agricultural fertilizer, landscaping, etc. places will let you weigh for free, or nearly free if for non-commercial use.

Here is the Michelin inflation chart
http://www.rvtirepressure.com/assets/images/extrapages/michelin_rv_load_inflation.pdf
http://www.rvtirepressure.com/assets/images/extrapages/michelin_rv_load_inflation.pdf

p.s. I disagree with the above advice, often the maximum sidewall pressure will result in a tire wearing abnormally as it is much higher not only than the actual pressure needed for the load, but also often well above the GAWR (Gross Axle Weight Rating) for the RV. For example my coach has a 6,000 pound GAWR for the front axle, and loaded down my coach is close to the GAWR therefore based on the chart I linked above I keep them at 80 psi which is 5 psi (safety margin)over the minimum for a 6,000 pound load for my size tires. If I were to run max pressure of 95 psi, this would give me nearly 7,300 pounds of carrying capacity, which is well over my 6,000 pound axle rating, but it would also cause a harsh ride, and the middle of the tires would wear out faster than the edges.

[downtheroad]

GizmosMom wrote:

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

Yes, there are 280 tire discussion pages....it's always been an 'interesting' discussion here on the Forum...

If you lower the air pressure, you are also lowering the capacity of your tires to carry the weight of your rig (payload). The lower you air them the more they will heat up. Heat is the tire killer. Too low and yes you can certainly damage your tires...

Some weigh their rigs trip read and loaded and air their tires accordingly. I keep it simple and air mine to the maximum as stamped on the sidewall....thus I get the maximum carrying capacity for my tires...

confused now????

[Johno02]

Get your rig weighed, and go by the tire cos recommendation. 80 sounds about right for a C.