Tire Pressure

[FastEagle]

Originally Posted by wildtoad

Not doubting you've seen this somewhere, but I've never seen this in relation to RV's. Could you provide a link that shows this?

Originally Posted by Ray,IN View Post
All tire mfgrs. say to never run less air pressure than what is listed on the federal tire pressure placard in/on the vehicle_IF you are running the original size tires.

In the reference you will find it at the top of page # 50.

http://www.mcgeecompany.com/wp-conte...ete-manual.pdf

[wildtoad]

Originally Posted by FastEagle

Originally Posted by Ray,IN View Post
All tire mfgrs. say to never run less air pressure than what is listed on the federal tire pressure placard in/on the vehicle_IF you are running the original size tires.

In the reference you will find it at the top of page # 50.

http://www.mcgeecompany.com/wp-conte...ete-manual.pdf

Thanks for the link, seems a lot of people are weighing their RV's for no reason. But then again, I think the lawyers were involved in coming up with the statement.

I called Newmar months ago when I noticed the difference between the tire chart and placard and their response was that their numbers were maximums, as in don't exceed the 92. Very similar answer to wording in the Goodyear RV tire guide.

As always, and very interesting subject.

[Tireman9]

Originally Posted by Ron Postma

Don't go above 120 psi this is the max air pressure of the tires. I run 115 steer 95 in the drive and 90 in the tag. If you run 120 in all tires you will not have any issues but the ride will be rough. I just went to Camp Freightliner and they say weigh your coach calculate the manufacturers pressure and add 10psi to the rear and 5psi to the front. As stated by Freightliner the placard is put at the max pressure because Freightliner does not know what the coach builder will put on the chassis. Freightliner is the one who puts the placard on not the chassis builder.

As a tire engineer I agree with the above. You also may not see a real ride difference between 115 and 120

[Ray,IN]

Originally Posted by wildtoad

Not doubting you've seen this somewhere, but I've never seen this in relation to RV's. Could you provide a link that shows this? If true then 95% of people would never need to weigh their units. Yet both the RV manufacturer and tire manufacturer state to get the thing weighed and set pressures according to the tire pressure charts.

In my case, the placard shows a REAR pressure thats about 12lbs over what Goodyear says is required for the GAWR.

Goodyear Inflation Guide pdf, pg 4
Tire inflation charts show the minimum pressure for the corresponding load, not the optimum.

[wildtoad]

Originally Posted by Ray,IN

Goodyear Inflation Guide pdf, pg 4
Tire inflation charts show the minimum pressure for the corresponding load, not the optimum.

Exactly correct but I'm not sure what is optimum. So somewhere between the Goodyear chart value which, based on whichever weight you choose to use ( actual measured, GAWR ), is a safe number to run the load and the pressure on the side wall ( the hard as a rock number ) is a good number.

I choose to use the GAWR and the Goodyear tire chart number which gives me a comfortable ride which is sufficient to carry my load. I realize a higher pressure may give me a ever so slightly improvement in MPG.

[Ray,IN]

Originally Posted by wildtoad

Exactly correct but I'm not sure what is optimum. So somewhere between the Goodyear chart value which, based on whichever weight you choose to use ( actual measured, GAWR ), is a safe number to run the load and the pressure on the side wall ( the hard as a rock number ) is a good number.

I choose to use the GAWR and the Goodyear tire chart number which gives me a comfortable ride which is sufficient to carry my load. I realize a higher pressure may give me a ever so slightly improvement in MPG.

Of course everyone is free to do as they choose with their property. This is what Goodyear says about running reduced air pressure:
"MPORTANT: It's a common practice for RV owners to lower tire pressure in their search for a smoother ride. This is not only dangerous, it's relatively ineffective, as the difference in ride quality is not significant."

[FastEagle]

Originally Posted by Ron Postma

Don't go above 120 psi this is the max air pressure of the tires. I run 115 steer 95 in the drive and 90 in the tag. If you run 120 in all tires you will not have any issues but the ride will be rough. I just went to Camp Freightliner and they say weigh your coach calculate the manufacturers pressure and add 10psi to the rear and 5psi to the front. As stated by Freightliner the placard is put at the max pressure because Freightliner does not know what the coach builder will put on the chassis. Freightliner is the one who puts the placard on not the chassis builder.

Is Freightliner the final stage manufacturer?

Does Freightliner take responsibility for final stage GVWR?

Does Freightlner certify the final stage (finished product)?

FMCSA regulations are not applicable for vehicles certified in accordance with FMVSS (Standards).

[mport68]

None of the 5 coaches I've owned have provided a "recommended inflation pressure". Rather, they have all provided a "maximum inflation pressure" that was based upon the maximum vehicle weight. I'm not saying that other coach manufacturers don't provide a pressure recommendation but i don't see how it could be accurate as one number can't account for all of the various loading configurations. In my limited experience, all of the manufacturers I've worked with have recommended that the coach be correctly weighed and pressure set accordingly. Michelin has such charts specifically for their brand of RV tires online.

[Tireman9]

There is some confusion with "Maximum" and "Minimum" inflation.

HERE are two blog posts on that topic if you want clarification and the facts.

For your own safety it is important that you understand the real meaning of these terms.

[Ray,IN]

Originally Posted by Tireman9

There is some confusion with "Maximum" and "Minimum" inflation.

HERE are two blog posts on that topic if you want clarification and the facts.

For your own safety it is important that you understand the real meaning of these terms.

That should be mandatory reading for everyone with a drivers license.

[Ray,IN]

Originally Posted by mport68

None of the 5 coaches I've owned have provided a "recommended inflation pressure". Rather, they have all provided a "maximum inflation pressure" that was based upon the maximum vehicle weight. I'm not saying that other coach manufacturers don't provide a pressure recommendation but i don't see how it could be accurate as one number can't account for all of the various loading configurations. In my limited experience, all of the manufacturers I've worked with have recommended that the coach be correctly weighed and pressure set accordingly. Michelin has such charts specifically for their brand of RV tires online.

Per federal law, there must be a federal tire placard on every vehicle sold. You have one somewhere that states "recommended tire pressure" unless it was deliberately removed.

[mport68]

Originally Posted by Ray,IN

Per federal law, there must be a federal tire placard on every vehicle sold. You have one somewhere that states "recommended tire pressure" unless it was deliberately removed.

What the placard actually says is "Cold Tire Inflation Pressure"... but unfortunately I was far from clear at getting my point across. The issue as I understand it is what is the correct amount of air pressure needed. The placard does in fact give numbers that should be used, absent any actual data for that specific coach. The posted numbers assume the worst case, fully laden condition that the chassis can support. So, if you do not know what load each tire will be subjected to, these are the default values that will provide a safety margin. However, if you do as recommended by both the RV and tire manufacturer and weigh your coach fully loaded you will likely find that the amount to safely operate is well below the value given on the placard. For example, my coach recommend 110 psi at the tag. However, based upon the tire manufacturers pressure charts, my tire needs 85 psi to safely support the actual weight. So, I run between 95 and 100 just to be safe.

[mport68]

I copied this from Winnebago's operators manual. It's found in the maintenance section under how to weigh your motor home:

"Tires must be filled to the recommended air pressure for the highest loaded tire set on that axle. For example, on the rear axle, if the left side weighs more than the right, fill the left tires to the pressure required for that weight, then fill the right tires to the same pressure as the left ones.

If your actual weight is considerably less than GAWR, you may be able to lower your tire pressure. See a tire dealer for a load/pressure chart.

[Tireman9]

Guys, and Gals... I have over 260 posts on my tire blog with 43 being tagged with "Inflation" and 22 with "Load" and 9 on "weight".
I obviously can't re-post all that info on this forum so how about those with any questions on what is the "proper" inflation for your RV take a few minutes and do a review.

[jwmaustin]

I think reviewing tire inflation is a good idea, it's always good to be better informed.

I have a question though regarding data that we could all supply and it's this:
If the recommendations are that we measure weights on all 4 corners (or each of 6 points for tag axle models?) AND it's recommended that we fully load with fuel, water, etc. then how much variability is really due to owners placing their loads in the motorhome?

If there isn't that much variability then why don't we publish what has been found for weights for a given model and those of us with that model can set pressures accordingly? So who has 4 corner weighed a WGO Ellipse or Tour 42HD? That's the data I want.

Bill

[Tireman9]

Originally Posted by jwmaustin

I think reviewing tire inflation is a good idea, it's always good to be better informed.

I have a question though regarding data that we could all supply and it's this:
If the recommendations are that we measure weights on all 4 corners (or each of 6 points for tag axle models?) AND it's recommended that we fully load with fuel, water, etc. then how much variability is really due to owners placing their loads in the motorhome?

If there isn't that much variability then why don't we publish what has been found for weights for a given model and those of us with that model can set pressures accordingly? So who has 4 corner weighed a WGO Ellipse or Tour 42HD? That's the data I want.

Bill

Problem with using someone elses weights is that there may be options or mods to the RV and yes some people travel with full water while others may only carry a few gal of water in the RV.

[jwmaustin]

Well actually everyone seems to say to weigh with full water/fuel tanks and empty black/gray tanks. Those are some of the heaviest factors. I know of very few heavy options or modifications. Gathering data would prove the point easily and get away from what otherwise are just someone's opinions. When I get a chance I'll start a post to do that.