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Old 10-12-2010, 04:21 PM   #15
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Tom and Patty..I was just taking a quick look through your picture album at the bottom of your post...they are really great, and you dogs and cat look like they are in eternal bliss. How did you put these together in an album like this for 1rv2?

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Old 10-13-2010, 09:18 PM   #16
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Reserve load Part #1

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Originally Posted by FastEagle View Post
Hi Tireman, FastEagle Here.


What is your basic explanation as to just how a tire manufacturers tire inflation table is supposed to be applied when used in conjunction with self propelled RV vehicles or RV trailer tires?

We see a lot of experts talking about the reserve load carrying ability tires are supposed to have. But we cannot find it in print. By using a load inflation table as you and many other highly knowledgeable people in the tire industry promote, we can end up with zero published reserves.

Here is a case I have specs for. Sorry itís for an RV trailer but if helps demonstrate how most of the RV manufacturers view their responsibility when it comes to selecting tires.

An RV trailer with two 7000# axles is delivered to itís new owner with four ST235/80R16E tires on those axles. The vehicle tire placard tells the owner to air those tires to 80 psi (matching the maximum amount shown on each tires sidewall) to obtain 3520# of load carrying ability from each of the tires. The vehicle manufacturer has satisfied his requirement to equal or exceed the DOT requirement for tires on those axles. The new owner has a total reserve load carrying capacity totaling 80#. I donít care who made those tires. They are going to fail and early. My guess would be less than a year if the owner is loaded close to GVWR.

The bottom line here is when you tell us to use the load inflation tables as describe in your thread above you are placing us in the same condition the vehicle manufacturer has put the above owner in.

Knowledgeable tire people will say the Light Truck tire has a greater reserve than the Special Trailer tire but NOBODY will publish it as fact with figures. These same people say ST tires degrade faster than LT tires yet they fail just as frequently when used under equal conditions.

When reading through the major 2007 DOT rules changing document many of those giving inputs into the decision making process recommended that RV tires be required to have a minimum of 12-15% reserve load carrying capacity above the GAWR. The rules makers disagreed and left the industry as is until such time as new rules are discussed again.

Iím a firm believer in a large reserve, especially for the RV. I have an RV trailer and I keep tires on it that will always give me a 20% reserve.

FastEagle

p.s. Here is a little wrench for your gears.
When an RV trailer manufacturer puts tires rated at 3420# @ 80 psi on both ends of a 6000# axle and tells the new owner via the tire placard that that is his minimum recommended requirement, what is the owner to do when you tell him itís OK to use the tire manufacturers load inflation table? According to the DOT the vehicle manufacturer sets the inflation pressures (using the information from the tire manufacturer) for the tires he has selected for that axle.
Hi FE
Lets see if I can shed some light to help those that are interested understand the various issues.

Lets start with by defining our terms.
"Reserve load" is generally understood as the mathimatical difference between the published load capacity at a given inflation and the actual static load on a tire. The "actual load" is generally considered "curb weight" for passenger cars.

Reserve Load is something most used when evaluating Passenger car applications and for a good number of cars the Reserve Load is in the 10% to 20% range. There have been a few notible exceptions where the Reserve Load ended up being less than the weight of four passengers with no luggage.

Now when we move to Truck appllications the history was that we were dealing with professionals who were required by law to not exceed certain axle load limits. In the Trucking industry, vehicles are load limited so the application was based on the max published load at the max published inflation with 0% Reserve Load.

Light Trucks are really an off-shoot of Heavy truck when it comes to the max capability. The fly in the ointment with LT is that there are a lot of people driving empty pickups around and they don't like the bad ride. If people used their truck as a truck there would be less of a problem. Some manufacturers publish dual inflation to address this problem. Too bad there are so many users who lower the pressure for a good ride but forget to inflate their tires when they load their truck.

Motorized RVs are basically like Light Trucks ( Class B & C) or more like heavy trucks (Class A) when it comes to tire sizing, loads & inflations.
I am not aware of any Official or un-Official "Reserve Load" built into the recommended inflation for these applications.

HOWEVER

There are some issues unique to RVs. Primarily those are related to a significant portion of RVs being operated with tires in an overloaded condition.
Unlike Heavy Trucks, few Class-A are pulled over and weighed and I do not think that Class-A have to go through weigh stations so the owners have no idea what their rig weighs and the do not check their inflation so don't know when they have lost pressure. These problems affect Class-C & B but to a lesser extent.

OK
I think this post is long enough. I will post Part #2 in the next day or so and will cover the effects of Load Calculations on the different applications then go into the unique ST applications.
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Old 01-21-2011, 10:05 AM   #17
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Here is a bit of safety information for those that may not know about it. The DOT will recall the GY G159 from use on motor homes starting this month. They are not suited for use in those positions.

G159 - Bing

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Old 01-23-2011, 11:58 AM   #18
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In case anyone's interested, I found a fairly useful tire size calculator online, http://www.powerdog.com/tiresize.cgi

there's a box to enter tire sizes, you can enter as many different sizes as you want, just press enter to add another tire size. Then press the "compute sizes" button, and it will list the sidewall width, tire radius, diameter, circumference, and revolutions per mile of all sizes you entered. The first size entered is used as a "base size", all other sizes are compared to it, showing difference in speedometer reading @60 mph, and odometer reading @10,000 miles...

For some reason, it won't take 1/2 size tires (22.5 comes up 22) but otherwise, it shows you an accurate difference between sizes.
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Old 03-19-2011, 03:31 PM   #19
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Here is another good one.

Yokohama Tires
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Old 05-05-2011, 07:47 PM   #20
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@154# per, I am overloaded before I get aboard...
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Old 07-05-2011, 02:32 PM   #21
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TOYO link for RV tire tables....

Quote:
Originally Posted by Nick-B View Post
I have Toyo tires on my Coachmen and I know they are popular with other RVers so here is the link to their Load/Pressure info:
LOAD & INFLATION TABLES | Toyo Tires

The link gets you there, but not to the RV tables. On this same site is a specific link and table for RV tires, but it isn't obvious unless you hunt for it. I stumbled across it and here it is:
RV TIRE CARE | Toyo Tires
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Old 08-06-2012, 10:12 AM   #22
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Reviewing some old posts and realized I never provided the part #2 to FastEagle's question.

I previously covered motorized RV load ^ inflation and suggested that after learning the MINIMUM inflation needed to carry your load you add a few psi (+10% is a nice calculation) This will give you Reserve air or Reserve inflation and this means you ahve reserve load. Now some suggest a specific reserve load % but I don't thine the end result will be much different.

Now multi-axle towables are a completely different story.
You should still get on a scale but this is to make sure you are not in the 57% of the trailer community that are overloaded to start with.

The cornering forces on multi-axle units place enormous side loads on the tires when cornering. These forces are trying to tear the belts and tread off the tire. The tire industry has the Finite Element software to predict these forces and they exceed a 20% increase over the side forces seen in other RVs. The only way an owner can help decrease these forces other than reducing the load by a very large amount, is to increase the inflation pressure to the max for the tire.
This is almost always reflected in the tire placard inflation which for many ST tires is 65 psi (read your placard and read your tire to learn what your max tire inflation is).

Hope this helps.
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Old 09-15-2012, 07:45 PM   #23
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Question More questions/answers - Oh I don't know - whatever!!

Just some more food for thought about tire pressure. I recently purchased a used Chinook 24 Ft motorhome. The tires were in ok shape (14000mi) but were old so I replaced all six. Then the inflation odessy began.

The tire place said to run the Michelins (LT225/75R16) at 65 F 80 R
While getting some work done the RV dealer set the tire to 60 F 65 R
The door sticker says (which is what the RV dealer used) 60 F 65 R
After an oil change the Chev dealers said to use 75 F 75 R
Using the Michelin chart it says to use (minumum) 45 F 50 R

The corner weights on the Chinook are (weighed fully loaded to go)
Driver side front 1725
Passanger side front 1600
Driver side back 3350 (Dual)
Passanger side back 3525 (Dual)

How much air would you put in the tires?
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Old 09-16-2012, 01:44 AM   #24
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Quote:
Originally Posted by PHCM USN RET View Post
Just some more food for thought about tire pressure. I recently purchased a used Chinook 24 Ft motorhome. The tires were in ok shape (14000mi) but were old so I replaced all six. Then the inflation odessy began.

The tire place said to run the Michelins (LT225/75R16) at 65 F 80 R
While getting some work done the RV dealer set the tire to 60 F 65 R
The door sticker says (which is what the RV dealer used) 60 F 65 R
After an oil change the Chev dealers said to use 75 F 75 R
Using the Michelin chart it says to use (minumum) 45 F 50 R

The corner weights on the Chinook are (weighed fully loaded to go)
Driver side front 1725
Passanger side front 1600
Driver side back 3350 (Dual)
Passanger side back 3525 (Dual)

How much air would you put in the tires?
check this resource:

Michelin North America RV Load & Inflation Tables

ie, minimum of 45 psi front cold, 50 psi rear cold. i add 10% for 'cushion' in my tires. that would be 50 front, 55 rear.
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Old 09-16-2012, 10:45 AM   #25
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I agree that you should consider your "minimum" to be 50/55 but assuming you have Load Range E (information you did not provide) I would suggest you run 60/65 as you will see slight improved fuel economy.
My Class-C RV needs 50/55 based on load but I run 65 all around and find the Chevy 3500 chassis provides good ride at that level. I am getting 11+ mpg.

Also get a TPMS to help avoid tire problems from punctures and slow leaks etc.
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Old 09-16-2012, 06:28 PM   #26
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Quote:
Originally Posted by PHCM USN RET View Post
Just some more food for thought about tire pressure. I recently purchased a used Chinook 24 Ft motorhome. The tires were in ok shape (14000mi) but were old so I replaced all six. Then the inflation odessy began.

The tire place said to run the Michelins (LT225/75R16) at 65 F 80 R
While getting some work done the RV dealer set the tire to 60 F 65 R
The door sticker says (which is what the RV dealer used) 60 F 65 R
After an oil change the Chev dealers said to use 75 F 75 R
Using the Michelin chart it says to use (minumum) 45 F 50 R

The corner weights on the Chinook are (weighed fully loaded to go)
Driver side front 1725
Passanger side front 1600
Driver side back 3350 (Dual)
Passanger side back 3525 (Dual)

How much air would you put in the tires?
The correct tire pressure is the recommended cold pressure (s) found on the tire placard. Some times vehicle manufacturers will make exceptions and those exceptions can be found in the ownerís manual.

There are other procedures to follow when deviating from the OE tire sizes found on the placard. However, the load capacity provided by the OE tires would then be the factor to use when setting new recommended tire pressure (s) for replacement tires.

When using tire manufacturer inflation tables donít forget to insure the load capacity reserves set by the vehicle manufacturer are honored.

FastEagle
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Old 09-16-2012, 06:45 PM   #27
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The vehicle placard is only valid if loaded to the max weight, with the original equipment brand, model and size. Any changes to that requires using actual vehicle weights and the tire pressure charts from the tire manufacturer.
You take the heaviest weight on an axle and use it for all tires across that axle. Cold pressure is at ambient temp and driven less than one mile.
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Old 09-17-2012, 09:49 PM   #28
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Quote:
Originally Posted by Mr_D View Post
The vehicle placard is only valid if loaded to the max weight, with the original equipment brand, model and size. Any changes to that requires using actual vehicle weights and the tire pressure charts from the tire manufacturer.
You take the heaviest weight on an axle and use it for all tires across that axle. Cold pressure is at ambient temp and driven less than one mile.
When you use that method what happened to the load capacity reserves the vehicle manufacturer provided?

FastEagle
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