Optimum Inflation for Toyo Tires

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.

JoelP

Well-known member
Joined
Nov 2, 2016
Posts
669
Location
San Jose, CA
I finally got around to having my coach weighed on my current trip, recording the weight of the front and rear axle as well as the dinghy.  I was glad to see that I was not overloaded per the placard. Then I went online to the Toyo website and downloaded their info on inflation of tires by size and was surprised to not find my tire size on this chart.  Perhaps I am looking at the wrong chart.  My tire size is 245/75R22.5. There is no "P" in the front of the size number, so I take it that this is a n ISO size standard. It's also labeled as an M154 and load range 6. Could somebody point me to the right chart to tell me how to best inflate my tires? 
 

blw2

Well-known member
Joined
Aug 9, 2012
Posts
3,325
Location
Saint Johns, FL
for my Yokohama tires i couldn't find it either.  they only publish truck tires.
I talked with someone at Yokohama that was supposed to be an engineer...or at least he was some tech support role

He explained that all these numbers from different manufacturers come form the same standards put out by the "tire and rim association".  Apparently it's a standard that they all buy, it's just that some folks choose to publish it and some don't. He advised em to use the numbers I had from Michelin for my previous tires.  Said it would be exactly the same as long at were're taking same size and same load rating

Just relaying what I was told, I have no real knowledge if it's true and correct or not....just seems plausible to me.
 

johnaye

Well-known member
Joined
Aug 6, 2016
Posts
273
captsteve said:
Here ya go...


https://www.toyotires.com/media/2155/2017_commercial_loadandinflation_tables.pdf
Thank you.  I also needed this
 

JoelP

Well-known member
Joined
Nov 2, 2016
Posts
669
Location
San Jose, CA
captsteve said:
Here ya go...


https://www.toyotires.com/media/2155/2017_commercial_loadandinflation_tables.pdf

I am still somewhat baffled about inflation.  The coach has a placard that says to inflate the front tires to 100 and the back tires each to 90 psi.

After weighing the coach as loaded I find that there is

7600 lbs on the front axle or 3800/tire.  If I add 10% this would be 4180 and the Toyo chart for 245/75R22.5 can bee interpolated to say I should inflate to 91.5 psi,and

15040 lbs on the rear axle or 3760/tire.. If i add 10% this woudl be 4136 and the Toyo chart for 245/75R22.5 can be interpolated to say I should inflate to 103 psi for dual tires.


Is this right?  How can it be so different than the pllacard on the vehicle.  It has the rear inflated to what the fronts are on the placard and conversely.  Am I reading the chart wrong?

Thanks!
 

SeilerBird

Well-known member
Joined
Feb 25, 2012
Posts
15,823
Location
St Cloud Florida USA
JoelP said:
I am still somewhat baffled about inflation.  The coach has a placard that says to inflate the front tires to 100 and the back tires each to 90 psi.

After weighing the coach as loaded I find that there is

7600 lbs on the front axle or 3800/tire.  If I add 10% this would be 4180 and the Toyo chart for 245/75R22.5 can bee interpolated to say I should inflate to 91.5 psi,and

15040 lbs on the rear axle or 3760/tire.. If i add 10% this woudl be 4136 and the Toyo chart for 245/75R22.5 can be interpolated to say I should inflate to 103 psi for dual tires.


Is this right?  How can it be so different than the pllacard on the vehicle.  It has the rear inflated to what the fronts are on the placard and conversely.  Am I reading the chart wrong?

Thanks!
The placard is probably listing the maximum psi. The recommended psi should be set by weighing and checking the manufacturers chart. The psi would change depending on how much weight it was carrying.
 

JoelP

Well-known member
Joined
Nov 2, 2016
Posts
669
Location
San Jose, CA
SeilerBird said:
The placard is probably listing the maximum psi. The recommended psi should be set by weighing and checking the manufacturers chart. The psi would change depending on how much weight it was carrying.

The weight I am carrying is <3% of the weight of the rig itself per the weights I just had measured, so I think the loading has only a small impact. The placard doesn't say max pressure.  It states a pressure to measured on a cold tire. If it were a max value then the Toyo chart numbers for the rear duals would exceed the placard value, if I am reading this chart correctly.
 

Alfa38User

Well-known member
Joined
Oct 4, 2007
Posts
6,676
The pressure on the placard is NOT the maximum pressure for that tire but may well be the minimum pressure required for an empty vehicle as it left the factory. The maximum cold pressure for any give tire is molded into the tire itself. As for the correct pressures, use the chart from the manufacturer for the weight that the tire is supporting. Don't forget on a dual tire rating the weight has to be divided by 2 for one side (or per wheel) weight figure or 4 for a full axle weight. (You have 4 tires supporting that total weight!!) If the chart gives a 'dual tire' figure use that instead of doing the math.

Many tire places simply inflate the tires to the max as shown on the tire as they have no idea what the rig weighs.
 

JoelP

Well-known member
Joined
Nov 2, 2016
Posts
669
Location
San Jose, CA
Alfa38User said:
The pressure on the placard is NOT the maximum pressure for that tire. The maximum cold pressure for any give tire is molded into the tire itself. As for the correct pressures, use the chart from the manufacturer for the weight that the tire is supporting. Don't forget on a dual tire rating the weight has to be divided by 2 for one side (or per wheel) weight figures or 4 for a full axle weight. (You have 4 tires supporting that total weight!!)

Many tire places simply inflate the tires to the max as shown on the tire as they have no idea what the rig weighs.

Yes I read the max pressure on my tires at 110PSI on the tires.  And, as you mentioned I divided the axle weight by 4, but you may have hit on something I could have done wrong.  The chart has single tire and dual tire recommendations. Do I divide by 4 and then look at the dual tire line, or do I divide by 2 and look at the dual tire line? I divided by 4 and looked at the dual tire line to arrive at my pressure setting. If I had divided by 2 it would have put me off the chart in weight, so it must be to divide by 4. That is what gave me 103 rear and 92 front, almost the inverse of the placard. Is that typical from what you have seen?  It seems to me that the dual tire number is not just to save me the math, but a reflection of how dual tires perform differently than single tires.

When I look at the title of the Toyo chart it states that this is a table of load limits for their tires.  That would say that Winnebago gave me a front tire placard recommendation that is for a far higher load than is necessary.  Most of the weight that I add is everywhere but in the front, which is primarily the weight of the gas engine and transmission.  (...and no comments please about my weight or my DW)

What is the impact of running at over or under pressure?  If within the max pressure range is it tire wear, ride comfort, suspension safety, or other?
 

Ernie n Tara

Well-known member
Joined
May 16, 2009
Posts
4,082
Location
Ft Myers, FL
Actually, the placard would most likely be the correct pressure at gross weight and the coach manufacturer's assumed weight distribution. If you are heavier on the rear tires (water full?) Then a higher pressure would be appropriate. If you are sure of the weights, then I'd use the tire manufacturer's chart plus a few PSI .

Ernie

 

Gary RV_Wizard

Site Team
Joined
Feb 2, 2005
Posts
73,539
Location
At our Silver Springs FL home
RV manufacturers usually set the placard psi based on the axle GAWR, meaning the assume the axle may be required to carry its max design load (weight) and set tire pressure accordingly.  They don't have any idea how you will actually load the coach when you get it, so they assume the max rated loading.  The axle GAWRs are shown on the placard as well, so you can verify that if you like.  Also verify the the placard is for the tire size you are using (245/75R22.5). If the placard shows a different tire size, you cannot use the psi values on the placard.

It's common for a coach to weigh in under the axle rating (GAWR) on the front axle, so they required inflation up front is often less than the placard shows for max load.  However, it is also common for the rear axle to be at or above its max axle weight. If the actual is above the max, then the psi in the table will exceed the placard value.


Per the 2010 Suncruiser brochure, a Suncruiser 37F on the Workhorse W22 chassis is equipped with a 8,500 lb front axle and a 15,000 lb rear axle.  95 psi would be the minimum for a fully loaded front axle, so it looks like Winnebago added 5 psi to that to allow some extra cushion.  For the rear, at max load it would be 3750 per tire and the table shows just under 90 psi for that weight. Only a tiny extra cushion there.
So, your rear axle is overloaded at 15,040 and adding 10% margin pushes it way over the rating.
 

John From Detroit

Well-known member
Joined
Apr 12, 2005
Posts
24,807
Location
Davison Michigan
The placard inside the coach....
The factory took a GUESS as to how you would load the RV based upon the way others do. Of course it is an ASSUMPTION and like many ASSUMPTIONS it is WRONG where you are concerned.

For example. Do you fill your fresh water tank before a trip? Makes a big difference (about 640 pounds on my RV)  How much do you lug in tools?  What make and model grill. Chairs. Scooter/bicycles. all add up and add up DIFFERENTLY for you than for me.

So the placard is WRONG. all but guarantied to be WRONG.
 

Gary RV_Wizard

Site Team
Joined
Feb 2, 2005
Posts
73,539
Location
At our Silver Springs FL home
Since the RV manufacturer is legally liable for the recommendation they put of the federal tire placard, you can bet the "wrong" information is highly conservative.    I prefer to say that the info on the placard is nearly always "sub-optimal".  ;)
 

JoelP

Well-known member
Joined
Nov 2, 2016
Posts
669
Location
San Jose, CA
OK I am convinced.  The placard has significantly different tires than I am using. I adjusted to the chart already.  Thanks everyone.
 

phil-t

Well-known member
Joined
Jul 10, 2017
Posts
871
Location
Ogdensburg, NY
JoelP said:
*******************************
What is the impact of running at over or under pressure?  If within the max pressure range is it tire wear, ride comfort, suspension safety, or other?

Under pressure can lead to tire failure, rather quickly.  You want the correct pressure for the best handling.

Seems you have a good handle on the tire pressure thing - good luck in your travels - stay safe.
 
Top Bottom