Setting Motorhome inflation for "Newbie"

Reading a forum post that said:

"We are moving across the United States for our FIRST trip in our 06 Mountain Aire. Don’t think that’s a great idea for a first trip, but that’s what’s gonna happen. LOL. I do not have access to a four corner scale. I do have access to a cat scale. I downloaded the Michelin tire pressure guide. From what I remember here, I take the axle weight and use the Michelin guide? I seem to remember someone saying to add 5 psi to compensate for the lack of a 4 corner scale?"

My reply:

You can read my RV Tire blog for more details for Motorhomes (but not towables)

1. If you have no scale reading follow the Vehicle Certification Label AKA (Tire Placard)

2. As soon as possible, get on a truck scale when you are at your heaviest (full of fuel, food, water, propane, clothes, people etc).

3. Using the axle load numbers: Confirm no axle exceeds GAWR (gross axle weight rating) (on placard) and the RV does not exceed GVWR (gross vehicle weight rating) (on placard). If you exceed either max weight rating you must move or eliminate some "stuff" in the RV.

4. If your weights are lower than GAWR then you MIGHT be able to lower your inflation a bit but there is some effort involved.

5. Since you will not have "4 corner weights" you will not know how much out of balance side to side you actually are. Some RVs have been found to be 1,000# out of balance on an axle.

6. I suggest at a minimum you assume one end of each axle is carrying 53% of the total axle load. You could use the 53% number to consult the Load & Inflation tables.  WARNING Michelin tables assume perfect 50/50 load balance which IMO is not realistic, so you need to calculate the individual axle end load ( divide Michelin number by 2)

7. Using the 53% load number and the calculated Michelin load number you now know the MINIMUM Cold Inflation aka MCI number. It is suggested you add 10% to that inflation number for inflation when setting tire inflation. This is your daily measured Cold Inflation Pressure aka CIP. This 10% covers you for day to day temperature and elevation changes.

8. If or when the measured cold inflation (or inflation reported by your TPMS) drops to your MCI number you need to add some air to get back to your 10% margin number.

9. I see no reason to ever bleed off pressure from your daily measured CIP unless your reading is higher than the inflation number molded on the tire sidewall. If you get that high you can bleed down to the tire sidewall pressure but never below the MCI.

Ya a bit of work but once you think about your goal - Stay above the MCI and below the inflation molded on the tire sidewall you are good to go. A TPMS makes the job of checking inflation on each day of travel much easier as you simply check each morning before you start out. TPMS will also give you a warning when or if you get a puncture od have a leaking valve and are losing air. A good TPMS will have some form of "early warning" when you start to lose a couple PSI while running down the road. This could prevent a serious tire failure.

4-Corner weights and a "Meaningful" measurement.

I was following a forum thread on using closed state scales to learn your "4 corner weights" This is possible in WA & OR and some other states. 
Some commenters felt the practice was not wise as the area around the platform scale might not be perfectly flat. I posted my thoughts on the topic.

Not sure if I understand the concern over the accuracy of using a large platform scale to try and get a handle on your side to side loading.

I have a blog post on "Measurable vs Meaningful" that some might want to review.

When setting the inflation based on the published Load & Inflation tables, you should always "err on the high side." This means if your measured weight were 2,005# you should go UP to the first weight that exceeded 2,005# and maybe even higher.

Let's assume the table for your tire gave 90 psi at 1,900#  and 95psi at 2,210#. I would recommend you select 95psi as your MINIMUM inflation.  But what would you do if the chart for your tire showed an inflation for 2,010# or 2,005# or 2,000#? Would you cut things so fine as to select the inflation for these loads?  I hope not. What might happen if 50 minutes after getting the tire loads you top off the fuel and buy some groceries? You are now most certainly over the measured 2,005#. Are you gonna run back to the scales?  I wouldn't, and I would not need to as I have a built-in cushion of load capacity over the minimum needed to support my actual load.

We haven't addressed the question of your tire pressure gauge accuracy. Unless you have access to ISO Certified laboratory gauges as I do, you probably need to assume that your gauge is off by at least one increment reading of the pressure scale. For some truck type stick gauges that means 5 psi. What is your cushion that covers your gauge accuracy?

My "cushion" results from a few actions.
1. I always go up in the charts to the next inflation level and if my measured load is within 100# of a level, I will go up TWO levels of inflation which would be 10 psi.
2. I also add 10% to the selected table inflation and again round up to the next "0" or "x5" pressure

The additional 10% means you can avoid having to chase the Cold Inflation level every morning when the temperature drops and pressure drops a few psi.

When I checked my "4 corner weights" on the state scale was the area beside the platform exactly level? No, it wasn't, but it looks close enough that even if my weight was off by 100# my other adjustments would more than compensate.

##RVT823

Another example of learning correct tire inflation

Quote:

Originally Posted by Ron Tireman9 and others....I just ran my coach over to the local Cat Scales at a truck stop nearby. As I stated earlier they do not make things easy and a 6" curb on each side of the scales prevented me from putting each side on separately so that I could get a close four corner figure. I settled on the two axle approach. All tanks were full, (water tank was actually just over 2/3, it fills very slowly and I got bored). Front axle came in at 11,400 lbs, rear axle was 16,560 lbs. My front axle is rated at 13,300 lbs and the rear is 21,000 lbs with a GVW of 34,300 lbs. 295-75R-22.5 tires. I have looked at the tables but would like to see what you folks come up with for approx. front/rear inflation? Thanks, Ron

Ron, you didn't say the brand tires. To my knowledge all major brands except Michelin have the same info for load & inflation and Michelin is same on maybe 95% and those that differ may only differ by 5 psi or so.

Since you only have total for an axle and do not know the heavy side we estimate one side at 53% -- So Front would be 6,042 and rear 8777 (4,389 per tire).

Most 295/75R22.5 LR-G need 110 to support 6,175 F (single) and 80 psi to support 4,540 in Dual.

Since I recommend a +10% of air for a good margin, that would suggest 121 psi front and 88 for the rear. BUT a LR-G is only rated for 110 psi so you need LR-H on the front. Also need to confirm the front wheels are rated for 120 psi and since even H are only rated for 120 that makes the recommended Front inflation 120 psi.

Clearly the estimate of 53% is causing the problem so it increases the need for you to learn the actual side to side load on the tires by going somewhere other than CAT truck stop scale.

It is CAT policy to not do one side weights and that is why they are making it harder to only get one side on the scale.

I suggest RVSEF

EDIT AND UPDATE   8/16/20

Locations with scales
https://www.dieselboss.com/service.htm
https://www.allstays.com/c/weigh-scales-locations.htm
https://www.publicscaleslocator.com/
SmartWeigh is another option

I checked around home and found a local building supply that had a scale that would give me 4 weights for $10. Only about 3 mi off I76 just East of Akron OH.

##RVT799

Quick post on RV weight

Read a question on an RV forum about "4-Corner weights vs. just getting axle weights." Here is my reply.

Getting 4 corner weights (actual load on each tire for trailers or each position on motorhomes) is definitely worth doing, once. Once you figure your numbers you are typically good to go for the life of the tires or unless you change something big.

Do it fully loaded,  i.e., fuel, water, canned goods, fishing gear, clothes, books, people, etc.

Based on actual data from RVSEF, very few RVs have side-to-side loading at 50/50%. Some owners have discovered one axle end as much as 1,000 lbs. heavier than the other!

Once you know for a fact that you have at least a few hundred pounds "cushion" (being under your RV GAWR [gross axle weight rating] and GVWR [gross vehicle weight rating]), you don't need to do corner weight again unless you make a major change or remodel of the RV (e.g., adding a residential fridge or granite counter-top) and have a reasonable balance to start with.

I do suggest at least once a year a quick check of axle loading by going through a truck stop scale. You can compare the truck scale numbers with your corner weight totals to confirm your RV hasn't suffered from weight creep, as some of the drivers may have noticed over the years.


Weight terminology tidbits:

SCWR (sleeping capacity weight rating)

The manufacturer’s designated number of sleeping positions multiplied by 154 pounds (70 kilograms) which is the official weight of people in cars and RVs.

CCC (cargo carrying capacity)

The GVWR minus each of the following: unloaded vehicle weight, full fresh (potable) water weight (including water heater), full LP-gas weight, and SCWR.
This new label permits the buyer/owner to determine the carrying capacity (CCC) based on a personal calculation of actual passengers carried, the amount of fresh water onboard, and the amount of LP-gas carried.

More info on terms and abbreviations can be found HERE



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When and Why some need to "De-Rate" their tires

Had a question from a TT owner about De-rating the tire load. He wanted to use P-Type tires on his trailer.

Can you explain why anyone would need to de-rate the weight rating just because a tire is used on a trailer? I don't understand why if the rating is 2510 lbs on one vehicle why wouldn't it be the same on another at the same pressure?

The quick and simple answer is that the service or environment seen by cars is not the same as the service seen by trailers. You don't design a home for northern Canada the same as a home in Mexico as the environment is significantly different.

Now if you don't like the simple answer here is a longer approximation.

When tires are designed there are certain things that can be expected. First off they are expected to pass all the regulatory tests. Some of these tests will be at or near the tire's max rated load. None of these tests are for 60,000 miles but may only last 2,000 miles at the max when running in 100F temperature on a curved drum (which is much harder than running on flat surface) and the tire is never be allowed to cool down as it is also run at say 50 mph. Outdoor testing may be at 100% load and 30,000 miles but the test car does come to a stop for 30 min or so every few hours. The test track however has no sharp turns or pot holes.

If a tire can survive the above in all probability it can run 60,000 on regular highways BUT occasionally at higher speeds and with occasional pot holes etc. We know that there is a "reserve load" of say 10% to 20% between the tire's load capacity at the placard inflation in normal car operation and there may only be 10% or less of the time the tire is asked to run anywhere near it's max load.

Now if that same tire is put on a small pick up or SUV the % of the time it may be required to run at or near it's max load may be 50 % or more.
It was learned many years ago with the introduction of station wagons that if we were to avoid premature tire failures something needed to be done. At the time there were only passenger and true truck tires so the only option was to reduce the load allowed when the passenger tires were placed in station wagon service. Later on, when SUVs were invented they replaced station wagons in the market place so the definition of "Multi-purpose" vehicles was coined and since pick up trucks were "civilized" to be more like cars and less like trucks and occasionally passenger type tires were applied to these trucks. Again the percentage of time the tire was asked to operate at its max load capability was much greater than when the same tire was placed on a car.
The "de-rating" was established at a factor of 1.10

Now in reality early RV trailers were single axle but would spend an even greater portion of the time at their max load. To counter that their service life was much less so the 1.10 factor was applied to passenger tires in trailer service.

If you look at the rated load capacity of a true LT type tire vs a P type at the same inflation you will see that the LT is rated at about 25% lower load capacity. This is because vehicles that are expected to be used as trucks ie a major part of their life fully loaded, the reality of the physics involved dictates that if you want to get 40 to 60,000 mile life you must reduce the load. This lower capacity is one reason there is no De-Rating for LT tires when placed on trailers.

It may help if you think of tire life as a formula in the form of

LIFE = 100,000 - (A x %of time at 100%load) -(B x % of time at 90% load) - (C x % of time at 80% of max load)-(D x %of time at speed greater than 50 mph)- (E x % of time at speed greater than 65 mph)- (F x number of 4" deep pot holes) etc, etc, etc.

If you think of A, B C etc as large numbers such as 50,000 or 20,000 I think you can see that it is easy to "consume" the finite tire life of 100,000.

Now in reality there is no such formula as it would have hundreds for factors, each of which is almost impossible to establish without hundreds of thousands of dollars research.

Hope this helps you understand why the De-Rating formula for P Type tires when placed in "mult-purpose or trailer service is  Load Max New = (Load Max on tire)/1.10


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Real life inflation calculations for Michelin XZA2 Energy on 3 axle Class-A RV

Had a post from the owner with the following facts presented.

Michelin XZA2 Energy 295/80R x 22.5 Load range H
Steer axle scale weight is 14200 (tire placard shows 110 PSI closest)
Drive axle scale weight is 17360 (tire placard shows 75 PSI dual closest)
Tag axle scale weight is 7800 (tire placard shows 75 PSI single closest)
Total gross weight is 39360 per scale

MFG front GAWR is 14600# max
Intermediate GAWR is 20000# max
Tag GAWR is 10000# max
GVWR is 44600# max


=================

OK as an Engineer I always feel Facts & Data are our friends.
Using info on Michelin web site, and assuming perfect 50/50 side to side balance (unrealistic)  I come up with F@110 psi which gives you a 2.8% Margin on load capacity
Drive & Tag 75 psi  for a 8.9% and 27% margin

However if we assume a 45/55% split which is more reasonable
F @ 120 we get a 0.3% margin
Drive at 80 psi gives a 4.8% margin
Tag @ 75 gives a 20% margin

Note I suggest that in a perfect world that once you know your actual individual axle end load, you use the tables to find the minimum cold inflation and then add 10% to that number for your morning cold "set" pressure.

For those smart enough to run TPMS, I would set the warning level to be the minimum cold inflation and not just the standard 20% below the morning "set" pressure. With the proper TPM system that gives not just the low pressure warning but also a rapid air loss warning you have a good chance of coming to a safe stop before damaging the tire or its mate from driving when officially flat i.e. having lost 20% from the minimum needed based on actual tire loading.

Hope this helps.


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How to weigh your RV for free

If you live in or travel through Oregon you can check the load on each axle and even get an approximation on your individual corner weights. I did this myself last week.

There are many truck scales across the state that are open and the electronic scale are left on after hours. You simply drive onto the pad and read the total load for that axle on the display panel located on a post about 40' ahead of you.

Now if there are no trucks using the scale you may be able to simply swing around or back up and get just the right side tire loads for each axle. With those figures its easy to subtract and get the approximate load on the left side positions.

See it in this picture where I am getting the weight on my Right Rear duals.

I say "approximate" as unlike the scale set-up used by RVSEF there will be a slight tilt away from the scale pad but I would think you should be within a couple percent of the actual side-to-side load distribution. I am pretty confident that most of you will have figures that are closer to the actual side-to-side weight distribution than just assuming you have a 50/50 side-to-side split on each axle.

With the individual corner loading you can then use the published Load/Inflation tables from your tire manufacturer company to learn the MINIMUM inflation you need based on the heavy side loads. Then simply add 10% to that inflation number for your "inflation margin" and you should be good to go. At least till you get on real, properly set-up individual RV corner weight scales.

Now I admit I do not know which other states provide this safety service to motorists, truck and RV owners, but for folks on the far west coast this is a great deal, at least till you are able to get the actual corner weights of your RV, or individual tire loads for trailers, confirmed by RVSEF.

If you know of another state that has scales available to the public as Oregon does, please post in the comments below as this information will help your fellow RVers


EDIT AND UPDATE   8/16/20

Locations with scales
https://www.dieselboss.com/service.htm
https://www.allstays.com/c/weigh-scales-locations.htm
https://www.publicscaleslocator.com/
This post relates to Motorized RVs NOT Towables. Trailers have SPECIAL considerations for setting the inflation that I cover in THIS post.


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Is it OK to Replace Bias tires with radials

My 25' 1985 trailer has a plate on the left front street side that indicates 7.00 X 15 and 45 psi. D range, I think.
Right now, there are Roadkings LT on it. I inherited the Airstreem from my aerospace engineer Dad and know based on 5+ years it's time to replace them So, what manufacture would you recommend and what pressure? GVWR is 6,800#, axles are 3,200lbs. I believe the original tires were bias.

It really isn't difficult to find a new radial tire for your RV but there are a few basic steps needed.

You gave the GVWR and Axle rating but made no mention of the actual load on each tire. There are a number of posts showing that the load is seldom split evenly between axles or evenly side to side.
There are worksheets available to help you calculate the individual loads if you can't find a location with individual scales (this is difficult to do so use the worksheet). Here are 2 sites with forms you can use.
Bridgestone Commercial Truck Tires
RV Trailer Weight Calculators - Towing Capacity - Ratings


OK Lets assume you get or calculate the individual tire loads. For this example I will use the following numbers 
LF 1,550      RF 1,390
LR 1,500      RR 1,440

I would recommend a 15% "Safety Factor" or "Reserve Load" when looking at the tire loading.
1,550 + 15% = 1,782#

I also recommend an additional "Safety Factor" of +10% on the air pressure
You need to find a tire capable of carrying at least 1,782# at its Max pressure -10psi

The +15% is a safety factor for possibly different loading in the future
and -10 psi is to allow you to set a pressure and not need to worry about changes in ambient day to day.

Now since we are talking a multi axle trailer you need to run the max pressure in the tire all the time. This has been covered in other posts in this tire blog but it has to do with the unique side loading for trailers.

Consult the tire Load/Inflation tables and tire specification sheets to find a tire that meets the above load & inflation capability and fits your trailer for width and OD.

One final consideration. Years ago when there were still many bias tires in the market the wheels were not always designed for radial tire loading. You should probably also either confirm your wheels are approved for radial tires or also get some new wheels.


It's not hard to do this but you do need to spend a little time doing the research correctly.

PM me if you need help

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Quick Summary here

I have been following a number of RV forums and want to do a bit of a summary for those that don't have the time or interest to read a number of posts on this Blog: Remember more than half of the thousands of RVs that have been checked have been found to have one or more tire and/or axle in overload. So nect time you camp you can be pretty sure that one or both of the RVs parked next to you are overloading a component.

- You should have a Digital tire gauge. I have posted the results of my tests of dozens of gauges that RVrs were using and the bottom line is that about 15% were off by more than 5 psi which  IMO makes that tire gauge a good door stop or tent peg. I have provided information on how to do your own gauge "Calibration Check" to confirm the accuracy of the gauge you use daily and how to maintain your "Master Gauge"

- If you follow the advice from the two Tire Engineers on this thread you will be setting the pressure based on the appropriate method here:
     - On your TV inflate to pressure based on the Door sticker and Owner's manual for "Fully Loaded" operation. BUT get on a scale at least once to confirm you are not overloaded.
     - If you have a multi-Axle trailer you should be running the pressure on the tire sidewall. I have written in my Blog and provided the technical justification and need to follow this advice. You should still go across a scale and calculate the actual tire loads to confirm you are not overloading one or more tires
      - If you have Motorhome you need to confirm your unit's "corner weights". Use one of the worksheets I have provided links to. Use Load/Inflation chart from your tire manufacturer, to confirm you are not overloaded and identify the heavier loaded tire on each axle. Using the pressure for that load add 10% (without exceeding the wheel max) and that is your Cold set pressure for all tires on that axle.
      - If you follow the above there should be no reason to be chasing your tire inflation around unless you have a major change in Morning temperature ( More than say 30°F ) as you would only need to "Top Off" the air once a month at most.

- Don't be too anal about inflation. Variations of 1 to 3 psi day to day are normal. You should not need to make adjustments unless the Cold pressure is 4 or 5 psi away from your goal. (Multi-axle trailers might try and get no lower than 3 psi below tire sidewall pressure)

- TPMS are a WARNING device and like Insurance we should all be using them. Also just like Insurance they cannot "Prevent" bad stuff from happening but with luck they may give sufficient advance warning to lessen the impact of the bad stuff that does happen.

- If you are parked for more than a day you need to cover your tires that will be in direct sunlight with WHITE tire covers. This protects against both UV and higher temperature damage which can shorten tire life.

Can I change from ST to LT tires on my Trailer or 5ver?

This question is a real "Hot Button" on a number of RV forums and blogs. People ask this question because they want a better or alternate selection of brands or they want to improve the durability of their tires.

The answers given seem to range from "Sure, Why not" to "Absolutely Not, Never do it" and some will even offer that they think you are breaking some law if you make any change from the type, size, Load Range or cold inflation from the OE tire information shown on the tire Placard.

As we all should know by now answers about tires are never simple and straight forward and changing tires is definitely one of the more involved answers.

First off, I am not a lawyer but an Engineer and as such I form opinions based on data and facts. So here is the answer based on my 40 years experience as a Tire Design Engineer.

Yes you may be able to change tires  

    

 there are some things you MUST do to ensure that any change you make will actually improve your probability of having better tire durability.

My plan is to provide an outline of the steps you need to take before you make any change. I will try and include each step and each of the points of data you need to collect and evaluate. If you skip a step you may end up with a less durable tire selection which could lead to tire failure, RV damage and even an accident.

Before we start you need to consider that the most conservative approach is to make no change and to simply use the tire Construction (Bias or Radial), Type (ST or LT) and size and Load Range and inflation as specified on the placard and specification documents. This represents the RV manufacturers recommendation based on a number of assumptions as well as some legal regulations the RV MFG must follow plus in many or some cases a desire on the Mfg part to keep their costs as low as possible.

So if you still want to move forward here are the steps you need to take:
1. You need to know the actual load on each tire. This is important because A. we will be basing some decisions on the tire loading    and     B. It is possible that there is a significant unbalance in the tire loading which may be the cause of poor tire durability. With sufficient unbalance it may be impossible to provide a tire selection that would lower the probability of having problems.
To learn the actual individual tire loads you need to either find a company such as RVSEF or agency that has individual scales or to follow the steps outlined on worksheets such as This one  or This one. I have hears some people say that they have been able to get the individual tire loads from their state police or state DOT.

2. Knowing the ACTUAL LOAD on each tire you need to confirm that no single tire is loaded more than the max load molded on the tire sidewall. This is an absolute rule. If any tire is overloaded you should not move the trailer until you either change the load or change the tire.

3. Assuming no tire is overloaded we want to make sure that all tires on en axle are inflated to the same inflation. For multi-axle trailers you can lower the internal tire structural shear forces (the forces trying to tear the tire apart) by running the inflation molded on the tire sidewall. Sometimes this is stated as the Max PSI and other times it is stated as the PSI for the max load. For our purposes we will consider this the proper cold inflation you should always run. 

4. We should have "Headroom" or "Reserve Load" or "Safety Margin" on the tire loading. I suggest 15%. However I know that for many trailers 15% extra capacity above the actual load is very hard to do. Especially since some RV MFG manage to so under-size the tires that even when the trailer is empty they may not have 15% margin.

5. If you don't have at least a 10% margin I would strongly suggest you need to consider changing tires to something with more load capacity when inflated tot he sidewall PSI.

OK so you have some homework to do. We will continue this in the next post.


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Real Life weight calculation Question and Answer

A reader said "I have a  32' Class A MH and am about to pull the trigger on tires. I have been so concerned about making sure I get the 'right' tires, meaning, ones that have the right load range and capacity.

So just today I FINALLY found a place to weigh the MH and here's what I have:
     Actual Weight          Sticker Info
Front Axle      4,960          6,000
Rear Axle    10,660          11,000
Total            15,620          17,000

I was concerned that the 235/85R16-E 10 ply load range of 3,042 was too close to the limit so instead of I was thinking of getting a G 14 ply rated tire.

But now that I see the actual weight, should I stick with the E - 10 ply range?

Here's additional info: The RV had 3/4 tank of gas, full tank of clean water, very little in gray water and me (175 lbs)

And is this how you figure "Reserve Capacity"?

Tire rating for 235/85R16 Load Range E = 3,042       
So is the reserve load range capacity minus actual weight?       
    
Front Capacity           3,042 x 2       6,084
Rear Capacity            3,042 x 4      12,168
Front Axle Weight         4,960
Rear Axle Weight         10,660
Front Reserve             6,084 - 4,960       1,124 - I can add this much weight to the front
Rear Reserve            12,168 - 10,660     1,508 - and this much to the back

Compare to Hercules H-901 Load Range G = 3756 (3415 Dual..why?)
Front Capacity     3,756 x 2 = 7,512
Rear Capacity      3,415 x 4  = 13,660
Front Reserve       7,512-4,960 = 2,552 *Much better compared to 1,124 lbs
Rear Reserve        13,660-10,660 = 3,000 *Much better compared to 1,508 lbs

So, gosh...now that I have actually put it all down on paper it's kind of a 'duh' moment, but here's the price difference:

6 - Cooper A/T3 - $1,159 Out the door
6 - Hercules H-901 - $1,532 OTD
Difference $373

Worth it?"

I offered the following reply
"Some comments and observations.

It helps if you use the complete tire type/size nomenclature.
I believe you have LT235/85R16 LR-E   the LT is Type. Some readers may have a trailer and have ST type tires and there are full metric tires with no leading letters. Each type has different load capabilities and ST are not intended for passenger carrying vehicles.


Second you failed to consider the correct load capacity in the dual position as your rear tires are. Tires in dual application ALWAYS have a lower rating than when in single as one of the pair is almost ALWAYS carrying more than 1/2 the load of the pair.
When you either read the tire sidewall or look at Load/Inflation charts you will see a different load capability for Single (as in your front tire) or Dual (two tires side to side as in your rear.

The load capacity for an LT235/85R16 LR-E in Dual application is probably 2,778#.  Note you should always consult the Load/Inflation tables or molded on the sidewall from the tire manufacturer of the tires you are considering as not all tires have the same load numbers. Some are slightly different for a variety of reasons.

So back to your questions.

"Reserve Capacity" would be the (max tire capability) - (the actual load) on a tire.

BUT you cannot simply assume the load on an axle is split 50/50 side to side.
Some owners find significant variation so untll you learn the individual tire loads I suggest you assume that one side is carrying 55% of the axle load.

Your heavy side Front could have 55% OF 4,960# OR 2,728#
Rear 55% of 10,660# or 5963#

Your front Reserve is 3,042#- 2,728# or 314# per tire

Your rear would be  1/2 of 5,963# or 2,982#
so the rear reserve is 2,778# - 2,982#  or a negative reserve or potential tire overload of 204# per tire.

With this information it is important that you first confirm the side to side load balance

Here is a worksheet

After confirming the real side to side split you need to re-calculate your reserve load and if needed unload or shift the load of stuff in the RV or buy the tires with more load capability BUT you should never exceed the individual axle ratings  GAWR or Vehicle rating GVWR shown on your certification label.

Finally the selection of tire brands. Do both brands offer the same warranty? Can you find dealers for both brands in the part of the country you normally travel? If you get a puncture and need a replacement tire it could end up costing more than a couple hundred dollars extra if you need a tire rush shipped in to match your current tires.

Hope this helps

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"I don't want to weigh my RV"

That is the statement I occasionally get from a few who say they have no intention of getting their RV weighed each time they go on a trip so they see no reason to ever get the RV weighed as they are certain they know they are not overweight.

With over 40,000 data points RVSEF can show that over 55% of the units they have weighed have one or more tires and/or axles overloaded, I am pretty comfortable in suggesting that RV owners need to learn the individual tire position weights at least one time.
It is not unusual for an RV to be out of balance by 1,000# or more.
Trailer owners need to do this to confirm they are not overloaded due to axle to axle imbalance or side to side balance. They still need to run tire inflation at the tire max.

Motorhome owners need to learn the "corner loads" before they calculate the minimum cold inflation for each axle.

Once you have learned the actual loads and done the calculations and table look-up you are good to go unless or until you make some significant change to your RV such as adding a residential refrigerator or possibly granite counter tops.

Not understanding the difference between "Measurable and Meaningful" some incorrectly think I am suggesting that they need to get their RV re-weighed every time they go on a trip as they may pack different items. Not wanting to do this they just throw up their hands and don't get the RV weighed.

Improper inflation can lead to overloading and excess heat generation. This is bad for fuel economy and tire durability and in extreme cases could lead to blowout failure or tread separation.

I have had my small Class-C 2008 coach (seen above) weighed three times.

My first time was just after I bought the RV and not having access to corner weighing I still wanted to know what my weights were with the "stuff" I had loaded for my first trip.

I knew I would pass a CAT scale about 15 miles from home so pulled in and got the following results
Front 3,940#  Rear 6,580#   Total 10,520# Based on these results plus the margin of inflation pressure I wanted I then knew what to set as my cold inflation.

Three months later I attended a large RV Rally and had RVSEF do corner weighing
LF 1,750  RF 1,850   Total Front  3,600#   -340#
LR 3,400  RR 3,250  Total Rear   6,650#   +40#             Total 10,250  +270#

It has been a few years since my RVSEF weighing and I have added a few items as "permanent" take along stuff and a few minor modifications to the RV that I felt had increased the load when preparing for a longer trip. I again decided to do a quick check so again visited a convenient CAT scale.
Front 3,820#   Rear7,020#   Total 10,840#   This indicates an additional 220# on the front axle and an extra 370# on the rear from the RVSEF weights

As you can see the RV has gained a some weight over the years, A bit like its owner I am sorry to say.

The good news is that the new weights do not require a change in cold inflation as the extra 320# is not large enough to put any individual tire into a higher inflation bracket. Plus my margin easily accommodates this change

As you can see it is easy to confirm that no significant change in weight has occured. There have been and will continue to be changes in the tire loading due to weight changes but those changes, while measureable are not meaningful so are not of concern. I also think you can see that excuse for never getting your RV weighed because you don't intend to or want to weigh the RV each trip is not a reasonable excuse.