Spare tire - mis-matched size What to do?

Class-A owner said:
"I use to advocate carrying a spare in my 2005 Monaco Diplomat. On that coach, it used a short 22.5 tire and it fit in my pass thru bay, unmounted. I could stuff a lot inside the tire and didn't lose much storage. Fast forward to my current RV and the 315's won't fit in a bay.

So......a lot of people say to just carry a spare, including a trailer owner with a rear mounted spare. It's nice to say and actually nice to carry a spare if you have room, but if you don't have the space, you need another plan. That plan is to have a roadside service plan and be willing to accept an odd sized or used tire to get you back on the road. Wait until you're in a major town on a weekday to resolve the issue with a new or correct size."

My reply:

While using an "odd" size on the front might get you moving (slower) mismatched duals will mean the larger OD tire is carrying more than design load.

I would limit the speed to 50 or less and be prepared to scrap BOTH tires as the internal structural damage is impossible to "inspect" for.

If you have two different size tires on your RV and can only carry one I would suggest the rear. Hopefully, you have confirmed your actual load on each tire position and have some margin available on the fronts. If you are running at 100% front capacity (bad idea) then the use of a smaller "rear" tire as a temporary front means you really need to limit both speed and distance you operate in that situation.

Overload does not always mean tire belts will overheat and a warning is received from your TPMS. The steel sidewall ply can fatigue from over deflection and you will have no warning and not know it till the sidewall fails catastrophically. 

All the above brings up the question of why did you have a tire failure in the first place?. Have you read THIS post.

A properly programmed TPMS should provide an early warning as soon as you lose 15% from your "set" pressure (slow leak) or 3 psi from your hot pressure within a couple of minutes (fast leak).  If you are also having a tire professional do a close and thorough inspection every year starting at 5 years for Class-A and Class-C or at 3 years for any trailer, it is unlikely for you to develop a belt separation without some advance warning.

Taking precautions is always better than trying to "fix" the tire after you have a flat.

NOTE. The above in no way should be taken as a suggestion that driving on an overloaded or under-inflated tire or mismatched duals is a safe thing to do. I am just offering suggestions for possible responses in an EMERGENCY situation where you feel you MUST move from your current location to a safer one.

Do inner duals fail more often? If so, why?

Read this on an RV Forum thread:

"Isn't it weird how it always seems to be the inner tire that goes bad or blows? Seemed to always be my experience (bad luck) when I was driving semi's for a living."

While I have never seen a documented study, I can certainly believe this observation can be made by many. There is Science behind the "Why" this may be true.

For those that have reviewed the post on Tire Covers that explains the effect of temperature on tires, you have learned that it is the higher temperature that accelerates the tire "aging" process. If you look at the temperature readings on sets of dual tires you will see that when the tires are inflated to equivalent pressures the temperature of the inner dual on Motorhomes will usually show as a bit hotter. The difference isn't a lot but the effects of that difference I believe are cumulative.

It is also true that older tires are more likely to fail due to the degradation of the rubber flexibility and strength.

Please do not take this observation and assume you need to start adjusting the inflation in your duals to run more air in the inner tire. Doing this could end up resulting in a shift in loading between the pair of tires to place more load on the inner tire, and we know that increased load results in increased operating temperature.

Tire operating temperature develops from complex actions of flexing of the belts and of the lower sidewall which are the two hottest locations on a tire. You might be able to lower the temperature in one location while increasing the temperature in a different part of the tire.

The best practice I can suggest is that you:
1. Confirm the tires in each pair of duals are a "Matched Set" (See THIS older post).
2. Ensure you know the actual load on each set of duals not just the total axle load.
3. Use the Load and Inflation tables to learn the MINIMUM Cold Inflation Pressure for the heavier loaded axle end.
4. Add a 10% inflation to that minimum number to establish your CIP.
5. Inflate all tires on the axle to the same CIP. (matching the inflation within +/- a couple psi is good enough.
6. Run a TPMS to monitor your pressure whenever driving.

Quick post on Dual tire air balance systems

Read a thread on an RV Forum on connecting two tires in dual position, with hoses to "balance" the inflation pressure. There were some claims made about performance improvements but IMO the conditions necessary to deliver those improvements are pretty extreme and improvements are tenuous.

The information on the function of this pressure balance equipment also ignores the potential for damage to the RV when one tire loses air but the driver is not immediately informed of the loss. There is even talk of serious air loss in excess of 25% of the pressure needed, only resulting in faster wear.

I found no mention of operating a tire that low possibly resulting in a catastrophic failure (coming apart and potentially doing thousands of dollars' worth of damage to the RV).

I can't understand why some would think that lowering the hot tire pressure (decreasing load capacity) would ever be a good thing to do.

Someone will probably point out that some of the systems that connect the air between a set of duals limit the amount of air transferred, but that still leaves a problem.

If you have two tires set to 80 psi and one gets a puncture and starts to leak, the "good" tire bleeds off air to the leaking tire until 5 or10 psi has been transferred. Now both tires are at 70 to 75 psi and are just starting to be overloaded.

But the leak continues and the tire going flat transfers its load to the "good" tire, resulting in the "good "tire seeing ever-increased the level of overload.

This can continue until one tire is flat and one tire is 100% overload. Now you are driving down the road with no knowledge you have a flat and a tire at 200% of rated load.

If you are lucky, you stop and discover the problem before the "good" tire fails, too, leaving you with two scrap tires.

This system does make airing up tires easier in that you only have one valve for the pair of tires, but I'm not sure if that "benefit" is worth the cost.

##RVT825

Important consideration if changing tire size: "Minimum Dual Spacing"

Knowing about the extra details of dual tire application is not anything car drivers were ever called upon to know. When you joined the RV world your first RVs were probably trailers and you don't have to know about special considerations with duals. If you now own a motorhome that has two tires on each end of the rear axle, then you have "duals" and need to know and consider some new information. I have written a number of posts on this topic and I suggest you take a look at each post by clicking on the word "dual" on the list to the left.

If you are considering changing tire size on your motorhome, there are a number of items you need to consider. I have previously covered the importance of matching tire OD if only changing one tire of a pair of duals. While you may remember reading that POST, you may be telling yourself that you don't need to worry about the matching dimension if you are changing all your tires. While you may understand the need to pay attention to load capacity and the physical dimensions of the tires themselves, there is also a CRITICAL dimension that you can't measure with a tape measure and that is called "Minimum Dual Spacing". You may or may not have noticed this dimension when looking at a table with tire dimensions. Not all tables have this dimension but it is very critical.

I have highlighted the Min Dual Spacing information and the rim width dimension which is also critical. It is important to remember that not all tires are approved for a specific rim width when looking at the upper range of load capacity.

 
Tires in a side-by-side, i.e., dual position MUST have a certain amount of clearance between them or the tire-to-tire contact of the sidewall may lead to failure of BOTH tires. Going from a 255 to 275 wide tire will probably mean you will not have the specified clearance unless you also change wheels. Only way to know is to check the wheel specifications from the manufacturer.
 

It is the distance from the center of one tire to the center of its mate, when mounted on the actual wheels you will be using. Now there is no single place you can make this measurement on a wheel as it requires calculation, as the mounting surface of the inner dual wheel is not the same surface as the mounting surface of the outer wheel.

Tire charts and dealers can tell you the minimum dimension needed as seen above but you need information from the wheel manufacturer to learn the dimension from the mounting surfaces to the wheel center-line.

So, along with load capacity, OD and tire width you also need to confirm your wheel width meets the tire specification as well as calculate the dual spacing from the dimensions provided for your wheels.

Special warning. I know that some motorhomes have steel inner wheels and aluminum outers for the dual position. You will quickly learn that the offset spacing is different for steel vs aluminum.


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Match Duals... Does anyone really do this?

I believe that sometimes people understand that there are suggestions and recommendations concerning the proper care and maintenance of tires but all too often they just don't bother to follow the published guidelines as they feel it may be too much work or some guidelines are simply put out to get people to buy more tires.

Let's look at one example. I have previously covered the importance of "matching" dual tires by measuring the Outside Circumference (OC) and ensuring that each pair are within 3/4" for this measurement. You can read THIS post and THIS one for more details. But is this practice followed by truckers who may put 100,000 miles on their rigs in just a year or so? I think this might help you believe that the practice is followed.

Here are a couple of pictures I was able to capture at a stop-light.

As you can see from these pictures, this driver has matched the level of wear on the front pair of tires. Now this isn't absolute proof that the OC was matched but given the relatively even wear rate of truck drive tires it's reasonable to assume the change in tread depth results in a similar change in OC.

You want to match dual tire dimensions as if one tire is significantly larger than the other it will be forced to carry more load than the smaller tire. This will result in higher operating temperature which is not good for long-term tire life.

While measuring tread depth and doing some calculations may seem reasonable this practice ignores the reality that all tires "grow" in use so a new tire and old used tire will actually measure different if you do an actual OC measurement than if you just do calculations based on tread depth measurement done to the 0.01" accuracy.


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Do you want to change your RV's wheels?

by Roger Marble

Here are some things to consider regarding changing the wheels on an RV.

For most RV owners, the wheels that came with the RV when new should work just fine. If you are running the original size tire and have confirmed you do not need to increase the Load Range of your tires to carry more load with a higher inflation, there is no reason to change your wheels, unless you have damaged one.

Now, if you want to change the look of your unit and switch to special chrome or aluminum wheels, then there are a number of things you need to consider:

What is the maximum load capacity of the new wheels?

What is the rated inflation of the new wheels?

Are they the same width and flange contour? This means the official size is identical, such as 16x7J. Note the letter is the shape of the area that contacts the tire. You should not change letters such as changing from a J to a K. One is not better than the other, but tires are designed for a specific flange shape.

Finally, if you run duals, then the "offset" dimension is very important. If you go smaller, your tires may rub, which could cause a problem.

All of the dimensions and ratings need to be stamped into the wheel or in writing from the manufacturer. I strongly urge you not to just take the word of the person selling the wheels.

If you think you need to change the wheels because you are changing tire size or rating to carry more load, you need to work closely with the supplier to be sure you are not overloading the axle, springs or other suspension components, the dimensions of the new wheels will properly fit the hub and bolts, and the offset will not allow the tires to rub.

Tires intended for dual application have specified clearance called "Dual Spacing," so be sure to confirm that dimension from the tire manufacturer before you go wheel shopping.


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How to match dual tires when replacing one new tire.

Had a question on my video on matching Dual tires.
"I get the importance of size-matching, but how are you going to get an adequate & accurate measurement of the remaining dual while it's still on the truck or coach? It'd be expanded under pressure, somewhat distorted where it presses against the ground, and would have some wear on it. Is one supposed to compare a tire under those conditions to a new, unworn, un-inflated tire & expect them to be within 3/4?"

Well I can understand the bit of confusion as "Dual Matching" can be a challenge when trying to replace one tire on an RV. Lets work through the process.
First off we need to be sure we are doing the correct thing in replacing just one tire from a dual pair. Normally people have one dual tire fail due to some form of damage and subsequent air loss. In the past, before TPMS, the driver would continue down the road till someone waved him over pointing out thr tire failure. This meant that for some unknown number of miles the remaining dual had been operated at 100% overload. The general guideline would be that you need to consider the remaining tire to have had its structure damaged and it should be replaced. There are many documented cases where only one tire was replaced and the damaged tire fails a few miles to a few weeks later. At that point the driver acts surprised there was a failure.

Today we have TPMS available so that in the case of a puncture or other slow leak the driver may get adequate warning so he can stop before the tire with low inflation suffers a catastrophic blowout because it was run with 20% or greater air loss. In this case the fully inflated tire may not have been overloaded for more than a mile or two as the RV moved to a safe place to pull over, so after internal and external inspection it may be safely retained and put back in service.

Now the RV owner is confronted with the challenge of how to properly match tires for dual application. The 3/4" circumference is the correct maximum difference for tires and tire growth and wear can make it a challenge to meet the goal.

When measuring a tire for dual matching it needs to be off the vehicle and fully inflated. If the tire is brand new you can expect even radial tires to see some size increase after a couple hundred miles so it is difficult to match new and used and get correct numbers.

The solution if you are replacing just one tire would be to confirm your front tires meet the 3/4" difference and then place a new tire on one front and the old tire on the other front position.

Meeting the 3/4" max difference is critical as ignoring this figure can result is a failure down the road even if the tire has been properly inflated.

How to replace a tire in "Dual" application

First off if you have a towable RV and your tow vehicle only has four tires you can go get a cup of coffee as this post doesn't apply to you. However, the information here can still be important to know and pass on if you ever happen to be sitting around a campfire and hear someone talking about replacing a failed dual tire.

Now lets be sure everyone understands what is meant by "Dual" application vs "Tandem".

Tandem means one following or behind the other. Most trailers have either two or three axles in "tandem" and each axle has just two tires on it. This utility trailer has tandem axles.

Dual means two tires side by side on the same end of an axle. Most Class-C and Class-A RVs have Dual tires in the rear drive position. A drive axle with dual tires has four tires on it. This version of "Bigfoot" has dual tires on each axle.

 Ok we have definitions behind us. This post will address the proper way to match a pair of tires for dual application. This is very important, as mismatched duals can result in overloading and in extreme cases could lead to tire failure.

If you are buying new tires you should find that all the tires are almost identical in OD when first inflated. If you were to accurately measure the tires after a few hundred miles use you would find that the tires have "grown" or stretched out a bit as they were heat cycled, but again the tires would be very similar in dimensions.

If you were going to try and measure the OD of a tire you would also learn that it takes special tools to get a direct measurement. The best way to measure how big a tire is is to measure the circumference. You can do this with a standard tape measure. You don't even need to calculate OD from the measured circumference as I will give you the guidelines based on circumference. You just need to be sure you keep the tape at the center of the tire.

Here I have affixed one end of a standard tape measure to the center of an inflated tire using masking tape.

I next carefully roll the tire around, keeping the tape taught and in the center.


When the tape comes around I can get a fairly accurate measurement of the circumference. In this example I didn't use the end of the tape as the tang doesn't lay flat, so using the 3" mark I see 95" for an OC of 92.0 inches.

Now you should match tires +/- 3/4" of circumference in dual application. 


If placing new tires in dual application you do not need to do this measurement but if trying to match used tires or a new tire with a used tire this matching is important.


BOTTOM LINE:
If you do not match the tires the larger tire will be forced to carry an increased load and in extreme cases can result in failure.

Can I mix different brands of tires?

When it comes time to replace one or more of the tires on their RV many shop based on price, so they are

confronted with the questions such as:
Do I need to replace all the tires at the same time or can I just buy one to replace the damaged tire or just a pair for the front axle?
Do I have to keep the same brand or size or design tire or can I make a change?

Lets separate RVs into two categories. Motorized units such as Class-A, B or C and Towables.

Towables normally have one, two or three axles and I believe that baring some mechanical problem such as bent or out-of-alignment axle or having had a puncture you will probably be able to replace two at a time so you can spread out the cost for new tires over a couple of seasons. You should replace both tires on an axle with identical size, brand and design as if you mix tires you will probably end up with the tires fighting each other which can cause irregular wear in extreme cases.
With four or six tires to worry about there is an increased probability for one to suffer a puncture before the rest of the tires wear out or "age out", so there are advantages to keeping all your tires, including the spare identical. That way if you need to replace just one tire you can use your spare and still end up with the same size, brand and design tire on each axle. If you do change brand, size or design on your trailer and then suffer a failure you may want to purchase two tires to keep all tires on that axle identical. If you take this route I would suggest keeping the spare that matches most of the tires on the ground.
A good bit of news for owners of towables. Since you don't have tires mounted in a "dual" position (dual means two tires on the same end on an axle) you do not have to worry about OD matching. With the shorter life of tires on towables it will definitely help with your budget if you plan and do rolling change of say one axle per year rather than all 4 or 6 tires at one time. I would also put the tires with the deepest tread depth toward the rear as rears are more prone to puncture and heavier tread will lower the potential for puncture.

Motorized RVs have a bit more to worry about. It is very important that all tires on each axle are the same brand, size, and type as mixing tires can cause steering, handling and even braking un-balance which could present

an unsafe condition. While you can have one type tire on the front and a different type on the drive and even a third type on the tag axle you should NEVER mix tires on an axle.
Previously I have discussed the advantages of confirming availability of tires that are identical to what you are using or you should strongly consider carrying a spare if you have a unique size or brand.
It is also critical that when replacing one tire of a pair of duals that both are within 3/4" circumference. If more different in actual measured size one tire will be forced to carry a greater portion of the load from that end of the axle and by now you should know that increased load can contribute to hotter running and in extreme cases.

Bottom Line  Yes you can change tire Brand or Size or Type but I strongly suggest you do your research in the comfort of your home or at a campground rather than on the side of the Interstate and on the phone with the tire service company. BUT if you change tires you need to be aware of the potential for different and possibly unbalanced handling on motorized RV if you make a change, and the smaller (lighter) the RV the more pronounced this performance difference can be.
Having a TPMS is a good investment as it can warn you if you get a puncture and you may be able to stop soon enough that you do not damage the tire beyond repair-ability.

Dual Tire Hose Extenders? Tips to avoid problems.

Some general comment on extensions for owners of Motorhomes and dually pick-ups.

When I was racing, I towed a 26' enclosed trailer with a 1-Ton dually and had steel braided hose valve extensions. We ran about 78,000 miles with no problems. When I got my Class-C my first add-on was  TPMS followed by steel braided extensions. With only 16,000 miles there have been no leaks or other  problems.

Now there are TWO main things that I would consider a MUST. 
First you need bolt in metal valves.  
Second you need a hard attaching point on the outer end of the hose to prevent movement of the hoses. The hoses come in different lengths so you should run the shortest hoses that allow you to easily bolt the outer end down and you need to support the end of the hose when pushing on it with your tire gauge or air chuck.

I have seen a claim that a metal valve failed because of fatigue from the hose but without significant movement of the hose there should not be enough to stress the valve stem.
Metal valve stems should be replaced or at least have all the rubber O-rings and gaskets replaced whenever you change a tire. The rubber parts age just as the rubber on your tire ages. Replacing when you replace tires eliminates the need of keeping track of the age of the O-rings and seals. There is a rubber interior to the hose and this will also age, so when I replace my tires I will get new hose extenders along with new valve rubber parts.

I have seen spring clips that are supposed to retain the steel braided hose but they don't look too solid to me. I have not looked at the rubber "grommet" that fits the hand holes but have to wonder if they hold the braided steel line solidly. Clearly they do not support the hose end so there will definitely be some movement.

You can see in my set-up that I have the Wheel Master 8001 hoses firmly attached to my hub cap. I do hold the extender hose when ever using a gauge or air chuck.

Valve extender hoses can work and make adding and checking the air on dual applications much easier. All you need to do is to pay attention to a proper installation that minimizes any movement or rotation of the hose extender.

What should trailer owners do?

Owners of heavy 5th wheel trailers seem to have a higher tire failure rate than other RV owners. I have been following the posts from a number of owners that have had a numerous problems. A recent question concerned the consideration of changing to 17.5 inch tires from his current 16 inch tires.

Lets call the owner "Tex. He wrote:
"What is confusing is that tire pressure charts don't apply here. This is an older trailer and I may be trading it soon, but say I were going to keep it and put 17.5" wheels on it. Would I inflate to the maximum of 150 psi or would I refer to a pressure chart?"

My reply: Tire charts are based on the ability of a single tire to carry a specific load at a specific inflation and speed on a test drum while running straight ahead. Most vehicles have four tires, one at each corner. A few like some one-ton pickups and vans might have dual tires but the load in dual application is reduced based on years or real life experience that indicates that if you run tires in a close side by side basis you cannot get the same life and durability as when those tires are run on opposite ends of the same axle.

Now multi-axle trailers have been around for a long time but again most of these vehicles run the tires at the reduced "dual" load and also are probably running at the max pressure the tire is rated for. The use of multi-axles on RVs presents a different problem. The loads are not reduced to the "dual" load and the pressure on most RVs is not maintained at the max for the tire. In fact most RV trailers are running one or more tires in an overloaded condition.

RV manufacturers produce many units that are significantly out of balance side to side as they leave the production line. Since cost cutting is a major objective for both the manufacturer and the RV buyer, larger tires are seldom provided and in some cases games are played by de-rating the GAWR to allow smaller (less expensive) tires to be used. I have even seen a case where the RV manufacturer got a letter from the tire importer claiming the tire was capable of carrying more load than was standard for that size. Of course this "special" information is not provided to the RV owner, who will probably buy a replacement tire that shows the correct size but is not rated to carry the same load.

The manufacturers do not take into consideration the side to side unbalance, as to do so would require them to provide larger (more expensive) tires. The other thing RV industry does not take into consideration is the forces to the tire structure due to running close axle spacing. Engineering analysis shows that when turning corners the forces trying to tear the tire apart can be over 20% higher in multi-axle applications than with tires at the corners of the vehicle.
The only options for the trailer owner are to up-size the tires (if there is room) or up-rate and increase inflation (if a higher Load Range tire and stronger wheels are available). Lacking the above being sure to run the tire at the inflation shown on the sidewall (i.e. max) will slightly decrease but not eliminate the overload forces.

No, you should not run 150 psi. I doubt you will find that is the rating for the 17.5 tires or rims. What you should do is consult the load inflation tables and after getting accurate loads on each individual tire run no less than the minimum inflation for the heaviest tire on each axle. If you want to be more realistic and possibly see better tire durability for your tires, I would certainly consider using the "dual" load to establish the minimum inflation. I would further run +10% pressure to avoid day to day temperature and pressure variations. I would also consider a TPMS mandatory.

Can you "Limp" home on a failed dual?

I have read a few posts on RV forum sites when the topic of what to do when a tire fails and you don't have a spare.

Many times it has been suggested that the person plans on "limping" home or to the tire service center with just one tire in the dual position of their RV.

While on the surface this might seem to be a reasonable approach, there are a few things that need to be considered.

First, unless you have a TPMS that warned you that one of your duals was loosing air, in all probability you have no idea how long you drove with one dual under inflated. If you don't know when the tire started to loose you also have no idea at what speed you drove on one under inflated tire and also on one overloaded tire.

If a tire looses more than 20% of its air it is considered to be "Run- Flat" by tire industry

If you have driven on a "flat" tire it is considered to have been damaged and should not be considered for future safe usage.

What is not obvious when you read the above is that is one tire of a dual goes flat the mate has now been overloaded. I covered some of the info in a post on the Special Considerations for Duals, but there is more that needs to be considered.

If you have one tire punctured and loosing air the mate is "taking up" the load for both tires until it is 100% overloaded. Driving at highway speed will do serious internal structural damage. Most of which cannot be seen with out special equipment like X-Ray so it is simply considered scrap so now you need to replace two tires.

Trying to "limp" means that you need to reduce your speed and according to the special tables in Tire & Rim Association for adjustments for speed, inflation and load your limp speed is not 30mph or 20 mph or even 10 mph but it is limited to 2 mph. That is TWO miles per hour Maximum. Any more and you are damaging your tire beyond repair.

The solution would be to call for service. I would only drive on a single tire for a hundred yards at most to get to a location where I could safely pull off the roadway.

If you feel your situation means you must drive on a single tire of a dual position then you need to accept that you will need to replace both the tire that suffered the failure and the tire that was 100% overloaded.  I would also remove the flat tire as you don't want it flapping around as it will do damage to your RV.

Special considerations for duals

Highways March 2011 had a post titled "Tire Snafu" on pg 40

A person mentioned that both rear duals tires got hot due to air loss and subsequent overload. One tire was identified with a leaking valve and was replaced but there was no suggestion that its mate might have also suffered internal structural damage from running hundreds to thousand miles in an overload condition.

Few tire dealer salespeople or even tire technicians have the training to see the tell tale signs of overload.

Here is a picture I call "Shades of Black".


We know the tire in the picture was run overloaded as it had an improper repair (plug) and had continued to slowly leak air for many hundreds of miles. By "reading" a tire when doing a true forensic level examination the experienced tire engineer will notice the darker inner sidewall portion of the tire. This darker shading comes from increased level of flexing that can occur when run in overload or under inflated condition. The darker black is physical proof that the subject tire had been operated for many miles while under significant overload.

This operation resulted in degradation and weakening of the tire's structure which meant that in all probability, it could fail catastrophically with little or no warning hundreds or thousands of miles later.

This type of structural weakening is not visible from the outside and is difficult to see even with a proper inspection of the inside of the tire which takes more than the few seconds most tire techs are given to do an inspection.

I don't expect the magazine writer to know this but when responding to complaints about tires I strongly suggested that they touch base with tire technical resources and to provide a little education to readers.

When one tire in a set of duals is run "flat" i.e. more than 20% under inflated, it means the mate was also operated in an overload condition. Unless there are some special circumstances, the operator seldom knows how many miles, at what speed, at what % overloaded the tire was operated. Only the most experienced tire engineer and not tire store personnel, have the training necessary to pass judgment of the probable condition of the tire. Many times the mate to the "failed" tire should also be replaced or retained as a spare for temporary use.

Failing to warn readers of this potential safety issue is not a good policy.

Valve placement

Quick post to answer George's question
"Valve extensions for inner dually tires
The awkward placement of valve on outer rear dual tires: why do they face inward and do they HAVE to be that way."

If you look at the valve placement, the "inside" of your outer dual is really the "outside of the wheel if that wheel was on the front or was the inside dual. This means all wheels can be the same. If the valve was on the outside of the outside dual you would need a different spare tire/wheel assembly as you can't have the valve on the inside of your fronts or inside of the inner dual and clear the brakes.