It's just a wheel, What can go wrong

 A wheel is just a wheel, isn’t it?

That wasn’t the exact phrase used in a recent post but it seemed to be the thought behind some of the comments I saw. Today’s topic will be of interest to anyone who has changed tire size or Load Range (ply rating to some). It also covers some important safety concerns that you must consider if contemplating such a change. This is a TECHNICAL matter which can be boring to some but there are Explosions in some of the videos to keep everyone interested and awake.

We and others have covered the information molded into the sidewall of all highway tires concerning the Maximum Load and Maximum Inflation limits for your tires. What you may not realize is that wheels have similar limits. If you are lucky these limits are stamped or cast into your wheels. If there, this information is not hidden by the tire but may be on the side of the wheel mounted toward the inside of the vehicle or in some cases on the surface that is bolted against the hub or brake drum.

Sorry to say that many of you will only find part numbers and manufacturing date code stamped into the wheel but nothing that looks like load or inflation. If you are in that boat you will need to contact either the wheel manufacturer or the chassis manufacturer. I would not depend on any verbal information from the average RV salesperson, but only accept some published information that answers the question based on the wheel part number marked on the wheel.
Here are the links to a couple wheel manufacturers. Accuride 
Alcoa

If you can't find the wheel inflation or load rating marked on the wheel the best I can suggest is to confirm the ratings from the OE tire as found on your RV Certification Label and consider those numbers the Max for load or inflation till you learn otherwise from the Wheel or RV company.

Now you may be asking why go to all the trouble. This was the basis of the question I was asked by an RV owner that wanted to know if there would be any problems using a Load Range E tire that had a rating of 80 psi on a wheel that originally had a passenger tire mounted on it.
So we get to the point of this post. WHEEL FAILURE.

OK first off this answer has not been approved by any lawyer.

Luckily wheel failure is an infrequent occurrence but if it happens it can not only ruin your day but as those ads on TV for new medications warn, the side effects could include serious injury or even death.

NOT KIDDING HERE. Every year more than one person manages to kill themselves by improperly inflating a tire when something goes wrong. The forces of compressed air are much like a bomb. The failure can happen while inflating or minutes to weeks later. One thing that can happen is the wheel flange bends or breaks and the tire exits sideways taking out anything or anyone in the way. If you want to have a better understanding of the forces involved I have collected a number of videos.

 
SAFETY video. This is "Zipper" failure from running a steel body tire when flat. But is shows the forces involved Example.

Be warned, This is a disturbing video Example shows what can happen when a large tire lets go.  The failure of a wheel has similar forces.  similar.

If you are lucky you will only blow your fender off when it lets go.
Now before you say you aren’t using tires as shown in the videos, I want to assure you that when a wheel fails from fatigue it could in all probability react similarly to what is seen in the videos. A fatigue failure usually occurs after many thousands of cycles so if you exceed the max inflation rating for a wheel, you can decrease the number of cycles it takes before the wheel might fail.
If interested, you can learn more about metal fatigue.

Bottom Line
You should never set the cold inflation at a level that is higher than the Max for either the tire OR THE WHEEL. Both the tire and wheel manufacturers take normal pressure increase due to operation heat into consideration so don’t bleed off hot air out. 

##RVT1023

Question of running year old tires or Running less than max psi

Question from Chris

Hi Roger,

I came across your website by way of referral from a member on a Keystone RV forum.  I have a concern regarding upgraded tires and wheels for a Keystone trailer I own.  

As most manufacturers continue to cut costs in value models, wheels and tires seem to be ground zero in their savings.  So, to help mitigate tire failure on my coach, I've upgraded my china bomb OEM 14" tires sized ST205/75R14 LR-C to ST225/75R15  LR ? and purchased new wheels to accommodate the new rubber.  My wheels are Sendel wheels that support 2540 lbs of load each. 

I purchased Carlisle Radial HD tires in LRD from Discount Tire.  Unfortunately, they received LRE tires in instead of the LRD tires.  The Discount Tire salesman quickly resolved the error and within 2 days, had LRD in stock.  I returned to the store to have them balanced and mounted on the wheels. The stock they received in had DOT date code of 1516. He told me that was the newest in all his warehouses. I didn't want year old tires so I rejected the sale.  

Then, I ordered the same tires from Walmart.com.  Same story, the DOT date code was 1616 and 2016.  Rejected that sale.  Finally, I ordered them from Amazon.com.  They arrived today.  Again, tires are around 1 year old and I'm sending them back.

My first attempt at ordering tires from Discount Tire resulted in LRE tires. They were much newer around Nov 2016. I think my quest for load rated D tires from Carlisle in size 225/75/15 is futile.

So now, I'm considering purchasing the LRE tires as I think the local stock is much more fresh than I can ever find with LRD. The only limit I have is my wheel capacity at 2540 lbs. If the LRE tire max inflation pressure is 80 lbs supporting 2830 lbs, will it compromise the tire if I inflate only to 65 lbs (in order to stay within the specs of the wheel)? The OEM tires were LRC on 14 inch wheels supporting only 1760 lbs at 50 lbs. Weight is not a concern as I will never come close to max weight limits with my trailer on either LRD or LRE tire. 

Another thing that worries me is the stiffness in the LRE rubber. Comparing the Carlisle LRD to the OEM Trailer Kings is night and day. The tire is just so much more beefy. Don't really want to rip apart the trailer because it's rolling on unforgiving rubber. 

Any opinions and recommendations is greatly appreciated.

Thanks in advance.

Chris M.

Concerned RV owner

+++++++

My answer:

OK you have a couple different issues.

You need to know that tires are made in batches. For relatively small markets it's possible that a company may only make an item once a year or even less frequently. While tire age is of concern when the tires are on the ground and exposed to sunlight and heat, it's less of an issue when in the factory warehouse.

One way to let your mind rest a bit is to ask when the warranty clock starts ticking. Some companies clearly state on day of application or first retail sale. Others say the warranty is based on DOT serial. If it's based on date of sale and clearly stated as such in the literature, I would be less concerned and just be sure that the sales receipt has the date and DOT serial of each tire identified and keep both warranty and receipt in a safe place.

Now, since you have taken the step of going from the ST205/75R14 LRC to ST225/75R15 LRD, you have increased the load capacity from 1760 @ 50psi to  2540 @ 65 psi. You have increased the reserve load capacity by over 50%, which should deliver very reliable service. While I do not have any data to go on, I think that when inflated to the same psi the LR-D and LR-E would have similar stiffness. It's the air that supports the load and it's the air that provides the majority of the tire stiffness.

For your application I would think there would be no problems with running LR-E tires at the wheel limit of 65psi.

So, bottom line, I think you can go with the year-old LR-D tires or run the LR-E at 65.

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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Changing wheels? There are some important dimensions and specifications to do this safely.

I recently read a thread on an RV trailer forum where some were considering changing the wheel diameter so they could get an increased selection of tire brands, sizes and load capacity to address tire failures. One person said
"I am looking at some nice 16" wheel tire combos but I'm wondering if they'll fit my trailer. They came off a different tow vehicle. Do I need to expect to swap out size up the hub where the wheel bolts are?"

I had some concerns as if someone is swapping wheels there are a number of dimensions and "fit" issues that need to be considered if you want a safe vehicle.

Wheel "offset" controls the location of the tire toward or away from the center of the vehicle. Tire Rack has a good tech page with drawings and definitions "The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offset can be one of three types (measured in millimeters).*"

Center bore may be critical as some wheels are "hub centric" which means the center of rotation is controlled by the fit of the wheel to the hub. Others are "lug centric" which means the fit of the lug nuts controls the wheel/tire run-out. "The centerbore of a wheel is the machined opening on the back of the wheel that centers the wheel properly on the hub of a vehicle."

Lug nut fit. Most steel wheels have a "cone fit" where the taper of the lug nut fits the taper of the wheel center. Aluminum wheels may have a simple cone fit with a straight taper or a radiused, or “ball” style. The two styles must never be mixed or you can ruin a wheel. The seat profile in the wheel dictates the nut or bolt seat style.  There is also a "mag style" that requires a large flat washer.
While it may be possible to initially use the wrong type nut the results will be a loss of torque and damage to the wheel with the potential of having a wheel come off the vehicle at speed.

Proper lug nut torque is another important number "If the vehicle is on a frame lift, and a helper is able to lock the brakes, the wheel fasteners can be final torqued while on the lift. Otherwise, lower the vehicle to the ground until the tires just begin to load (enough to prevent rotation while torquing). If the vehicle is on the ground with its full weight on the tires, you may be fighting a slight lateral load while final tightening. This is perhaps an arguable point, but final tightening before the suspension is fully loaded helps to obtain a more precise centering of the wheel fastener seats."

Improper mounting and lug nut torque can contribute to what feels like an out of balance tire.



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If your RV came with Bias tires you need to read this.

SEMA, or Specialty Equipment Manufacturers Association, put out a nice document explaining why it is important to understand that mounting radial tires on old wheels that were originally designed and built for Bias tire application may not be a good move.

Now this really only impacts people with "Classic" RVs but maybe some have a hobby that involves old classic cars.

If so I STRONGLY suggest you download and review THIS information.

While we are on the topic of Bias tires there is one very important thing to remember if you decide to keep running them on your vehicle. You should NEVER mix Bias and Radial type tires on an axle of your motorhome, and if you have a multi-axle trailer never mix the two different types on the trailer.

The sidewall stiffness difference can result in handling or braking problems and even tire failure in an extreme case.


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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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Wheels and how to change them

Sometimes an RV owner wants or needs to change their wheels. Just as with tires there are engineering terms and strength considerations that need to be understood so when you make a change you will not be compromising the safety or durability of your RV, or its tires.

As with tires there are some terms that we require a clear understanding before proceeding. A "wheel" has two parts, even if cast as a single piece of aluminum. The "Rim" is the part that contacts the tire and the air chamber in the tire. The "Disk" is the part that has the bolt holes and center hole that attaches to the vehicle. Each parts served different purpose and has different design requirements.


 Here is an engineering drawing that identifies the important dimensions of the "Rim" portion of a wheel. Each of these dimensions is specified in the published standards books such as the Tire & Rim Association Yearbook here in the US. If you look at the dimensions in both the European ETRTO and Japaneese JATMA you find the dimensions are identical. This is because the intent is to ensure proper interchangeability and fit no matter where the tire is manufactured. Most of these dimensions are specified to a tolerance of 0.01".
Two items may be of interest. Both of these are specified in inches, no matter where they are made. Even in countries that only use the Metric measurement system. While the Diameter is specified to a high degree of accuracy you will find it impossible to find a location that is actually measures 16.0" in diameter as the location is actually the intersection of the slope (5° in the above drawing) and the vertical defined by "A" or wheel width in the above drawing. The rim width "A" is specified in 1/2" increments and can be measured with a tape measure. When you look at tire specifications you will usually see a specific width mentioned such as 7.5". This does not mean you cannot mount the tire on a rim of a different width but again there are only a few widths that are "approved" for each tire size by the tire manufacturer so you must only select a rime that meets one of the specified widths.

Now if we look at the "Disk" part of a wheel you can see it in this drawing.

 Here we have an interesting situation as the Tire & Rim association does not specify any of the dimensions on the Disk portion of a wheel. These dimensions must match specifications from the axle or hub manufacturer. These include Bold Circle ( see the good explanation from Tire Rack). Center Bore,  Offset and Backspacing as shown in the picture.
It is important to understand that Offset and Backspacing are not identical dimensions and while Backspacing can easily be measures Offset is much more difficult.

Most Trailers and Class-B RVs without dual tires, will have wheels that look a lot like this picture with the Offset being a small number in the 1" to 3" range. Larger Motorhomes with dual application will have large Positive (outward) offset as seen in this picture of an Accuride wheel.

 This positive offset is what controls the "dual spacing. This spacing is specified with a minimum dimension in the spec page of LT and TBR tires intended for dual application.

If you are considering changing your wheels you not only need to consider the load and inflation rating of the potential new wheel you also need to ensure you have an acceptable width, center bore, bolt circle and offset to meet the vehicle, axle and tire manufacturing specifications.

There is another post here on wheels that you should also review before considering making any change in wheels as a wheel failure can be quite catastrophic.

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Should you carry a spare tire in your RV?

Here is a video I recorded at the 2012 FMCA national rally in Indianapolis for RVtravel.com and its daily newsletter RV Daily Tips.

Wheels we all have em

I was asked to comment on changing wheels.

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 change 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 and 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.