How to replace a tire in "Dual" application

First off if you have a towable 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 meaasurement 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.