Tires for Towable RVs and Tow Vehicles
by Warren Petkovsek
Let’s talk about tires today. Tires are not only essential for any vehicle to operate on or off the road; they are also the most critical safety concern for any motorist including and especially RVers. The scope of this article will be limited to towable RVs and tow vehicles and will not include motor homes. That could easily be a complete article so we’ll save that for another day.
Many serious and even fatal accidents have been directly attributed to catastrophic and sudden tire failure otherwise known as blowouts. Even tire failures that didn’t result in accidents have caused a lot of damage and ruined more than one RV vacation. You owe it to yourself and your family to prevent tire failures. You can easily accomplish this by educating yourself and becoming a “tire expert” like me. Well, like it or not, school’s in session. Let’s make “tire class” as informative and painless as possible. Heck, it may even be fun. Here we go.
Proper tire inflation is critical to the performance and safety of every vehicle, especially RVs. Sometimes we think, “If a little is good, then a lot is better”. This is not true with regard to tire pressure. If we overinflate our tires the tread will crown slightly in the center and will wear out quicker there. This crowning will also reduce the contact patch or the amount of rubber on the road and result in less wet traction; a very dangerous condition. Overinflated tires also cause the vehicle to ride much rougher and who wants that?
Underinflated tires are also dangerous because they run hotter due to increased sidewall flex and friction due to rolling resistance. The rolling resistance also reduces fuel mileage. Under inflation is also a major cause of tire failure. The tire doesn’t actually carry the load; the air inside the tire does. Let’s talk some more about a tire’s load capacity.
There’s a lot more to selecting replacement tires than looking at the size stamped on the sidewall of the old tires. It is vital that we match the tire with the weight it has to carry. Let’s suppose that the rear tires of your tow vehicle weigh 3,200 pounds each when loaded up to travel and the trailer is loaded and hitched. You would only know this if you weigh each wheel of your trailer and tow vehicle. You really need to do this! If you have single rear wheels and load range “E” tires then the tires can carry that weight if inflated to the recommended 80 psi air pressure. But what if your rear axle weighs only 4,400 pounds or 2,200 pounds per wheel? Then your “E” rated tires can carry that load at 50 psi and not be overloaded or underinflated. If this is your normal load you may want to use “D” rated tires which can carry 2,800 – 3,000 pounds at their maximum recommended pressure of 65 psi. If your vehicle came equipped with “D” rated tires and you want to increase your safety margin by upgrading to “E” rated tires that’s OK too. Just check with your tire professional to be sure that your wheels can handle the additional load and air pressure.
Tires come in all sizes tread designs, methods of construction and load carrying capacities and we need to know the proper tire for both our trailers and our tow vehicles. With regard to size and tread design – some folks purchase tires with regard to nothing but appearance. Let’s look at the big, radically lifted 4X4 with huge tires that have an aggressive mud tread. Chances are that this is a show truck that will never leave the pavement, but I digress. Let’s stay on the subject of tires.
Oversize tires with a larger than stock diameter will change the overall gearing of your tow vehicle and adversely affect its towing performance. Many off-roaders use larger diameter tires to better navigate over rocks and obstructions, but anyone that uses larger diameter tires must also change the gear ratios in their truck’s axles in order to maintain proper gearing and performance of their trucks. Larger tires may also cause clearance problems thus restricting steering and even suspension travel on your tow vehicle.
Generally speaking, you just can’t go wrong by replacing tires with the original equipment size tire that came from the factory on your vehicle or trailer. You can find the recommended tire size and inflation pressure for a vehicle on a sticker located on the driver’s side door jamb. On a towable RV this sticker is located outside on the left side near the front. Oh, you can put a slightly wider tire on your tow vehicle as long as you keep the original tire diameter. Example: You can replace a tire size P235/75 (any wheel diameter) with a size P255/70 tire. The new tire will only be 70% as tall as it is wide, but it is also slightly larger so things even out and the tire diameter stays the same. If you have any doubts about this be sure to speak to your tire professional before you make a decision. This tire width upgrade only applies to tow vehicles. There is no reason to install larger or wider tires on any trailer. That would serve no purpose.
Let’s talk about tread patterns. Very aggressive or knobby mud treads are OK if you need them, but in most cases that is rare indeed. These types of treads are noisy on the road, they don’t generally wear as long as less aggressive treads and they will also reduce your fuel mileage. That noise you hear is the knobby tread making impact with the pavement which equates to rolling resistance which, in turn, lowers fuel mileage. The large void spaces in the knobby tread also reduce the contact patch or the amount of rubber in contact with the road which degrades wet on-road traction and accelerates tread wear.
Highway treads are much less aggressive than knobby mud treads and they more resemble the tires found on passenger cars. The advantages of this type of tread are longer tread life, better fuel economy and a larger contact patch. This is the type of tire tread found on eighteen-wheelers because these trucks will (realistically) never leave the pavement. If you operate your vehicle solely on paved roads then this is the best and safest tire for you. This is also the only tread design that is suitable for your trailer. A more aggressive tread on a trailer would serve no practical purpose.
The final type of tread design is the all terrain tread. This is a good compromise between aggressive treads and highway treads. This design provides good wet traction on paved roads, they look good and they provide enough off-road traction for most of us. Actually, if you need more than an all-terrain tire for off-road traction then you better have a winch on the front of your truck.
Regarding the fancy aftermarket wheels or “mags”; I’m generally opposed to them. My concern is that the aftermarket wheel may not be rated for the same load or air pressure as your stock wheels. If you’ve just got to change wheels then make sure the tire guy proves to you that the new wheels are as adequate as the old ones.
Many towable RVs come equipped with ST or “special trailer” tires. These tires are to be used on trailers and never on anything else. They generally have a lower speed rating than regular tires, but the rubber compound in ST tires is designed to retard deterioration of the rubber due to ultraviolet light. I’ve used these before with good results, but I’ve done a lot of research and I believe that a LT or “light truck” tire could accomplish the same thing by carrying the same load, lasting just as long and be more readily available at tire stores. My new fifth wheel weighs 16,000 pounds and it came equipped with LT tires so I guess I’ll have the opportunity to prove out my research. I’m very confident in this.
Earlier I mentioned that ultraviolet sunlight is harmful to the rubber compounds in tires. This is much more critical for our trailers than with our cars and tow vehicles. The reason is that trailers are stored for extended periods and the tires are exposed to sunlight for quite some time. The vehicles that we drive are used often enough that the tires roll and thus warm up on a regular basis releasing anti-aging chemicals in the rubber. This is why we should cover our trailer tires to protect them from sunlight whenever the rig is parked. I even cover mine in a campsite. There are tire covers available at RV dealers and specialty RV stores such as Camping World and they are cheaper and easier to store and carry than, say, plywood.
As if we weren’t already in “information overload”, there is even more vital data that is molded into the sidewalls of tires. As I mentioned in a previous article, tires have a shelf life. Statistics show that most tire failures occur during the sixth year of tire age – NOT service. If you have tires that are over six years old then you are on borrowed time. The bad part is that the tires you buy may have been sitting on a shelf or in some warehouse for several years and then they are sold as new tires to the unsuspecting public. We can avoid this by checking the manufacture date of the tire. The last four numbers of the DOT code that is molded on the tire’s sidewall will tell us this date. My new fifth-wheel came with tires that were marked “3107”. This means that the tires were manufactured during the thirty-first week of 2007 or in June of the year that the trailer was delivered to me. That’s good! If any new vehicle that you want to buy has tires that are more than three years old, I believe that you should insist on the dealer either replacing the tires or giving you a tire allowance so that you can have them replaced. I mean, why give up half of your tire life? I’ll elaborate with some examples.
I was told all this information about tire age years ago, but I was somewhat skeptical. Even after eight years of use the tires on my first travel trailer still looked new. I carefully checked air pressure before and sometimes during each trip and I weighed each wheel to ensure that the tires weren’t overloaded. But one of them did fail and the blowout was truly spectacular. I just happened to be looking in the mirror when the unfortunate event occurred and there was no doubt that the tire was holding air at the time. I know this because the explosion was truly of epic proportions. I was very lucky that the disintegrating tire didn’t cause damage to the trailer which is often the case with RVs. Two other RVing couples that are both friends of ours each bought used fifth-wheels and both experienced multiple blowouts; one on their first trip and the other shortly after. They had no clue how old the tires were or even that tire age mattered. The really bad thing about multiple tire failures on the road is that you have to replace them with what is available wherever you are. You may not have many choices and you may not get the price you want not to mention the inconvenience.
‘One more thing. We all have to level our rigs in campsites by driving up on boards. It is very important that the boards are wide enough to support the entire tread of the tire. This means that none of the tire tread can hang over the edge of the board. If any of the tire hangs off of the board damage to the belts may occur. Remember, there is a lot of weight on the tires and that can cause damage. I use 2” X 12” boards for this purpose and my tires are always completely supported.
In conclusion, If you or anyone you know has ever experienced a blowout then one or more of the following will be true: (1) The tow vehicle or trailer may have been purchased used and the owner has no idea of the chronological age of the tires. (2) The owner has no idea if the tire is properly inflated and (3) he has no idea how much weight the tire was carrying. Remember, an overloaded, over age or underinflated tire is just a blowout waiting to happen. Please remember to weigh your rig, check your tires and be safe on the road.
Resources and suggested reading:
RVing from A to Z by Bill Farlow
Cottage Publications, Inc. 1991
Smooth Rolling, RV Care, Safety and Performance
TL Enterprises, Inc. 2000
Warren Petkovsek has been an avid RVer for over several decades. He lives in
Lumberton, Texas with his wife Myra. A former teacher, band director and
professional musician, Warren is now retired from the petrochemical industry.
In addition to being a freelance writer he is also a school volunteer, a Texas State Park volunteer and has been a Boy Scout Leader for many years. Warren would be delighted to answer any RV related questions that you may have and would be delighted to send you
some or all of his other articles. He can be contactded at firstname.lastname@example.org