Follow these recommendations to keep your motorhome rolling along safely.
By Roger Marble, F399427
Car ownership doesn’t prepare you for maintaining motorhome tires. The durability and reliability of car tires have improved to the point that many people may never need to touch them or learn how to change one. Some cars today don’t even come with a spare. But for many RVs, tires are the weak link that can disrupt travel. Regardless of motorhome size, overloaded tires are the chief cause of failures.
As a retired tire engineer, I can offer suggestions that draw on my 40 years of experience in tire design, testing, evaluation, and quality assurance. Follow this advice, and you’ll likely enjoy many years of problem-free travel. In addition, once you take the initial steps I outline, you’ll need to spend only about 15 minutes a month on tire maintenance.
Avoiding problems with RV tires involves two simple steps:
1. Know the proper tire inflation pressure for your RV.
2. Ensure that your tires are always inflated to that level.
The important concept in the first step is “your RV.” Not the RV your brother-in-law uses. Not the inflation level the guy in the campsite next to you follows. Not even the inflation level provided by the RV manufacturer on the tire certification label, otherwise known as the “tire placard.”
Some people point out that the RV manufacturer is responsible for informing you of the minimum tire inflation pressure. That’s correct, but it is based on an assumption, and therefore the numbers may be too high or too low when your RV is packed for a trip.
Determining the proper psi for your RV tires takes some effort, but you need only do it once, unless the RV’s weight changes significantly. Examples of such changes could include adding a generator or a residential refrigerator, or refinishing the interior with granite countertops.
To learn your RV’s true weight, pack it with all the clothes, food, fuel, water, and other items you expect to carry. Then, with family members and pets who will be traveling with you on board, visit a scale that can weigh RVs and have the vehicle weighed by individual wheel position. This is important, because the required air pressure is based on the load on each individual tire.
The RV Safety & Education Foundation (RVSEF) offers motorhome weighing by individual wheel position at FMCA international conventions and other events. Once the load being carried by each wheel position is known, motorhome owners are provided the minimum inflation pressure needed to carry that load. For more information, visit www.rvsafety.com.
If you will not be in a location where RVSEF is weighing vehicles, another option is to do some research to find a large truck scale that has enough side clearance so that the tires from just one side of the RV can be positioned on the scale. Possibilities include moving and storage companies, feed stores, gravel pits, recycling companies, and truck stops. Be aware that in order to obtain an accurate weight reading, the RV should be as level as possible. At many truck stop scales, the adjacent area is sloped to allow water runoff and is not suited for single-side weighing.
Michelin has compiled a booklet that explains how to weigh an RV. It includes a worksheet for recording weights and calculating tire loads. The booklet is online at www.goo.gl/wqR3tn.
Once the worksheet is complete, you’ll know the actual load on each tire position. The next step is much easier and needs to be done only once. It involves confirming the minimum cold inflation pressure (CIP) needed in order for the tires to carry the load.
Each tire manufacturer provides load and inflation tables specific to their products to help you determine the correct tire inflation pressure for your motorhome’s measured load. For links to the websites for many different brands of tires, visit my RV tire blog: http://www.rvtiresafety.net/2015/04/links-to-load-inflation-tables.html.
Simply look for your tire brand, find the table that has your size tire, and look for the inflation level that carries your load or greater. This is the minimum cold inflation pressure. Don’t be tempted to use a lower level of inflation if the numbers are close. Always go up in inflation.
Let’s return for a moment to weighing the RV. If it will be awhile before you can obtain individual wheel weights, look for a truck stop scale where you can obtain the individual axle loads. Don’t assume that the weight is distributed equally on each side. To address side-to-side imbalance, I suggest you assume a weight split of 47 percent to 53 percent. Use the 53 percent number when consulting the load and inflation tables to arrive at a minimum cold inflation pressure. This should be only a short-term solution until you can get individual tire loads.
When tire inflation pressure is measured, the tire should be cool and in the shade. It must not have been driven or exposed to direct sunlight for at least 2 or 3 hours. When a tire is hot, the air inside it expands, so the reading will not be as accurate. Therefore, many people check tire pressure in the morning before starting out, or late in the evening after a day of travel.
Changes in ambient air temperature can cause minor fluctuations in tire inflation pressure. To eliminate the need to adjust the tire pressure every time that happens, I suggest increasing the cold inflation pressure by 10 percent. With this extra margin, as tire pressure goes up or down a few psi, you probably will not need to add air until the pressure drops about 5 psi. Just remember to never allow the pressure to drop below the minimum CIP.
Also important: All tires on each axle should be inflated to the same psi, using the psi of the tire bearing the heaviest load to inflate all tires on that same axle. This ensures more uniform stopping and steering response.
In recent years, a number of RV tire pressure monitoring systems (TPMS) have become available. Such systems monitor tire inflation as you’re driving and issue a warning if a tire is damaged by a nail or other object and loses air. I suggest finding a TPMS that has user-replaceable sensor batteries, a long-term warranty, and early warning of initial pressure loss. I also suggest selecting a system that can provide an early-morning pressure reading while you finish your coffee. That way, you don’t have to use a digital pressure gauge to check the tires every day of travel.
So there you have it. Have your RV weighed by individual wheel position when it’s fully loaded. Or, weigh it yourself, use a worksheet to calculate the actual loads on your tires, and then look up the recommended tire pressures. Check those pressures every travel day or, better yet, monitor them with a TPMS. Follow this advice, and you’ll significantly reduce your odds of experiencing a tire failure.
Information about RV tires, including maintenance tips, how to weigh an RV, and tire load and inflation guidelines, is available online from the following RV tire manufacturers:
Continental, C12084*: www.goo.gl/pzQuzU
Michelin, C5502*: www.goo.gl/jxM8wG
Information about locations and schedules for wheel-by-wheel weighing of RVs is available at these websites:
Escapees RV Club SmartWeight, C3326*: www.escapees.com
RV Safety & Education Foundation, C5999*:www.rvsafety.com
RV Weigh-Mobile Weigh Station, C13128*: www.rvweigh.com
*FMCA commercial member