17 October 2014

Tire Pressure: Getting It Right

Few things are more important to the safety of your family and your truck than your tires. The trouble is, there is a lot of misinformation and complacency out there. Few people really know the proper tire pressures required and even fewer people check them on a regular basis. First off, let me say I'm no expert. I neither design nor sell tires for a living. But I do have a lifetime of experience with them, having owned over a dozen trucks and travel trailers, and having read numerous publications and articles on how to properly inflate and care for them. It's hoped that this article will spark interest on tire safety and serve as a gentle reminder on the importance of periodic inspections.

Without a doubt, improper inflation is the greatest cause of tire damage and failure. Indeed, driving on an over- or under-inflated tire is dangerous and can lead to a tire overheating and bursting. If you've ever suffered a blowout at highway speed, you know how dangerous it can be. Moreover, an over- or under-inflated tire can experience excessive tread wear thus leading to the reduced life of the tire. Not only that, but driving on an under-inflated tire can also increase the rolling resistance, leading to reduced fuel economy. With the price of fuel being what it is today, every mile counts. With the high cost of fuel some owners like to over-inflate their tires to decrease rolling resistance. But the benefit of greater fuel economy is offset by the greater risk of suffering a major blowout (not to mention a rougher ride). It simply isn't worth the extra risk.

There are two basic approaches you can take on proper tire inflation. The first is to use the inflation values recommended by your truck manufacturer. These values can be found either on a placard located on the driver's side doorjamb or in your owner's manual. The placard for my Ram 3500 calls for my Firestone 275/70R18E front tires to be inflated to 60 psi and the rear tires to 80 psi. It's important to understand that the inflation values on the placard assume a maximum payload, which is why 80 psi is required for the rear tires. The second approach varies both the front and rear pressures based upon the combined weight of your truck and truck camper. For this approach, you'll need to take your truck and truck camper to the scales to get weighed then refer to your tire manufacturer's tire inflation chart and inflate accordingly. The Firestone tire inflation chart for Medium Truck (MT) and Light Truck (LT) tires can be viewed by clicking here. When using these tables remember to multiply the listed values by two if you're going by the actual weights for each axle of your truck.

Doorjamb tire and loading placard for a 2013 Ram 3500. 
 
Which approach is best? The Tire Industry Association's website recommends the first though the second works well, too. Which do I actually prefer? I prefer to use the first approach since my truck camper comes close to maxing out my truck's payload rating, though when unloaded I do like to air down my rear tires to 50 psi so my ride is smoother and less harsh. And for those who are curious, if I were to use the second approach with my camper mounted, I would put 50 psi in my front tires and 70 psi in the rear tires. As you can see, the differences between the two approaches are pretty minimal, so I prefer to go with the slightly higher inflation values strictly for the better fuel economy. The bottom line is that you can't go wrong using either approach. They're both right, though many feel more comfortable staying with the truck manufactures' suggested inflation values.

There are a few things you need to keep in mind when checking your tires. First, always measure a tire's pressure when it's cold. What is a "cold" tire? It's a tire that has been driven on less than one mile and a tire that hasn't been sitting in the hot afternoon sun. This is important because driving at high speeds in the heat of the afternoon sun can raise a tire's pressure as much as 6 psi. Because of this I like to check and fill my tires first thing in the morning when it's the coolest. When filling, never exceed the maximum psi value listed on the tire's sidewall. Load Range E tires, those typically found on 3/4 and one-ton pickup trucks, have a maximum pressure of 80 psi.

The maximum tire pressure brings up a good point and a common mistake made by some newbies. As we just discussed, a tire driven at high speed can see an increase as much as 6 psi. For a Load Range E tire recently filled at the maximum pressure of 80 psi cold, this means you could see a reading as high as 86 psi immediately after returning from a road trip. This is nothing to be alarmed about. Tires are engineered to handle the extra heat and corresponding rise in pressure that driving at high speed naturally causes. This extra "hot" tire pressure is perfectly normal and doesn't need to be bled off. Doing so is a common mistake made my newbies. Don't fall for it. Besides, tire pressures are to be taken cold, not after returning from a long road trip.

Even over inflation can cause catastrophic failures like this.

How often should you check your tire pressures? I like to check mine before each getaway with the camper and each time before I go to the fuel pump. It's important to check your pressures regularly due to a process called permeation. Tires lose air normally through this process, but changes in temperature can affect the rate at which your tire loses air. This change is accelerated in hot weather though a tire can still lose one or two pounds of air per month during the winter. When checking your tires, make sure all of the valve stems are equipped with valve caps to keep out dirt and moisture. This is especially important if you like to drive off-road. Oh, and speaking of valve stems, always make sure that your LT tires are equipped with metal stems to handle the higher pressures. Believe it or not, some tire shops are guilty of making this mistake.

No doubt you've heard some good things about the use of nitrogen in tires. Proponents claim that nitrogen is denser than air and less prone to permeation thus enabling a tire to stay properly inflated longer. This, they say, leads to better fuel mileage and less wear and tear on your tires. Yes, the claim is true, but the cost for nitrogen--anywhere between $5-12 per tire--far outweighs any benefits derived from the gas. Now if it was free, I'd certainly use it, but it isn't. In my opinion, nitrogen is just a scam, another way to fleece the public. Those who claim otherwise are usually those with a vested financial interest in the subject. Remember that.

Lastly, since we're on the topic of tire care, it's important for all truck and motorhome owners to carry both a tire repair kit, like the Safety Seal Pro Tire Repair Kit, and a portable air compressor, like the VIAIR 450P Portable 12 volt Air Compressor. Many RV owners, like myself, like to boondock and travel far off the beaten path. Having these with you gives peace of mind knowing you can repair a leak and air up your tires at any time. These items, of course, should be part of a well-stocked emergency roadside kit, a kit that every vehicle owner should own.