Tires: You find them hard to live with, but you can’t live without ’em. And if you think the tires on your car or truck are a pain, trailer tires are even worse. That’s mostly your own fault, because you never look at them and you never check them, so they feel unloved. Here’s what you need to know to keep your trailer tires happy.
First, trailer tires are completely different from car and truck tires, so don’t get some cheapo specials from Honest Eddie’s Tires. The sidewall — the area from the rim to the tread — is strengthened on trailer tires to handle the considerable weight of a boat and not flex while wheeling around curves on the way to the water.
There is a spot on the side of every tire that is the Cliff’s Notes to everything necessary to know: capacity, dimensions and age. It is where owner meets tire. It should always — always! — have the letters “ST” or, at the very least, a molded label that says Trailer Use Only.
This is the one thing everyone knows about tires: They need air. But how much? On the sidewall are labels that include the proper inflation level for a cold tire — one that hasn’t been driven and is being checked in the driveway — or a hot tire — one that’s been driven, even around the block. This will read in PSI (pounds per square inch), which will also be the reading on the tire-pressure gauge that should be in every glove box.
Trailer tires are created in one of two ways: bias ply or radial. Which way will be marked on the sidewall. Bias-ply tires are generally stiffer, almost always less expensive and better for short-haul trips. Radial tires build up less heat during long trips, they create less road noise or “drumming,” and they have a greater load capacity than a similarly sized bias-ply tire.
One important caveat: Never, ever, mix bias-ply and radial tires on a trailer. It should go without saying to never mix tire sizes on a trailer.
Once again, the sidewall will indicate a load range or, simply, a max weight, in pounds. The listed weight is what that single tire can support safely. Let’s say the max load for a single tire is 1,700 pounds. That means a single-axle trailer can safely carry 3,400 pounds — total. That includes the weight of the trailer itself, the boat, the motor, and the fuel and water in the tanks. Oh, don’t forget the ice chest stuffed with six packs. A single-axle trailer can carry a load right up to the maximum limit, while double-axle trailers can carry about 12 to 15 percent below the max load — in our hypothetical case, around 6,000 pounds.
A trailer tire will have a row of large numerals on the sidewall to indicate the size, width and wheel diameter. Let’s look at a tire that shows ST200/60R15. The ST means it’s a trailer tire. The 200 is the width of the tire, in millimeters. The 60 is the ratio of the height to width; in this case, the tire height is 60 percent of its width, or a fairly “low profi le” tire. The R means radial (a D would indicate a biasply tire). The 15 means the tire requires 15-inch rims.
Old Age Ain’t Fun
Getting old is just as tough on trailer tires as it is on boaters. Aside from road hazards and alignment problems, tires can just wear out. Cracks in the sidewalls point to dry rot, often in combination with the effects of sunlight, which is why many boaters (and RVers) put little “hoodies” over their tires, to keep the sun away. Tires will naturally stiffen with age, and every tire is required by the Department of Transportation (DOT) to have the date of manufacture molded into the sidewall. Look for a set of four numbers. The first two indicate the month and the last two the year, so “0501” means the tire was manufactured in May 2001.
Just because a tire is 10 years old doesn’t mean it has to be replaced. If it has been taken care of and inspected for wear, it will be just fine. The older the tire, however, the more it needs to be checked.
Lazy Man’s Tire Pressure
Yes, it’s a pain to walk around and bend down to check the tire pressure on each tire, which is why the task is often overlooked, sometimes with dire consequences.
The good news is that modern technology offers a solution: a wirelessly connected tire gauge right in the car. Several companies offer kits for $100 or slightly more. They install easily by screwing tire sensors onto the tire stems (they usually include four). A receiver plugs into an accessory plug in the car. The bonus is that in addition to showing the pressure for all tires, it also displays the tire temperature, which can point to bearing or brake problems that are heating the tire.