You don't get down the road without tires and you're certainly likely to risk a tire failure caused breakdown if you don't have the correct tires for your trailer and expected loads.
There are differences between automobile tires, truck tires and trailer tires. So the first thing to do is purchase tires labeled for trailer service. Next, the tires need to be rated for the load you will be carrying. Tire load ratings are printed on the sidewalls of the tires and tires are also classified by load ranges. Most trailer tires fall into load ranges B through E.
- Load Range B: 4-ply rated
- Load Range C: 6-ply rated
- Load Range D: 8-ply rated
- Load Range E: 10-ply rated
The greater the ply rating, the more weight that the tire can support.
For example, a typical ST225/75/15 trailer tire with a Load Range B rating can safely carry about 1,750 Lbs. The same tire with a Load Range E rating can safely carry over 2,250 Lbs.
The total load capacity of the tires combined must exceed the total gross weight of the trailer and its cargo. With live loads such as horses and livestock, we recommend increasing the load rating by at least one letter (e.g., going from a C to a D) since animals tend to shift in trailers when being hauled.
Finally, a tire's ability to carry its rated load is dependent upon it being maintained at a proper air pressure. A low tire may only safely handle half its rated capacity, then overheat, then come apart while traveling at speed.
Typical proper tire pressures for maximum load carrying capacity:
- Load Range B: 35 psi (240 kPa)
- Load Range C: 50 psi (350 kPa)
- Load Range D: 65 psi (450 kPa)
- Load Range E: 80 psi (550 kPa)
Tires can also deteriorate with age, often starting with tiny cracks appearing on outer sidewalls. If these blemishes appear on your tires, have a reputable tire shop inspect your tires to determine if the problem is cosmetic or is indicative of a more serious problem. Even if such tires pass inspection, they warrant close scrutiny until replaced.
Trailer tires should also be balanced, the same as is done with the tow vehicle's tires. Balancing reduces vibration and improves tire wear.
Here's an often overlooked key point. If you upgrade to a higher rated tire, remind the tire shop to check and install high pressure valve stems on your rims if the pressures in your new tires warrant it! No point in spending good money on higher pressure tires to have one destroyed because a valve stem fails.
There is increasing data indicating that trailer tires over 5 years of age start to internally deteriorate, even when stored indoors or out of the weather. When purchasing tires be sure to have the tire shop check the date of manufacture. Don't spend good money on aged tires. Also check the ages of your tires when you make your annual trailer inspections. Tires over 5 years old will become causes for concern and you should start budgeting for their replacement.
The manufacturing dates are required to be indicated on the sidewalls of tires sold in the US. The image below provides an example as to how these dates are shown.
Trailer tire chains are often ignored equipment, even though in many states you are required to carry chains for your tow vehicle and trailer during winter months. (Check the regulations for your state.)
Aside from the risks of losing control of an unchained trailer if you hit the brakes on an icy road, simply getting stranded while hauling precious cargo can offset the relatively minor expense of purchasing and carrying chains. Winter weather can change without notice, so be prepared.
Wheel Studs, Lug Nuts and Wheel Bearings
We have noticed that trailer tires appear to be more prone to loosening of wheel lug nuts than passenger vehicles. When lug nuts work loose, the wheels can actually cut into the studs. Lug nuts should be periodically checked and any worn studs replaced.
Trailer wheel bearings are another often overlooked cause of breakdowns. They need to be periodically repacked with grease and set to the proper tension. Otherwise they can overheat and fail. Over 20 years ago when we published the original "Survival Guide" trailer safety piece, I received a phone call from a gentleman who read the piece and decided to have his horse trailer checked before making an interstate trip. When the service center jacked the trailer off the ground, one of the wheels fell off. Wheel bearing maintenance is a critical safety issue!
Electric brakes are critical devices for any trailer and most states now require brakes to be installed on all axles. (Most older trailers can be easily retrofitted.)
The tow vehicle's brake controller sends electric current to an electromagnet. When current is applied, the electromagnet is attracted to a smooth surface on the inside face of the brake drum. That attraction tends to pull the magnet in the direction that the drum is turning. As friction tugs at the magnet, it pulls an actuator arm that in turn pushes the brake shoes against the drum. The stronger the electric current, the firmer the electromagnet drags against the drum and the harder the brakes will apply.
Brake shoes are kept in proper position by a slack adjuster, shown just below the magnet in the next picture. Proper adjustment is needed so that the entire brake shoe presses against the drum, not just the portion nearest the point of actuation.
Setting a brake controller too high or a rusty drum can cause the magnet to grab, causing the brake to lock up which is dangerous and can cause incredible tire wear.
While on the subject of brakes, we're going to jump back into the tow vehicle's cab. Brake controllers are one area where we don't spare any expense.
The controllers on older vehicles were operated by the tow vehicle's service brake hydraulic system. The harder you pressed on the brake pedal, the more power was sent to the trailer's brakes. However newer vehicles having anti-lock braking systems require more sophisticated controllers. The two types of controllers commonly available are proportional and time delay.
The best controllers are proportional as they sense inertial changes when the tow vehicle is braking and provide variable voltage to trailer brakes depending on the amount of braking force that the controller calculates is necessary.
With time delayed controllers, the controller sends a fixed current to the trailer brakes shortly after the tow vehicle's brakes are applied. It is important to know which type of controller you have as their operating characteristics and how you adjust them are distinctly different!
(For more information regarding controller characteristics please visit Trailer Brake Controller Information.)
When changing trailers and when changing loads carried in or on trailers, the brake controller needs to be adjusted to provide the proper amount of drag when brakes are applied: enough that you can feel the trailer brakes apply, but not so much as to jerk the combination or cause trailer wheels to lock up.
Depending on the design of the trailer, some suspension components may require periodic lubrication to minimize wear. Whether serviceable or not, worn bushings, shackles and related components can contribute to a sloppy suspension, less control and reduced road-worthiness. Worn suspension components are typically not prohibitively expensive to replace provided that they get replaced before they do damage to other suspension members.
Body and Flooring
As trailers get older things start to work loose. Pop rivets are classic problems as sheet metal and trim can wear away on the rivets due to vibration and the body shifting. Once a rivet fails, other nearby rivets are likely to fail. It's a simple task to visually inspect a trailer, and to drill out and replace loose or broken rivets.
Some trailers tend to develop cracks in areas where body components are welded together. Such cracks should be repaired before the problem becomes a major issue. Door and gate hinges can also develop cracks that will need attention if spotted.
Horses and livestock trailers typically have rubber mats covering wooden floors. Moisture and time can weaken these floors until animals literally fall through during transport. These floors must be inspected at least annually with floorboards that show signs of rot, are split or are warped, being replaced forthwith.
Trailers with bolted-on couplers need to have the coupler bolts checked periodically. We only use "Nylock" vibration resistant aircraft nuts on such components. The coupler's locking mechanism needs to be kept free from debris that could prevent the coupler from locking properly onto the hitch ball, and we lubricate moving components with graphite as graphite doesn't tend to attract dust or moisture.