Trailers Support

Trailer Ratings and Selection Factors

Since all trailer manufacturers do not use common terms and reference points in arriving at their ratings, an understanding of those factors is very important to proper trailer selection. A customer with a trailer that is not quite up to the job to be done will find it to be a continual source of irritation, and therefore is unlikely to be a repeat customer. ZIEMAN trailers are rated by Gross Vehicle Weight Rating at an un-restricted speed of 55 MPH. The gross vehicle weight rating, or G.V.W.R., is the maximum total allowable weight of the trailer and its load at the stated operating conditions (i.e.: 55 MPH and above for ZIEMAN trailers). This brings up three critical points.

First, in the case of semi-trailers (See Figure 1 above), the entire G.V.W.R is NOT intended to be carried by the tires and axles. Rather, a portion of the G.V.W.R. is assigned to the hitch. This is in fact the definition of a "semi-trailer": 'any trailer so constructed that some part of its weight and that of its load rests upon, or is carried by, another vehicle'. So any trailer of this general layout is a "semi-trailer", no matter how small it may be. The above leads us to two conclusions.

a.) THE TRUCK MUST HAVE THE CAPACITY TO CARRY THE WEIGHT TO BE IMPOSED AT ITS COUPLER POINT. For example, the rig shown in figure 1 with its 4,000 lb. hitch weight would be inappropriate for a 1/2 ton pick-up truck!


As a rule of thumb, the hitch weight should be at least 10% of the G.V.W.R. for stable towing. Also, the load must be far enough forward so that the tires and axles do not carry a greater share of G.V.W.R. than they are rated for. For example, if a builder rated his trailer 25,000 lb. G.V.W.R., and each of the 3 axles were rated for 6,000 lb., that would leave 7,000 lb. to be carried by the hitch. 7,000 lbs. is an unrealistic hitch weight for anything smaller than a 10 wheel dump truck.

The second critical point is the distinction between PAY-LOAD, the actual load capacity of the trailer, and the G.V.W.R. The actual maximum LOAD that may be carried is the G.V.W.R., lessthe weight of the trailer itself. When selecting a trailer, be sure to add the weight of any machine options when totaling up the weight of the LOAD. It is good practice to add several percent to the spec. sheet values to allow for fuel, accumulated mud, the addition of minor options at a later date, etc. The weight of all standard ZIEMAN trailers is shown in the current catalog. Also, remember to add the weight of any trailer options. If total weight is near the maximum, that is , near the rated G.V.W.R.., then check with ZIEMAN factory on the weight of any options.

The third critical factor is the speed rating referred to at the beginning of the article. This can be most confusing, since some manufacturers use reduced speed ratings in their literature. The basis of reduced speed ratings comes from tire characteristics. Tire industry standards permit an overload of 9% when speed is limited to 50 MPH, 16% at 40 MPH, 24% at 30 MPH, and so on. However, these criteria CAN NOT be blindly applied to an axle rating. Are the axle, brake, wheel, spring, and other components capable of carrying an increased load? And at what cost in durability?

If you observe a competitive trailer's load rating to be greater than the equivalent ZIEMAN model with identical tires, CAUTION. This can only mean one of two things. Either the tires are rated at some reduced maximum speed, or an excessive amount of the total weight has been assigned to the hitch. Who can be sure that customer or his driver will observe the 50 MPH restriction, or other restriction, as the case may be?

And what about the legality of operation using reduced speed ratings? Many states now enforce tire load laws. For example, California regulations limit tire loading to the unrestricted tire rating unless the vehicle displays a sign on the rear stating 'MAXIMUM VEHICLE SPEED IS XX MPH'. The sign must in 4 inch block letters, black on yellow background. In most cases, a customer with a trailer loaded to the 50 MPH rating would have to follow this procedure and speed limit to avoid an overweight or overspeed citation.

For these reasons, all ZIEMAN models are rated at the unrestricted 55 MPH G.V.W.R. If you select a trailer based on these ratings, following the guidelines above, you can be assured of successful operations under all conditions and in any State. For special conditions and circumstances only, reduced speed ratings are available through the factory. This allows the case by case examinations that reduced speed ratings really deserve.


G.V.W.R.: Gross Vehicle Weight Rating.Payload capacity plus trailer weight; or gross axle weight rating plus a realistic hitch weight.AlsoSuspiciously high G.V.W.R. and capacity claims generally require either a reduced speed or an excessive and possibly unsafe hitch weight.
G.V.W.: Gross Vehicle Weight, actual payload plus trailer weight.
Rated Capacity:G.V.W.R. minus trailer weight.
G.A.W.R.: Gross Axle Weight Rating, generally the lightest rating of the wheels, tires, suspension, or the axle.The G.A.W.R. is shown on the certification tag.
Rated Hitch Weight:Payload plus trailer weight minus the G.A.W.R. of all axles.
Actual Hitch Weight: Actual payload plus trailer weight minus the total actual weight measured on the tires. For safe trailer operation the hitch weight should be a minimum of 10 to 12% of the Gross Vehicle Weight.

Trailer Safety Tips

You & Your Zieman Trailer

PLEASE NOTE: Trailer laws covering such things as brakes, lights, safety chains, licenses, etc., will vary from state to state. Be sure that your trailer is in full compliance with your state laws. Your trailer dealer usually can help you in this regard. If not, contact your nearest State Motor Vehicle Department Office for full information.

The key to carefree trailering is proper matching of equipment and trailer. A proper match is one in which the trailer is designed and built to carry the full weight of your equipment and gear, and which provides proper support.

All Zieman trailers have a certification label attached to the forward part of the trailer. It is required to show the gross vehicle weight rating (G.V.W.R.) which is the load carrying capacity plus the weight of the trailer itself. Be sure that the total weight of your equipment, gear and trailer do not exceed the G.V.W.R. If you don't know the correct weight of your equipment and gear, don't guess - have it weighed. This usually can be done at a local public scale.

Improper weight distribution can cause a trailer to "fishtail" (sway from side to side) as it moves down the highway, putting excessive strains on both towing vehicle and trailer, increasing gas consumption and sometimes causing an accident. The most effective way to guard against fishtailing is to make sure that the weight load on your trailer is properly distributed.

It is extremely important that 7 to 12% of the total weight of your loaded trailer should be felt at the trailer coupling ball when the tongue is parallel to the ground. A bathroom scale can be used in most cases to determine the weight on the trailer hitch ball. Check the information supplied by the trailer manufacturer to see if there is a specific percentage for your particular model. For example, if the gross weight of trailer, boat and gear is 1,500 pounds, the weight on the tongue should not be more than 180 pounds, nor less than 105 pounds. (Some auto manufacturers say that tongue weight should not exceed 200 pounds when using a weight- carrying hitch with full-size cars.)

If the weight down on the coupling ball does not fall within the proper range, you should take immediate steps to achieve it. If only a small adjustment is required, you may be able to solve the problem simply by shifting some of the gear from back to front or vice versa.

The importance of an adequate down load on the hitch ball cannot be overemphasized.


9. Connect trailer wiring harness to lighting system of tow vehicle and check operation.

With a trailer in tow you are operating a vehicle combination that is longer, heavier and sometimes wider and taller than your car or truck. This means you will have to make a few adjustments in your normal driving practices to compensate for the difference. Here are a few tips to help you enjoy carefree trailering:

Before you make your first trip with your trailer, make at least one short trial run to familiarize yourself with its handling characteristics and to be sure everything is working properly - lights, brakes, hitch, etc.

There is less strain on your car, trailer and equipment at moderate to slow speeds. Also, many states have lower speed limits for vehicles towing vehicles.

You'll need more of both when passing and stopping, especially if your trailer is not equipped with brakes.

Install outside rear view mirrors on both sides of the tow vehicle. Make it a habit to check the mirrors at frequent intervals to be sure your trailer and equipment are riding properly.

Trailer wheels are closer to the inside of turns than the wheels on your car or truck, this means you should swing wider at curves.

With a trailer in tow you'll need more time and distance to accelerate, get around a slower vehicle and return to the right lane.

Be prepared for sudden changes in air pressure and/or wind buffeting when larger vehicles pass you from either direction. Slow down a little and keep a firm hold on the steering wheel.

Wind resistance against the load and trailer can reduce your gas mileage significantly, especially at higher speeds. Streamline your rig with a cover, and make sure any hatches are closed securely.

Even if your trailer has brakes, a sudden stop could cause it to skid, slide or even jackknife. (Be especially careful to avoid the necessity for quick stops while turning.) Smooth, gradual starts and stops will improve your gas mileage and put less strain on your tie downs, etc.

Well before you stop, turn, change lanes, or pass, use your light signals to let other vehicles know what you intend to do.

If your tow vehicle has a manual transmission, traveling in lower gear when going up steep hills or over sand, gravel, or dirt roads will ease the load on your engine and transmission. If your tow vehicle has an overdrive gear (manual or automatic) you may get better gas mileage in a lower gear.

Make it as easy as possible for faster moving vehicles to pass you. Keep to the right side of the road and be prepared to slow down if they need extra time to return to their proper lane.

Allow at least one car and trailer length between you and the car ahead for each 10 mph on your speedometer.

The general rule is stay cool. Don't panic and don't do anything any more suddenly or violently than you have to. A sudden bumping or "fishtailing" may be a flat tire. Don't jam on the brakes or mash the accelerator to try to "drive out of it". Stop slowly and in as straight a line as possible. If conditions permit, allow your rig to coast to a very slow speed and try to avoid braking, except when your wheels are straight ahead and the trailer and your tow vehicle are in line. If your trailer begins to fishtail as you accelerate to highway speed, back off a little and it should cease. If it begins again as you accelerate, stop and check your load. It probably is not evenly distributed side to side or it is too far back so the hitch load is low. Redistribute your load before continuing.

To avoid any problems or breakdowns on the highway, you should make a final check of the following items before every trip and each time you stop for gas:

  • TRAILER HITCH - Is it securely in place on the tow vehicle?
  • COUPLER - Is is locked to the hitch ball? To be sure it is, raise the trailer tongue.
  • SAFETY CHAIN - Is it properly attached to the trailer hitch? It is tight enough to keep it from dragging on the ground but with enough slack for tight turns?
  • LIGHTS - Are they connected to the tow vehicle and working properly? Have a second person step on the brake and operate the turn signal as you check the lights to be sure.
  • TIE DOWNS - Is your load tied down and tightly in place?
  • WHEELS - Are tires properly inflated? Be sure to check while they are cold. Are lug nuts tight?
  • BRAKES - Are they working? Is break-away chain or cable attached?
  • EXTRA GEAR - If you are carrying baggage, extra gear or equipment, is it secured to prevent movement or loss on the highway?

Trailering Safety Tips (Commercial)

As manufacturers of equipment hauling trailers, we at ZIEMAN are vitally interested in highway safety. Experience has shown that trailers and other equipment often become hazardous through either misuse and abuse or lack of proper maintenance. In the interest of customer satisfaction and safety, we present these tips in the hope that they will be passed on to the operator at every opportunity.***********************************************

Perhaps the single most important consideration is selecting the proper equipment to do the job. The trailer selected should have ample capacity to handle the intended load, plus an allowance for machine accessories, required fluids, and accumulated mud, etc.

The most probable cause of poor trailing is a miss-matched truck and trailer or an improperly positioned load. Too often, trucks are marginal in size for their loads. The truck manufacturers rating for Gross Combination Weight, (GCW), should be consulted if any doubt exists. Note, G.C.W. is the total weight of the truck, plus the trailer, plus the load.

Trucks with long rear overhang, such as long-bodied stake or tilting platform trucks, also tend to be less satisfactory towing vehicles. The long overhang permits trailer side forces to be magnified, and possibly cause weaving. A heavy hitch load on a long overhang can also unload the front truck axle to the point that steering response becomes poor, again resulting in unstability.

An improperly balanced load can easily cause poor trailing. The load should be positioned so that from 10 to 20 percent of the total trailer and load weight is carried by the truck at the pintle hook. Fifth wheel trailers are generally designed to carry a greater percentage on the fifth wheel. Specific models vary, but the ratings are available on the rating tag on the trailer, or from the factory.

A handy solution to the positioning problem is to bolt a stop chock of lumber or angle iron across the front of the trailer bed. The proper position need then only be determined once. After the chock is properly installed, the operator need only park the machine against the chock to be assured of proper load positioning.

If several different types of machines are to be regularly transported on a trailer, a reference line may be painted across the deck. Then a small matching mark is painted on each machine, in line with the deck mark. (This with the machine properly positioned for best towing, as previously discussed.) Then, in daily operation, each machine is simply loaded such that its mark lines up with line across the trailer deck.

Once the load is positioned at the proper location, the next order of business is to keep it there. Good quality tie-down chains are a must. Too often, to save time, tie-downs are improperly used, or even omitted! Loose or unsecured equipment is very hazardous on the highway.

Tie-downs should be applied from structurally strong points on the machine, out diagonally toward the four corners of the trailer deck. This method prevents the load from "walking" in any direction. Although chain binders should not be over tightened, all slack should be removed and a definite pre-load applied to the chains. For long hauls, the tie-downs should be checked and re-tightened after the first 20 miles or so, to remove any accumulated slack.

A general procedure for hooking up is highly recommended. A simple walk around inspection is very effective when regularly practiced. Starting with the coupling hook-up, look for proper coupler closure. Safety chains should be in good condition and attached to a solid portion of the truck frame in such a way that they can't work loose. The hitch area should be looked over for proper bolting and for possible cracked welds. The electrical plug should be firmly inserted into its socket. If applicable, the break-a-way cable should be attached to the truck (not to the pintle eye) securely. Walking on around the trailer, check for tire wear, tire damage, tire inflation pressure, and possible wheel damage. Check that light lenses are intact and clean, ramps and other attachments are properly stowed for travel (if applicable), and the load is securely tied down as discussed above. Again check the wheel area, on passing the opposite side. Having walked all the way around the trailer and arriving at the hitch area again, check to see that the tilt bed locking mechanism is securely engaged in the locked position (if a tilt bed trailer is being used).

Two last items are: turn on the vehicle lights and check for proper functioning of all the lights, and then make a brake check when initially pulling away. This is done by applying the trailer brakes only when first pulling away at two to five M.P.H. It should be obvious that if no braking action is evident, the trip should be discontinued until the problem is corrected.

This simple walk-around procedure can be quickly learned. If it is built into a constant habit by operators, an increased level of safety and equipment reliability is the result.

One important area alluded to in the inspection procedure was tire care. Proper tire care means frequent inspection. Tires should be inflated to recommended pressures. Under-inflation causes poor trailing characteristics in addition to severely shortening tire life. The recommended full load pressure is inscribed on the sidewall of the tire. This is the "cold inflation pressure" and should be checked and brought up to the correct level before the tire is operated. That is: when the tire has had at least one half hour to sit and come to thermal equilibrium. It is normal for truck or trailer tires to heat up during use. This is caused by the flexing that the tire material undergoes. When the air in the tire is thus also heated, its pressure increases, since it cannot simply expand. The point is, that this excess pressure should never be bled off back down to the cold inflation pressure. The loaded operating pressure can be as much as 20 percent over the recommended cold inflation pressure, but this is taken into account by the tire designer when the cold inflation pressure recommendation is calculated.

Low inflation pressure causes excessive flexing, and thus the generation of excessive heat. Excessive heat is the number one enemy of tire life. Too much heat severely weakens the tire material and the bonds between various layers of the internal construction. If the heat level is really excessively high, the tire may immediately blow out, or even catch fire! Proper inflation pressure cannot be over stressed.

Obvious care should not be overlooked either. Imbedded stones and other foreign objects should be removed before they work their way in deeply. Grease and oil should be wiped of. In smog prone or other high ozone areas, the use of silicone based rubber care spray is recommended to prevent excessive cracking that can lead to more serious internal damage.

Bald tires are another danger area. Trailer tires should have ample tread to give good traction on slippery surfaces and to offer good braking adhesion. Also, the danger of blowouts due to striking obstructions is considerably reduced if tires have a deep tread.

Tires should also be reasonably matched. Do not intermix various ply ratings of tires, or radial ply tires with bias ply tires. The resultant miss-match in rolling friction and side stiffness contribute to poor trailing performance and instability.

On dual wheels, tires should be of the same diameter. If they are not, braking force and traction will be uneven. Loads will be distributed unequally on bearings, spindles, and the tires themselves. This condition is easily checked by measuring the rolling circumference of the tires with a steel tape. The circumference of one tire should be within one percent of that of its dual mates. For example, if one tire measures 104 inches in circumference, the other should measure within plus or minus 1-1/16 inch. (1-1/16 inch is one percent of 104 inches, rounded off to the nearest 1 /16 inch).

Wheel care is of no less importance to trailer safety. Correct wheel nut torque will prevent the majority of wheel problems. Loose wheel nuts are by far the most common cause of wheel problems. Bolt hole elongation, hairline cracks in wheels, and broken studs are direct results of improperly tensioned wheel studs. Loose nuts can also cause damage to stud and nut threads, and to ball and seat faces.