All you need to know about Steerable Axles for Trailers

In this post, we will look at a relatively old concept in automobiles but the one that is yet to see the daylight in Indian heavy transport segment. We will talk about rigid axles vs steerable axles.

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The first question that comes to mind is

What is the need for steerable axles?

Well, when talking about the front axle the answer is quite obvious. But what about the rear axles. Do they need steering as well?

Looking at the image on the right we can see that a vehicle takes a turn about an axis of rotation and for all the tires to roll without sliding sideways it is necessary for them to be exactly perpendicular to the line joining the axis of rotation and the center of the tyre. This is the basic reason why the inner wheel of the front axle turns at a higher angle than the outer wheel.

Now consider a multi-axle vehicle. If the rear axles are not steered the lines drawn from the rear wheels will not meet the steering axis. This means that wheels on these axles will not only roll but also slide sideways. This has many adverse effects:

1. First and foremost this will lead to excessive tyre wear considering the immense load per wheel and the

   Tire Mileage with and without Steerable Axles for Trailer

   sideways slippage. The above image shows an estimate of tyre mileage with and without steering in one of the axles (third axle) in a three axle trailer[1]. This of course also causes additional wear of the pavement surface.

2. The vehicle swept path i.e the area that a vehicle requires while making a turn is substantially increased with rigid axles. This can clearly be seen in the below image[2].

    

3. The sliding of wheels adds to the resistance to motion. This increases the engine effort to pull the same load at the same speed which in turn increases the fuel consumption. 

   The image shows that the fuel saved with steering systems could be about a liter per 100 km for a distribution haulage vehicle. This means that the system would eventually pay off itself with the costs saved in tyre wear and fuel.

4. The slipping and sliding of wheels will also exert excess lateral forces on chassis which can limit the weight carrying capacity of it as the maximum load that it can carry without these unnecessary forces will surely be higher.

What are the various mechanisms for steering axles?

There are many types of mechanisms developed for steering axles of articulated trailers. Some of them are highlighted below :

1. Self Steering type:

   This is a popular mechanism used in most of the applications. There is no control over the steer angle but the wheels steer themselves by the forces developed while steering. There are two types of self-steering mechanisms :

   • Free Castering Type:

     Caster is the angle that the axis of rotation of wheel makes with the vertical when seen in side view. The wheels of office chair aligning automatically with the direction of motion of chair is a simple application of caster angle. In free castering type, the wheels are given a caster angle that causes the wheels to steer freely when the vehicle takes a turn. The centering force is not good enough in this type of mechanism hence the high-speed performance and also stability while braking deteriorates with this type of steering. Also, when taking reverse the wheels need to be locked to prevent damage to the axles as wheels tend to take a 180

     o

     turn.

   • Automotive type:

     This type of mechanism is similar to the free castering type except for the fact that it has a mechanism that helps to increase centring force. This increases stability in high speed as well as while braking.

2. Linked Articulation Type:

   A force-steering axle type that uses a steering linkage mechanism that alters the steer angle of an axle group as a function of fifth wheel articulation angle between the vehicle unit, the axles are attached to, and the hauling unit. This type of axles are costly and complex compared to the automotive type but have smaller swept path, lower high speed off tracking and higher stability

   .

3. Command Steering:

   These type of axles are steered by command i.e. by creating a force to steer the axles similar to the front axle of the hauling vehicle. They are of two types

   • Hydraulically Steered:

     In this type, a couple of hydraulic single acting cylinders are attached at the fifth wheel of the vehicle which reciprocates with the relative motion between the hauling unit and trailer. This motion is transferred to hydraulic cylinders fitted to the axles in the trailer. This type of mechanism also provides lower high speed off tracking and higher stability.

   • Electronically Steered (active steering):

     This type has an electronic sensor at the fifth wheel that measures the relative motion between the tractor and the trailer. This information is passed to a controller which computes the optimum steer angle of trailer axles also taking into consideration additional factors like speed of vehicle. This controller then drives hydraulic cylinders fitted to the trailer axles. This also comes with a remote to steer manually which comes in handy while taking reverse as the automatic steering is not of much use while reversing. From all the types this is the most versatile one having covered most of the disadvantages of rigid axles. This theoretically provides the best performance at low and high speeds

     . Watch the below video to see how it works.

     http://www.youtube.com/watch?v=fMQie9Jdi5I

What are the applications that its suited for?

1. Distribution haulage is one application where this can prove to be of great use. In India, the in-roads are usually too narrow for trailers, but with steerable axles, maneuverability is not a big issue. So trailers with steerable axles can be used for distribution purposes in cities instead of fixed container trucks which means more goods transferred per trip i.e. less cost of fuel per unit transported. In times when our government has introduced FDI in retail, this could actually prove to be very useful. Also in these applications, the vehicle has to take a lot of slow speed corners where steerable axles could help to reduce tyre costs.

2. Greater maneuverability is one advantage that could come in handy transporting long cargos in hilly areas. The rigid axle trailers face a genetic disadvantage in these conditions as shown by the below image.

   Transporting something like wind mill turbine blades through hilly regions of India using trailers with steerable axles would become much easier as the swept path is greatly reduced.

3. There are also some disadvantages associated with the new technology. First the increased complexity would increase the maintenance cost and require more skilled mechanics (but in contrast require less skilled drivers). Also, in most steering types high-speed stability is compromised. 

   Further, to bring this new technology would require a new Gazette and many regulations amendments in CMVR which is a very slow and tedious procedure in India. Amendments in CMVR for Hydraulic Modular Trailer&#;s which were introduced about 2 decades ago have only been made recently. 

4. Steerable axles could help increase the number of axles in a trailer without increasing the tyre scrub. This could increase the GCW of the vehicle and help decrease the overloading menace. Also, this could help fit heavier axles at a greater distance without affecting the low-speed performance.
5. Nimbus Logistics has in-house mechanical engineers and industry experts, which helps us be in sync with the latest technology and developments happening around the world. This helps us provide innovative and cost-efficient solutions to our clients.

Nimbus Logistics is an ODC and Heavy transport specialist with more than 4 decades of experience transporting Super Heavy and Super ODC cargo. We believe in ethical logistics and transparency. These articles are one of our initiatives to bring more transparency to the much chaotic Indian Transportation Industry. Please support us by sharing our articles and like our facebook page to be the first one to read all our future articles. 

Selecting an equipment trailer might seem straightforward, but there's actually a lot to consider. Knowing what you need from a trailer is crucial when starting the selection process.

When choosing a trailer for hauling equipment, rental businesses need to take into account their customer base and size as well as the type and weight of their equipment. For example, a customer base of professional contractors who drive ¾- and 1-ton pickups and who might rent a mini excavator with attachments would be best served with a tilt-bed trailer with a stationary deck, according to Chris Pokornowski, sales coordinator at Towmaster. This type of trailer would have a gross vehicle weight rating (GVWR) of around 16,000 pounds, hauling about 8,000 to 10,000 pounds of load with electric brakes. The stationary deck could carry the attachments and the main tilt deck would carry the mini excavator.

On the other hand, Pokornowski says, a customer with a less heavy-duty towing vehicle renting a small skid-steer loader with a pallet fork attachment might be best served with a ramp-style trailer with pallet fork holders. This trailer would have a GVWR of 9,990 pounds, hauling about 5,000 to 7,000 pounds, and possibly equipped with hydraulic surge brakes or remote controlled electric brakes.

Obviously it's important to know what you want from a trailer. In order to get the most value from your investment, it's best to look beyond the rated payload capacity to other factors that can impact an equipment trailer's performance.

According to Bill Dovey, product champion with JLG Industries Inc., versatility, capacity, quality and brake configurations should be at the top of your list when selecting a trailer. "You have to rent units that will meet the requirements of a variety of customers," he explains. "You have to consider the width and length of the equipment as well has how it will be loaded and unloaded at the site."

So, where should you start?

Capacity concerns

There are many factors to consider when selecting a trailer. Options can include the type of ramp, type of flooring, type of tongue jack, siderails and tailgates, tie-downs, winches, spare tires and more. Even the type of coupler will need to be decided: a 2-inch coupler is the most common, but one might need a 2 5/16-inch coupler because of the trailer load capacity.

Speaking of capacity, what will be carried on the trailer needs to be the first item considered. Be careful not to underestimate the weight of what you will be carrying. Take into account full gas tanks, accessories and added attachments that might be carried.

Size is also important. Be careful the trailer is not too small - dimension-wise it should carry your load. Take into account the configuration of the equipment or load to be carried. Because of the weight distribution of the equipment, which can vary significantly when attachments are added, you'll need a trailer large enough so that equipment can be positioned to give proper tongue loads. Insufficient tongue weight will cause dangerous swaying and unsafe towing.

Quality questions

Beyond the basic features, suppliers suggest comparing construction quality and design factors. Structural integrity in design, such as one-piece frames to limit the number of butt or joint welds, is important.

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Other quality factors include the maximum design width between the fenders, within the constraints of 102-inch overall legal limit width, which is important to allow a broad range of equipment to be hauled. Designs that allow the movement of the rear loading ramps to move in and out to accommodate varying wheel treads as well as spring-assisted lift devices on the ramps for the operator are helpful. Axle placement on the trailer is crucial to ensure proper and safe towing.

Because not all trailers are built alike, component specs should be checked to ensure the trailer is actually designed to handle the rigors of heavy hauling.

Component ratings can vary widely for models even within the same capacity class. For example, the axle wall thickness on a 25,000-pound axle might be .416, .625 or .750, depending on the manufacturer. Vertical travel on hydraulic removable goosenecks can range from 16 inches to as high as 45 inches. And flooring thickness can vary substantially. Nominal thicknesses can mean various things, so find out what the actual deck thickness of the flooring is and what kind of flooring is being used.

Cost-effective brakes

There are a variety of braking systems available on today's trailers: air, electric, electric/hydraulic, hydraulic/surge. The type of braking system available typically depends on the size (GVWR) of the trailer.

Air brakes are used on the larger trailers, usually those over 40,000-pound GVWR. This size has large brake shoes and various size air chambers to apply the brakes, giving the vehicle the stopping power needed.

Trailers between 26,000 and 40,000 pounds GVWR might have either electric or air brakes depending on the axles available. This is usually determined by the towing vehicle the customer is planning on using.

Electric brakes are the most common from 3,000- to 26,000-pound GVWR. They can be used with a variety of towing vehicles via the use of an electric brake controller that is independent of the tow vehicle brakes.

With electric/hydraulic brakes, you'll need an electric controller in the tow vehicle, which controls an electric pump on the trailer, which in turn applies hydraulic pressure to the brake shoes.

Hydraulic surge brakes become operative when the towing vehicle decelerates, causing the trailer to apply a pushing force against the hitch. The pushing force actuates the hydraulic cylinder in the hitch, transferring high-pressure brake fluid to the trailer wheel cylinders.

Hydraulic surge brakes have been the industry's standard braking system on trailers up to 12,000-pound GVWR for many years and are desired by many rental businesses because of their ease of hook-up (no wiring, no separate actuators, no delays). With electric brakes, a brake kit or electrical hook-up is necessary.

Maintenance factors

A trailer must be serviced like any other piece of equipment, therefore maintenance features need to be considered when purchasing.

Maintenance-related features include items such as rubber-ride axles, which eliminate the need to maintain spring shackle bushings on a regular basis, and sealed modular wiring systems with internal ground wires and integral circuit breaker protection, which protect the trailer as well as the tow vehicle.

Additionally, a trailer design that lends itself to quick replacement of hitch couplers, jacks and "hydraulic brake controllers" - if allowed by individual state law - makes replacing these highly abused items a simple maintenance repair issue for rental businesses.

The supplier connection

A final consideration during the selection phase is the supplier itself. A knowledgeable trailer manufacturer that can match the trailer to your equipment and understands your industry is a must.

Purchasing from a manufacturer that provides experience along with knowledge of the industry, as well as consistency of parts and components goes a long way toward your benefit. More importantly, if you need an insurance liability policy, they'll be in the wings.

When buying trailers for your rental business, the first thing you should ask of a manufacturer is, "What is your liability coverage? Have you asked the DOT inspector into your plant? Does one of your management team attend the meetings provided by various truck and trailer organizations to stay abreast of changing laws?" Don't be afraid to ask some questions.

Suppliers should be your source of information for the trailer industry; after all, they are the experts. Ideally, the salesperson can make the customer feel comfortable enough to ask the questions needed to allow a better understanding of his/her needs, Pokornowski says.

Don Huber with Trail-Eze agrees. "The best thing the customer can do is ask questions."

Maximizing the payload

To maximize hauling efficiency, you might want to move two or more machines in a single payload. There are, however, some added considerations involved.

When sizing a trailer to haul multiple machines, first determine the dimensions of the longest machine the trailer will carry. You need to have adequate deck length and dimensions to ensure proper weight distribution. If in doubt, ask your trailer supplier to perform a weight distribution analysis to determine if specific machines can be safely transported in a single load.

The legal maximum gross weight can also be a limiting factor. A permit is required if the truck, trailer and payload exceeds 80,000 pounds. Technology that is helping in this area is known as an air scale system. Air scales are becoming more popular because operators will know where they are weight wise before they leave the rental yard.

A final factor to consider when hauling multiple pieces is how they are positioned on the trailer so that the tongue weight remains proper.

Off loading one piece of equipment from a trailer without repositioning the others can put undo strain on either the trailer or the tow vehicle. Having too much tongue weight might bottom out the springs on the tow vehicle, making it ride and drive extremely rough. In extreme cases, too much tongue weight might make the tow vehicle hard to control, because the weight might be lifting the front end of the tow vehicle off the ground. In the reverse, too much weight remaining behind the axles might cause the trailer to sway while towing. The swaying might not start until after the driver reaches posted speed limits on the highway, pushing him into a situation he can't safely recover from.

The best way for rental businesses to avoid overloading their trailers is to know the weight of what is being loaded. Every trailer must have a vehicle identification tag that will show the carrying capacity of the trailer. Employees must know the weight of any item they are loading. This can be found in the equipment owners manual or direct from the manufacturer. Be sure to take into account the total weight with fuel and attachments. Be cautious of renting a trailer by itself. Customers must know the same information and load the equipment on the trailer within the safe limits.

Many times trailers are taken for granted and treated as a secondary item. This shouldn't be the case. Be sure to buy a quality trailer of the design that best suits your applications, and your trailers will serve you well over many miles of roads.

Don't be misled by trailer ratings

There are different ways trailer manufacturers will "size" their trailers. But it's up to you to ensure the chosen trailer will safely handle your equipment. For example, a trailer manufacturer might give you a gross vehicle weight rating (GVWR) of 100,000 pounds (50 tons). But if you subtract the trailer weight - which on average for a 50-ton unit is going to be anywhere from 18,000 to 20,000 pounds - then you have a 40-ton carrying capacity. "You want to find out what the load rating is and if it is concentrated or if it is a distributed load," says Huber at Trail-Eze. "That is one of the biggest tricks in the industry. That is a big issue and it will make a big difference in your dollar figure." So the key words you need to use are hauling capacity.

You also need to know the weight capacity in a concentrated area. This is how much weight is going to be carried over a given area. This is especially important with certain types of equipment. For example, a forklift has a high concentrated load area. The entire weight of the machine is transferred to the trailer deck through the small contact areas of the wheels. With an excavator or a dozer, the amount of track in contact with the trailer helps determine the concentrated load.

Again, you have to be very careful when looking at the concentrated load rating. Some manufacturers might say concentrated at 10 feet, but if you read the fine print, it says the center of the deck only. If you're hauling an excavator, for example, your weight is going to be in the front, but if you're hauling a scraper, your weight will be in the rear and on the front.

Types of trailers

There are several types and classes of trailers typically used by the rental industry.

Lowbed trailers, sometimes referred to as "goosenecks," offer capacities from 25 to 55 tons or more. These trailers are towed by using a special coupler attachment inside the bed of a pick-up truck. Models feature a fixed gooseneck with ramps or a hydraulic "tail" for rear loading applications, or a hydraulic detachable goosneck for front loading. Costs vary depending on the size and configuration. A 25-ton fixed gooseneck might be priced at $20,000, while a 50-ton hydraulic detachable gooseneck can range from $40,000 to $50,000.

Tow-behinds can be pulled by a tow vehicle using a ball or pintle hitch coupler. These can be broken down ito five basic types:

Box trailers can be fully enclosed or have sides and a tailgate. They are generally used for hauling cargo.

Flatbeds are normally used to carry various types of equipment, which is loaded using ramps.

Tiltbeds have a flatbed but instead of using loading ramps, the bed tilts to the ground to allow equipment to be pulled or driven onto the trailer.

Dump trailers feature an open box trailer that is used primarily for bulk material such as sand and gravel. These units tilt hydraulically to allow easy loading.

Drop-deck trailers allow the complete trailer deck to remain level as it lowers flat to the ground for easy loading of equipment.

It's about making it last

Equipment takes a beating in a rental inventory. That's why it's particularly important to choose equipment that's built to last. But what are the earmarks of high-quality and durability?

"There are companies out there who will offer a low-dollar trailer, but will it last?" asks Chris Pokornowski, sales coordinator at Towmaster Inc. "A rental fleet manager needs a product that will last many years with minimal maintenance. In most cases, the low dollar trailer has a nice price tag at first, but in the long run, it tends to be a maintenance nightmare. What is the easiest way to find out if you are making the correct decision? Ask around - it's that simple."

Pokornowski adds, "The rental industry can't afford down time, so when making your decision, ask around to see what trailes will last. You will find your answer in a hurry."

Look for features that denote durability. These include the structure and suspension. To assess the structure, Pokornowski suggests crawling under a trailer to see what it's made of. "Take a look and see if there is plenty of steel and good cross member spacing. You will see right away if the trailer manufacturer has put time into producing the trailer or it appears that the trailer has been rushed through production."

With regard to the suspension, many companies use a spring suspension. "A standard spring suspension usually gives you a two-year warranty policy," Pokornowski says. "In addition, there are many wear areas that require frequent maintenance. Towmaster's Drop Deck Tilt trailers are produced with a Rubber-Ride Torflex suspension. This suspension has minimal wear areas and it comes with a standard five-year warranty policy."