Building the right Towing truck
Choosing a Chassis and Wheel Base that fits you best
There are many different terms and specifications used when you are building a new wrecker or even when you are looking at a pre-owned wrecker or tow truck. Today we are going to review a few of those and see how they help you decided what is the best combination for your next wrecker or what the capacities of your current unit are.
- Front Axle weight (FAW) is the actual amount of weight on your front axle when it is being weighed
- Gross Axle weight rating (GAWR) is the rating the manufacturer has given the axle and its components and should not be exceeded.
- Wheel Base (WB) is the length between the center of the front axle and the center of the rear axles. For a tandem rear axle unit you would measure to the center space between the two axles or wheels, for a tri axle you would measure to the center of the middle axle. Twin steer units are measured between both front axles.
- Overhang is the length from the center of the rear axle or axles to the point on your under lift that you are lifting. i.e. the center of the forks or the center of the tire lift.
2016 CB30HD with a Fassi Crane Built for C&L Towing in New Jersey
Many customers have different wheel base and chassis requirements Many times it depends on the roads you travel most often including conditions of roads, width of roads and local requirements from DOT. A customer in a rural area may require that one of their trucks has a short wheel base in order to use it for recoveries across narrow country roads. Another customer may require a long wheel base for hauling heavy units long distances. When choosing your chassis or wheel base you should determine what the truck will be doing the majority of its time and then work with your manufacturer to create the right mix for you.
Our example truck the, CB50, is been built for both towing and Recovery. The customer needed to keep front axle weight while towing and knew that the best way for him to do that was to add length to his wheel base. Here are the specifications for this truck:
- Front axle Weight (FAW) 14,000 lbs
- Rear axle Weight (RAW) 28,000 lbs
- Gross Vehicle Weight (GVW) 42,000 Lbs
- Wheel Base to center of Tandams 330"
- Overhang 138"
As a rule to maintain safe steering, Braking and control of your vehicle you should never have less than 50% front axle weight. For this unit that would be 1/2 of 14,000 lbs or 7,000 lbs. The formula used to calculate this is as follows:
FAW/2 = Safe Weight X Wheel Base/Overhang= total Capacity
14,000lbs/2 = 7,000lbs X 330" = 2,310,000 / 138"= 16,739 lbs
Now lets look at how much difference FAW makes. In the next two examples I am only going to change the weight of the front axle. The first will be by adding 2,000 lbs to the total FAW and the second will be removing 2,000 from the total FAW.
16,000lbs/2 = 8,000lbs X330" = 2,640,000 /138" = 19,130 lbs
12,000lbs/2 = 6,000lbs X 330" = 1,980,000 / 138"= 14,34l lbs
As you can see from the numbers above the actual front axle weight almost directly transferred to the Total lift capacity in this scenario. When I added 2,000 lbs to the front axle we gain just over 2,000 lbs total capacity. When we removed the same weight from the front axle we lost almost that same amount total capacity.
Now lets see how this translates to wheel base. In this scenario we will just change the wheel base. We will shorten the wheelbase in 10" increments to see how the over all total capacity changes.
14,000lbs/2 = 7,000 lbs X 320" = 2,240,000 /138"= 16,231 lbs
14,000lbs/2 = 7,000 lbs X 310= 2,170,000 / 138" = 15,724 lbs
When we took away wheel base in these examples we only lost about 500lbs of capacity for each 10" reduction. On this heavy of a unit its not that concerning but on a lighter unit with less front axle weight it can make a large difference.
For our final example lets look at what happens when we change the over hang. We will add 10" than 36" as if you had the under lift extended.
14,000lbs/2 = 7,000lbs X 330" = 2,310,000 / 148"= 15,608 lbs
14,000lbs/2 = 7,000lbs X 330" = 2,310,000 / 174"= 13,275 lbs
By adding just 10" of Overhang we lost 1,131 lbs. When we added 36" we lost 3,464 lbs of total capacity. Since the Overhang works like a giant lever it is almost twice as effective removing FAW as adding wheel base is to gaining FAW!
From everything we just stated the FAW is very important when choosing your chassis. If you know you are often towing loaded Tri Axle Dump trucks, drilling rigs front packers and the like than you will want to consider getting some weight to the front. How can you do this? Some simple ideas are placing the Hydraulic tank as far forward as you can on the frame, making the front tool box carry the heaviest items in your truck like chains, forks and snatch blocks. You could specify that you would like a weight added to the front of the chassis that does not exceed the capacity of the axle. One of the most useful items you can put on your truck for some added weight is a side puller. Adding a few thousand pounds just behind the cab could transfer 2/3rds of its weight to the front axle plus yuo have a usable tool for side recoveries.
Wheel base is important as well but in many cases can only be adjusted when the unit is being built. There are options like adding a Pusher or Tag axle to your truck that will gain or remove wheel base depending on where its mounted. In some cases this can also remove some weight from the front axle so be careful how you use this.
As effective as having weighted front axle is decreasing your Overhang. As we saw above just 10 inches of overhang will remove over 1,100 lbs. You are at a large disadvantage if your truck already started out with a large overhang Check with your manufacturer on the actual overhang the unit has. Most North American manufacturers are aware of this but you should "know before you buy" so that there are no surprises the first time you go over the scales.
Once you have decided on these facts for your new wrecker it is time for the fun stuff like lights, toolboxes and gadgets. Designing you new unit should be a fun process for you and having all the right information will make it easier. When the time comes to build your next unit we hope we can Custom Build it to your needs. Click the link below for more information about our units.
2015 CB50 Built for George's Towing of Massachusettes