Trailer Weights and Sliding Tandems

Sliding tandems.

If you didn’t learn this in CDL School, you will get a crash course on how to set your tandems and what states require what lengths. You are expected to take notes and remember this information. It could cost you THOUSANDS of dollars in fines if you don’t. California and Georgia specifically being the worst.

If you need to slide your tandems forward, you will exit the truck, walk to the rear driver side, pull the tandem-locking arm out and secure it. Get back in the truck and you will set your trailer brakes (red knob), pull down on your Johnson bar, and release your tractor brakes (yellow knob), and put the truck in reverse and go backwards till the trailer stops. Get out and release the locking arm, and verify your pin is back in the hole. If it’s not, you need to rock the truck by going forward and backwards until the pin is back in the hole.

If you need to slide your tandems to the back, you will exit the truck, walk to the rear driver side, pull the tandem locking arm out and secure it, get back in the truck and you will set you trailer brakes (red knob), pull down on your Johnson bar, and release your tractor brakes (yellow knob), put the truck in low gear and pull forward till the trailer stops moving. Get out and release the locking arm.

Now, you’re probably saying...well how do I know how far to slide them and which way to go?

There’s a “BASELINE FORMULA” for that.

Tandem Setting Formula (Tandems Forward)
Each hole = 250 lbs. (on a standard trailer)
Maximum Gross Weight (Truck/Trailer/Cargo) = 80,000 lbs.
Maximum Front Steer Axles Weight = 12,000 lbs. (Front Tractor Axles) Maximum Drive Axles Weight = 34,000 lbs. (Rear Tractor Axles) Maximum Trailer Axles Weight = 34,000 lbs. (Rear Trailer Tandem Axles)

Example 1
Gross Weight = 80,000 lbs. Front Steers = 11,200 lbs. Drive Axles = 36,000 lbs. Tandems = 32,800 lbs.
Your load is not legal. You are 2,000 lbs. overweight on your Drive Axles.
To figure out where your tandems need to be, use the following formula
Drive Axles 36,000 lbs. Minus Tandems – 32,800 lbs.
-----------------
3,200 lbs. (Difference)

Divide the difference by 2 (2 axles, Drives and Steers)
3,200 lbs. / 2 = 1,600 lbs. proportioning weight


Now take the proportioning weight and divide by 250 ( this is the # of lbs. per hole)
1,600 lbs. / 250 = 6.4 holes


In this case, your drive axles have too much weight. Therefore they are the problem.

So to properly proportion your load, you will always SLIDE TOWARDS the problem. So you will slide your tandems FORWARD 7 holes (since we can’t technically slide
6.4 holes). 

Mark it with chalk before you slide.  When you slide the tandems FORWARD, the truck is going in reverse. Set your trailer brakes, release your tractor brakes, pull down on your Johnson bar, and put the truck in reverse and slowly back up. Your load should now be legal.

Tandem Setting Formula (Tandems Back)
Each hole = 250 lbs. (on a standard trailer)
Maximum Gross Weight (Truck/Trailer/Cargo) = 80,000 lbs.
Maximum Front Steer Axles Weight = 12,000 lbs. (Front Tractor Axles) Maximum Drive Axles Weight = 34,000 lbs. (Rear Tractor Axles) Maximum Trailer Axles Weight = 34,000 lbs. (Rear Trailer Tandem Axles)

Example 2
Gross Weight = 79,400 lbs. Front Steers = 11,600 lbs. Drive Axles = 30,600 lbs. Tandems = 37,200 lbs.
Your load is not legal. You are 3,200 lbs. overweight on your Trailer Tandem Axles.
To figure out where your tandems need to be, use the following formula
Drive Axles 37,200 lbs. Minus Tandems – 30,600 lbs.
-----------------
6,600 lbs. (Difference)

Divide the difference by 2 (2 axles, Drives and Steers)
6,600 lbs. / 2 = 3,300 lbs. proportioning weight


Now take the proportioning weight and divide by 250 ( this is the # of lbs. per hole)
3,300 lbs. / 250 = 13.2 holes


In this case, your trailer tandem axles have too much weight. Therefore they are the problem. So to properly proportion your load, you will always SLIDE TOWARDS the problem. 

 
So you will slide your tandems BACKWARDS 14 holes (since we can’t technically slide 13.2 holes).

When you slide the tandems BACKWARD, the truck is going forwards. Set your trailer brakes, release your tractor brakes, pull down on your Johnson bar, and put the truck in low/1st gear and slowly drive forward.

Use chalk to mark your tandem holes so you know where to slide.

Now, if you don’t have enough holes to slide forward or backwards, your load must be re-worked (unloaded and re-loaded and redistributed) by the shipper because you will not be able to get it DOT legal.

NOTE: A standard trailer will have holes that account for 250 lbs. of weight being moved forward or backward. If you go to a different company that uses different trailers, each of the holes may account for 400#, 500#, or 750# of weight. So be sure to remember, this is a baseline formula, and to adjust it as necessary. But the principle remains the same.
 

Occasionally, you MIGHT see a trailer that has a push/pull button release for the tandems.
Pull it out to slide.

Push it back in when you’re done to secure the tandems

Scaling a Load

You will be shown how to get your load scaled at a CAT SCALE or other scaling house. You will need to know how to slide your tandems and how to calculate for fuel.
1 gallon of diesel fuel weighs 8 lbs. Your truck holds 100 gallons of fuel in each tank. Your truck has 2 tanks. So it can hold 200 gallons of diesel fuel, which will weigh 1600 pounds. This must be figured into your load. Truck and trailer empty will usually weigh about 34,000 pounds combined.

If you have to slide your tandems to get weight from one axle to another, remember, each hole you move forward or backward is equivalent to 250-300 pounds.
(See the formula in the previous section above).

If you scale at a shipper, DO NOT ever assume their scale is accurate. Use their scale to get an idea of what your weights are, and then go to the nearest available CAT Scale (usually at any truck stop) and scale your load.

Note the discrepancy here. The shipper’s scale is in white.


Axle Weights
It’s in your state’s commercial driver’s manual. You need to know the axle weight restrictions/limitations for each state, because they will vary from state to state. However, the majority of the states have the same standard. Research it, make a chart, and keep it handy. You will be expected to know these items. In general, this is the acceptable status quo for axle weights across the nation.
Steer Axle – 12,000 lbs.
Tractor Drive Axle – 34,000 lbs. Trailer Rear Axles – 34,000 lbs. --------------------------------------- MAX GVWR – 80,000 lbs.

 

However, in Colorado, it’s
Steer Axle – 20,000 lbs.
Tractor Drive Axle – 36,000 lbs.
Trailer Rear Axles – 36,000 lbs.
---------------------------------------

MAX GVWR – 80,000 lbs. (The axle weights can exceed 34,000 lbs., but the MAX GVWR cannot exceed 80,000 lbs.)