Scaling Out Help For Heavy Haul

I just got done with my 5 weeks training and during that time i drove a KW 680 with a 53ft reefer. Now that i'm done they are telling me i will be running the heavy haul fleet. The tractor has 2 rear axles with a third drop axle and the trailer is the same with 3 and a 4th drop axle. They are going to send me out sometime here soon to learn how to scale out. Although I would like to get a head start so if anyone can point me to some info on how to do this or knows how to themselves I would really appreciate and help. Thanks again.

First thing that you have to do is measure your overall bridge. Put all axles on the ground and measure from the center of the steer to the center of the last trailer axle. Then you need to measure from the center of your drop axle to the center of your last trailer axle. Then you have to look at the chart for the number of axles and the measurement that you have taken.

I will give you an example from my truck. With my overall bridge length I can legally haul 105,500 so I subtract 12k for the steer axle and that leaves you with 93,500 to scale with your inner bridge. Now in order for me to scale that weight I need an inner bridge of 58' and that is not going to happen with a 53 foot trailer and still get 12k on the steer. My inner bridge is approximately 54' so I can legally bridge 91,500 so I go with 103k and save 500 pounds of wiggle room. My truck is really heavy compared to what you will be driving but if you are pulling a van you will probably be around the same tare weight as me at 40k and that leaves me with 63k I can put on the truck.

Now the good thing is that unless you are loaded completely wrong you will be under on the axle groups. You should be able to go to 42k with the drop axle and the drives and 52k on the trailer as long as the spreads are correct. For the drives you need 8' from the center of the drop axle to the center of the last drive axle. For the trailer you need 15' from the center of the front axle to the center of the last axle on the trailer.

What tends to bite people is the inner bridge. My boss seems to think that I can legally gross 105,500 because if you add up the axle groups, 12,000 + 42,000 + 52,000 equals 106,000 but because of the inner bridge being shorter than 58' this lowers the limit.

Keep in mind, that extra 20k you are going to be carrying is going to take you a lot longer to stop.

Wow thank you so much for the reply. So because I can't slide my trailer axles if there is more weight on them then my drives do I just deal with that as long as I'm legal or is that when the amount of pressure on the drop axles comes into play?

You are always going to be heavier on the trailer than the drives because you have more axles on the trailer. A lot of people make it out to be a big deal to have more on the trailer but in this scenario it does not matter as you are not going to be pivoting on the back axles like you do with a tandem. That is because all the axles are at the back of the trailer.

As for air pressure, I never mess with it on the trailer. I have the gauge marked where my weight is good but that only gives me the tridem not the drop axle. Since I know where the gauge sits when I have 52k on the quad what I do is once the needle goes past that mark, I put the drop axle down and keep it at or under that mark on the gauge.

Now on the tractor I have adjusted the air pressure but that was because I was a little heavy on the drives so by reducing the air pressure to the drop axle (which was light) I could transfer some weight from the drives to the steer but beware, this will also add some from the drop axle back onto the actual drive axles too.

For the most part you do not ever adjust the air pressure. In the last 3 years, I have only done it one time.

Oh wow, I think I just opened a thread I wasn't ready for.

Oh wow, I think I just opened a thread I wasn't ready for.

Lol, it will come with time. Oh the confusion.

Most drivers will never deal with this stuff because they are only running at 80k.

Well that gives me a good idea of how it works. Now hopefully they get me out to see my new truck so I can learn it all hands on. Thanks again for sharing your wealth of knowledge with me.