Understanding Lowbed Capacity

You won't legally scale out a 75,000lbs excavator on a tandem lowboy. You would be too heavy on the rear tandems of the trailer for most states axle allowable weights.

From what skyking1 posted for new hampshire regs:

Looks like bridge review kicks in at 108,000 for a 5 axle and 120,000 for a six axle- you don't want to have to bridge review (in missouri they call that "superload" and its time and $$$). Also- No tandems with a individual axle over 25,000lbs.


So starting with these values- the tractor is going to weigh around 20,000, the trailer is going to weigh around 18,000. That's a rough estimate. Daycabs are lighter, tandem trailer is lighter than tri axle. Double frames and lift axle on tractor adds weight etc. You might get the tractor under 18,000 and the trailer under 15,000, but that's about it.

So you're talking 33-38,000lbs just the truck and trailer. Add in a 50,000lbs excavator, and now you are 83,000 to 88,000lbs gross. I usually figure 1/2 of the weight of the entire tractor/ trailer/ load is on the rear axles. So in this case, you're probably going to have 40-44,000 on the rear tandems with a three axle truck and a two axle trailer. Which would be easily doable with what those state specs say.

So instead of a 50-55,000 excavator, lets do the same thing with a 75,000lbs ex. 38,000lbs of truck and trailer plus 75,000 of ex. is 115,000lbs gross. 1/2 of that on the trailer is 57,000 on the rear of the trailer- would put your rear axles over 28,500 per axle- so you need a triple axle trailer, to get the axle weights on the rear of the trailer down. With a tri axle you would be just over 19,000 per axle which is where I need to be in my state - I can't permit more than 20,000 per axle. So you would be fine with 3 axle truck and 3 axle trailer with the 75,000lbs ex.

I have a two axle landoll type traveling axle trailer. 37' in the flat of the deck. Its a paver special trailer and stupid heavy. I usually don't buy permits with anything I haul with it- and I can be legal weight (under 80,000) with around 44,000lbs up on the deck. If it gets much heavier than that, the 10r tires on it tend to heat up and I'll just eat tires with it. I could haul 50,000 with it, but you wouldn't want to go very far in hot weather. Its rated for 35 ton. Deck height gets to be a issue with it. You better have short equipment to haul.

My 50 ton lowboy is a hydraulic removable neck, with a side drop deck, with three axles, 24' well. I haul three different cranes on it, from 35-70,000lbs. I'm actually fine on my triple axle rear of the trailer with the big crane, I'm a little heavy on the tractor drives instead. If I was any heavier, I'd need 4th axle on the truck (to meet my more stringent state axle weights).

I think you could carry around a 55,000 lbs excavator on a three axle truck and two axle trailer with no problems. For a 60-80 thousand lbs excavator- I think you are probably looking at a three axle truck and three axle trailer. If at the upper end of that all the time, I would want a 4th axle on the truck- or for sure heavier drive axles on the tractor.

If you're to the light side with a tractor and trailer, I think you could do the 60,000lbs excavator (33,000 tractor trailer + 60,000 = 93,000 gross divided by 2 = 46,500 on the rear tandems) But that's going to be about it. It wouldn't be legal in my state, but from that link it shows it would be legal for you.

You need your actual state regs- it should be available from them, so you've got the full regs before you go shopping. I don't have near the experience of the guys that haul all over- I only do permits for 7 different vehicles and we only go to two states. I'd want to look at NH regs pretty good before I went shopping.

Someone that heavy hauls all the time in your state will know your regs like the back of his hand and will be able to tell you what the best set up is to be legal there. From what I've seen of NH, its much like my terrain, lots of short steep hills, and narrow roads. So shortest trailer and tractor possible, and don't skimp on the HP of the truck, and get the engine brakes.

When maintaining your tires, inflation is the most important thing to check. Carefully and regularly check the tires on your low bed trailer. Purchase a pressure gauge that you can trust to give you an accurate reading of the inflation level.

Check the inflation after the tires have cooled down. At the heaviest load a low bed trailer can carry, the tires can be inflated to the maximum atmospheric pressure limit. However, this limit should not be exceeded no matter how heavy the load is.

Use valve stem caps to maintain air tightness at all times. Valve caps also help keep dust and moisture out. Even if a tire is properly inflated, its sides may bulge.

Bulging is caused by low tire pressure, which is the worst-case scenario for trailer tires. After checking and inflating your tires, check the pressure again within 48 hours. To avoid crashes, don’t forget to inflate your tires in a safe cage.

Due to the increased temperature, the tire pressure will rise when using the tires. It is possible for the pressure to rise as high as 10 or 15 psi. such a high pressure means that the tire is underinflated, overinflated, or the wrong size.

High pressure also indicates that you are driving too fast. When several of these conditions occur at the same time, it can cause inflation to exceed healthy levels.

Always make sure that all drive lines have the right size tires and that the load remains within the specified limits. Don’t drive too fast, especially if the trailer is fully loaded.

Make sure the axles are aligned in place. If the wheels are not properly aligned, it can make the road rougher. Because of this, tires wear out faster and more severely.

You know the reasons why tires are under or over-inflated. Make sure you fix the problem before you travel. Don’t rely on past inflation records.

Air pressure should be checked with a good gauge before each transport or at least once a week. When checking your tires, don’t forget to look for cracked, warped, and rusted rims.

In other words, if the rims are bent or cracked, don’t weld them. Instead, repair the rims the way the manufacturer tells you to. If you weld a broken rim, you may cause more damage to the tire and wheel.