Twin Steer or Reverse Steer Tag or Ideas?

[lumberjack]

Back story:
Monday of this week I found a knuckle boom crane (used chassis, new crane, at the dealer) that according to engineering report the truck weighed 42.6klbs on 3 axles, 23' spread from steer to rear tandem. The weight split was 12.2klbs/30.4klbs, 42.6klbs gross.

When they were doing the temporary tag Tuesday they had a weigh ticket showing 18klbs/29.5klbs and 47.6k total (yes, the total on the ticket is 120lbs more than the sum of the two axles).

Wednesday, coming into TN, I was stopped on the scales. The readout showed 19.5klbs/31.2klbs, 50.7klbs gross.

Obviously it's less than ideal that the truck has somehow gained 8klbs, but the main problem I see is the 19.5klb steer axle will be very hard on residential driveways, which is the main application for the truck (residential tree removal). A secondary problem is the drastic reduction in payload. Mississippi allows for 54klbs on the truck as configured.


The salesman for the truck is here in town for training tomorrow and Monday. I plan on bringing the massive weight gain tomorrow and that 19.5klbs on the steer axle flat out doesn't work for the trucks intended application (the truck was specifically built for tree removal).

One fix to get the axle weights under control is to add a pusher axle. The crane is rear mounted, the idea being it will commonly back onto customer's driveways vs pulling in. I don't want a rigid axle, because the whole point of the truck is to be maneuverable. Ironically adding the pusher axle will put my front axle overweight if I pick it up.

I've heard of two "reverse steer" pusher axles, Watson & Chalin and Hendrickson (in the Euro market). I left a message for W&C Friday but haven't heard back from them. Does anyone have experiance/feedback on reverse steer lift axles? My understanding is they have linkage that changes the caster of the axle for self steering while backing up.

Another idea is to go twin steer. I know Simard is a common name for aftermarket twin steer applications. I can only imagine the cost is "high", does anyone have feedback on the practicality of adding a second steering axle?

The pusher give me 57.5klbs of gross capacity according to bridge law, but my weight will be around 52klbs... still, that will almost double my legal payload while getting my axle weights down to ~13klbs on average... far more driveway friendly, although still more than I'd like. Down the road I may look into adding a pin on tag axle to get the weights down to ~11klbs and gain a substantial amount of payload (66.5klbs gross).


Since we all like pictures:
Here's the side profile of the truck. The pusher would need to go where the fuel tank is currently. The boom is not in this position for transport, just to move it on the same property without having to drop the grapple saw. The felling grapple saw weighs 900lbs.


Here's the truck working on our property.... the third tree I've removed with it.

 

[lumberjack]

And here's it dropping off a mini grapple shear (450lbs) at the shop and loading a dirt pan (2900lbs) and mower (2200lbs) onto the flatbed.

 

[DARO]

How much reach dose the boom have?

 

[lumberjack]

84' of hydraulic side reach at ~17' height, 1320lbs at that distance.

 

[DARO]

That is sweet

 

[crane operator]

I'm assuming the knuckle all folds up in the rear area , putting most of that weight behind the tandems. Just looking at it, I would say a pusher right in front of the tandems, non steer, would be my preference, if your really trying to get down your steer axle weight. Then if your wanting to decrease more, a rear mounted tag, steerable or non.

None of that will decrease the chances of point loading when crossing a curb. You're 50k and adding 2k or more with each axle you add, nothing is changing that without going to a lighter unit, unfortunately there's no free lunch.

What suspension is on the truck, air ride or spring?

Very few "boom" trucks go to twin steer- its simply too expensive of a carrier for initial cost, most are adding tag axles front or rear, depending on turntable and tandem locations.

If you really want twin steer- I think it would be easier to find a different chassis already set up for it, as to convert yours, but anything is doable.

First picture- front rig is around 48-50,000, three axle carrier, don't worry too much about driveways, sidewalks it always depends on the sidewalk and I make that clear before crossing one, I don't accept liability for them.

Second rig- white and red, is just under 80,000. Twin steer (spring), tandem (walking beam), rear tag (second picture shows the tag better). Rear tag is air ride, fixed (non steer). Crane is around 44,000 on just the rear tandems without tag. If going into poor conditions, you want to release the rear tag air, and I can also remove a pin and allow the whole thing to float, otherwise you can pick your tandems up too much, making you spin out/get stuck.

Third rig- white and black, is just under 100,000. twin steer, tandems, tag in front and behind tandems. Rear tag is a floating steer axle, one in front of tandems is fixed. Both air ride suspensions. Walking beam rear suspension on tandems, front steer springs. Rear tag gets raised when backing up. Front is releasable also.

I added the tag axle on the red and white rig and both tags on the black and white rig. I am only allowed 20k/ axle in missouri on my oversize/weight permits. If you get over 54k gross, you will need to look at your individual state laws, you don't want to push yourself into permit only travel if you can help it, unless its only a yearly fee, and no routing.

On the air tags. I prefer a fixed non steer tag, the capacity is much better and fewer moving parts. A lot of the dump trucks by me have the steerable tags and they can carry less and are less durable. I went with a steerable tag on the rear of my black and white colored rig because its so far behind the tandems, I was afraid a non steer would drag too much when cornering. It is a 20k axle with float tires on it.

 

[crane operator]

This is what will be cheapest to do:

The second picture is what a twin steer mack is like, but it would take big $ to switch to.

 

[crane operator]

A picture of it all folded up for transport would give a better idea of where the weight is for adding axles. If its boom forward , will be different than all folded up tight on the rear. A behind the tandem tag is going to increase your steer axle load, one right in front of the tandems will decrease your tandems and the steer axle loads, how much depends on the boom location, and where you place the axle.

 

[lumberjack]

Not to seem unappreciative of the information, but to clarify a few points for sake of identifying my problem.

I also understand it takes weight to support the boom and its weight. The issue is the truck weighs 8klbs more than engineering said it would and 3klbs more than they said it did right before I left.

The physics of where to put the pusher axle isn't a question. We know what the axle weights are (fixing to go get a printed ticket from the local Cat scales), from that and measuring the axle positions I can calculate to accuracy of the weights what the axle loads will be with the axle installed, including running the numbers to calculate what the optimal load is. I can also calculate the effect of moving/adding/removing any weights to the truck, for example my thought was to make the front bumper pin on so I could easily remove it and set it on the back of the deck. To illustrate that the axle loads are the answer and not the visual representation of the truck... the front bumper weighs nearly 2klbs and the headboard has ~2klbs added to it.

The pusher needs to be as far forward as the chassis will allow to reduce the load on the steer axle.... adding a tag axle will take load off the drives and shift some forward to the front axle(s).


With that out of the way:
On the last picture, the white and red Grove... did you add the tag axle?

Do you have any idea what twin steer costs as a ballpark? $30-40k? I haven't found a reference online yet, so I'm shooting from the hip. I know adding hydraulic assist (4x4) to the front axle costs $30-40k.

Do you know of any reverse steer lift axles? Running a rigid axle like on my tri axle grapple truck wouldn't be fun with it being so far from the drives, just like on the white/red Grove.

Being a crane service (my assumption) vs the contractor to the customer, I think your liability for the driveway is considerably less as well as the damage to your reputation if it happens consistently (customer would blame contractor, if blame was assigned). Also, this truck will be on concrete driveways on the vast majority of its jobs; I assume your jobs are considerably more varied.


Switching chassis at this point isn't something that's terribly exciting... my presumption is it would cost ~$20-30+k to move the crane to another chassis (engineering, potentially a new subframe, and the associated labor). This chassis is low miles (135k) and low to mid hours (~9.2k).

 

[crane operator]

I added the tag axle on the red and white rig and both tags on the black and white rig.

Axles are home built add ons. Both rear ones are pinned on- I can remove them if I need to for a tight jobsite. I got the axles from a local junkyard, they probably came from dump trucks. I can get some pictures of how I attached them if you want.

The red and white one does not steer, the white and black one does.

I would bet switching chassis would be cheaper than adding twin steer. Is the dealer going to stand that cost because it weighs more than they said, or is it on you?

I've never been around a reverse steer axle, my rear steer tag on the black and white one has a pin that will drop to lock the axle from steering if you were backing up. I never use that pin, I just raise it. But you could do something like that.

 

[crane operator]

The only reason I was asking how it sets stowed, is that boom position is probably the easiest way to transfer weight off of your steer axle. If it would fold up and stow behind the turntable instead of ahead, that would change a lot, but it looks like the outrigger boxes are in the way to do that. I'm assuming they added the heavy bumper and headache rack for capacity chart requirements.

It also looks like the easiest place to mount a axle would be right in front of the front tandem. Looks like only a storage box and racks on each side, much easier than moving fuel tank and hydraulic tanks. I was looking at cheap and easy if its up to you, if its the dealer changing everything- tell him to get it to meet his sales specs.

 

[lumberjack]

I would love to see how your axles pin on, that would be very handy. I have some ideas on how to make it pin, but nothing concrete. I don't know that I Would ever actually add the removable tax axle, but the idea has crossed my mind.

They did add the weight to the truck for stability. One nice thing about the truck is that it doesn't have to be level to work, which makes setup pretty easy! Also the tires stay in contact with the ground.


I asked the dealer what it would cost to swap trucks, he said ~$35k. Twin steer is $50k according to him.


It's true that adding the pusher in front of the drives would be easier, but to get the most weight off the front, the axle needs to be as far forward as possible. With the pusher taking 13000lbs (assuming 2klb installed weight), it would take 6400lbs off the steer and 4600lbs off the rear. From today's ticket that would put my weights at 12940lbs/13000lbs/13100lbs/13100lbs. Moving the fuel tank, tool box, and hydraulic tank will add some to the steer axle.



Took this picture for you today.

 

[crane operator]

I asked the dealer what it would cost to swap trucks, he said ~$35k. Twin steer is $50k according to him.

Ouch

I'll take some pictures of my two pin on axles, they're not fancy but they work.

 

[lumberjack]

First for profit job with the truck, it was a success.






I talked to W&C, their reverse steer axle is what I thought it was, a steerable lift axle with some added linkage that shifts the caster to negative to self steer in reverse.... seems like exactly what I am looking for. I took some measurements from the truck to do the calculation on the axle weights. I am considering adding a pair of axles to lower the weight per axle even more as well as more legal payload while traveling.

 

[td25c]

Being a simple hillbilly........ The first thought that came to mind is move the drive axils forward about 2 feet give or take putting more weight on the rear drivers & take some off the steering axil ?
How much could that cost , 5 to 8 thousand at a truck shop ?

This sounds more like a weight distribution problem with chassis & wheelbase . No need for tag axil in my opinion at 50k gross after you get proper load on the rear tandem .

 

[Junkyard]

Where was ballast added and what all is it? Has it been ballasted per a spec or just where they could stick the stuff? Think of it like a race car on the scale, right front too heavy? Ok let's move a chunk of weight back or over. If it's a space issue I've go some tungsten but it's very cost prohibitive!

Although you are correct as far is payload, there's not much room weight wise for that. It's always a trade off isn't it? Lol. Nice looking truck for sure. With some big boxes and a monster welder it would me a me a heck of a service truck!

Junkyard

 

[fast_st]

So there's only 15k on each rear axle? how about scooting them both forward a foot? Seems like you don't have a lot of cargo capacity on the flat deck over the road. Need a fancy axle shifter like a landall to mess with the guys at the scales

 

[lumberjack]

The ballast is added for stability. For example, the front bumper and headache rack weigh ~4250lbs combined.


Moving the drives forward also has the benefit of decreasing the turning radius. Still, for driveways I would like to add an axle to lower the axle loadings.

If I moved the drives forward 17.5", they would have approximately 34klbs on them, 16,140lbs on the steer.
If I moved the drives forward 14.8", all axles would have ~16,713lbs on them.
If I didn't move the drives, 4 axles with an even weight distribution (12,935lbs), the pusher would need to be installed 86" behind the steer axle. The front of the fuel tank is at 83", the back of the outrigger box is at 72" so it will have to be a bit further back than that.

I'll run some more scenario and see what I come up with. Moving the drives forward, adding a tag and pusher sounds like the best of every world... better weight distribution, better turning, no compromise in stability, better payload on the deck, better ability to carry a front heavy tag trailer.... just costly.

 

[td25c]

Yeah lumberjack ... That looks like a nice rig & knuckle boom set up perfect for your work . I sure like the saw attachment on it .
If you like the truck & plan on keeping it I would not hesitate moving tandems forward to solve the problem .
Nothing worse than a truck that's to heavy on the steering axil . They drive like a monkey riding a football on the road at speed and get stuck to easy when off road
Time to drill some new hole's in the frame & shorten the driveline Mate !

Move the drives about 2 foot forward and you will notice a huge difference in that truck .

If ya want to get wild move the drive axils 4 foot forward & install the tag axil on the rear . That would sure allow you to walk around job sites with most of the weight on the rear drivers and tag axil down for on the road for stability at speed .

 

[crane operator]

Pictures of my 70 ton's tag. It's a steer axle- probably a 20k, its pretty big. I made everything else. You can see the brake pod that drops a pin in the steering arm to lock the axle straight. I never use it, I just pick the axle up (its air up air down). I can drop the rear jack and remove the center bottom pin, allowing the axle to float up and down on the upper two pins, works good going offroad and when raising the front of the crane way up, to avoid overloading it or picking the drives off the ground.

I can also put all three jacks down and leave it set in a parking lot, if I have to get close to something. I wouldn't do that on rough ground, you would have a hard time getting hooked back up, but I rarely drop it.