Truck tandem axles

[john in la]

Saw a guy delivering gas to a station yesterday.
Asked him how he like his new truck and trailer.

He hates it.
Said loaded it drives fine since it piviots on the center of the tandem axle like any normal truck.
But when empty it is like driving a extra long wheel base unit because both the truck and trailer piviot on the back axle.
Not the type of unit you want when trying to get out the car lot of a gas station.

I never understood why the always make the forward axle the lift axle.

 

[guido]

Hello John in La,

In the old days the rear axle was the one that lifted. It was called the tag axle. I don't think It matters which one lifts, just saves the tires when empty. There is a DOT spread axle standard for the weight capacity,

Guido.

 

[grizz02]

generally they don't send straight tanks to stations usually there used for bulk plants truck and trailers are used for stations

 

[mmfan55]

I have seen them both ways. Advantage and disadvantages to both

 

[oliver fan]

If he would quit complaining he would realize the truck rides a lot better empty on 3 axles instead of 5.

 

[showcrop]

Here in the east dump trucks have the lift axle ahead of the fixed tandems while log trucks have it behind the tandems. The difference is in the length of the load. Fuel tankers here are 95% 53 foot tractor trailers delivering to very tight metro area gas stations. I wonder how that driver would do blind side backing a 30 ft three axle bumper pull trailer behind a dump truck with a third axle behind his fixed axle.

 

[D beatty]

Both can be a pain in the neck. In the winter a liftable axles can get you into trouble. I have seen a number of drivers run with axle up in winter and pull into a lot with a lot of packed snow and drive axle will melt into snow pack and tag axle keep drive axle hanging. Tags are bad news backing from street to sharp incline.

 

[Janicholson]

Local tight space delivery or exit would be time consuming and a little disconcerting when it changes wheel base and turning axis. Straight line highway would be better and cross wind stability should be better. Jim

 

[willie in mn]

My theory. Your privilege whether to agree or not.
Basic load planning 12000# on steering, 34000# on tractor tandem, 34000# on trailer. equals 80000# gross.
1- to get maximum weight usage, the kingpin has to be between the tandem axles.
2- if when empty the rear axle is lifted & the pin is behind the forward axle, the weight on pin tends to lighten the steer axle, making handling very snaky.
3- if moving the pin ahead of the forward axle to eliminate the handling problem mentioned above, when loaded it would transmit too much weight onto the steering axle.

Any time more than 12000# is placed on the steering, it has to be taken off one of the tandem groups to stay under 80000#.

In my not so humble opinion, I don't think running one power axle & one tag saves anything. Sure, one axle has free rolling tires, no torque wear on them, but the drive tires get all the torque, wearing out much sooner. The ride isn't much different either, especially with the modern air ride cab.

Willie diesel pilot, retired.

 

[jacksun65]

Saves money if you run tolls based on axles on road, 3 vs 5 a lot less tire wear. You couldn't give me one to drive in winter. I used to pull out trailers for lift axle trucks if there was snow on the ground. The ride stinks on those trucks empty because the trailer is 50% of your ride. So truck hits bump then trailer hits bump but since trailer is dragging and kingpin is forward of rear axle it jerks the front of truck up.

 

[Bob Bancroft]

Kind of reminds me of Jon F MN's Volvo. Remember that? Tandem axle tractor with only one driving. I'm sure it was the forward one. He got along fine with it, except for parking in his drive, in the snow, empty! I believe weight distribution was all automatic. I don't think he had any control over that. I don't recall any axle lifting like this one.

Do these axles lift automatically when unloaded?

 

[grizz02]

that's why we run truck and trailer with 8 axles one being a lift on the tractor so we can haul 105.500

 

[flying belgian]

A hundred years ago I worked for a farmer that had a tri-axle straight grain truck. lift tag was behind drivers. You could not get that thing out of a muddy field. If you put pressure to the tag so you wouldn't sink in then the drivers would spin. If you lifted the tag to put traction on the drivers then the front got so light that you could not steer it. Really a problem to get it turned toward the field approach. Also a problem on snow. Either you could not get traction or you could not steer. Nice truck going down a dry hyway. 24' box. Could hall a heck of a load.

 

[D beatty]

All our air tag axle could be lifted by releasing air pressure and had a dial that we could set the amount of air to air bags.

 

[john in la]

A lot of the gravel trailers in Louisiana run a air lift 3rd axle on the trailer.
It is in front of the trailer axles.
The valve to lift and lower the axle can be in the cab but the dial to adjust the pressure has to be on the trailer.

If you had access to the dial in the cab it is easy to adjust the pressure while on the state scales shifting the weight from the truck to the trailer and back to the truck.
The state has since gone to full truck scales so it makes little differance anymore but the law is still on the books.

This truck may be automatic as the axles were raised while the driver was just finishing unloading and picking up his hoses.

 

[jon f mn]

Mine was the front drive, rear tag. It was also all automatic in that the tag was always a little lighter than the drive which was computer controlled. It did not lift, but would dump all the air in the right circumstances. They are quite a bit lighter and are more fuel efficient. Mine worked fine except as said in sand or in a parking lot in the snow. On the highway it worked as good or better than any twin screw I've driven. It rode real well and I never had an issue with that. It was one of the good points of that truck.

 

[D beatty]

You would have to make sure there wasn't an officers standing out side
because you can hear any release of air.

 

[D beatty]

Dump air way before you get to toll booths. They use to watch for that. With the new I pass i don't think they watch as much.