Tandem steer

I've noticed a shift to tandem steer prime movers lately.
Most road trains will have an 8- wheeler out the front and I can't see why.
It's not as if they can throw more weight onto the prime mover, all the trailer pins are same setback.
I saw one with a Hiab and another was a bulk cement rig so he would have a pump mounted somewhere. The rest are just sleeper cabs.
Even the purpose built stuff has tandem steer. 5-trailers behind a tri drive tandem steer KW.
Around town the tippers have gone to tandem steer, tandem drive plus lazy. Some big capacities there.

.
Jeffo.......... A lot of the local deliveries are being done by tri axle ( be they lazy , or pusher setups) truck & dog etc etc.........
If you have ever tried to manouvre a tri drive, single steer thingo around a wet building site... you will appreciate why they go for a
tandem steer, (as well as a bit more payload ) , because the single steer just does not want to go around corners, preferring to go straight ahead.......
As for road trains, i feel a twin steer is a safer option..... (horses for corses possibly though) ...as you do have to push that extra axle through the mire......
Years ago BP were using 8 wheeler movers, they said it was a safety factor..........( steer blowouts etc etc.....)
Soooo i guess it boils down to what terrain the vehicle is going to be used in, is the deciding factor......
It would appear that for pushers and lazies, when the truck is loaded, (regulations ) you cannot lift an axle to get out of trouble,, (so iam told by a bloke
who has just put a tri axle rear end on his truck............)
Maybe, these days engines are getting so heavy, the single steer maybe over loaded........maybe..........i dont know.........
..........................Billy..........................

Interesting observations there Guys, seems like a lot of things these days, axle configurations are being rethought. Quite a few years ago, mobs like BP were running 8&10 wheeler prime movers with up to 3 or 4 trailers behind on tanker work, in both the Territory and WA, Possibly FNQ as well??. Back in the 90's maybe about the time B doubles started coming into their own, remember seeing a KW twin steer, bogie drive with either a pusher or a lazy being set up with a big food grade s/steel tank behind the sleeper cab and a turntable behind that, obviously going to be used as a lead vehicle for double work. Bloke told me it was going onto milk work up around Mareeba way, waiting to see how NSW was going to jump with doubles, maybe long term plan to cart milk down as far as Casino. Don't know what happened to it, if ever it did get the OK to cross the border or not. Also, 8 and even a few 10 wheel prime movers used on heavy haulage many years ago, Atkinson and Scammel come to mind, probably some photos hidden away on this forum
Dave

If my memory serves me correctly, the Regs in NSW say that the lazey axle air bag pressure cannot be controlled from the cab of the vehicle, but if stuck, you can reduce the down force air from a valve outside the cab. Apparently this was designed to stop drivers altering the axle weights when approaching weigh bridges or being pulled up by the Mermaids.

Years ago a mate had an Isuzu T/T with a lazey on 60-40 split Hendrickson. When he went into paddocks to collect bagged spuds, he would often get stuck, so he wanted me to rig a system to lift the lazey when needed. It all looked too hard until I figured that if I put an air bag on top of the diff, pushing against an extra cross member, it would achieve the same result. It worked a treat, but the valve had to be outside the cab to be legal.

One of my few better, easier solutions

Here in the States, before twin A hitch Pups were common, Roadway Express had a lot of those 60/40 spring ride lazy axle set ups with that air bag over the drive axle that Wee described. Theirs were set up that you could only use them in the low side of the Roadranger gear box.

I'm thinking it must be a safety decision.
I guess when you already have 70 + wheel/tyres on a road train a couple of more won't matter.
And yes Billy, even a tandem wants to push that single steer straight ahead in the wet.

"It's not as if they can throw more weight onto the primemover,all the trailer pins are the same setback"

Doesn't matter where the trailer pin is Jeffo.
Its where the primemover turntable is.
Most 6X4 roadtrain primemovers have the turntable at dead centre.
My current 8X4 Volvo has the turntable 13 inches in front of D/C.Gives me 10 .6 t on the steer (allowed 11t) and 17.0t on the drive.
I have a 450 litre fuel tank behind the cab.
I carry bulk cement and all my tanks have one full height baffle.My compressor is trailer mounted on the semi.
I load 6.6 tons in front of the baffle and 21.7 tons behind for 22.5t on the tri.
I can pull the same semi behind a 6X4 but load 3.3t and 21.5t for a 6.5t/17t/22.5 GVW.
Twinsteer prime movers are not legal tender in SA.,NSW. or Vic.
Tri axle / single steer primemovers are the same as above and Queensland too,since 2008.
However all states allow 8X4 (single steer) and 10X4 body trucks (rigids).

Previous to this I had a T908 and T650 both were single steer/bogie drive with lazy. i.e 8X4.
Turntable on both of these was 4 inches BEHIND dead centre primarily to keep the front axle down to 7 tonnes.

Have seen at least two NSW rego 8x4 Prime movers wih tri axle traiers in Sydney in the last 3 months

I see what you're saying Cement but pin dimension is the factor that allows how much you can throw to the turntable.
In your case you're altering the pin load by loading the cement differently, 6x4 V's 8x4 prime movers.
Moving the turntable simply alters the weight distribution going to either the drive or to the steer.
I've also seen a local single drive with Hiab and is turntable is sited well aft of the diff, looks frightening.
Going way back, you could pick a single drive semi from a tandem just from the pin position, 3' and 4' rings a bell.
Common to break their back if you tried to load up for a tandem but the pin was only 3'.
But I digress, these 8x4 prime movers certainly look great.

.
.Spotted at Blacktown to day..... ( taken from bike cam)…………….





...........................Billy..........................