is there a big difference in fuel consumption between a 6x2 44 tonner, than a 6x4 44tonner?
Don’t know, but would think there will be some difference given that the extra transmission will cause increased drag.
Definately increased tyre wear i’d have thought.
Usually used on STGO.
limeyphil:
is there a big difference in fuel consumption between a 6x2 44 tonner, than a 6x4 44tonner?
The best people to answer that question would be wire etc who would probably work with 6x4’s in the way that most drivers here would work with 6x2’s or 4x2’s.But the question would probably be better put as do the advantages of 6x4 units outweigh the disadvantages?.I reckon that the yanks have found over the years that 6x4 units offer more advantages in traction and stability under braking etc to outweigh their very slight,if any,disadvantages in fuel consumption or weight.
Carryfast:
I reckon that the yanks have found over the years that 6x4 units offer more advantages in traction and stability under braking etc to outweigh their very slight,if any,disadvantages in fuel consumption or weight.
Or it may be just due to the fact that using 48 or 53’ semis with axles close to the rear would overload the pin on a two axle tractor unit.
Are these still the axle weight limits?
All States must allow on their Interstate highways loads of 20,000 pounds on single axles,
34,000 pounds on tandem axles, 80,000 pounds total for a
vehicle,
80,000 = 36.29tonnes
34,000 = 15.42tonnes
20,000 = 9.0tonnes
I haven’t got any driving experience in the USA except for a hire car from New York to Indianapolis and ending in San Francisco but was interested in some nice fuel trucks around Bakersfield where I spent some time.
6x4 also used where traction can be an issue for a 6x2 unit, like our place where the yard is permanently wet and covered in muck, you can see the 6x2s sliding all over the place, where the 6x4 unit tackles it easily. The 6x4 is also blessed with a 500hp(ish) engine and a manual gearbox, whereas the 6x2s are 360hp and automatic.
Wheel Nut:
Carryfast:
I reckon that the yanks have found over the years that 6x4 units offer more advantages in traction and stability under braking etc to outweigh their very slight,if any,disadvantages in fuel consumption or weight.Or it may be just due to the fact that using 48 or 53’ semis with axles close to the rear would overload the pin on a two axle tractor unit.
Are these still the axle weight limits?
All States must allow on their Interstate highways loads of 20,000 pounds on single axles,
34,000 pounds on tandem axles, 80,000 pounds total for a
vehicle,80,000 = 36.29tonnes
34,000 = 15.42tonnes
20,000 = 9.0tonnes
I haven’t got any driving experience in the USA except for a hire car from New York to Indianapolis and ending in San Francisco but was interested in some nice fuel trucks around Bakersfield where I spent some time.
If it was just a question and issue of weight then the yanks would have been using 6x2’s for years like us instead of 6x4’s??.Those old weight limits there don’t seem to have changed for years according to newmercman and it’s surprising that they have’nt increased them using those Canadian type tri axle trailers by now.But I always thought that they could run double artic outfits coupled with a drawbar dolly on Interstate work in the 1950’s and 1960’s and that seemed to have changed at some point before the 1970’s?.
The legal weight for an eighteen wheeler in America is 80,000 lbs. [36.2 tonnes].[ 36287 kg Canadian] That is without any oversize or overweight permits.
legal U.S. weight per axle is: STEER 12,000 lbs DRIVES 34,000 lbs TRAILER 34,000 lbs
legal Canada weight per axle is: STEER 5443 kg DRIVES 15422 kg TRAILER 15422 kg
The average length of an eighteen wheeler varies greatly depending on the type of cab they are driving. But the overall average is 70-80 ft. long. The length of an eighteen wheeler’s cab [by wheelbase] usually averages between 245″ to 265″ wheelbase. This is measured from the center of the rear wheel to the center of the steer.
The trucking industry is pushing Congress to pass a bill allowing significantly longer, heavier trucks on roads. A coalition of families of truck accident victims, politicians and labor unions is fighting to stop the proposed legislation.
The coalition’s focus is on a proposed increase in truck weight limits from 80,000 pounds to 97,000 pounds [44 tonnes], an increase of more than 21 percent.
The legislation allowing for bigger, heavier trucks would mandate that commercial trucks pulling 97,000-pound loads have six axles rather than five. Proponents of the weight increase argue that the extra axle would help truckers with braking.
So those monster Kenworths etc are running at just over 36 tonnes… 
Santa:
The legal weight for an eighteen wheeler in America is 80,000 lbs. [36.2 tonnes].[ 36287 kg Canadian] That is without any oversize or overweight permits.legal U.S. weight per axle is: STEER 12,000 lbs DRIVES 34,000 lbs TRAILER 34,000 lbs
legal Canada weight per axle is: STEER 5443 kg DRIVES 15422 kg TRAILER 15422 kgThe average length of an eighteen wheeler varies greatly depending on the type of cab they are driving. But the overall average is 70-80 ft. long. The length of an eighteen wheeler’s cab [by wheelbase] usually averages between 245″ to 265″ wheelbase. This is measured from the center of the rear wheel to the center of the steer.
The trucking industry is pushing Congress to pass a bill allowing significantly longer, heavier trucks on roads. A coalition of families of truck accident victims, politicians and labor unions is fighting to stop the proposed legislation.
The coalition’s focus is on a proposed increase in truck weight limits from 80,000 pounds to 97,000 pounds [44 tonnes], an increase of more than 21 percent.
The legislation allowing for bigger, heavier trucks would mandate that commercial trucks pulling 97,000-pound loads have six axles rather than five. Proponents of the weight increase argue that the extra axle would help truckers with braking.
So those monster Kenworths etc are running at just over 36 tonnes…
That’s nothing new they’ve been running at those weights and lengths for years but there’s a good reason for the specifications which their industry has followed for years of generally conventional 6x4 tractor units and two axle trailers as that’s the best and most stable configuration for those weights.The 6X4 helps with engine braking,traction and resistance to jacknifing,while the conventional offers better protection in a truck accident and better living space etc.But the Canadians have shown that the 6 axle set up is even better and would allow them to use higher weights safely.Their present five axle set up is already a better spec configuration at around 36 tonnnes in the context of axle loading and braking etc than we were using safely at 38 tonnes and six axles for 44 tonnes seems fine especially with their advantage of double drive.As usual they’re showing us how it should be done but like here they’ve got the hysterical anti truck brigade trying to stop them.But I’m still wondering what happened to those doubles train outfits over there years ago?.
The reason they still use double drive is simple, they don’t like change, a few of the more forward thinking companies are now adopting single drive, they get better tyre wear, better fuel economy & lower tare weights, with a dump valve on the undriven axle & a diff lock on the drive axle they are better in the snow than the 6x4s too.
Most trucks here don’t have a diff lock, they have a power divider, in slippery conditions a single drive with a diff lock would be much better, especially if you could dump the air out of the undriven axle to put more than 17000lbs on the driven axle.
All the talk about weights going up to 97000lb is just that, talk, when you consider that there are up to ten times (guesstimate) more trailers on the road than units, you’re talking about a lot of axles, it would take years & a huge pile of money to accomplish so I can’t see it happening myself.
As said wheelbases range from 220" to 270" on standard line haul tractor units, there are some that are longer, up to 310" in some cases, sometimes to accomodate a 150" sleeper, sometimes just for the stretched ‘outlaw’ look. In Canada if you want to pull a 53’ trailer 244" is your limit (except with a special permit) my Pete is 244" & with a 53’ trailer behind me I need a lot of room to manouvere. My unit is about the same wheelbase as a big 6 wheel rigid over there so you can imagine how unwieldy it is, it does ride nice though. For most interstate routes the distance between the king pin & the center of the trailer axles is 41’ except Michigan, 40.5’ to the center of the rear axle & California, which is 40’ to the center of the rear trailer axle, Michigan doesnt seem to worry about it but California are very strict.
My 550hp at 36.3 tons has the same power to weight ratio as 660hp at 44 tons, it’s nice, but when you consider some of the mountain passes are 11000ft climbs (compared to Mont blanc at just over 7500ft) we often need every one of those 550 ponies. Wire has 600hp but then he’s just a show off 
80,000lbs might sound very restrictive for such long trucks but there is a reason behind it. When you are thinking how much higher axle weights in the UK are you must also consider how much tax revenue is available to maintain the roads. Fuel tax in the US is much less compared to the UK with a gallon of Diesel costing just over $2.65 a gallon. You read right, thats Dollars a US gallon! Also there is practically no road tax and of course the much quieter roads over here mean that for every given mile of road there is far fewer vehicles paying the tax at all.
Some US States have more lenient regulations to suit their own particular requirements and all of Canada allows higher weights than the UK already.
Just to be pedantic, the measurement for tractor lengths is taken from the centre ofthe steer axle to the centre of the rear bogie. I know this because i have a 265" tractor and i need a permit for some Canadian provinces.
Regarding Limeyphils original question of fuel consumption. I guess that driving through two drive axles does use more fuel than a 6x2 chassis but 6mpg is considered good here anyway! I usually get around 5.3mpg out of my Peterbilt and use around 130 gallons of diesel a day on average. My rear axles have both diff and crosslocks and with the snow in the rocky mountains theres no way i would want a 6x2.
In any case it would not be legal to drive on the road with the centre axle lifted while loaded or even with the airbags dumped on the centre axle.
Michigan allows huge weights on multi axles such as this steel hauler.
The Canadian prairie provincies allow two 53’ trailers to be coupled on designated routes.
These pup triples must be a handfull to reverse. Wouldn’t fancy driving one in the snow either.
265" wheelbase can be a nuisance at times on my tractor unit.
Wire, mine just has the cross locks, all that means is I get 2 wheels spinning instead of one! Your bloke specced that motor up really well. I reckon a single drive with all 34000lb going through it & a diff lock would be better for outright traction though, of course, you couldn’t run down the road like that, but it might mean less times out in the freezing cold putting on your chains. Or you could stay away from the Rockies in the winter 
If you run with a spreadaxle trailer you can put 40000lb on your trailer axles, with a mid lift you can go to 20000lb on the axle on the ground & with 12000lb on the steer you could legally run on 4 axles up to 72000lb gross weight.
wire:
80,000lbs might sound very restrictive for such long trucks but there is a reason behind it. When you are thinking how much higher axle weights in the UK are you must also consider how much tax revenue is available to maintain the roads. Fuel tax in the US is much less compared to the UK with a gallon of Diesel costing just over $2.65 a gallon. You read right, thats Dollars a US gallon! Also there is practically no road tax and of course the much quieter roads over here mean that for every given mile of road there is far fewer vehicles paying the tax at all.
Some US States have more lenient regulations to suit their own particular requirements and all of Canada allows higher weights than the UK already.
Just to be pedantic, the measurement for tractor lengths is taken from the centre ofthe steer axle to the centre of the rear bogie. I know this because i have a 265" tractor and i need a permit for some Canadian provinces.
Regarding Limeyphils original question of fuel consumption. I guess that driving through two drive axles does use more fuel than a 6x2 chassis but 6mpg is considered good here anyway! I usually get around 5.3mpg out of my Peterbilt and use around 130 gallons of diesel a day on average. My rear axles have both diff and crosslocks and with the snow in the rocky mountains theres no way i would want a 6x2.
In any case it would not be legal to drive on the road with the centre axle lifted while loaded or even with the airbags dumped on the centre axle.Michigan allows huge weights on multi axles such as this steel hauler.
The Canadian prairie provincies allow two 53’ trailers to be coupled on designated routes.
These pup triples must be a handfull to reverse. Wouldn’t fancy driving one in the snow either.
265" wheelbase can be a nuisance at times on my tractor unit.
wire most of that is just what I’ve been saying but I can’t understand how newmercman seemed to overlook those diff locks and crosslocks without which a 6x4 becomes a liability not an asset?.But that issue of dumping air on the undriven axle of a 6x2 to give it traction is something that they stopped here not long after they started using them when we went to 38 tonners with 2 axle trailers and 3 axle units.I was surprised that even in Canada those double artics seem to be limited in the way that they can be used but I’m sure that those were also allowed as two 45 footers on US interstate work before the 1970’s but I might be wrong?.I’ve actually got a photo of the first 45 ft doubles outfit used in Canada if I can get it on here.As for me I’d rather have a 6x4 even to go over the alps in the winter or spring let alone the rockies and a wagon and drag in that configuration would be even better in my view and the fuel difference could look after itself.Those yanks don’t like change for good reason.
Nice photo Carryfast. Look at the size of that Kenworth steering wheel!
Yeah i know what you mean Newmercman. The KW’s at Big Fright only had a crosslock between the the drives. I guess the idea is that as the diagonal opposite wheels are locked together you can chain one axle up. I once had to do this at BF coming up the Vancouver side of the Transcanada towards Hope, BC.
wire:
Nice photo Carryfast. Look at the size of that Kenworth steering wheel!
Yeah i know what you mean Newmercman. The KW’s at Big Fright only had a crosslock between the the drives. I guess the idea is that as the diagonal opposite wheels are locked together you can chain one axle up. I once had to do this at BF coming up the Vancouver side of the Transcanada towards Hope, BC.
It’s difficult to see the logic in that spec wire as we ran 6X4 Foden gritters/ploughs on the council and never used chains at all in snow a lot worse than that.Were you loaded up to max on the drives there?.But if newmercman is right they would have changed the spec to 6x2 by now which I’m sure they have’nt.
a few years ago when I used to attend the biggest US truck show ( the Mid America show in Louisville Kentucky) I fell in drinking on night with the owner and drivers of a fairly large company, and had this very same conversation, I convinced the owner of the company enough that the weight saving of using a 6x2 tag on air with tandems on the back axle to achieve the same bogey weights along with the tire wear saving when running empty that he asked me to meet hiim at his stand next day to meet with the sales reps from various USA manufacturers - he was in the market to buy trucks at the show. He was definatly up for it - he saw all the benefits and very little problems - keen wasnt the word
Not one manufacturer would sit down and talk and see if it could be done, and the reason they gave?
Not an economic reason, this was back when every US truck compnay was spending thousands trying to get drivers, the driver shortage was acute, and the manufacturers -Including Volvo USA, who could do it almost off the shelf said they reason they dont market 6x2’s in the USA was LACK OF DRIVER ACCEPTANCE- drivers wanted 6x4 and wouldnt work for a company that didnt offer it 
therefore companies wont buy them, and therefore it wasn’t cost effective to offer it as an option 
Mind you, you have to remember this is the year me and Lucy almost collapsed with laughter, (genuinely) when we saw the and I quote from the sales blurb
A NEW REVOLUTIONARY TARPING (sheeting) SYSTEM FOR FLAT BED TRAILERS
Or what you and I would call - A Curtainsider 
and this was only 5 or 6 years ago 
Yanks gotta love em 
Rikki-UK:
a few years ago when I used to attend the biggest US truck show ( the Mid America show in Louisville Kentucky) I fell in drinking on night with the owner and drivers of a fairly large company, and had this very same conversation, I convinced the owner of the company enough that the weight saving of using a 6x2 tag on air with tandems on the back axle to achieve the same bogey weights along with the tire wear saving when running empty that he asked me to meet hiim at his stand next day to meet with the sales reps from various USA manufacturers - he was in the market to buy trucks at the show. He was definatly up for it - he saw all the benefits and very little problems - keen wasnt the wordNot one manufacturer would sit down and talk and see if it could be done, and the reason they gave?
Not an economic reason, this was back when every US truck compnay was spending thousands trying to get drivers, the driver shortage was acute, and the manufacturers -Including Volvo USA, who could do it almost off the shelf said they reason they dont market 6x2’s in the USA was LACK OF DRIVER ACCEPTANCE- drivers wanted 6x4 and wouldnt work for a company that didnt offer it
Mind you, you have to remember this is the year me and Lucy almost collapsed with laughter, (genuinely) when we saw the and I quote from the sales blurb
A NEW REVOLUTIONARY TARPING (sheeting) SYSTEM FOR FLAT BED TRAILERS
Or what you and I would call - A Curtainsider
Rikki.On that 6x2 versus 6x4 debate like on most things to do with road transport I reckon that those yank drivers have got it right on that one except give me a wagon and drag over an artic any time for anything which does’nt need a full length load deck.I just wish that the driver shortage had been acute enough over there in the early 1980’s and their immigration rules would have let me go over there back then.
I dunno if they have it right, at 13.6 metre trailers i generally weighted to the limit rather than cubed out, so does 53 foot at a lighter limit make that much sense?
as far as traction goes…
a 6x4 with diff and cross locks with give some more grip agreed… in a straight line, try and turn a 6x4 with all locks in on a slippery surface it just dont happen , a 6x2 with a tag that you can dump the air on, will not only load extra traction on the single drive, but also add weight to the steer axles-
OK you may be technically overweight on both axles, but unless you are really dumb enough to do it while your on a weighbridge your never going to get done for it
In many ways the Americans are way ahead of us, in terms of basic vehicle design and optimal use - well thats not one of them
Things are definately different here for sure but from my experiance not usually for the worst even if it seems that way.
The driver acceptance thing is still big here even now. That is why the trucks are all conventionals for a start and also why they have such huge sleepers. You might think it is funny to put such an emphasis on the wishes of drivers but think what trucks in Europe might of been like by now if the same attitude had been taken there!
When i first arrived here i was on flat deck work and i used to wonder why i was struggling with tarps when a tilt or Euroliner would have been better but then i realized that most trailers don’t have chassis. I pull a reefer now and if i had a picture to hand i could show you that the body of the trailer actually is the only thing to it. If you like it is like a square “tube” with a bedplate and kingpin fixed to the underside at the front and a sliding tandem axle bogie fixed to the underside at the back. This enables a 53’ refridgerated trailer coupled to a long conventional tractor with a 70" sleeper and double drive to weigh less than the much smaller European equivalent. Say Daf XF 4X2 tractor and triaxle Shmitz Cargobull Fridge. My whole outfit weighs around 34,000lbs (15,454kgs).
Obviously flatdeck trailers are the exception and do have a traditional chassis but so too would curtainsiders have to. In that case there would be the disadvantage of a trailer that was equivalent to a flatdeck but which weighs more than even a boxvan.
Also nothing is more able to adapt to carrying any size load than a flat deck which is really important when an operator is looking for a reload 5,000kms from home.
I agree… most people would be surprised here to see a picture of a brand new flat bed trailer from the USA , they are not flat… they bow, almost a gentle arch,
as you can see here
they are that lightweight they are designed to “level out” with the weight of the load… aluminium is the metal of choice in construction , steel used for the running gear, as opposed to the UK where most trailers are almost totally steel contruction.
Carryfast I never overlooked the diff locks, I never had a say in the ordering process as the truck was 3 yrs old when I got it
Personally for highway use I would have the rear axle driven, with a full locking diff, the leading axle I would have undriven & liftable, that way I could put all my drive bogie weight through one axle, with decent tyres (which I have) that would be all you need for traction. It would satisfy even the strictest chain laws too as you could chain up all 4 rear tyres if needed. The benefits would be well worth it, 20% of the power the engine produces is lost by the time you put it on the road with a 6x4, that drops to 12% on a 4/6x2, that is wasted fuel, the drag/rolling resistance from the drive pattern tyres needed on a driven axle against running trailer tyres on the mid lift contributes to more wasted energy too. My reloads are usually very light too so I could run up to 50% of my time with the wheels up, increasing my efficency & therefore the money in my pocket even further.
Think about this, Scandinavia has some pretty extreme weather, the roads are not exactly flat either & they run at 62.5ton with a 6x2 configuration, why then do we need double drive at almost half the weight? The answer is, we don’t, but that’s the way it’s always been done so that’s the way it always will be.
The only way to get a lift axle here is to order the truck as a 4x2 & have one retrofitted or convert an existing truck.
One thing I will say though is reluctance to change is not a bad thing, the good old days are still around for us truckers over here & I wouldn’t change that for the world 