Spread Trailers

Baz, my level of ignorance is just above door mat, but I beleive that the spread was purely a legal issue, carrying capacity was determined by axles and distances between them. To achieve a greater capacity, the axles needed to be further apart... somehwere I have a picture of the old A Mk1 with a Vaughans spread, the front, drive, and spread were almost each exactly the same distance apart. Made very hard work of turning and cut the bitumen up.


-3 deg in Central Victoria... why would anyone want to live there???

/me

co-incidently a fella is advertising in the Old machinery Magazine (TOMM) saying he plans to write a history of McGrath Trailers and wants people to contact him with any info - 0417 345141

I know even less than Sarge, but like to hear more from people who do know.
Is the scrub on a spread bogie any worse than a tri axle ?

What a fantastic topic for discussion, i've been told about the freighter hydraulic suspension but not seen it before. have also seen a pic in the 40th Anniversary issue of Truck n Bus 1976 of a Murray Goulburn milk tanker built by Tieman with a 2.7m spread on Franklin air bags. Looking forward to MANY MORE photo's thanks in advance.

I know even less than Sarge, but like to hear more from people who do know.
Is the scrub on a spread bogie any worse than a tri axle ?

I know very little about spread bogie trailers as well, but I understood it was an eastern states thing, to spread the weight out over the bridges. As far as I know, there was no requirement for spread bogies in South Australia, but they were here, I guess they drifted over the border.

I would think the scrub on a spread bogie would be much worse than on a tri, from my experience a tri tends to pivot on the centre axle, but a bogie and more so a spread bogie, just drags around sideways.

RnR.

121" was the normal wheelbase for a single drive prime mover, 9'1" spread is only a foot less.

Like Sarge and AtkiPete, I'm not an expert. However, I remember in the early 70s my uncle (a livestock carrier) having a conversation with my grandfather about being booked for being over weight on the drive, and cursing the fact that if he had known he could easily have opened up the spread a little more redistribute the weight. He also explained how spread trailers had been introduced, as sarge suggests, to take advantage of the formula used by the Country Roads Board to determine maximum axle weights at the time.

A few years later, ('76) I remember my brother Bill telling me that the original spread bogies were basically two single axles, ie suspensions not connected. Later that type was made illegal because they damaged the road, so from then on axles had to be interconnected as per Swishy's post. Bill showed me the huge grooves carved in the road near Horsham where trucks turned out of the roadhouse onto the highway and you could see how the front axle of the spread in those tight turns just became a grader.

Spin forward to 1980 and my first job as a truck driver, I remember my new boss telling me that he had gone for single drive with triaxle trailers because, with the tri pushed forward to keep the weight down on the drive, you could get a ton more payload and there was much less tire damage even though there were more tires. So that would suggest the answer to AtkiPete's question is that triaxles don't scrub as much as spread bogies.

But what do I know

The main requirement behind the bridge formula was to get the first and last axle as far apart as possible and this was why, for example, the Atkinsons had their front axles pushed forward until the wheels were virtually rubbing on the bumper. Similarly, Volvo and Scania brought out axle-forward versions of their cab overs, while the Americans were already there due to old Yankee laws which created the GMC cracker box and Kenworth slimline. With the rear trailer axle at the extreme end the spread axle took up weight somwhere in between determined by the formula. I suspect that the formula rules were relaxed in the late 70's because that was the end of the Volvo G88 and return of the setback front axle with the F10. Triaxle trailers seem to have been introduced about much the same time.

South Oz didn't need spreads, they allowed 8 ton per axle behind the cab, sounds good, yes , it wasn't too bad, but, there was no allowence and in the case of a spread each axle was weighed seperatly :'(, they were not very "load sharing" and many blokes got booked on 1 axle being overweight.
This load sharing was over come with the hydraulic rocker suspension, which were ruddy near impossibe to slide with a load on.

The law killed the wide spread - blamed for doing too much damage to roads. The tri axle had arrived prior to the ban on wide spreads.

So - some were converted back to closed bogies and others to tris.

WISC - There was also a 10' 1" wide spread too - but (I think) was restricted to 38' & 40' trailers only. Again - all to do with the 'bridge forumla'.

Even with compensating suspensions - they either pivoted on one axle or the other. So were a bit tricky to reverse - one moment everything pivoting on the rear axle, next minute on the lead axle.

The early ones were designed to go behind single axle prime movers (which were still all the go at the time) - but when put behind a bogie drive - the extra weight over the goose neck caused them to break in half.

For some reason wide spreads and bogie ACCO 3070's didnt go well together either - cracking the trucks chassis just ahead of the front drive axle.

Oldfulla