Thread: Who knows about coaches?

Originally Posted by Brian Hjelm

106 kph @ 1500 based on 504 tyre revs per mile. That combo gives an overall ratio of 2.7:1. I would be concerned about the ability of a 300-335 hp engine to pull that gearing on any circumstances but dead flat and no headwind. You would probably have the pedal on the metal in any other circumstances. What weight do you anticipate? Buses have large frontal area. All these criteria come into the equation. The relatively low tare of a bus might be the saving grace here.

I have been advised by many, both here and on the road that the tag is superfluous, ergo the maximum GVM would be 22.5 tonne. Using Harlie's figures, which are very close to my roughly calculated guestimate, 15 tonne is close to the mark. Add 5 tonne for a trailer and I still have a relatively light GCM of 20 tonne.

Originally Posted by V8Ian

I have been advised by many, both here and on the road that the tag is superfluous, ergo the maximum GVM would be 22.5 tonne. Using Harlie's figures, which are very close to my roughly calculated guestimate, 15 tonne is close to the mark. Add 5 tonne for a trailer and I still have a relatively light GCM of 20 tonne.

Ian, here are a couple of handy formulae.

Road Speed =

(Engine Revolutions per Minute x 60)
--------------------------------------------------
(tyre revs per kilometre x overall gear ratio)

Horsepower requirement is a function of gross weight, frontal area, and road speed. The total horsepower required is the sum of three individual requirements. (1) Rolling resistance horsepower. (2) Grade resistance horsepower. (3) Air resistance horsepower.

Using the tables in Motor Truck Engineering by James Fitch and assuming 100 kph, 1st class highway, 1% grade, 20 tonnes gross, 96 sq. ft frontal area, we have:-

rolling resistance hp - 80.4
grade resistance hp - 72
air resistance hp - 111
required net hp - 262.4

Engine driven accessories consume from 12 to 25 hp and 17 is used as a benchmark for calculations unless a particularly heavy draw is made by certain accessories like two air compressors not one, particularly large output alternators and a/c compressors. So add 17 hp to that and you require 280 hp to maintain 100 kph on good level road. At 110 kph the requirement rises to 378 hp. This is why the guy who commented that the 8V92TA's "did it easy" was on target. The smaller engines are going flat out, full load where the 8V at 435 hp had plenty in reserve.

Ian, on thinking about it, perhaps a two axle bus with an 8V92TA would be the way to go. Those 8V's are economical where they are not being used continuously or nearly so at full load. I don't think from my experience of operating them that they would use any more than a smaller engine of any type that has the hammer down most of the time. And, you are only running 20 tonnes not line haul at 43 or more. On the shuttle we ran to a schedule of 14 hours Brisbane-Sydney New England Highway and Putty Road. Could do it in 12 hours if necessary without having to push too hard.

Originally Posted by Brian Hjelm

Ian, on thinking about it, perhaps a two axle bus with an 8V92TA would be the way to go. Those 8V's are economical where they are not being used continuously or nearly so at full load. I don't think from my experience of operating them that they would use any more than a smaller engine of any type that has the hammer down most of the time. And, you are only running 20 tonnes not line haul at 43 or more. On the shuttle we ran to a schedule of 14 hours Brisbane-Sydney New England Highway and Putty Road. Could do it in 12 hours if necessary without having to push too hard.

They were 'interesting' days, sometimes I miss them.

I remember Rex Laws and Redline Coaches redline by name and that was where the tacho sat! and the little red LOW Vacuum light on

In later years I had need to travel on VIP one driver buses,Syd-Bris O/night about 100klms north of Coffs Harbour the bus started to wander as the driver dozed off, a passenger got him to stop, and asked if anybody had a bus license, nobody had but 2 of us had truck licenses, so we shared driving until Ballina, the first time I had driven a full air braked vehicle, being used to Vacc over Hydraulic, a replacement driver was waiting in Ballina.

when we moved up here to Qld I started driving School Buses, Bedfords SB's BLP's Vam's Vacc over Hydraulic and full air manual syncro,manual crash, and Allison autos.still like a nice smooth crash box like the old Commer CBEW with rear Perkins 6-354 100kph with a full load of school kids on,it was Vacc over Hydraulic.could do 5 close stops before low Vacc light and buzzer came on, a mostly flat run

My favourite was an SB3 with a 330 Diesel was originally Kirklands Coaches,was a petrol 300 but converted to diesel,used to do Lismore area,I can still remember seeing Alstonville on the destination scroll it is now my ex-bosses motor home,it had a low ratio diff in it for climbing the hills an doing stops, flat out empty 51MPH,full load 80 primary's 51MPH loved it 4spd J2 syncro box smooth as.vacc too.

cheers

Originally Posted by Brian Hjelm

Ian, on thinking about it, perhaps a two axle bus with an 8V92TA would be the way to go.
...

Good luck find one of those. There was several 2 axle Landseers built around 1990. They were fitted with 6v92t & 6speed Spicer or 6 speed ZF syncro, no toilet and shorter at 34-35ft. Loaded weight of 4t lighter made them a bit of a rocket.

Originally Posted by V8Ian

I have been advised by many, both here and on the road that the tag is superfluous,
...

Don’t rule out a tag axle completely. Down side is extra weight, and dragging in parks. But the tag adds a LOT of stability.

Remember a coach has similar windage to a fridge semi which has 6 axles, I can report that 2 axle coaches (even the otherwise identical Landseers) are quite exciting at highway speed with strong winds, they really get pushed around.

Also coaches don’t really make good tow vehicles due to basic geometries. They have a BIG rear overhang (distance from axle to tow point) and were never balanced for any significant ball weight. The “pie wagons” that Greyhound used to tow for freight and companies like Downunder Tours tow for camping gear weighed about 4t and believe me, you really knew it was there, I would hate to tow one with a 40’ 2 axle coach. If it was me towing 5t, I would want the extra axle for towing and highway stability.

Denning fitted a dump valve as an option that wound deflate the tag bags completely so it was only axle&wheel weight on the tag tyres for maneuvering, (it was actually for getting weight on Drive when bogged), easy retrofit to any air suspension to get this functionality. Later came the units that lift the tag off the ground.

Originally Posted by harlie

Good luck find one of those. There was several 2 axle Landseers built around 1990. They were fitted with 6v92t & 6speed Spicer or 6 speed ZF syncro, no toilet and shorter at 34-35ft. Loaded weight of 4t lighter made them a bit of a rocket.

Plenty older ones with 8V71N's though and a dead easy conversion to a turbo 92.

I wonder what happened to the 8 x 4 touring coach being built by George Roman at his Carina home? It was to have an 8V92TA. I couldn't hazard a guess at how many years it sat there being slowly constructed as money became available.

Ian, my brother-in-law has a converted coach for sale. May I PM you with some information about it?
In the late '70s I was going to build a "café-racer" type motorcycle. When I did the costing it turned out to be cheaper and quicker to buy a new motorcycle of a similar type, which I did (Yamaha SR500, great bike except the brakes were absolute rubbish).