Picking a Suitable Truck
© Dr. B. C. Paul 2000
Revised 2009
Hi!
The Rear Dump Truck
Truck Configurations

Rear Dump
• Solid bed elevates and dumps
material over the back

Solid bed can take abusive
handling and loading
•
•
•
•
Can be lined
Traditional liners steel
Carbon composites now
Lighter bed liners avoid loss of
payload
Variations

Most manufactures offer
different bed for different
material weights
• Coal and iron ore for example

Trucks are sized by weight and
volume - most limiting controls
productive service
• Like to get both to limit at same
time
Maneuverability Issues




Back dumping forces drivers to back
into spaces blind
Most rear dumps are two axle with
double tires on rear - fair
maneuverability
Some very large have had double
rear axle - hard to turn
Articulated versions are smaller but
highly maneuverable - often have
flotation tires for soft underfoot
The Tree Axle Rear
Dump
Rear Dump Power

Have relatively high HP to
payload ratios
• makes very gradable
• gas mileage marginal makes best for
short in pit hauls


Generally geared low so 42 mph
typical peak speed
Weight centers on drive tires for
traction (can have 4 wheel
drive)
Powering Haul Trucks

Diesel Engine (common in US)
• gas guzzlers frequently around 1 mpg

Trolly Electric
• Rare in U.S. because it limits mobility to
areas with developed lines

Trolly Assist
• Keeps down engine size
• boost power on steepest grade
• Loosing ground because full electric
drive systems loosing to mechanical
Three Axle Bottom
Dump

More of a tractor trailer
arrangement - open top and
bottom opens to unload
• More popular with lighter material
like coal because of bed bottom
abuse issues

More of vehicle is hauler
• less power to payload
• larger bed relative to size
The Three Axle Bottom
Dump
Properties of Bottom
Dumps


Geared higher for more speed
Gives poor gradability
• SMCRA limits most ramps to 10%
anyway


Speed and payload to power
favors longer hauls - coal to
processing facility
Have lower loading height works better with FELs
Impact of Bottom Dump


Can’t stand impacts
Allows truck to use regular
truck dump
• Dump time may be 25% of rear
dump


Material must be free flowing
and not prone to freeze
Three axles tend to maneuver
poorly
Getting the Best of Both
Worlds





Two Axle Bottom Dump
Improved Maneuverability
Looks like a three axle body
only solid and on two axles
Has Intermediate Power to
Payload ratio
Bottom dump still means light
free flowing non freezing
material
Two Axle Bottom Dump
My Considerations




My Benches are relatively narrow so I
would like maneuverability – favors rear
dump
The Hauls are moderate length with some
steep grades and rolling resistance on the
sand dunes – favors high power to payload,
again rear dump
Oil Shale is kind of heavy and blocky, could
beat on truck bed – one piece beds of a
rear dump would be handy
I’ll pick a rear dump
Turns Out That Was Also
The Choice of the Problem








You have been assigned to pick the trucks and
loaders for President Ahmadinejad’s “Truck fleet of
International Peace and Love”. The following
trucks are to be considered
Cat 769D Dual Slope
Cat 773E Flat Floor
Cat 777D Flat Floor
Cat 789D Dual Slope
Cat 793 C Dual Slope
(Specifications for all these trucks are available in
the 35th Edition of the Cat Handbook)
It is often very handy to have your truck specs
available – a copy of the Cat Handbook is great
Reading Cat Specs
Truck Model
Truck Data Label
Numerical Values
Truck Weight
Total truck weight and
Payload can be 157,000 lb
(78.5 tons)
Basic Body and Chasis
Is 70,706 lbs
I could carry a load of
86,294 lbs (>43 tons)
But if I use a bedliner it
Will cut my payload
By 7280 lbs
And leave me with
79,094 lb payload (<40t)
A Truck Can Be Limited By
Weight or Volume
If I heap the truck it can
Handle 31.7 yd^3
(but that could mean a
High load at the middle
Of the truck
Struck even with the top
Is 21.6 yd^3
Truck Size
Width 16’8”
For 2 way traffic you would
Probably want a road 2.75 times
this
Probably want about 1.5 times width
For single direction traffic
1/4th truck
width
Loading Height
Loader will have to be
Able to get over 10’2”
To get over the side of
The truck
(that does not guarantee
It can heap the truck)
Turning Corners
Clearance to turn a full
Circle is 66’7”
Traction Games
How much of the weight
Is on the drive wheels
Can control traction
When the truck is empty
50.3% of its weight is
On the rear drive wheels
When full 66.7% is on
The rear drive wheels
Of course you can put
4 wheel drive on but that
Is pricey to buy and
Pricey to maintain
More Considerations


I would like a big truck so I can
minimize the number of trucks I
have to run
Problem is that big trucks have
a big turning radius and I have a
narrow bench
• Need to consider how I will load
for maneuvering