7109.19,31-34
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FSH 7109.19 - FLEET EQUIPMENT MANAGEMENT HANDBOOK
R-1 SUPPLEMENT 7109.19-91-1
EFFECTIVE 09/12/91
CHAPTER 30 - USE AND STORAGE
31 - VEHICLE LOADINGS. The old description of trucks which used the nominal rating such
as 1/2, 3/4, or 2-ton is no longer applicable. The gross vehicle weight and gross axle weight
ratings determine the load capability. The data plate on the door or door frame of every truck
lists the gross vehicle weight rating (GVWR). The gross axle weight rating (GAWR) for each
axle is also listed. These ratings are not to be exceeded when loading the truck. A heavily
loaded vehicle should be weighed on truck scales to determine if the vehicle or either axle is
overloaded.
When ordering trucks, inform the Forest Equipment Manager what the truck will haul and the
terrain on which it will travel. Based upon this information, the Forest Equipment Manager will
determine the appropriate gross vehicle weight and gross axle weight ratings for the truck.
The following table 31-Exhibit 01 lists the standard 5 sizes of the R-1 Model 52 slip-on
engine/tank units. Recommended truck GVWR sizes which are capable of hauling these Model
52 slip-on units are listed.
R-1 Supplement 7109.19-91-1
Effective 09/12/91
7109.19,31-34
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31 - EXHIBIT 01
Model 52 Engine Minimum Sizes
Specifications:
1. R-1 standard Model 52 Engine tank capacities are:
200 gallons
300 gallons
600 gallons
750 gallons
1000 gallons
2. Flatbed sizes and GVWR's required:
Tank Size
a. 200 gallons
Bed Size
Min. GVWR
Preferred GVWR
8' wide X 9 1/2' long
11,000
12,000
Comments: 4 X 2 or 4 X 4 trucks that are 10,000 or 10,500 GVWR are not acceptable in this group.
These type trucks will be overloaded when equipped as a "fire ready" 200 gal. pumper. Care must be
taken to prevent overloading the 11,000 lb. GVWR 4 X 4 trucks.
b. 300 gallons
8' wide X 9 1/2' long
14,500
14,500
Comments: Super Duty Fords and HD 35 Chevys are ideal for either the 200 or 300 gal. tank. Another
truck that is used for the 300 gal. tank that is very suitable is a 19,600 GVWR Ford F-600 or Chevy C-60
type.
c. 600 gallons
8' wide X 12 1/2' long
24,000
26,500
Comments: The Ford F-600 or F-700 and Chevy C-70 are the type truck that is best suited for the 600
gal. tank. A 7,000 lb. front axle on the F-600 and a 9,000 lb. front axle on the F-700 is required to ensure
that the front axle will not be overloaded.
d. 750 gallons
8' wide X 12 1/2' long
24,500--26,500--28,200
Comments: An F-600 type truck with the 7,000 lb. front axle on a 24,500 GVWR is acceptable. The F700 type truck will require a 9,000 lb. front axle on a 24,500 or 26,500 or 28,200 GVWR because of the
heavier base truck weight.
e. 1,000 gallons
8' wide X 15' long
28,000
31,000
Comments: 9,000 lb. front axle on a 28,000 lb. GVWR truck may be overloaded in some cases. When
equipped with a foam unit and diesel engine, a 12,000 lb. front axle may be required.
NOTE: Forests that install custom manufactured tanks or non-standard capacity tanks on trucks
will require special attention in matching the tank to the vehicle. Proper truck component
R-1 Supplement 7109.19-91-1
Effective 09/12/91
7109.19,31-34
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specifying will ensure that front axles and total vehicle GVWR ratings are within manufacturers
specifications.
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Effective 09/12/91
7109.19,31-34
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31.3 - Trailer Towing Requirements. Towing a trailer is not a simple matter. The gross trailer
weight, the trailer brakes, the coupling, the hitch, the gross vehicle weight, the differential, the
transmission, the engine, the cooling, and the driver must all be compatible. If any one of the
above fails to perform, a tragedy can result.
For tongue type, tag-a-long trailers, gross trailer weight (GTW) is not to exceed 75 percent of the
towing vehicle gross vehicle weight rating (GVWR). In no case shall the actual loaded weights
exceed gross axle weight ratings (GAWR).
If there are any indicators that the weight of the trailer is causing the truck to slide downhill in
mountain use, more weight is needed in the truck or a bigger truck is needed. In these cases,
trailer weight (GTW) is not to exceed 75 percent of the actual truck weight.
For fifth-wheel or gooseneck type trailers the guide to use is the manufacturer's published
GCWR ratings. These ratings reflect a combination of proper truck components including
engine size, transmission, rear axle ratio, frame, and suspension.
In general, it is possible to pull a heavier fifth-wheel trailer than a tag-a-long type trailer because
more weight is put on the towing unit. However, in no case shall the gross combined weight
rating (GCWR) exceed published manufacturers GCWR nor shall any individual axle exceed the
specific gross axle weight rating (GAWR) stamped on the manufacturer's plate.
It may be necessary to actually weigh specific truck trailer combinations to determine if the
proper configuration is being used.
The following are definitions of terms used in trailer towing:
1. Definitions
a. GTW - Gross Trailer Weight: Actual scale weight reading of a loaded trailer.
b. GTWR - Gross Trailer Weight Rating: The maximum loaded weight at which the
trailer is designed to operate. The GTW shall never exceed the GTWR. When operating over
rough roads, the Cargo Load (CL) shall be decreased in accordance with the formula in 31.05, 7
(reduce payload by 10 percent).
c. GCW - Gross Combination Weight: Total weight of a fully equipped truck and trailer
with cargo, driver and passengers, fuel, water, and equipment.
d. Hitch: The connection that is rigidly mounted to the towing vehicle. The hitch should be
permanently stamped with the towing capacity. The hitch may be a ball type, pintle-hook type,
or fifth-wheel plate or pin type. Homemade hitches are not recommended unless fabrication is
made by a qualified welding shop or truck body shop.
R-1 Supplement 7109.19-91-1
Effective 09/12/91
7109.19,31-34
Page 5 of 13
e. Coupling: The connection that is rigidly mounted to the tongue or gooseneck of the
trailer. The coupling device should be permanently stamped with the towing capacity. Coupling
devices may be ball socket, pintle-eye, or kingpin type.
f. Load Equalizing Hitch: A special linkage that transfers trailer tongue load from the
tongue to a point on the towing vehicle frame that is midway between the front and rear axles.
With the trailer tongue load centered between the axles, front and rear wheels share the load
equally.
g. Static Tongue Load: Weight of trailer as measured at the trailer coupling, which is the
point attached to the towing vehicle. The figure normally used is approximately 10 to 15 percent
of the GTWR, which provides for effects of braking forces. However, the tongue load shall
never exceed the tongue load rating of the coupling. Lateral sway (fishtailing) is caused by
tongue weight which is too low and truck oversteer (railroading) is caused by tongue weight
which is too high.
h. Kingpin Weight: The amount of trailer and cargo weight imposed at the kingpin of a
fifth-wheel type trailer.
i. Fifth-Wheel: This is the type hitch used for "gooseneck" trailers.
The fifth-wheel is mounted directly to the frame of the towing vehicle and incorporates a locking
mechanism to secure the kingpin located on the gooseneck of the trailer. Placement of the fifth
wheel is critical. Since as much as 50 percent of the trailer cargo may bear on the fifth wheel, it
must be placed the correct distance ahead of the rear axle centerline so that neither the front or
rear axles is loaded in excess of its rating.
j. Trailer Classification
Class 1 - All types of tagalong trailers up to 2,000 lbs. GTWR. Minimum ball and
coupling 1-7/8 inches diameter with 5/8-inch shank. Maximum tongue load is 200 lbs.
Class 2 - All types of tag-a-long trailers over 2,000 lbs. GTWR to a maximum 4,000 lbs.
GTWR. Minimum ball and coupling 2 inches diameter with 3/4-inch shank. Maximum tongue
load is 400 lbs. A frame mounted hitch or under bumper receiver shall be used.
Class 3 - All types of tag-a-long trailers over 4,000 lbs. GTWR to a maximum 6,000 lbs.
GTWR. Minimum ball and coupling 2 inches diameter with 1-inch shank. Maximum tongue
load is 600 lbs. A sway control attachment is recommended. An under bumper receiver shall be
used.
Class 4 - All types of tag-a-long trailers over 6,000 lbs. GTWR to a maximum of 10,000
lbs. GTWR. Ball and shank shall have a minimum breaking strength of the coupling and hitch.
Maximum tongue load is 1,000 lbs. A sway control attachment is recommended. A load
equalizing hitch (under bumper receiver with ball mount and spring bar assembly) shall be used.
R-1 Supplement 7109.19-91-1
Effective 09/12/91
7109.19,31-34
Page 6 of 13
Large trailers such as those for equipment hauling pulled behind a dump truck are acceptable
when the respective hitches (normally pintle hitch components) are rated for the loads pulled and
the truck has a custom made heavy duty frame hitch. Tongue weight on equipment trailers shall
not exceed 20 percent of the weight of the load and trailer.
Fifth-Wheel Type Trailers: Often called gooseneck type -- are now manufactured in a variety of
types; e.g., horse hauling and camp trailers. The capacity of such trailers is limited by the
capacity of the towing vehicle.
2. Requirements
a. Electric brakes are required on all trailers from 1,500 lbs. GTW through 12,000 lbs.
GTW.
(1) Controls shall be the electronic type. In the past, both hydraulic over electric or
electronic type were acceptable. Hydraulic over electric requires tapping into the hydraulic
brake system and is no longer acceptable with the antilock brakes on new trucks. Electronic
types do not require tapping into the hydraulic brake system.
(2) All electric trailer brakes (trailers over 1,500 lbs.) require a breakaway feature to apply
the trailer brakes in event the trailer coupling fails. Trailers equipped with electric brakes must
have a wet cell battery to power the brakes when the breakaway feature is actuated.
b. Airbrakes are required on all trailers over 12,000 lbs. GTW. Towing vehicles must be
only those equipped with airbrakes. Electric brakes or electric over hydraulic brakes will be
allowed on some special fifth wheel trailers over 12,000 GTW where up to 50 percent of the
weight goes to the towing vehicle.
c. Two safety chains are required on all trailers except fifth-wheel type. Safety chains will
be crossed under the tongue and fastened to the towing vehicle in such a way as to prevent the
tongue from dropping if either the hitch or coupling should fail. These chains shall have no more
slack than is necessary to permit proper turning. Aggregate breaking strength of the chains shall
be minimum 1 1/2 times the weight of the trailer and load.
d. Mirrors: Towing vehicles shall be equipped with a mirror on each side with a minimum
of 19.5 square inches each for vehicles under 10,000 GVWR and 50 square inches each for
vehicles 10,000 GVWR and bigger. They shall be adjusted so each side of the trailer is visible to
the driver.
e. Tires on towing vehicles should be kept inflated to standard inflation pressures given in
the Owner's Manual. Note: Refer to the vehicle identification and rating plate affixed to left
door pillar of most trucks. The gross vehicle weight must include the trailer tongue weight as
part of the cargo load.
f. Break-in Schedule: In addition to break-in instructions given in Owner's Manual, it is
recommended that new vehicles be operated 500 miles before towing a trailer.
R-1 Supplement 7109.19-91-1
Effective 09/12/91
7109.19,31-34
Page 7 of 13
g. Vehicle Maintenance: When FS vehicles are used only intermittently for towing trailer,
preventive maintenance will follow standard practice. If an automatic transmission equipped
vehicle is used, change the transmission fluid each 5,000 miles of heavy, continuous trailering
when the transmission lacks an external oil cooler -- 15,000 miles with an external cooler.
Manual transmission and rear axle lubricants shall be changed each 15,000 miles of continuous
trailer towing. Likewise, engine oil shall be changed each 90 days or 2,000 miles.
h. Trailer sway should not exceed 3 inches to either side of the path of the towing vehicle.
Some of the causes of sway are improper loading, tire pressure, speed, improper or worn
coupling and tongue.
i. Trailer wiring. The many different wiring systems now in use on trailers and towing
vehicles lack uniformity. As a consequence, there are instances when the wiring on a particular
towing vehicle is compatible with only one trailer. Thus the wiring has to be rearranged when
another towing vehicle must be used.
In order to standardize trailer electrical wiring, the following representative sources, and circuits
can be utilized.
(1) For large trucks, class 360 and above use only a seven conductor jacketed cable (SAE
J1067) for all jumper cables. This cable consists of No. 8, and No. 10, and five No. 12 copper
conductors. Representative sources:
Manufacturer
Belden
Whitaker
Part Number
735652
999W
(2) Jumper cables are not normally used for light trucks and medium trucks up to class
360. As an option, use a seven conductor jacket cable (SAE J559) for jumper cables. This cable
consists of one No. 10, and six No. 12 copper conductors. Representative sources:
Manufacturer
Belden
Standard
Part Number
735650
CJ12-7L
(3) Use seven conductor electrical sockets and plugs in accordance with SAE J560b.
Recommended installation includes a plug on the trailer and a socket on the truck.
Representative Sources:
Plug: Manufacturer
Part Number
R-1 Supplement 7109.19-91-1
Effective 09/12/91
Echlin
Standard
7109.19,31-34
Page 8 of 13
TC6215 or TC6250
TCP77M
Socket: Manufacturer
Echlin
Standard
Part Number
TC6200
TCP77F
Note: When the government contracts short-term use of a commercial trailer, that is an RV or
office trailer, the contractor could be required to furnish an adapter such as Echlin Part No.
TC6555 or equivalent to adapt the trailer's six-conductor jumper cable to the Forest Service
seven-conductor socket.
(4) Representative sources for brake controllers and related parts:
Manufacturer
Part Number
Description
United Parts
89175
Electronic controller
(Trucks 1988 and newer)
Kelsey Hayes
89175
Electronic Controller
(Trucks 1988 and newer)
United Parts
89183
Pulse Preventer (so brakes don't
apply when 4-ways are on with
electronic controller)
Use A 30 amp. in line circuit breaker for charging circuit
Kelsey Hayes
81740B
Hydraulic over electric
controller (Trucks 1987 and
older)
United Parts
89100
Hydraulic over electric
controller (Trucks 1987 and
older)
(5) Representative sources for the breakaway feature.
Kelsey Hayes
801
Breakaway Switch
Bargman
50-85-003
Breakaway Switch
United Parts
89102
Breakaway Switch
R-1 Supplement 7109.19-91-1
Effective 09/12/91
7109.19,31-34
Page 9 of 13
Note: 12-volt storage batteries are required as part of the breakaway feature on all trailers
equipped with electric brakes. So called "dry-type" batteries are not to be used. The trailer
storage battery must be given the same care as vehicle batteries (refer to FSH 7109.18, DriverOperated Handbook, page 14.23). Always check battery for proper charge before moving trailer.
R-1 Supplement 7109.19-91-1
Effective 09/12/91
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Page 10 of 13
(6) Socket wiring on towing vehicles and trailers may be color coded, but is not required.
However, the following minimum wire sizes are required:
No. 12 wire for all ground circuits.
No. 12 wire for all electric brake circuits.
No. 14 wire for all battery charging circuits.
No. 16 wire minimum for lighting circuits.
It is essential that wiring be done by personnel who understand the circuitry involved. They
must have proper equipment and tools to make durable and resistance free connections and
splices. All wiring must be routed and secured to prevent snagging and movement. All costs for
wiring either the trailer or towing vehicle shall be borne by program funds.
The following exhibits, 31.3 - Exhibit 01, 02, 03 describe the various circuits and their positions
in the plug and socket.
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Effective 09/12/91
7109.19,31-34
Page 11 of 13
31.3 - EXHIBIT 01
WIRING CIRCUITS - TRAILER WITH AIR BRAKE
Conductor Wire
ID
Wire
Color
No.
WHT
White
12
Ground return to towing vehicle.
BLK
Black
16
Clearance, side marker, and identification
lamps only when such circuits are controlled
by separate switch on towing vehicle.
YEL
Yellow
16
Left turn and hazard signals only when
trailer is equipped with separate turn signal
lamps. On trailers equipped with
combination stop and tail lights, this circuit
would be "Left stop and turn signal."
RED
Red
16
Stop light and anti-wheel lock device. On
trailers equipped with combination stop and
tail lights, use "yellow" above. Use red for
anti-wheel lock device if trailer is so
equipped.
GRN
Green
16
Right-hand turn and hazard signals only
when trailer is equipped with separate turn
signal lamps. On trailers equipped with
combination tail and stop lights, this circuit
would be "Right stop and turn signal."
BRN
Brown
16
Tail and license plate lights. When towing
vehicle does not have a separate switch for
their control, add clearance and marker
lights to this circuit and do not use "black"
above.
BLU
Blue
14
Auxiliary. Normally not used on air-brake
equipped trailers.
Circuit
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Effective 09/12/91
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Page 12 of 13
31.3 - EXHIBIT 02
WIRING CIRCUITS - TRAILER WITH ELECTRIC BRAKE
Conductor Wire
ID
Wire
Color
No.
WHT
White
12
Ground return to towing vehicle.
BLK
Black
16
Backup lights, when trailer so equipped.
YEL
Yellow
16
Left stop and turn signal.
RED
Red
12
Electric brakes.
GRN
Green
16
Right stop and turn signal.
BRN
Brown
16
Tail, license, and clearance lights.
BLU
Blue
14
Charging circuit for breakaway battery.
Connect to battery side of starter solenoid of
towing vehicle.
Circuit
R-1 Supplement 7109.19-91-1
Effective 09/12/91
7109.19,31-34
Page 13 of 13
31.3 - EXHIBIT 03
SEE THE PAPER COPY OF THE MASTER SET
FOR SECTION 31.3 - EXHIBIT 03.