ADDING SUB-FRAMES
On vehicles with heavy additional equipment or which will be carrying
heavy loads, a sub-frame should be added to avoid applying concen
-
trated mass to the frame.
See SECTION MODULUS in SIDE RAIL DATA (pages B16, B17,B18
and B19) regarding tests for frame strength when a sub-frame is added.
1. PRECAUTIONS WHEN INSTALLING SUB-FRAME
1) ALLOWABLE STRESS
The following table shows the maximum allowable stress for Gross Vehi-
cle Mass of 385.83 in/s
2
(9.8 m/s
2
, 1G).
a Driven mainly on good quality roads
Allowable Stress 8.532 psi {59MPa, 6.0 kgf/mm
2
} or less
b Driven mainly on poor quality roads
Allowable Stress 5.688 psi {39 MPa, 4.0 kgf/mm
2
} or less
2) DETERMINING THE SUB-FRAME SHAPE
a The front of the sub-frame should be recessed to avoid concentrated
stress.
• Wooden sub-frame
• Bracket-shaped steel sub-frame
b The front end of the sub-frame should be placed as close as possible
to the rear of the cab. Be careful not to apply concentrated stress to
the frame directly behind the rear of the cab.
c When there is reinforcement material inside the side rail, make the lap
with the sub-frame as great as possible.
C13
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