Subaru 2003 Legacy - Manual (Page 330)

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the illustration below. When weighing the tongue load, be sure to posi-
tion the towing coupler at the height at which it would be during
actual towing, using a jack as shown.
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Tongue load
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The tongue load can be adjusted by proper distribution of the load in
the trailer. Never load the trailer with more weight in the back than in
the front; approximately 60 percent of the trailer load should be in the
front and approximately 40 percent in the rear. Also, distribute the
load as evenly as possible on both the left and right sides.
Be sure that all cargo is firmly secured to prevent a change in weight
distribution while driving.
OM-H2787