Chevrolet Impala 2007 Impala Owner's Manual page 288

Weight of the Trailer Tongue
The tongue load (A) of any trailer is an important
weight to measure because it affects the total
or gross weight of your vehicle. The Gross Vehicle
Weight (GVW) includes the curb weight of the
vehicle, any cargo you may carry in it, and
the people who will be riding in the vehicle. And if
you tow a trailer, you must add the tongue load
to the GVW because your vehicle will be carrying
that weight, too. See Loading Your Vehicle on
page 279 for more information about your vehicle's
maximum load capacity.
288
If you're using a weight-carrying hitch or a
weight-distributing hitch, the trailer tongue (A)
should weigh 10 to 15 percent of the total
loaded trailer weight (B).