Matching
a Tow Vehicle & Trailer 101 (As seen on RVTV) by: Mark J. Polk
What is all this confusing talk about
weights? The weight issue is probably the most critical and least understood
issue you will confront when purchasing a towable RV. It is
critical because a mismatched tow vehicle and trailer can put you and your
loved ones safety in jeopardy. It can also result in expensive repair bills
for damage and premature wear to major components on your tow vehicle. It is
the least understood issue because the buyer is not educated on weight
concerns until it is too late.
Trying to cover everything
involved on this subject in a short article is like trying to find the
needle in a haystack. For a more in depth look at these topics check out our
newest video production
“Trailer Towing, Weights Hitch Work & Backing”
Let's start with the tow
vehicle. The vehicle manufacturer determines tow vehicle ratings. Extensive
testing is done and many factors are considered such as; engine size,
transmission, axle ratio, chassis, suspension, brakes, tires, cooling
system, and tow packages. Any time a vehicle or trailer is given a rating it
is based on the weakest link in the chain. For example, the axle on a
trailer may be capable of supporting 5,000 pounds, but if the tires on the
axle can only support 3,000 pounds the axle is rated for 3,000 pounds. This
is why it is crucial that you never exceed a manufacturers rating.
You can take five ½ ton
trucks with the same engine, and tow ratings can vary by 4,000 pounds. One
of the major factors affecting tow ratings is the rear axle ratio. Very
basically, the axle ratio is a comparison of how many times the drive shaft
rotates versus the wheels. If you have a 3.73:1 axle ratio it means the
drive shaft rotates 3.73 times for each rotation of the wheels. The higher
the numeric value of the rear axle the better it tows, but you compromise
gas mileage. The key to selecting the tow vehicle is to figure out what your
requirements are and to know exactly how it is equipped so you can determine
the correct tow rating. Tow ratings are extremely important, but there are
other weight issues concerning the tow vehicle that are often overlooked.
There's a very simple
formula we can use to determine how much we can safely tow, but first there
are a couple of weight ratings you need to understand:
Gross Vehicle
Weight Rating (GVWR): is the maximum
permissible weight of the vehicle or trailer when fully loaded for travel.
This includes the unloaded vehicle weight, all fluids, cargo, optional
equipment and accessories. The tow vehicle and trailer each have a GVWR.
Gross
Combined Weight Rating (GCWR): is the maximum
permissible combined weight of the tow vehicle and the trailer together
when they are fully loaded for travel.
Unloaded Vehicle
Weight or Dry Weight (UVW) or (DW): is the
actual weight of the tow vehicle or trailer as built at the factory. The UVW
does not include passengers, cargo, dealer installed options, personal
belongings, water, or LP gas.
Gross Vehicle
Weight (GVW): is not a rating, it is the
actual weight of the tow vehicle when it is fully loaded including
passengers, cargo, a full fuel tank and accessories like the hitch.
Gross Trailer
Weight (GTW): is not a rating, it is the
actual weight of the fully loaded trailer including all options, cargo,
personal belongings, food, water and LP gas.
Armed with this information,
let's look at a typical buying scenario. We know for a fact that our tow
vehicle is rated to tow 8,800 pounds and it has a GCWR of 15,000 pounds.
When I account for the cargo in the truck, three additional passengers, and
after market accessories my actual tow rating is 8,040 pounds. Keep in mind
that any weight you load in or on the truck reduces the tow rating by that
amount.
|
Tow rating for the
vehicle 8,800 lbs. |
|
Cargo in the
tow vehicle - 150 lbs. |
|
Three
passengers - 450 lbs. |
|
Dealer
installed options - 160 lbs |
|
Actual tow
rating 8,040 lbs. |
Now let's look at our towing
formula: Tow Vehicle GCWR - Tow Vehicle GVW = the Maximum GVWR for a
trailer we can purchase.
The GCWR for my truck is
15,000 pounds. Now I subtract the GVW of my truck when it's fully loaded for
travel and this equals the maximum GVWR of a trailer I can consider
purchasing. The only way to determine the actual GVW of the tow vehicle is
to take the fully loaded vehicle to a set of scales and have it weighed. The
GVWR can be found on the Safety Compliance Certification label, located on
the exterior left front of the trailer.
|
Tow vehicle GCWR
15,000 lbs. |
|
Tow Vehicle
GVW - 6,832 lbs. |
|
Maximum GVWR
of Trailer = 8,168 lbs. |
So let's say we found a
trailer with a floor plan we like that has a GVWR of 8,000 lbs. The UVW or
Dry Weight of the trailer is 6,350 pounds. Keep in mind we have to add any
dealer installed options, cargo loaded in the trailer, any water we add to
the fresh water holding tank and LP gas. This gives us a gross trailer
weight of 7,075 pounds. Ask the RV dealer to show you the weight label that
is inside the trailer for accurate trailer weights. Unloaded Vehicle Weights
found in a manufacturer's brochure are normally for the base model of the
trailer and do not include options the dealer may have ordered on the unit.
In the majority of cases there is a significant difference between the GVWR
and the UVW of the trailer.
|
UVW or DW of trailer
6,350 lbs. |
|
Dealer
installed options + 100 lbs. |
|
Cargo in the
trailer + 300 lbs. |
|
Water 8.3 X 32
gallons + 266 lbs. |
|
LP gas 4.23 X
14 gallons + 59 lbs. |
|
Gross Trailer
Weight 7,075 lbs. |
Let's see if this will work:
Remember our GCWR is 15,000 pounds. When we subtract the weight of our
fully loaded tow vehicle and our fully loaded trailer we still
have 1,093 pounds to spare before we exceed our GCWR.
|
Tow Vehicle GCWR
15,000 lbs. |
|
Combined
Weight of (fully loaded)
Tow Vehicle &
Trailer - 13,907 lbs |
|
= 1,093 lbs. to
spare |
This method will almost
always works, unless you have the tow vehicle and the trailer loaded to
their maximum GVWR, which when added together can exceed the GCWR. This is
more likely to happen when the tow vehicle is a light duty vehicle like a
mini van, small SUV or light duty truck. In this situation you simply add
the GVWR of the tow vehicle to the GVWR of the trailer then select a tow
vehicle that is rated for the combined weight.
If your original
calculations are based on estimates you need to verify all weights by going
to a set of scales and properly weighing the vehicle and trailer. Keep in
mind this is a crash course and there are many more weight factors and
considerations we did not even touch on. Gross Axle Weight Ratings (GAWR),
tires, tire inflation, proper hitch work, trailer brakes and much more need
to be addressed. I cover a lot of this information in my “Trailer Towing,
Weights, Hitch Work & Backing” DVD. I hope this helped to clear up some of
the issues concerning matching your tow vehicle and trailer to ensure a safe
towing system.
Happy Camping,
Mark
Mark Polk is the owner of RV Education 101.
RV Education 101 is a North Carolina based company that produces
professional training videos, DVDs and e-books on how to use and maintain
your RV. Our goal is to make all of your RVing experiences safe, fun and
stress free. www.rveducation.com
