Understanding towing capacity
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 most buyers are not aware of weight concerns
until it is too late. I’m hoping this article helps explain the terminology and
technical details of safe towing in an easy to understand guide.
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 for each
different vehicle 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:
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 aftermarket 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. For example:
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.
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.
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.
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 minivan, 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 article only covered towing basics! My advice is to
also check additional weight factors and considerations such as Gross Axle
Weight Ratings (GAWR), tires, tire inflation, proper hitch work, and trailer
brakes. 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
and Safe Travels!
Helpful Links: