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have received several e-mails lately asking which is the
best tow vehicle. This is a very difficult question to answer
because there are so many factors that go into the make
up of a tow vehicle. Often the e-mails I receive are isolating
one factor and treating it as though it is the only factor
of importance in tow vehicle selection. It got me to thinking
that while we have examined most of these factors in detail
at one time or another, I have never really written out
a complete list. The following is a summarized list of specifications
to look at when assessing a tow vehicle, with some of my
personal thoughts in each category.
Wheel Base
A longer wheelbase is better for towing, but there is a
trade off in manoeuvrability. It also takes a stronger equalizing
hitch to transfer weight to the front wheels of a longer
wheelbase tow vehicle. When towing a fifth wheel, wheelbase
is a very small factor, and a short box truck handles virtually
identical to a long box model. The short box has less chassis
flex so it will ride slightly better than a long box.
Rear Overhang Ball to Axle
A shorter overhang is better, but which is really better
- a short overhang and a short wheelbase, or a long wheelbase
with a long overhang?
We look at the overhang as a percentage of the wheelbase.
For example, a 116" wheelbase and 40" overhang comes out
to a 35% overhang ratio. A 130" wheelbase with a 50" overhang
comes out to a 38% overhang ratio - in this case not as
good as the shorter wheelbase. Of coarse, an even better
combination would be a 130" wheelbase with a 40" overhang,
which would come out to 31% overhang.
Rim Diameter
Larger diameter wheels allow you to have a lower profile
tire, and still have the same tire load capacity.
For example, a 215/65R x 15" tire has the same load capacity
as a 215/60 x 16" tire, but the sidewall is 11mm shorter,
and generally, shorter sidewalls have less sway.
Rim Width
The width of the tire is the three-digit number in millimetres.
In the case below, 225mm or 8.8" wide. The ideal situation
is to have a rim that is almost as wide as the tire, in
this case an 8" rim width would be ideal. Today, many SUV's
and pickups come with tires 10 or 11 inches wide on 7" wide
wheels, so we can dramatically improve the handling by simply
installing wider rims, or (more often) narrower tires. (Page
Top)
Tire Width & Profile
For example: 225/60R x 16". We want the tire to be as close
to the same width as the wheel rim as possible.
The profile is the height of the tire sidewall as a percentage
of its width. In this case 225 x.60 = 135 Millimetres. Generally,
a tire with a shorter sidewall has less side sway and more
precise handling, but also less load capacity. For example,
a 225/60 x 16" works very well on a Mini Van, but won't
carry a Suburban or full size Pick-up.
Tire Type; Light Truck, Performance Or Passenger
(Performance tires usually carry 44 PSI)
Performance tires are best, but usually have less traction
in snow and a shorter tread life. Light truck tires do not
have as much traction or as precise handling as performance
tires, but offer excellent tread life. We often find that
light truck tires have to be used for their load carrying
capacity. Passenger tires are usually the least effective.
Rear Suspension Type. Independent, Live Axle OR Mono
Beam
Independent suspension is a substantial advantage for a
tow vehicle because it projects the suspension stance out
to the width of the track. It also has a fraction of the
un-sprung weight. A live axle is least desirable.
Suspension Type - Front. Independent, Twin I Beam Or
Live Axle
Again, a full independent suspension is superior. Twin I
beam is better than a live axle.
Live Axle, Distance Between Springs - Front
Sometimes called suspension stance. In most cases, the wider
the better. This is not a factor on vehicles with independent
suspension since the suspension stance is the same as the
tire track.
Live Axle, Distance Between Springs - Rear
Same as above.
Spring Stiffness
Firm springs are better than soft ones, but not to the point
that they are so stiff that they will not work in concert
with the equalizing hitch. A slightly stiff but supple suspension
is best. If the vehicle sits low at the back when you connect
a travel trailer, then the problem is usually in the equalizing
hitch. It is OK for a truck towing a fifth wheel to sit
a bit low at the back, as long as the suspension still has
reasonable travel.
Shock Stiffness
Generally, you cannot have too much shock control. It is
far better to have soft springs and stiff shocks than the
other way around.
Curb Weight
A heavy tow vehicle has a slight advantage especially if
it has a low centre of gravity. You are better off with
a light, low profile tow vehicle with independent suspension
etc., than a heavy, tall one.
Height
There is a slight economy and handling advantage to a lower
tow vehicle. (Page Top)
Inches, ground / bottom of rocker panels. Middle of car
What we really want is a lower centre of gravity. For example,
an SUV and a Mini Van are about the same overall height,
but the SUV carries its weight much higher and pays a price
in handling.
Steering System, Rack & Pinion or Steering Box
Rack and pinion steering has much better steering feel,
and gives you more precise handling.
Power Curve Charts for Engine
These are graphs that show the horsepower and torque produced
by an engine, ranging from idle to its RPM red-line. If
you can find them they will give you a better reference
for determining gear ratios.
An engine that produces its torque over a broad RPM range
is great for towing. This is why engines that have four
valves per cylinder usually perform much better than two
valve engines.
Some engines are now available with variable valve timing,
which further widens the power band.
Horsepower
Generally, more is better.
Torque
Again, more is better, but look for it over a large RPM
range.
Final Drive or Rear Axle Ratio
The best axle ratio depends on many factors. Generally,
a numerically higher ratio is better - but not always. Some
of the factors are the tire size and the RPM that the engine
produces power at. For example, you need a numerically lower
ratio in a Cummins diesel that produces its power at 1600
RPM, than you do in a 24 Valve V/6 that needs to run at
2600 RPM. Though axle ratios are often tied to weight ratings,
they are really more determined by aerodynamic drag.
First Gear Ratio
There are advantages both ways - a numerically higher first
gear ratio will give you more kick of the line, but it will
climb steep low gear hills at a lower speed.
With numerically higher first gear ratios, there is likely
to be flat spot between first and second gear, unless,,
of coarse, you have a 5 speed transmission - then you can
likely have your cake and eat it too. (Page
Top)
# of Transmission Gears
More is better, especially with a diesel engine that has
a narrower power band.
# Valves per Cylinder
Multi-valve engines tend give you the broadest power range.
They let you have low-end torque and high rpm horsepower
out of the same engine.
Drive Train - Front, Rear, or 4WD
Front or rear drive does not really matter in the selection
of a tow vehicle, although front wheel drive has a slight
traction advantage, and more efficient power delivery. Four-wheel
drive has great traction, but usually some power and economy
losses compared to either front or rear wheel drive systems.
Supercharging or Turbo Charging
Can be great for short bursts of power, but you don't want
to rely on constant boost for towing.
Tow Vehicle Drag
This is not something you can look up anywhere. The drivetrain
has to tow the trailer, and it has to push the tow vehicle
as well. For example, a 3.8 Litre V/6 in a mini van gives
excellent performance with an aerodynamic trailer, but if
we took that same engine and installed it in a 4x4 1 ton
dually, it would be doing all it could to move the tow vehicle.
Rear Gross Axle Weight Rating (GAWR)
This is the load capacity of the rear axle of the tow vehicle.
Usually, it is not a big concern for towing a travel trailer
with an equalizing hitch that is properly set up. It is
important with fifth wheels, where all the pin weight is
carried on the back axle. To determine the amount of pin
weight your truck can carry, weigh the back axle, and subtract
the total from the rear GAWR. Remember to allow for loading
of the fifth wheel and truck.
The Bottom Line...
When you look for a vehicle that satisfies as many of these
criteria as possible, you come up with something like a
Corvette. Ah - but you don't want to tow with a CorvetteÉ
after all, where would you put the kids and the bikes? Now
that you know you are going to compromise, look for the
vehicle that suits your lifestyle the best, while giving
you the maximum towing prowess. (Page
Top)
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