Explanation

Explanation

TowCarCalculations has developed several on-line
programs which can predict and compare the pulling performances of your car
hooked-up to your caravan. The programs are able to compute the top speeds on
flat roads and on gradients. Hill starts are part of the information too. Even
acceleration figures are predicted as well as the proper use of the highest
gear. Also the effect of wind on your outfit is calculated. And no, we don’t
forget the changing weight ratios between van and car either.Have a look at the possibilities in the menu later on, but we advise you
to read on first…
Windtunnel

Star Rating System – Whattowcar Assessment Score©

Towing capability is summarized by a five star ranking, highlighted in three
colors. The color depends on the caravan/towing vehicle weight ratio for safety
reasons. All green stars indicate a perfect match between caravan and car but if
you see red stars then the caravan is too heavy for safe towing, either when the
going gets tough or it’s simply not allowed by law. Towing with an outfit with
orange stars should be legally OK, but you have to pay special attention to the
distribution of weight, noseweigt and tyre pressures. But you do that anyway,
don’t you?

The weight ratio (thus the color of the stars and the specific text in the
comments) is based on a mix of European ‘standards’. The match percentage in the
verdict is based on the UK standard Towing Code (loaded caravan / car
kerbweight). But beware of possible differences between UK-kerbweight (incl.
fluids) / EC-kerbweight (incl. driver) / Dutch-tax-kerbweight (incl. nothing).
Our database inconsequently contains the latter two. So please check these
weights before making decisions. When stars persist in the red, it might be the
case that towing with this specific car is not allowed at all. We know of some
Aston Martins… ;-)

The number of stars indicate the general towing capability and performance of
your car hooked-up with the selected caravan. The more stars the better of
course.

Safety and stability index


Based on the weight ratio, towball weight and the dimensions of the caravan
we calculate the stability index. It gives an indication of the safety reserve
of the outfit.

Speed index and maximum gradient

The speed index is to be used as an indication to make a quick
comparison easy between different cars or outfits. The figure represents the
average of the following top speeds:
- Absolute (often in a lower
gear)
- In top gear
- During (head) wind
- On motorway
slopes
Based on 85% of maximum throttle (power) and avoiding excessive high
revs.The gradient is the computed maximum you will just be able to get away on
1500 m above sea level. (If you get enough
traction)

Above that we provide six different ratings in special areas. Three of them
on flat roads and three for performance in mountainous regions.

Performance on leveled roads Top speed

Acceleration and take over

Towing ability
Performance in mountainous
regions
Drive off uphill

Driving on motorway slopes

Driving on steep
roads

Compute your outfit on-line

In just a few clicks you can obtain an on-line computation of your favorite
outfit. Just select your car and caravan from the lists. If your caravan is not
listed, select ‘A standard caravan’. In the next screen never mind the choice
you have in selecting caravan model. Airflow (look at the pics here to compare)
must be selected in the next screen where you fill in the metric
dimensions of your caravan as well. One foot is 0.305 metres and one inch is
2.54 cm. We do provide speeds in mph though… An important parameter is the
drag or wind flow (Cw) of your caravan, see the images below and identify your
type. For the payload of your car you must notice that the kerbweight does not
include passengers, towbar and accessories.

Very good

Average
(most modern
caravans)
Poor

Rounded edges not only on the lower part but also at roof level means very
good airflow. The roof front itself is flattened.
Average drag example. Rather big rounded edges, but mainly on the lower half
of the front.
Poor airflow is achieved because of the small radius of the edges and the
high roof level.

Interpretation of the presented data

Perhaps the most valuable computations are when you compare them to others.
Enter your current towcar and compare it with one in those brochures scattered
around on your desk…

On screen the difference between 70 or 80 mph seems not that relevant – but
the towcar that manages this top speed of 80 mph in fifth will easily maintain
60 mph (96 km/h) even with a bit of headwind or on a slight incline. Besides the
figures the program presents a plain text verdict. Even if we predict the
combination on certain aspects as (rather) poor, you can certainly still enjoy
driving the selected outfit. It then depends on your personal requirements.

Are the results accurate?

The exactness of the calculations is very high, but only if your input was
correct. Extensive roadtests are performed to check these outcomes. But
differences between your practical experiences and our predictions can occur.
There are not that much studies done of car/caravan combinations in windtunnels.
If you encounter substantial differences, please feel free to contact us. Weird predictions due to
mistakes in the database we would also like hear about.

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