|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
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
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...
Star Rating System
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 and towing is 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, tyre pressures and speed.
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.
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
||Performance in mountainous
||Drive off uphill
||Acceleration and take over
||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.
(most modern caravans)
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...
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
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.