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...

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

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.