Imagine you are towing downhill. There's a strong crosswind blowing. You look in your mirrors and see the caravan starting to sway from side to side in your mirrors.
In towing circles this is called 'snaking', and it's not a pleasant experience. If the caravan doesn't come back under control it can lead to a serious accident.
The best way to deal with a snake is to prevent it from happening in the first place. The more stable your tow car (and the more sensible your driving) the less likely it is that a snake will start.
Lots of qualities contribute to a car's stability. One of the most important is how the car weighs relative to the the caravan or trailer it is towing. This is sometimes referred to as the matching ratio. The Camping and Caravanning Club recommends towing a caravan weighing no more than 85% of the car's kerbweight, especially if you are new to towing. This is sometimes called 'the 85% rule', which is a little misleading as it's not a legal requirement. But as a rule of thumb it has served caravanners well for many years.
The upshot of the 85% guideline is that, all else being equal, a heavy car will be more stable than a light one towing the same caravan or trailer. Go too far the other way, with a light car and a heavy trailer, and you risk the tail wagging the dog.
However, it would be too simplistic to state that just because a car is heavy it will be stable while towing. Many other factors come into play, including the the distance between the front and rear axle, how well controlled the ride is, and whether self-levelling suspension is fitted to keep the car level when heavily loaded.
It's hard to be sure that a particular make and model will make a stable tow car just because it drives well in everyday driving. So it's worth checking out our 2017 Tow Car of the Year Award winners.
You should also check that the car can legally tow whatever caravan or trailer you plan to match it to. To find the legal limit, take a look in the sales brochure, the handbook, or check the car's VIN plate.