If you read caravan magazines or look for tow car advice online you will see a lot about the “85% rule” for the caravan and car weight ratio.
According to this rule the caravan’s MTPLM ( Maximum Technically Permissible Laden Mass) should not exceed 85% of the car’s kerbweight.
This “rule” was invented by the caravanning fraternity before the 1997 licence restrictions, when the weight of the entire outfit was irrelevant as you could tow up to a combined (car + caravan) weight of 8250kg.
It should be made clear that the “rule” is not in fact a rule with any legal standing, it is a recommendation, and a bizarre one at that!
The idea is to increase safety by eliminating any “tail wagging the dog” pendulum effect of towing a heavy caravan with a light car. To that end they have completely ignored the practicalities of a family caravan holiday and assumed the worst ie. that the car will be towing with only a driver and zero luggage, and at the same time the caravan will be fully laden.
In reality the car would be laden with people and their luggage (ideally up to it’s GVW) and the caravan will be as unladen as possible with only the larger items inside that can’t fit in the car.
In this way the car will weigh 5-600kg more than the kerbweight and the caravan will weight less than it’s MTPLM (maximum loaded weight) and your ratio of caravan to car weight will be nowhere near 85%.
As an example, let’s take a car with a towing award from last year, the Skoda Octavia Estate 2.0 TDi SE L DSG
it has a kerbweight of 1374kg (kerbweight is unladen weight plus driver of 75kg)
with the 85% rule it can tow a caravan weighing 1167kg – even the lightest 4 berth is 1245kg –
but it’s GVW (laden weight) is 1944kg and it’s actual towing limit is 1800kg.
To fit under the 3500kg limit you can tow a caravan with an MTPLM of 1556kg, which is a reasonable figure for a family caravan.
Now with the car laden at 1944kg and even if the caravan is fully laden to 1556kg, you have a ratio of *80%.
If you had stuck to the Caravanning fraternity “rule” you would have a ratio of **60%, which makes the 85% rule a nonsense.
*80% maths – GVW (car) 1944kg MTPLM (caravan) 1556kg = 80%
**60% maths – GVW (car) 1944kg MTPLM (caravan) 1167kg = 60%
An average family sized caravan weighs approximately 1500kg MTPLM. To be able to tow this at the 85% rule you would need a tow car with an unladen weight of 1765kg (like a Mercedes E-class Estate) but then the GVW of a car this size will be around 700kg more, giving you a GVW of approx. 2500kg. This in turn limits the size of what you can tow to 1000kg.
Funnily enough Practical Caravan TV tested a Mercedes E class Estate on the show today and was it towing a 1500kg caravan, to stay with the 85% figure? No, it was towing a large twin-axle number from Swift, whilst they quoted the Mass in Running Order for the caravan, not the MTPLM.
You will hear a lot of noise about towing a caravan that weighs more than 100% of the kerbweight of your car being illegal. This is not true. It was written into law in but removed in 2013.
My view is that if it’s safe to tow a caravan ( as decided by the caravanning fraternity!) at 85% of the kerbweight, with no proviso that you can’t tow with an unladen car, then it’s safe to tow with 80% when the car is laden.
I will say and I hope this is making sense, that you should not tow a caravan that is fully laden, with a car that only has a driver and no luggage if you are going over the 85% rule…