Advice Mazda CX5 Tow Car with a Sterling Eccles

[Raywood]

Hi AnastieByte
The thing to remember is that the kerb weight is, to all intents and purposes the weight your car would be when completely empty apart from the driver. As you have established yourself, this is unrealistic in real life although you won't really know accurately the amount of extra weight inside the car at any given time.

Conversely, the MTPLM of your caravan is its maximum permissible weight. In reality it won't always weigh this much, but again, short of weighing it each time you take it out, you won't be able to establish precisely how much less.

In my humble opinion, it's therefore sensible to limit the MTPLM of the caravan to less than the kerb weight of the towing vehicle. But how much less? As far as I can tell, the ratio of 85% was selected arbitrarily some decades ago, before car manufacturers specified their own maximum towing limits. It remains as a recommendation simply because nobody has done enough testing with caravans (as opposed to other types of trailer) to come up with anything better.

The two main caravan clubs also recommend that 'experienced' towers can tow a caravan weighing up to 100% of the car's kerb weight. Define 'experienced'? I don't think anyone else has. It's all subjective.

I think you're being very sensible in the way you're approaching this. Doing the towing course can only be a good thing. My suggestion after that is to go for a few weekends away, when you won't need to load the caravan to its capacity, and get used to how it handles. Don't assume that less weight will automatically equal greater stability - in our experience our caravan is more stable on the road if it has some weight in it than it is unladen. Once you've gained a bit more confidence with your own combination, you can safely load it more heavily for longer trips.

Good luck and enjoy

The 85% figure was the result of work carried out b y Bath University for the CC. It was a very long time ago and modern cars and caravans have moved on since then, if done again a higher figure might be produced.
Personally as someone who investigated accidents I find the idea of 100% a bit too high for absolute safety. One problem though is different combinations that look similar on paper are often very different when on the road so a hard and fast rule is not possible.

 

[ProfJohnL]

Hi AnastieByte
The thing to remember is that the kerb weight is, to all intents and purposes the weight your car would be when completely empty apart from the driver. As you have established yourself, this is unrealistic in real life although you won't really know accurately the amount of extra weight inside the car at any given time.

Conversely, the MTPLM of your caravan is its maximum permissible weight. In reality it won't always weigh this much, but again, short of weighing it each time you take it out, you won't be able to establish precisely how much less.

In my humble opinion, it's therefore sensible to limit the MTPLM of the caravan to less than the kerb weight of the towing vehicle. But how much less? As far as I can tell, the ratio of 85% was selected arbitrarily some decades ago, before car manufacturers specified their own maximum towing limits. It remains as a recommendation simply because nobody has done enough testing with caravans (as opposed to other types of trailer) to come up with anything better.

The two main caravan clubs also recommend that 'experienced' towers can tow a caravan weighing up to 100% of the car's kerb weight. Define 'experienced'? I don't think anyone else has. It's all subjective.

I think you're being very sensible in the way you're approaching this. Doing the towing course can only be a good thing. My suggestion after that is to go for a few weekends away, when you won't need to load the caravan to its capacity, and get used to how it handles. Don't assume that less weight will automatically equal greater stability - in our experience our caravan is more stable on the road if it has some weight in it than it is unladen. Once you've gained a bit more confidence with your own combination, you can safely load it more heavily for longer trips.

Good luck and enjoy

The 85% figure was the result of work carried out b y Bath University for the CC. It was a very long time ago and modern cars and caravans have moved on since then, if done again a higher figure might be produced.
Personally as someone who investigated accidents I find the idea of 100% a bit too high for absolute safety. One problem though is different combinations that look similar on paper are often very different when on the road so a hard and fast rule is not possible.

As far as I have been able to ascertain, the University of Bath have done no research into establishing the towing ratio. They did do some selective research into the effects of caravan loading, and that was carried out at 85% ratio but it was not to verify the efficaciousness of the selected ratio. The report only looked at one caravan and car combination so could not be used to establish a general case.

It is my own opinion that 85% may actually be too high, as there are numerous incidents of instability, whether they end in disaster or not.

 

[Raywood]

From my experience of accidents, and because these are rare the numbers are low, all the cases of instability I have come across involved cars where the ratio was very high. It is not enough to say there are none with lower ratios, but it is clear that the higher the ratio the higher the risk, although it might be said that drivers who ignore the ratio advice are more reckless by nature.