Hi Doc

Your recent correspondence re coping with snaking while towing caravans or large trailers is a good example of making simple things more complicated. I have been towing caravans for 40 years and, as vans get ever bigger, travel at higher speeds, and suffer more with buffeting and crosswinds, the standard over-run brakes fitted as standard are inadequate. That’s partly because when you brake the effect is reactionary, and the over-run exaggerates the snake rather than reduces it. The various complicated anti-snake devices offered by some chassis makers are an over-complicated and expensive response to the problem and, I am told by users and dealers, not very reliable either.

In the 1990s, a simple brake-assist anti-snake device was offered for fitting to trailer caravans called Trail-Air. It was so simple, and extremely successful, and I still have one on my Vanmaster caravan after 20 years use; but sadly it was poorly marketed and is no longer available now. It comprises of a little 12-volt compressor and control unit mounted inside the van which is powered from the brake light circuit via the 13 pin connection. When you brake, the van brakes are immediately applied via an air diaphragm on the brake linkage. The slightest snaking, and you touch the foot brake, which applies the caravan brakes instantly without slowing the outfit. For general braking i.e. slowing down, the harder you press the brake pedal the more braking effect you get on the van. Very effective, not expensive, and simple. I have only replaced the brake linings twice in 20 years and Iím amazed that someone hasnít picked it up and manufactured it. Your practical stuff is the best part of the magazine… usual disclaimers. 

Thomas Lloyd

Hello Thomas. Hmmm. As I have confessed, I am not a towing man, so I am entering an area with which I am rather unfamiliar, and I must rely on what remains of my analytical brain to understand not just what snaking caravans are all about, but also the various theories for its prevention and also for correction.

What you are now suggesting is that today’s caravan overrun braking systems and other anti-snaking (or snaking correction) devices are not as effective as the now unavailable Trail-Air system to which you refer. With respect though, all such systems are necessarily reactive, unless they can detect the pre-conditions that initiate the snaking, and prevent the instability before it happens. Trail-Air is/was a compressed air system, that operates the overrun brakes in parallel with the towing vehicle’s own braking system, and thus presumably does not operate in a simple slowing down situation, such as when you lift off the accelerator and the momentum of the caravan generates significant forward weight transfer, which would operate most overrun brakes. I think you are thus suggesting that such overrun braking systems can create instability, which is counter to what is generally accepted wisdom. 

We can’t beat this subject to death ñ and it did start with reference to the instability caused by passing vehicles, a situation which seems to have rather got left behind now. I would hardly wish to offend you Thomas, as a loyal reader, but are you really suggesting that more sophisticated systems like the AL-KO ATC system have their shortcomings, and are also not that reliable?

Are you sure that your lack of snaking problems is not so much the effectiveness of the Trail-Air device, but your driving/towing skills developed over 40 years, the lack of which may well be responsible for a good number of accidents that result from instability. I think that might well be the case!

Anyway, many thanks for writing, and for your kind words about my writing! Hopefully I’ll be around for another few years yet! Very best regards, 

Doc D