No, Prof is right and agree the heavier the towcar v van the better-just saying, that after many miles of near 100% limit re the manufacturer specs and totally ignoring kerbweight-which we were most defiinitely over; max kerbweight of a Duster was 1400kg v our 1450kg caravan we never had even the slightest wobble and we didn't have ATC! Just saying, don't panic!
I have towed many different combinations of car and caravan related to one of the jobs I had, and in my experience there can be surprising differences that cannot be just explained by paper weight ratios. If necessary we added ballast in the form of water containers to trim the caravan and set an appropriate lose load.
A few combinations that on paper should be good, proved to be decidedly unsettled, and others that were close to or over 100% (but always within the vehicle weight limits) or over in some cases proved to be very stable.
On balance there were fewer issues with low ratio outfits, which is why I still suggest keeping trailer weights small especially so for newcomers.
I do believe the UK industry weight ratio advice is seriously flawed and has been used by too many as a hard target so it has become a dogma, It is frequently used to suggest it will provide a "safe" tow, and it has often been misquoted as being a "RULE" neither of which are true, I have witnessed outfits that were definitely under 85% involved with incidents of instability, and there is no reference in the statutes about this advice having any legal authority!
I don't like the industry advice today , becasue the formula (Caravan MTPLM/ Tow vehicle Kerbweight) relates two extremes of loading which will never be experienced in practice. It ignores any reference to the vehicles actual specifications regarding GTW, so for some vehicles the calculation does produce an industry guidance figure that exceeds the pulling vehicles legally permitted GTW!
Towing weights are complicated enough without having guidance that can actually produce an illegal result.
To be fair to the industry advice was derived in the days when there was far less technical information available about cars, I believe it was produced because there were some people who drove some grossely mismatched even dangerous outfits, becasue there were no guidelines to help them make a more sensible choices. Its need stems from the fact that caravans are inherently unstable and represent very difficult loads to tow, a fact that is as true today as in the past.
Since our membership of the EU, it has meant our car manufacturers have had to publish more and consistent information about their products. we now have access to detailed information about the cars GTW and other key data that describes the cars capabilities. Ironically publishing kerbweight is not a requirement.! Given this wealth of defined and accurate information a revision to the calculation is well overdue.
Not only has the depth of information improved but the vehicles have also had some significant changes such as the increased use of diesel engines and turbo's offering better low RPM torque and more power, the introduction of better brakes, and vehicle suspension and stability system improvements.
It should be possible to produce a revised formula that uses some of the type approval data of vehicles to produce customised advice for any towvehicle and caravan combination. Some of the matching websites do attempt this but they are hamstrung by omissions or errors in their databases.
Do not go away with the impression that I anticipate a revised formula to allow heavier caravans to be towed, When the calculations are done and safety is taken into account it may suggest even lower trailer weights or speed should be considered.