One other thing to bear in mind if you have an OEM BMW tow bracket is that it connects into the vehicle electronics and the vehicle then 'knows' it has a trailer connected and modifies some of the on board stability & handling programs.

The tow ball limit may be because the OEM bracket (in the UK at least) towball is detachable and it can only take 120kgs. I think in the UK, there is no minimum (sensible to have a 10% load though) limit but the advice I have had is get as close as you can to the 90% of the manufacturers rating. The other advice I have had - and followed - is that the trailer laden weight never exceeds 85% of the tractor kerb weight. That way the trailer should never be able to 'drive' the tractor. Having been involved in a serious accident 10 years ago where I was towing a UK Government trailer with a UK Government Discovery (without ever having been trained to do so) - and the trailer was 120% of the tractor weight in 50mph cross winds with as it turned out inadequate anti-sway protection, I learned very quickly to follow the advice of the Police Accident Investigation Officer - who had his own caravan - and we all got training afterwards. Funny how that only tends to happen after an 'incident'. Managers had refused to train any of us up to that point.

Good luck with the tow test though.

__________________
Me:
Current: 2011 E71 40D Vermilion Red/Beige Nappa

Wifey:
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