There is no "normal". Each car is defined by the manufacturer during homologation (gaining of type approval) with some being none what so ever (no towbar authorised) right up to 3.500KG. The Discovery can tow considerably more than its GVW.<div abp="1062">
The 85% rule is aCaravan club (and other motoring organisations) general guideline as being a safe maximum covering most peoples experience with towing. It has no legal status and is dependent on the rating of the vehicle not being exceeded within that limit.<div abp="1064">
As to why the B-Max has such a low limit, primarily because Ford decided they did not want to get approval for any more.The higher the limit, the higher the structural considerations, better cooling and so on.
just to update on the towing issue-
Ford advise that the max legal l weight that my B max 1.6 auto is allowed to tow is 400kg.
GTM of 2180-GVM of 1780= Max train mass of 400kg
but many may be still confused as I am when
registration document says 'the technical permissible maximum
towbale mass of the trailer is 480kg' why is this figure higher than
the legal limit, when most would refer to this as being the maximum
allowed?- see point 2 below
Ford Dealers similarly advise
480kg as maximum towing capacity, clearly this is above the legal
There are several weights for a single vehicle<div abp="1301">
<div abp="1302">Unladen Weight = Dry Weight = no fuel, water, driver and for EV, batteries ( useful for shipping calculations
<div abp="1304">Kerb Weight = Car + fuel, water, standard tools & spare, driver of 75 Kg( I wish
<div abp="1304">Gross Vehicle Weight = Maximum Authorised Mass = Kerb Weight+ Passengers/cargo.
<div abp="1304">Gross Train Weight = Maximum weight of vehicle and trailer combined.
<div abp="1304">This last one is a curates egg. The weight of the trailer has to be its maximum plated weight irrespective of its actual load. People have been prosecuted for towing an empty car trailer because the towing vehicle could not have legally towed it if fully laden.
<div abp="1304">However the car does not need to be considered at anything other than the rolling weight.
<div abp="1304">The 80Kg discrepancy comes about because the vehicle could be at its Kerb weight or GVW. As that difference is even more than the rated weight then engineering limits are in effect.
<div abp="1304">At below 750Kg the trailer is unbraked which makes a massive difference to the loading conditions for the towbar so easier to design.At 1/4 of the GVW there is a low engine load consideration to make although there is a change for the 1.0L
<div abp="1304">So it can take 480Kg unless fully laden when it drops to 400Kg. The driver is always responsible to ensure that the train is properly loaded.
the bmax is rated to pull a 750kg braked trailer.
though some models this is restricted to (when fully laden) a restart on an 8% gradient, (about 1 in 12) others will pull that with restart on a 12% hill. (about 1 in 8)
un-braked trailer weights are lower, see you car handbook.