Towing Limits: Don’t Get Busted!
WORDS BY JOSEPH VAN WOERKOM
Those who tow heavy trailers always need to be sure that they do not violate any of the many weight restrictions that their vehicles and trailers are subject to. Vehicle limits include Gross Combined Mass (GCM), Gross Vehicle Mass (GVM), Maximum Braked Towing Capacity (MBTC), Maximum Towball Down-force (MTD) and front & rear axle load ratings.
I was reminded of this when corresponding with a reader on how best to educate the public to correctly select a suitable tow vehicle given a particular caravan. Or the reverse, how to select a suitable caravan given a particular tow vehicle. The problem is twofold.
Firstly, not all people are aware that the ball weight needs to be included as part of the vehicle’s payload. Usually this is kg for kg but some vehicles, like the Nissan Patrol, have a graduated reduction which allows the total vehicle mass to be higher than the GVM when towing.
Then there’s the fact that a vehicle’s ‘real world’ towing capacity may be a lot less than is stated in its advertising. This is not to say that the manufacturers have got it wrong, but rather that the advertised towing capacity may not a realistic figure for caravanners.
This is because people typically expect the vehicle will always be able to loaded up to the vehicle’s payload limit. The last thing most would expect, apart from perhaps needing to subtract the trailer’s ball mass, is that the vehicle’s payload could be affected by the weight of the trailer.
Stated in a technical way, most people would expect a vehicle’s GCM to equal its GVM + MBTC and to be able to tow at MBTC without exceeding the towbar’s down force limit.
However, this is not always the case. Firstly there are vehicles where the manufacturer has specified the GCM to be much lower GVM + MBTC and so the cargo the vehicle can carry when towing at MBTC is severely reduced. Then there are vehicles which can only tow at MBTC if the trailer’s ball weight is much less than the Australian de facto standard of 10% of total trailer mass.
The examples below may help explain:
Toyota Landcrusier 200 VX
Kerb Mass: 2665
Recommended maximum trailer mass: 3500
Effective towing capacity as % of MBTC:100%
Maximum payload when not towing:685
Maximum payload when towing recommended maximum trailer mass: 335
Maximum payload when towing MBTC: 335
Ford Ranger WildTrack;
Kerb Mass: 2200
Recommended maximum trailer mass: 3111
Effective towing capacity as % of MBTC: 89%
Maximum payload when not towing: 1000
Maximum payload when towing recommended maximum trailer mass: 689
Maximum payload when towing MBTC: 300
Mitsubishi Pajero MY14 Exceed;
Kerb Mass: 2347
Recommended maximum trailer mass: 2500
Effective towing capacity as % of MBTC: 83%
Maximum payload when not towing: 683
Maximum payload when towing recommended maximum trailer mass: 433
Maximum payload when towing MBTC: 503
Isuzu D-Max 4×4 LS-U Crew Cab
Kerb Mass: 1935
Recommended maximum trailer mas: 3333
Effective towing capacity as % of MBTC: 95%
Maximum payload when not towing: 1015
Maximum payload when towing recommended maximum trailer mass: 682
Maximum payload when towing MBTC: 515
Note that for the Pajero to be able to tow its MBTC, the trailer’s ball weight must be no more than 6% of the trailer’s mass due to the towbar downforce limit being reduced to 180kg for trailer masses above 2500kg. This is considered very light for Australian conditions.
Have these examples surprised you? How did you assess the towing capacity of your new tow vehicle? Drop me a line at [email protected] and let me know if you have had any problems complying with any of the various weight limits.
1) The mass limits were sourced from the relevant manufacturer’s web site
2) Except where noted all calculations are based on a 10% ball mass
3) The effects of weight distribution devices have been ignored.