Technology and technical innovation are the keystone in research into limiting weight on board a recreational vehicle: you need to find the perfect balance of dimensions, liveability and space used. New materials and technical solutions have allowed some. European manufacturers to offer lighter vehicles.
Words Michel Vuillermoz
In the 1990s, a 6.5-metre-long overcab was considered a large vehicle: it stopped short of 3 metres in height, the width didn’t exceed 220 cm and the total weight was often 3100 kg, that is, the limit for the first generation of the Fiat Ducato 14. There was also the 3,500 kg Ducato Maxi of course, but many vehicles also made use of the “little” Ford Transit 120D for passenger compartments of 554 cm in length and total weight of 2720 kg, or the entry-level version of the Fiat Ducato, the 1000 kg (2600 kg fully laden). Today, these numbers are a distant memory: except in rare cases, the European market identifies a 6-metre vehicle as compact and a 7-metre one as medium-sized, with layout in which the passenger compartment is dominated by the space dedicated to the rear bedroom. The dimensions, the engine power, the equipment and the comforts have increased. What hasn’t changed, however, is the weight limit that a vehicle needs to stay under so it can be driven in normal circumstances with a standard category-B driving licence: 3500 kg and not a kilo more.
Beyond this figure, legislation means that the driver has to be in possession of a higher-category licence (C1, C or D) with all that that involves both for the individual (obligation to renew every 5 years at most, restrictions – including serious ones – in the case of medical issues) and for the vehicle (annual MOT, lower speed limits, different motorway toll calculation in some countries). This is a complication that not all potential buyers want, or often have the requisite knowledge, to manage successfully, effectively entering a kind of grey area: they own a medium/large-sized recreational vehicle type-approved for driving with a B-category licence, fully equipped but unable to comply with the weight limit, even by limiting the passengers to two people.
The explanation can be supplied quickly: the concept of recreational vehicle has evolved significantly in the last two decades, transforming from simply a vehicle for camping to a home on wheels. Overcabs, low-profiles and motorhomes have started to grow in size, forcing customers in search of more compact solutions to focus on campervans. In the last five years, these have become a genuine commercial phenomenon at a global level: the sales figures, increasing constantly, can in part be attributed to the market positioning of outfitted vans, offered at rates distinctly lower than those of the classic panelled versions.
Compact doesn’t always mean light
You need only glance at the technical specifications of some of today’s most popular campervans to see unladen weights of little under 3000 kg, even for vehicles of just 541 cm in length. The problem of weight thus seems increasingly to transcend types and dimensions. But is all this really inevitable from a technical, design and cost perspective? Objectively, no. It’s not inevitable, but it’s not easy to solve. You can’t expect to solve it by eliminating standard equipment like engine-powered climate control (18/20 kg), spare wheel (30 kg) and service battery (30/35 kg on average) or by asking passengers to sacrifice a minimum of drinking water in the tank (already a limited quantity) each time they travel. No one – and I mean no one –travelling in their campervan with wife and two kids, in addition to draining the waste water before setting off each morning, will also drain the entire drinking water tank to get to the 20 litres theoretically permitted. The only possibility to create recreational vehicles that are hospitable, fully equipped, commercially appealing and compliant with the regulations in force is to start again from a blank slate in the design, choice of components, of materials, of solutions to propose, in the volumes.
Mechanics and chassis
Each element has its own weight, starting from the mechanical base: a Fiat Ducato 35 Light 130 Multijet II, chassis cab for conversion in standard configuration with original ladder frame and 403.5 cm wheelbase, has a tare weight of 1655 kg and the numbers vary by 10/20 kg for the shorter versions (1645 kg with 380 cm wheelbase, 1635 kg with 345 cm wheelbase). The manual climate control weighs 18 kg, the Comfort-Matic automatic transmission 17 kg, the various active safety devices (ESP, Traction+, Hill-Holder, Cruise-Control…) no more than 3 kg. Added together, including all these components, the outfit for a low-profile or overcab starts from a chassis of just under 1700 kg. This certainly isn’t a high figure, which can be significantly reduced by opting for a non-standard AL-KO AMC chassis, made of galvanised steel, equipped with independent rear suspension and designed specifically for each outfit, so as to permit a significant lowering of the floor (14/22 cm), useful for the creation of double flooring perhaps. Depending on the options selected, the weight saving with respect to a normal chassis cab with high ladder frame and classic rear leaf-spring suspension can be as much as 140 kg. The chassis represents the backbone of the vehicle to a certain extent: it’s the base on which the platform, and consequently the entire body, of the vehicle rests. Many variants and possibilities relating to thicknesses, materials and assembly systems come into play here, with different schools of thought. There are examples of particularly thick platforms (as much as 60/70 mm) which, strangely, are combined with the thinnest possible walls (30 mm) and oversized roofs (50/60 mm), as if to suggest that the greatest heat losses on a vehicle are linked to floor and roof and not to the walls. Or there are walls with greater thickness combined with thinner roofs. It is not a given, however, that a conspicuous thicker floor or wall automatically translates into greater insulation. A high-quality insulating material (polyurethane or RTM) ensuring maximum rigidity and strength permits a dramatic reduction in the elements of the internal skeleton, which made of wood or composite resin do not in any case have a negligible weight in the case of 5-metre walls and platforms and 7-metre roofs. A better, more modern body without wooden (or similar) elements and with systems of assembly in line with contemporary technologies could bring two advantages: lower weight and greater safety in case of accidents. Conversely, of course, higher-quality materials cost more.
Double flooring in 3.5-tonne vehicles
The creation of a cavity in which to channel systems, house technical components in a protected and heated position and create storage compartments has always been the prerogative of the most exclusive and sophisticated vehicles. It does have some basic rules however. The build can’t be the same as a vehicle without false bottom, because while the aesthetic differences between the two may be minimal, technically they’re enormous. The main platform is the lower one. This is what insulates the vehicle from the outside and warrants adequate insulation together, naturally, with the lower portion of the walls, in which the insulation is too often provided merely by sheet metal, inappropriate for the task of preventing heat loss. If present, the double flooring has to become a cavity at the service of interior comfort, a compartment that accumulates heat for the well-being of the passengers and protection of the technical installations, electrical wiring included, also significantly increasing the life of the vehicle over time. At times, instead, you see vehicles where this seems turned on its head, with a thin lower platform and floor with thickness that even exceeds 50 mm. Vehicles that feature more insulation between their internal components than against the outside, with a part of the systems (typically the recovery tank) installed as an independent element in the underbody.
Electricity and gas on board
From the perspective of electricity, the spread of the new generation of lithium batteries can provide a significant contribution in a future which is now near: developed with LiFePO4 (Lithium Iron Phosphate) technology, they made their début on the most prestigious recreational vehicles (original equipment on the exclusive Frankia Platin models) and constitute the heart of the Smart Energy Pack proposed by Hymer for its vehicles. So electricity lasts longer, in line with the ever greater demand from the complex and advanced domestic automation on board, but weighs less: a 100 Ah LiFePO4 battery weighs just under 15 kg, less than half the weight of a battery of similar power with GEL (29 kg approx.) or AGM (32 kg approx.) technology.
Another heavy element is the gas: two classic 10 kg cylinders, as well as being difficult to manage, are heavy items with a tare weight between 11.5 and 12 kg each. Between contents and container, you easily arrive at 45 kg on each vehicle. A gas-free vehicle could save a lot of weight. The internal climate control would be entrusted to the increasingly sophisticated systems powered directly by the fuel for the vehicle with diesel or induction hobs and fridges with high-performance compressor elements (Thetford T1090 or Dometic Coolmatic) that are lighter than three-ways of similar capacity.
The internal furnishings
The war on weight, at least in the build and production stage, involves refinement, lightening and improvement work: thinking you can solve everything just by reducing the thickness of the furniture, however, is asking for trouble. The furnishings on a recreational vehicle must be robust, since they’re subject to a great deal of stress due to wear, vibration, twisting of the chassis and jolts from ruined road surfaces. The idea of replacing a 15 mm laminboard panel with a 10 mm one without altering the manufacturing technique and material may prove a grave error. The only solution is to diversify the materials, with load-bearing sections and secondary elements differentiated according to the task they have to carry out, maybe with new synthetic elements able to incorporate light weight and strength.
On board a motorhome as at home, but more than 3.5 tonnes
It’s no use thinking of being able to offer, in a vehicle type-approved for a maximum weight of 3.5 tonnes, a wall unit with maxi domestic fridge freezer in terms of capacity and weight (41 kg), a kitchen module and grill and gas oven worthy even of a Michelin-starred chef but with a weight to match (between 35 and 40 kg depending on the model), convector heating (20 kg plus one with ducted air) perhaps in combination with a tall radiator dedicated to the toilette (another 10 kg) and, again in this environment, a cassette WC with ceramic body (17 kg compared to the 8 of a “normal” plastic one). These elements reproduce the comfort of a normal dwelling and for this precise reason deserve to be installed on vehicles of more than 3.5 tonnes teamed with mechanical bases originally designed to handle greater weights and volumes and which ensure large safety margins.
On the contrary, a low-profile, an overcab, a motorhome or, above all, a campervan with a total weight of 3.5 tonnes is a vehicle created as a convenient extension of your car, not a replacement for your home. Customers often don’t understand this, and no one explains it to them…
We’ve presented some exemplary companies who are working on lightweight construction. This is the challenge of the future: offering adequate weight on 3.5-tonne vehicles, allowing users to drive safely with peace of mind.
Carthago’s lightweight construction
Given the impossibility of using two very thick superimposed platforms on a vehicle with a total weight of 3500 kg, it is necessary to assess their composition thoroughly as well as the supporting framework. An excellent example is provided by Carthago, which exploits an excellent, light and high-performance structure on its “Superlightweight” ranges. The lower floor is made up of a sandwich with lower fibreglass lining (2 mm), 40 mm RTM insulation and 6 mm laminate internal lining for a total thickness of 48 mm. The 14 cm cavity features a partition structure made of galvanised steel suitably milled to lower the weight, permit excellent air circulation and, simultaneously, the passage and positioning of the hot air ducts and all technical components of the systems. The floor, on the other hand, is made of 20 mm multi-layer phenolic lined inside with the classic linoleum. All this, together with a self-supporting aluminium/RTM/aluminium body with medium thicknesses (38 mm of which 30 insulation) and intelligent furniture construction, with quality materials milled where possible to eliminate the unnecessary parts, has enabled the prestigious German brand to offer high-class low-profiles and motorhomes, distinguished by technical solutions that stand out but are compatible with a total weight limit of 3.5 tonnes: purely by way of example, a C-Tourer I 144QB with marine-style central double bed at the rear and length of 699 cm has a kerb weight of 2970. A few more kilos can also be gained by reducing the width of the outfit: for this particular vehicle, passing from a body width of 227 to 212 cm permits a saving of 45 kg, bringing the tare weight to 2925 kg. The comparison is made possible by the presence of the C-Compactline I 144QB series in the Carthago catalogue, identical to the C-Tourer I 144QB in terms of layout and technical features but 15 cm narrower. For both, of course, the mechanical base i provided by the Fiat Ducato 35L with non-standard AL-KO chassis.
The weight-saving solution from Hymer
Equally interesting is the lightweight development proposed by Hymer: in the last five years, the Bad Waldsee factory has invested heavily in technical research, developing the Exsis I and T (motorhomes and low-profiles) ranges to meet the needs of category-B licence holders. With compact dimensions, height limited to 277 cm and width to 212 cm at body level and 222 cm at band level, the latest generation of these products has seen the introduction of the new AluPual (or Pual 2.0) body with aluminium internal and external structure containing the classic polyurethane foam for a total wall thickness of 34 mm. This is coupled with a 41 mm platform (fibreglass/polystyrene/fibreglass with polyurethane structure), entrusted to an AL-KO chassis teamed with the mechanical base of the Fiat Ducato, and furnishings completely redesigned to preserve style and sturdiness but lightened in all non-essential and load-bearing sections, to reach an objectively outstanding result: you need only glance at the technical specifications of the Exsis models to see extremely limited tare weight figures. By way of example, one of the central models in the range, the I 588 motorhome (699 cm in length, layout with rear twin bed on garage) offers a kerb weight of just 2840 kg, thus permitting a useful margin of 660 kg.
Even more significant, if possible, is the subsequent development step taken by the manufacturer in Bad Waldsee, the new SLC, SuperLightChassis. Developed to be combined with both the classic Fiat Ducato and the brand-new front-wheel drive Mercedes-Benz Sprinter VS30, as of this year it is fitted on the B-Klasse Supreme Line models and, above all, the brand-new B-Klasse Modern Comfort series, a big development for 2019. A genuine paradigm shift in the concept of the chassis, no longer merely a base on which to build a double floor but a structure absolutely integral to the vehicle, it brings together significant advantages in every area of the design and assembly of the vehicle: it further limits the unladen weight (saving up to 70 kg), lowers the centre of gravity without reducing the ground clearance, avoiding approach and departure angles worthy of a Formula 1 single-seater, and permits the creation of a maxi double through floor (from a minimum of 25 to a maximum of 35 cm usable vertical extension) despite the presence of a total height kept under 3 metres (296 cm) and a more than adequate internal height (198 cm). A chassis that, of course, offers greater rear track (198 cm) and wheelbases studied according to the external length (390/400/420 cm for lengths of 699/719/739 cm): enough for the new B MCs to be advertised as capable of offering 4 type-approved places also for the larger versions, complying with the 3.5-tonne limit, and not sacrificing a rear garage able to hold 350 kg or drinking water and recovery tanks with a greater-than-average capacity (180 and 150 litres).
