How to load a 4x4 with­out break­ing the law (or the rig).

HOW TO SAFELY – AND LEGALLY – LOAD YOUR FOUR-WHEEL DRIVE

4 x 4 Australia - - Contents - WORD AND PHO­TOS BY SI­MON MUSTEY

YOU’VE just pur­chased the four­wheel drive you have been dream­ing about. Now you can head to a 4WD shop and load up your rig with all the ac­ces­sories that will help you in the ad­ven­tures that lie ahead. Then it’s time to hook up the ’van and leave the hus­tle and bus­tle of your pre­vi­ous life be­hind, with­out a care in the world.

Or per­haps you’re a tradie with a life’s worth of tools in the back of the dual-cab, a rig that dou­bles as your young fam­ily’s ad­ven­ture ma­chine on week­ends.

But are you com­pro­mis­ing your fam­ily’s safety by us­ing an over­loaded ve­hi­cle? It’s all too easy to over­load your rig with ac­ces­sories and gear that, if an ac­ci­dent hap­pens, may cause your in­sur­ance com­pany to leave you high and dry and deny your claim.

In the words of bushcraft and sur­vival ex­pert Mors Kochan­ski: “The more you know, the less you carry.”

To get the case study un­der­way, we have cho­sen two pop­u­lar 4x4s – Toy­ota’s 2000-se­ries Land Cruiser and Mazda’s BT-50

AC­CES­SORIS­ING YOUR 4WD

PRIOR to tak­ing your new ride on its first big jaunt, it has be­come cus­tom­ary to head to a 4WD ac­ces­sory shop and throw the whole cat­tle dog (and your credit card) at your new ma­chine.

When se­lect­ing the nec­es­sary bull­bar/ winch com­bi­na­tion, or which rear drawer set-up to in­stall, does the weight of the ac­ces­sories en­ter the de­ci­sion-mak­ing process? It cer­tainly should.

For the same rea­sons For­mula 1 race­car en­gi­neers con­sider weight and – per­haps more cru­cially – the place­ment of that weight, you should con­sider how the ex­tra weight you’re plac­ing on the ve­hi­cle af­fects over­all weight and, im­por­tantly, whether it alters the 4x4’s han­dling.

To get the case study un­der­way, we have cho­sen two pop­u­lar 4x4s – Toy­ota’s 200-se­ries Land Cruiser and Mazda’s BT-50 – and added typ­i­cal tour­ing 4WD ac­ces­sories. Let’s see how they stack up.

As you can see in the ta­bles above, the Land Cruiser is al­ready over­weight be­fore you even start to pack the es­sen­tial items like ba­con and beer or even pas­sen­gers.

It is im­por­tant not to un­der­es­ti­mate how much ex­tra stuff weighs. Ex­tra weight is your en­emy, and any way you can re­duce the load (re­gard­less of the GVM up­grade) the bet­ter. You will im­prove fuel econ­omy, re­duce main­te­nance loads, and give the ve­hi­cle and its oc­cu­pants a fight­ing chance to bet­ter en­joy this great coun­try.

For in­stance, if you go on two trips and some­thing doesn’t get used, get rid of it – un­less the piece of equip­ment is safety-re­lated, such as a first-aid kit or a fire ex­tin­guisher.

Ad­ding weight to each end of the ve­hi­cle will make a 4x4 pitch more un­der brak­ing

WEIGHT DISTRI­BU­TION

NEXT time you’re at a ten-pin bowling al­ley, grab a cou­ple of the bowling balls – one for each hand – and spin around in a cir­cle with your arms out­stretched. Then try the same thing with both bowling balls held close to your body. Not only will this pro­vide a spec­ta­cle for on­look­ers, but you’ll now have a prac­ti­cal ap­pre­ci­a­tion of the ‘mo­ment of in­er­tia’.

The fur­ther away the weight is from the axis of ro­ta­tion, the harder it is to start and stop. It’s no dif­fer­ent corner­ing in your ac­ces­sorised 4WD, with most of the weight added to each end of your ve­hi­cle. Ad­mit­tedly, a bull­bar mounted be­tween the front and back seats prob­a­bly isn’t go­ing to be of much use.

The same prin­ci­ple can be ap­plied to 4WD LT (Light Truck) tyres. Th­ese tyres will not only be heav­ier in the side­wall con­struc­tion, but also a lot thicker and heav­ier in the crown and shoul­der. The added force re­quired to ac­cel­er­ate and brake the ad­di­tional weight will in­crease fuel con­sump­tion, brake pad and ro­tor wear, and de­crease the ser­vice life of com­po­nents such as wheel bear­ings.

Ad­ding weight to each end of the ve­hi­cle will make a 4x4 pitch more un­der brak­ing and ac­cel­er­a­tion, as well as am­plify body­roll. This can ac­tu­ally blow out your stop­ping dis­tance un­der heavy brak­ing, as the front brakes are be­ing asked to han­dle more of the brak­ing du­ties.

If you’re re­plac­ing one of the two tanks in your 4WD with a long-range tank, re­place the tank lo­cated be­tween the wheels first, as the added weight will have less ef­fect on han­dling.

Don’t for­get that in­creas­ing the height of the cen­tre of grav­ity won’t help your on-road han­dling char­ac­ter­is­tics at all. It will in­crease body­roll and ex­tend stop­ping dis­tances un­der heavy brak­ing, due to pitch­ing and the re­lated load trans­fer to the front.

If you have the choice of a qual­ity alu­minium or a steel roof rack, the alu­minium rack could save you up to 20kg, and when load­ing ve­hi­cles for ex­tended out­back tour­ing, the roof rack isn’t the place for heavy items. I’ve seen more than 100 litres of fuel and spare tyres on roof racks. You cer­tainly wouldn’t want to drive an off-cam­ber track like that.

In most 4WDS, the ma­jor­ity of the added weight from ac­ces­sories and load will be in the rear of the ve­hi­cle. In the case of the Toy­ota 200-se­ries, there’s an ad­di­tional 300kg with a full 180-litre lon­grange diesel tank, twin-wheel car­rier and draw­ers! And that’s with­out a sin­gle can or

bot­tle of your favourite tip­ple.

When a 4WD has ad­di­tional weight bias to the rear, it will tend to over­steer. That’s when the rear tries to over­take the front, spin­ning you around. Most man­u­fac­tur­ers de­sign ve­hi­cles to be as neu­tral as pos­si­ble, be­fore un­der­steer­ing at the limit. Un­der­steer is when the front runs wide, and all you have to do to get it back on line is get off the throt­tle a lit­tle. That’s a lot safer than try­ing to wres­tle an over­loaded tourer that looks like it has en­tered a drift­ing com­pe­ti­tion.

An­other rea­son weight distri­bu­tion is im­por­tant is tyre load sen­si­tiv­ity. As the weight in­creases on a tyre, the co-ef­fi­cient of fric­tion starts to drop off. So, if the rear tyres are sup­port­ing more load, they will over­load sooner than the front tyres when corner­ing (as the co-ef­fi­cient of fric­tion drops off). Be­fore you know it, you’re look­ing at the same scenery through the wind­screen that was in the rearview mir­rors mo­ments ago.

AXLE LOAD­ING

AS WELL as an over­all weight, ve­hi­cle man­u­fac­tur­ers will spec­ify an over­all weight al­low­able for each axle. So even if your to­tal weight is un­der the spec­i­fied GVM, you may still be over the in­di­vid­ual axle’s weight.

In the case of the Land Cruiser 200, Toy­ota has spec­i­fied a front axle load of 1630kg and a rear axle load of 1950kg, giv­ing a to­tal of 3580kg. This is 230kg over the Land Cruiser’s GVM of 3350kg, so it al­lows a lit­tle un­even load­ing of the axles with­out ex­ceed­ing the GVM.

TOW­ING

IF YOU didn’t think it was com­pli­cated enough, there are fur­ther con­sid­er­a­tions when tow­ing. Again, we’ll use the Land Cruiser as an ex­am­ple. If you add the max­i­mum braked tow­ing weight (3500kg) and the GVM (3350kg) to­gether you get 6850kg, which hap­pens to be the GCM (Gross Com­bined Mass). So at GVM, you’re able to tow the 4WD’S full rat­ing of 3500kg. How­ever, that’s not al­ways the case.

Now, let’s do the sums on the Mazda. Just like the Land Cruiser, it has a braked tow­ing ca­pac­ity of 3500kg. With a GVM of 3200kg, it gives you a to­tal weight of 6700kg. This is 700kg in ex­cess of the Mazda’s GCM of 6000kg. So you’ll need to strip weight out of the ve­hi­cle or tow some­thing lighter.

The Tow Ball Mass (TBM) also af­fects rear and front axle loads and GVM. When you’re tow­ing 3500kg, with ei­ther the Mazda or the Toy­ota, if your TBM is 350kg you can add that weight di­rectly onto the 4WD’S GVM.

Mov­ing onto axle loads: Imag­ine your

In the case of the Land Cruiser 200, Toy­ota has spec­i­fied a front axle load of 1630kg

For new ve­hi­cles, it’s best to get your GVM up­grade in­stalled be­fore reg­is­tra­tion

4WD as a see­saw – the bull­bar is the far seat, the rear axle line is the pivot point, and the tow bar con­nec­tion is the near seat. Plac­ing a load on the near seat (tow bar) will pivot through the rear axle line and lift some of the weight off the front wheels. Us­ing the Toy­ota as an ex­am­ple (wheel­base: 2850mm; over­hang: 1300mm), let’s look at how much weight you’ll lift off the front of the car.

Ad­di­tional rear axle load as a re­sult of TBM = (over­hang ÷ wheel­base) x TBM. So, in the case of the 200, with a TBM of 350kg you’ll ex­pe­ri­ence a lift­ing force of 160kg on the front wheels and 510kg of rear axle load (350kg + 160kg). Now that’s a lot for any ve­hi­cle to carry.

For tow­ing, it’s bet­ter to have a longer wheel­base with a shorter over­hang. With less lever­age, any­thing that dis­turbs the trailer will have less ef­fect on the ve­hi­cle.

GVM UP­GRADES

BE­FORE you give up and throw the keys in the bin, there is sal­va­tion in the form of a GVM up­grade.

In the case of the Land Cruiser, you can in­stall an up­grade that will lift the GVM from 3350kg to 3800kg, giv­ing you a mas­sive pay­load in­crease of 450kg.

How­ever, it’s not all beer and skit­tles. The GVM up­grade won’t af­fect the GCM. So in the case of the Land Cruiser, you’ll now only be able to tow a max­i­mum of your GCM mi­nus the GVM.

In the case of the LC200 with a 3800kg GVM up­grade, that’s 3050kg (6850kg mi­nus 3800kg) of tow­ing ca­pac­ity at the new up­graded GVM.

For new ve­hi­cles, it’s best to get your GVM up­grade in­stalled be­fore reg­is­tra­tion. The kit needs to be a “fed­eral com­pli­ance kit” and, un­for­tu­nately for DIY types, a GVM up­grade kit needs to be fit­ted by an Ap­proved Pro­duc­tion Fa­cil­ity ac­cred­ited by DOTARS. Once the ap­proved kit is fit­ted, and the com­pli­ance plate af­fixed to the ve­hi­cle along with a new tyre plac­ard with re­vised axle ca­pac­i­ties, you’ll be able to drive the car with its re­vised GVM. The GVM up­grade will be na­tion­ally recog­nised, so there won’t be any prob­lems when it comes time to move the ve­hi­cle on.

For a 4WD that has al­ready been reg­is­tered, you’ll need to have the ve­hi­cle signed off by an en­gi­neer (at ad­di­tional ex­pense) once the kit is fit­ted. Your 4WD with GVM up­grade will now be able to be driven na­tion­wide. How­ever, as the GVM up­grade is com­plied at a state level, when it comes time to sell, the up­grade is only recog­nised in the state where it was com­plied. If sold

in­ter­state, the new owner will need to have the kit re-com­plied with that state’s road au­thor­ity.

In the case of the 200, the kit will in­clude new heavy-duty coil springs front and rear, new shocks front and rear, the re­vised com­pli­ance plate, tyre plac­ard, and a KDSS valve ad­just­ment warn­ing de­cal (where KDSS is fit­ted).

Nearly all 4WDS could use a lit­tle more un­der­body clear­ance, so giv­ing your pride and joy a cou­ple of inches of sus­pen­sion lift at the same time as the GVM up­grade kills two birds with one stone.

Bear in mind, the GVM up­grade won’t make your 4WD in­vin­ci­ble. You’ll still need to dis­trib­ute the load cor­rectly and re­mem­ber that jump­ing sand dunes in the mid­dle of the Simp­son Desert will bend your chas­sis just as eas­ily with or with­out the up­grade.

READY TO ROLL

BE MIND­FUL that the over­all weight of your rig doesn’t ex­ceed the 4WD’S GVM. Also try and keep the weight as low and as cen­trally lo­cated as pos­si­ble – if you don’t want to throw han­dling out the win­dow.

When tow­ing, the tow ball mass will add to your GVM. The lever­age cre­ated by the dis­tance from the tow ball con­nec­tion to the back axle will see in­creased rear axle loads above the tow ball mass and re­duced loads on the front wheels that can af­fect brak­ing and han­dling.

If you’re driv­ing a wagon with a lim­ited load ca­pac­ity, a GVM up­grade could be in or­der. Just bear in mind this won’t in­crease the GCM and it could com­pro­mise the 4WD’S tow­ing ca­pac­ity.

When tow­ing, the tow ball mass will add to your GVM

An over­loaded rig can mean in­sur­ance headaches if you have an ac­ci­dent.

Land Cruiser 200’s gross ve­hi­cle mass is 3350kg.

GVM for the BT-50 is 3200kg.

Draw­ers and a dual car­rier rear bar adds 120kg to the Cruiser. An ex­tra bat­tery can add 30kg. Ad­ding a fridge and slide to the BT-50 sad­dles it with an ex­tra 80kg.

An alu­minium roof rack can weigh up to 20kg less than a steel rack so check out your op­tions. The roof will also have a weight rat­ing, usu­ally no more than 80-100kg for a large 4x4 wagon.

Heavy me­tal is good for ve­hi­cle pro­tec­tion, but weight is your en­emy

Most GVM up­grades com­prise new springs and shocks plus the needed com­pli­ance ap­provals and certification.

A GVM up­grade could com­pro­mise your rig’s tow­ing ca­pac­ity so it pays to check the num­bers.

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