DEFIN­ING TERMS

4 x 4 Australia - - Gear -

BE­FORE we delve into the won­der­ful world of ve­hi­cle load­ing and how it af­fects le­gal­i­ties and a ve­hi­cle’s han­dling, it’s use­ful to un­der­stand the terms com­monly used.

TARE WEIGHT:

This is the ve­hi­cle’s weight with flu­ids, usu­ally with only 10 litres of fuel in the tank.

KERB WEIGHT:

The weight of a rig when it’s ready to drive with full tank/s, an aver­age driver of 68kg (they don’t fre­quent my souvlaki shop!) and 7kg of lug­gage. How­ever, tare and kerb weight def­i­ni­tions dif­fer from man­u­fac­turer to man­u­fac­turer.

GVM:

Gross Ve­hi­cle Mass is the max­i­mum al­low­able ve­hi­cle weight, in­clud­ing all oc­cu­pants, ac­ces­sories and lug­gage.

GCM:

Gross Com­bi­na­tion Mass is the to­tal com­bined weight of your ac­ces­sorised, fully loaded ve­hi­cle and any­thing you’re tow­ing.

AXLE LOAD­ING:

In ad­di­tion to GVM, ve­hi­cles also have a max­i­mum al­low­able load on both the front and rear axles.

ATM:

Ag­gre­gate Trailer Mass is the max­i­mum al­low­able weight of the trailer you’re tow­ing, as des­ig­nated by the man­u­fac­turer.

TBM:

Tow Ball Mass is the weight on the tow ball im­posed by the trailer, usu­ally around 10 per cent of the ATM. For a trailer weigh­ing 3500kg, you’ll have a TBM of around 350kg.

CEN­TRE OF GRAV­ITY:

An imag­i­nary point in the ve­hi­cle where you could the­o­ret­i­cally bal­ance the whole car on one (very strong) fin­ger.

MO­MENT OF IN­ER­TIA:

When you’re turn­ing around an axis, the fur­ther the weight is from the axis of ro­ta­tion the harder it will be to start and stop.

TYRE SLIP AN­GLE:

When turn­ing, there is a dif­fer­ence in an­gle be­tween where the wheel is point­ing and where the ve­hi­cle is track­ing, due to the flex­i­bil­ity of the tyre.

TYRE LOAD SEN­SI­TIV­ITY:

Con­ven­tional pneu­matic tyres don’t be­have as your high school physics class might sug­gest. As the load in­creases, the co-ef­fi­cient of fric­tion de­creases. The peak lat­eral (corner­ing) force in­creases as the ver­ti­cal load on the tyre in­creases, but at a di­min­ish­ing rate.

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