Tech Torque

4 x 4 Australia - - Contents - FRASER STRONACH

POWER, torque, weight, gear­ing, ground clear­ance, wheel travel, tyres and elec­tronic trac­tion con­trol are just some of the things that make or break a 4x4. But what at­tributes are more im­por­tant than oth­ers? Can power al­ways over­come weight? Can trac­tion con­trol al­ways make good on poor wheel travel? And can you make up with a lack of torque through low gear­ing?

Rat­ing what counts when it comes to a 4x4’s abil­ity is dif­fi­cult, but the list, in roughly de­scend­ing or­der, would look some­thing like this:


THIS is the big­gie. With­out de­cent ground clear­ance, you re­ally have noth­ing go­ing for a 4x4 in any sort of off-road en­vi­ron­ment. Re­gard­less of whether you’re on sand, in mud, or on rocky and rough ter­rain, you aren’t go­ing any­where with­out de­cent ground clear­ance. And the softer the sand, the deeper the mud, or the more rocky and bro­ken the ground, the more that clear­ance be­comes in­valu­able. With more clear­ance you can also carry more mo­men­tum with­out risk­ing dam­age to the ve­hi­cle’s vi­tals or body and body pan­els, and there’s less need for ex­tra-low gear­ing. Too much ground clear­ance is only a problem when the ve­hi­cle sits up that high that side-slope an­gle and roll-over sta­bil­ity is un­duly com­pro­mised.


LESS weight means you less read­ily sink into any soft sur­face – sand, mud, or what­ever. What’s more, it re­quires less of just about ev­ery­thing else – power, gear re­duc­tion, trac­tion, etc. – to move a lighter ve­hi­cle up a hill than it does a heav­ier ve­hi­cle.


ALONG with ground clear­ance and less weight, wheel travel makes up the ‘holy trin­ity’ of 4x4 at­tributes. Long wheel travel al­lows you to tra­verse bro­ken ground more eas­ily, with less re­liance on diff locks or trac­tion con­trol. As with ex­tra ground clear­ance, it also al­lows you to carry more mo­men­tum across any sur­face, so there’s less chance of bog­ging in soft sand or mud.


YOU don’t get far off-road with­out suit­able tyres; al­though, it’s much more than just tread pat­tern at play here. In broad terms, the im­por­tant things are tyre con­struc­tion (Light Truck is more ro­bust than Pas­sen­ger), side­wall height (the higher the bet­ter, for su­pe­rior dam­age re­sis­tance and air-down ad­van­tage) and speed rat­ing (the lower the bet­ter as high-speed tyres are lightly built, even if this sounds con­tra­dic­tory). Tread pat­tern is vi­tal when it gets muddy, but not as im­por­tant when you’re not in mud.


DE­CENT torque out­put is the only way to get the us­able off-idle and low-rpm drive­abil­ity and stall re­sis­tance you need off-road. Ex­tra low gear­ing can over­come a low torque out­put, but only to a cer­tain de­gree.


WHEN a 4x4 runs out of wheel travel and loses solid con­tact with the ground, you can’t go past a lock­ing dif­fer­en­tial. Those that lock au­to­mat­i­cally (gen­er­ally called elec­tronic or ‘e’ lock­ers) are much more use­ful and con­ve­nient than driv­eren­gaged lock­ers.

Lock­ers are gen­er­ally found on the rear axle; al­though, full-time 4x4s need lock­ing cen­tre diffs (ei­ther auto or man­ual), while a hand­ful of 4x4s (70 Se­ries, Wran­gler Ru­bi­con and Mercedes G-wa­gen) have front lock­ers as well. One note of cau­tion here, some driver­switched rear lock­ers on cur­rent 4x4s can­cel the trac­tion con­trol on both axles, so they don’t nec­es­sar­ily de­liver on their prom­ise.


TRAC­TION con­trol was once a poor man’s diff lock, but re­cent ex­am­ples – sec­ond and third gen­er­a­tion trac­tion con­trol sys­tems – are be­com­ing very ef­fec­tive. Trac­tion con­trol is part of the an­swer, but not the full an­swer, to lack of wheel travel in mod­ern car-like 4x4s.


YOU don’t need heaps of power when off-road – at least away from soft sand, and only then when you have a heavy 4x4. As above, torque is what’s needed off-road, while power is a more crit­i­cal on-road at­tribute.


THIS is a sim­ple, cheap and ef­fec­tive way to get low gear­ing and still use an oth­er­wise stan­dard gear­box. How­ever, dual-range gear­ing isn’t es­sen­tial as long as you have a suf­fi­ciently low first gear, which is some­thing made pos­si­ble when you have a gear­box with a stack of ra­tios such as with mod­ern eight- and nine-speed au­to­mat­ics. On the other hand, with au­to­mat­ics, a torque con­ver­tor with a high-stall ra­tio can be a so­lu­tion and help over­come the need for dual-range gear­ing.

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