Does Toy­ota’s KDSS make a dif­fer­ence?

Some Pra­dos come with Toy­ota’s Ki­netic Dy­namic Sus­pen­sion Sys­tem, others don’t. So what’s the dif­fer­ence?

4 x 4 Australia - - Contents -

NOT ALL Pra­dos are me­chan­i­cally iden­ti­cal, and that’s not just due to the dif­fer­ence be­tween diesel and petrol en­gines, or the avail­abil­ity of a man­ual gear­box with the diesel. More ex­pen­sive VX and Kakadu mod­els come with Toy­ota’s Ki­netic Dy­namic Sus­pen­sion Sys­tem (KDSS), a fea­ture not fit­ted to, or avail­able with, the GX and GXL mod­els.

For on-road driv­ing, KDSS lessens body roll for flat­ter and sportier han­dling, yet it also pro­vides more wheel travel for su­pe­rior per­for­mance in rough off-road ter­rain. It does this by au­to­mat­i­cally ad­just­ing the ten­sion on the sus­pen­sion’s sway bars (also called an­tiroll bars).

The trou­ble is, the cheap­est way to get KDSS is on the $73,990 VX. That’s a $12,000 ask over the best-sell­ing GXL auto – the clos­est NON-KDSS Prado to a VX. How­ever, you get more than just the KDSS when you step up to a VX from the GXL (see VX Up­grades break­out, page 92).

While we have driven ev­ery spec-level Prado, from GX to Kakadu, we have never had the chance to com­pare a NON-KDSS Prado against a Kdss-equipped one to see the dif­fer­ence it makes. To this end, we have lined up a GXL and a VX.

We chose the VX over the more ex­pen­sive Kakadu due to the lat­ter hav­ing fea­tures such as height-ad­justable rear sus­pen­sion and vari­able dampers that would throw un­wanted vari­ables into the mix. We also chose a GXL auto, as the VX is auto-only. The only

vari­able we couldn’t con­trol is that the GXL comes with 17-inch wheels, while the VX runs with 18s.

THE THE­ORY

TO UN­DER­STAND KDSS, it’s best to start with what a sway bar is and what it does. Ba­si­cally, it’s just a tor­sion­bar spring that con­nects op­po­site wheels across ei­ther axle. It in­creases the sus­pen­sion’s roll stiff­ness in­de­pen­dent of spring rate, so it pro­vides flat­ter hand­ing with­out un­duly com­pro­mis­ing ride qual­ity.

A sway bar isn’t a nec­es­sary part of a sus­pen­sion sys­tem, and for an off-road ve­hi­cle where wheel travel is para­mount, it’s not what you want.

The first-gen­er­a­tion Range Rover (1970), the 4x4 that pi­o­neered all-coil, long-travel, live-axle sus­pen­sion, wasn’t fit­ted with sway bars for most of its quar­ter-cen­tury-long pro­duc­tion life. The end re­sult was ex­tremely sup­ple long­travel sus­pen­sion that worked bril­liantly off-road. How­ever, there was a fair de­gree of body roll when driven hard through cor­ners and, as more and more peo­ple bought their Range Rovers purely for on-road use, there was pub­lic de­mand for a flat­ter-hand­ing ve­hi­cle, which was achieved by fit­ting sway bars. Un­for­tu­nately this also di­min­ished the Range Rover’s leg­endary off-road abil­ity.

This com­pro­mise be­tween off-road wheel travel and on-road hand­ing is, of course, one of the clas­sic de­sign dilemmas of a mod­ern 4x4 that’s ex­pected to per­form well both on- and off-road.

One solution is to man­u­ally ‘dis­con­nect’ the sway bar(s) for off-road use and then re­con­nect it for on-road use. Up-spec vari­ants of Nis­san’s GQ Pa­trol have a me­chan­i­cal

re­lease for the rear sway bar op­er­ated via a lever in the cab, while the Jeep Wran­gler Ru­bi­con has an elec­trome­chan­i­cal re­lease for the front sway bar op­er­ated via a dash­board switch.

The other solution is to have some means to vary the ten­sion on the sway bars – softer for off-road; firmer for on-road – which is ex­actly what KDSS does.

With KDSS, one end of each sway bar is con­nected to the chas­sis via a hy­draulic cylin­der, rather than be­ing di­rectly at­tached to the chas­sis. Th­ese two cylin­ders, one at the front and one at the rear, are then con­nected via hy­draulic lines that al­low an ex­change of hy­draulic fluid be­tween the two.

When the ve­hi­cle is corner­ing on-road and tries to lean over, the pres­sure from the front and rear cylin­ders is can­celled out, which doesn’t al­low an ex­change of fluid be­tween the two. With the ends of the sway bars locked solid, the sway bars then have to twist – as they do in a con­ven­tional sus­pen­sion – to sup­press body roll.

In an off-road sit­u­a­tion, where rough ground will have the wheels on one side of the ve­hi­cle trav­el­ling in op­po­site di­rec­tions, fluid can flow be­tween the two cylin­ders. This re­laxes the sway bars for greater wheel travel. On the Prado’s rear axle, KDSS in­creases wheel travel from 465mm to 565mm (more than 20 per cent).

The other ben­e­fit of be­ing able to re­lax the sway bar for off-road use is that a stiffer sway bar can be em­ployed in the first place on the VX, which leads to flat­ter

on-road hand­ing.

KDSS, as fit­ted to the Prado, has some mi­nor elec­tronic con­trol on what is other­wise a sim­ple hy­drome­chan­i­cal sys­tem. The first­gen­er­a­tion KDSS, as fit­ted to the Land Cruiser 200, is purely hy­dro-me­chan­i­cal with no elec­tronic over­ride.

KDSS came about af­ter Toy­ota pur­chased the rights to Ki­netic Sus­pen­sion Tech­nol­ogy, a Western Aus­tralian com­pany spe­cial­is­ing in off-road sus­pen­sion.

THE RE­SULT

SO, HOW well does it work? Sur­pris­ingly well, in fact. And while we have al­ways been aware of the dif­fer­ence KDSS makes, it was il­lu­mi­nat­ing to drive th­ese two back to back.

Jump­ing from the GXL to the VX on-road, you could in­stantly feel the flat­ter hand­ing, the shaper turn-in and the bet­ter body con­trol. The VX is also no­tice­ably smoother when en­ter­ing cor­ners and when tran­si­tion­ing from lean­ing over to an up­right stance. The Kdss-equipped VX is also a crisper and sportier on-road drive than the NON-KDSS GXL. Some of the ben­e­fit here comes from the VX’S 18s, but the crit­i­cal dif­fer­ence, namely the re­duced side­wall height, is only in the or­der of eight per cent, so it’s not a sig­nif­i­cant amount.

Off-road, es­pe­cially on bro­ken and rough ground, the VX feels sup­pler and is cer­tainly more ca­pa­ble with all the ex­tra travel. In mud and sand, where travel isn’t so much the is­sue, the ben­e­fit lessens.

The sad part of this tale is the price hike from a GXL auto ($61,990) to the VX ($73,990). How­ever, you do get plenty of worth­while kit with the VX – un­like the more ex­pen­sive Kakadu, which in­cludes ad­dons with lit­tle value.

It’s just a shame KDSS isn’t fit­ted to the pop­u­lar GXL, or at least of­fered as an op­tion on the Land Cruiser 200 GXL diesel.

Kdss-equipped VX has less body roll and flat­ter han­dling.

KDSS in­creases wheel travel, al­low­ing the VX to tackle ob­sta­cles.

The lack of KDSS means the GLX has less body con­trol.

Less wheel travel hin­ders the GXL in the rough.

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