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?
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.
