Can anyone describe what CATS actually does?
 

Ive done some research online and so far all I've learned is that it adjust the suspension according to conditions; it has sensors to detect things like acceleration and so forth and adjust accordingly, but I still don't know what it does in terms of driving experience. Ive had my working and not working, and I could barely tell the difference in terms of ride stiffness (I'll bet most people wouldn't know if it was on or off). This is a pricey option and struts very expensive, and yet I can't tell if it's more than a gimmick. Can anyone describe exactly what it does (besides stiffing a strut), and under what conditions, and how does it help performance driving?

I am no expert on the CATS. System but I noticed two main things with it.

First, when you slam on the brakes, it prevents nose dive to a really high degree, in fact this is the most impressive part of it. Conversely when you hit the gas the nose does not go in the air.

Second, when taking fast turns, it prevents a lot of body roll and keeps the car flat.

Hope this helps!

The S-Type description from JTIS doesn't say much but the XK version of the same year is a lot more thorough.

Avos also had his CATS shocks rebuild and dyno tested so has some plots of what the difference really is in this thread:
https://www.jaguarforums.com/forum/x...shocks-112799/

Soft vs hard affects both compression and rebound but a much bigger change in rebound.

The first two replies summarize it well,


CATS uses several inputs,

G-sensor/accelerometer,
steering wheel angle sensor,
control-arm-angle sensor at each corner,
individual wheel speed,
etc,

with these inputs, the CATS computer controls the dampers at each corner. This control is basically adjusting the dampers valving on the fly, allowing softer/harder performance from the damper...

What this translates to is a suspension that can adapt between softer and harder, which means flatter handling, smoother ride, etc.

Interesting. I guess that's why it's not so noticeable when the system doesn't work, because in essence it means it's working all the time. You don't lose performance per se, you lose the minor comfort improvement when performance is not actually needed and it reverts to the soft setting. With my low profiles I really feel the road anyway, so don't notice much improvement when they go "soft"

You probably ought to notice the diving on braking if it's not working.

We almost forgot to mention the most impressive part of the CATS system...where its $500+ dollars a corner in parts to buy new shocks!

Quite costly new parts on an originally expensive low volume 10-15 year old imported car. Who'd have thought?

That doesn't follow if the default is to go hard. From what I can tell from the above, the shocks go soft when not needed (soft being a subjective term) and the fronts stiffen up in response to deceleration to prevent the diving. If they are already as stiff as they can get, which is the non-functioning default, the results should be the same. it's just that when you want them soft, they will stay stiff. And I can't believe I'm saying that with a straight face.

Buy a like-year Cadillac! Air-adjusted "active" struts are $1,450 EACH!!!! - and no longer made. (There is a "passive" workaround, with a fixed value resistor that fools the control module).

Moral of the story: Suspension repair/upgrade exceeds the book value of the car.

Crazy. And it's not like it provides a whopping benefit for the price.

I can attest to all the behaviors noted above. Nosedive on braking in my ST-R is practically zero and the car doesn't go nose-up as much as it just *squats* and GOES under hard accel... We have plenty of twisty roads (and I favor them, highly, on my daily commute), and the harder I drive it, the flatter it corners. The transient behavior is nice, too, because of the valving adjustments on the fly: the car goes from ever-so slight understeer at turn-in, to absolutely neutral mid-corner, to slight oversteer on exit - exactly what you'd expect from a stiffness profile that moves from hard at the front, to hard on the outside, to stiff at the rear :) If you know how to throttle-steer, it makes for maximum fun-quotient when you drive it hard!

Ken

The CATS is very noticeable on the XJ with air suspension, when it stops working. The shocks default to firm mode if there is an error and it totally changes the feel of the car. It becomes really heavy and stiff and rides like you've filled the car with lead bricks. It's probably less noticeable on a coil-sprung car though...

Haven't had much opportunity to throw it around like that. Seems whenever I'm on one of the few windy twisting paved roads around here, there's either traffic or an anxious chaperone in the passenger seat :icon_smile: