Can someone explain to me how X-REAS works? Does it have an intelligence (ie sensors, control units, etc)? Or is everything mechanical? I know the fluid is diagonally linked.

Can someone provide describe how it works at a detailed technical level?

Thanks

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What is Xreas exactly?

handles corners better than the cayenne

I think it's marketing crap. So the the shock compresses at one corner and the opposite corner gets more pressure. If it worked so great, why don't sport cars use it?

I pulled it out and quickly found that the aftermarket coilovers actually improved my cornering despite the lift.

see pdf How to identify X-REAS suspension

Actually... higher end sports cars use a similar principle, though they may not have hydraulically linked shocks (Corvettes with their MRCS, LandRovers actually use some funky fluid system for some of their older systems I have noticed).

As a general rule of thumb your average Shock loses performance after about 50k, even faster on more sporty vehicles. I liked my XREAS, but it just wasn't designed for serious offroading which is why I went with an OLW 2.5" Kit.

As for answering the OP, basically the way XREAS works is very simple. When one of paired shocks compresses (i.e. Left Front Shock & Right Rear Shock) the extra fluid is forced through the lines to a main piston cylinder in between the shocks located on the frame rail, the fluid pushes the piston and causes a dampening effect that pressurizes the fluid in the paired shock to compensate for the cornering force.

Its a purely passive hydraulic system.

Just hit 50K miles how can I tell if the shocks are worn out? I do/did >90% highway driving.

You would tell.

Seriously. When your shocks die, you will notice. The "return" will be horrid and not very responsive. It will max extend far to easily. So, for example, you are driving on a potholed road; it would just feel horrid. If the shocks were good, you would feel the bumps but the shock response would be quick and accurate. Not jarring and lazy.

Does it "die" or does it bleed out slowly? I know I may not notice something that would progressively get worse over 20K miles or so.

My xreas is nearing 100k on a truck that has been used very hard off-pavement. I suppose it makes sense that it has softened but I'm incapable of comparing present time to 7 years ago. I fairly often find myself on a particular spot on the freeway that produces a pretty severe roller coaster. The kind of spot that makes things real dicey for vehicles with worn out shocks. The truck still dampens it well with no discernible bouncing.

XREAS - The bottom of the front is connected to the top of the back on the other side. so if i turn LEFT hard then the RIGHT front shock compresses and sends more pressure to the rear LEFT which gets stiffer? This doesn't sound quite right?

I don't know how to think this one through!? any engineers or physics people?

I'm nearing 100K as well and have similar concerns. It still corners well and I don't seem to notice any excessive bouncing over freeway expansion joints.

The truck does nosedive (not excessively) during braking, but I figured that's because I put on high-performance pads and slotted rotors.

you are forgetting about the center control absorber



X-REAS was designed to help improve vehicle on-road handling performance. This technology links each of the vehicle's shocks to it's diagonal counterpart via a gas hydraulic chamber. During cornering or when traveling over bumpy surfaces, the gas hydrauilc chamber acts like a bank "borrowing" fluid from the cross-linked shock bearing the least amount of force and "loaning" it to the shock sustaining the greatest amount of force. This exchange of fluid helps the 4Runners wheels maintain contact with the driving surface and helps lessen vehicle body sway, pitch and roll, making for a more comfortable ride.

Turn hard LEFT and the right front stiffens by borrowing fluid from the left rear which has unweighted. Quickly go from that to a hard RIGHT - like an emergency maneuver - and you have the recipe for a rollover. Xreas seemlessly adjusts to dampen the whole cycle.