Super Hicas Questions

[hardmoney]

Ok Ive done my searchs and cant seem to find any real info on Super Hicas,The most I can find is a few threads in the 240 forum explaing what it is.What Im wondering is how to test its working properly.Sometimes hanging a corner Ill feel the back end kinda swing out like the tires are low on pressure other than that i never really notice it.Any way I think ive read it only adjusts about 1% at speeds over 20 or 30mph. I know a few years back Q45tech said something about how he had put washers between the ball joint and tie rod for a tighter fit? Anybody have anymore info on this?

[Highway Q45]

If you have the factory service manual that came with the Q45 there are test procedures and a troubleshooting guide in ST-46 to ST-63. I have the Super Hicas and can honestly say I only noticed it when doing a real high-speed evasive manuever when a large rock appeared in my lane. As tail happy as the Q45 is I was surprised how fast it recovered. I can sometimes feel it on high speed sweepers when the steering starts to feel like it's near it's limit of grip. The main complaint I have is it's complexity in relation to any tangible benefits and parts are incredibly high. The PS hose on the drivers side runs right next to the header and I blew that hose from the heat; the short OEM hose was $160 so I installed fireproof tubing before replacement. There's not really much info on it for a Q other than a reference I found quoted below:

Quote »You may have heard of Passive Rear Steer. Familiar to many generations of Europeans long fond of hot hatchbacks such as the Peugeot 205 GTi, passive rear steer has consisted of toed-in rear wheels.

Since toed-out wheels display appetites for changing direction, toeing the rear wheels inward generated cornering forces at the rear more quickly and made driving on the limit more accessible (to varying degrees).

HICAS, on the other hand, would actively toe both rear wheels by manipulating the lower control arms at the rear, in an attempt to either add stability - or maneuverability in emergency situations. As in the new M today, the system reacted to vehicle speed, and to how far and how quickly the steering wheel was turned.

When the vehicle moved at high speed, the rear wheels would turn in the same direction as the front, no matter the speed of the steering input. This toed the inside wheel outward, and the outer wheel inward. The inside wheel, therefore, transferred less weight to the outer wheel, causing the rear weight transfer to be lower than that at the front and generating understeer. The same would occur under medium speeds and slow steering inputs, albeit that a slight delay in the system would permit the chassis to 'set' in the corner before understeer took hold.

However, at medium speeds and with an abrupt steering wheel motion, the rear wheels would turn first in the opposite direction of the front to enable maneuverability, and then back to the same direction before terminal oversteer could take hold. This was one of the key differences between Nissan's system, and other four-wheel-steering variants.

Unfortunately enough, HICAS disappeared after the 1994 model year, as Infiniti began softening suspension bushings and lightening the Q45’s steering. Today, Active Rear Steer has reappeared on the 2006 M35 Sport and M45 Sport models, the system appears to be similar.

From the above explanation, it seems clear that the system was geared to provide understeer, long the favored behavior for mainstream vehicles. This continues today, teamed with a roll axis (the virtual connection between a vehicle's two roll centers) that further encourages understeer.

As we have noted before, more even than the camber and toe angles of the wheels, the roll axis provides the opportunity to alter chassis behavior and modulate front and rear lateral weight transfer. In the new M35 and M45, note that a double-wishbone suspension sits in place of the multi-link front suspension in the outgoing M45, even as the multi-link at the rear is retained. Given that the roll center of a double-wishbone is generally higher than that of a multi-link, this suggests a roll axis that slopes further upward than it once did.[/quote]
Modified by Highway Q45 at 5:27 PM 1/2/2006

[elwesso]

I would more likely suspect sway bar bushings.

[hardmoney]

Thanks for the reply Wes, however the low tire pressure feeling the car has going around corners is actually the Hicas working. As as matter of fact its the only time I feel it working! Thats whats led me to believe that Nissan would never offer an expensive option like this that the owner only gets to feel every so often. Besides that Ive already replaced all the bushings on the car with urethane.

[maxnix]

Thats whats led me to believe that Nissan would never offer an expensive option like this that the owner only gets to feel every so often.

The Y50 has an electronic version of this. Lighter and more reliable, but only noticed as one approaches the limit.
Modified by maxnix at 5:54 AM 1/3/2006

[MinisterofDOOM]

Remember not to confuse HICAS (the hydraulic version) with Super HICAS (the electronic version).

[Q45tech]

The standard Q has bushing stiffness controlled more rear tow in [on deceleration] and neutral [zero to toe out] on acceleration.

The assumption is you will be decelerating into a corner and at the apex you will start accelerating. Amazing stability when you drive it as it was designed if the rear alignment is set properly and the toe arm bushings are new.

Without HICAS.