[SouthernDevGirl]

At the encouragement of my wife, Tiffany, who entered into a discussion on turning radius, I've invested some time to create iterative models in determination of the steering cut angle and the pivot-point of the chassis when the steer-tag is at its maximum cut (believed to be 23 degrees).

Factoring the information provided here and elsewhere, attempting to split differences where they exist, I believe the following is likely the best representation:

(note: I've rounded to the nearest inch for simplicity)





I don't claim this to be definitive, it's merely my best attempt without having definitive details of maximum wheel-cut.  

I do realize the radii are slightly off from the published specs; however, based on my models it appears the published specs are rounded for simplicity.

If the wheel cut were any higher than 45 degrees, none of the published data would align unless the pivot-point was 1' or more further behind the drive-axle.  In that instance, other numbers would not align to published data.

If anyone has calibrated / accurate measurements or definitive specifications on front-wheel cut, please let me know and I will update.

[jdkskyking]

Very interesting information and a good reference as to the turning radius performance of the ZF RAS system (Rear Axle Steering).

In recent years, I have gained some additional knowledge of the ZF steering system both front and rear. There are components in the RAS system that can impact how the tag axle operates. One being the pressure accumulator. Based on information I received from the factory, the accumulator itself has a ten year lifespan. 
The accumulator should also be serviced on an annual basis. I believe the service consists of checking the nitrogen pressure provided there is no system hydraulic fluid leak noted during service inspection. I believe 250 psi is used on my 2005 system. 

If the accumulator nitrogen pressure leaks down the system may not operate as designed and impact operation especially when backing up. Backing and turning is impacted significantly, the tags can turn in the wrong direction due to the forces acting on the tires. The accumulator pressure also assists in keeping the tag hydraulic actuating cylinder centered while traveling straight down the road. 

FYI - The ZF RAS system is a closed looped hydraulic system that is completely independent from the engine driven hydraulic system with one exception. The two hydraulic systems share a common part, the forward master cylinder. 

ZF RAS .pdf Size: 2.79 MB  Downloads: 24

BTW... Bosch is now the supplier of the ZF steering components.