Jaguar independent rear suspension
This article concentrates on the first generation Jaguar IRS, which firmly established the marque's reputation for suspension sophistication, combining as it did smooth ride with excellent roadholding and low levels of noise, vibration, and harshness (NVH).
[1] A Mark 2 saloon fitted with a prototype IRS demonstrated a reduction in unsprung weight of 190 lb (86 kg) compared with a live axle.
The IRS is built into a fabricated steel crossbeam-like subframe unit, that allows it to be relatively easily removed from the vehicle as a complete assembly.
This feature has made it suitable for adaptation as a non-standard component on other vehicles, like from kit-car builders and low-volume specialty car makers.
In order to insulate the passenger compartment from noise, vibration and harshness (NVH), the independent rear suspension was designed to be carried in a separate crossbeam assembly attached to the vehicle body by four rubber vee-blocks.
The bolts that attach the differential to the subframe have small holes through their heads so that they can be safety wired to prevent them coming undone, which would otherwise be difficult to detect since they can only be accessed when the whole suspension assembly is removed from the car.
The outer end of the lower link pivots about a fulcrum shaft, which runs longitudinally through the bottom of each hub carrier.
The position and shape of the rubber vee-blocks and Metalastik bushes are designed to ensure sufficiently rigid suspension mounting for good control whilst successfully isolating the body from NVH.
Each radius arm attaches to its lower link at a point just outboard of the bottom spring mountings and pivots vertically about its fixing bolt.
Safety straps retain the radius arms in proximity to the vehicle body should one of the front securing bolts happen to come loose.
The crossbeam and lower links maintain the correct toe angle of one wheel relative to the other, however due to the relative angles of the trailing radius arms, body roll results in the entire cross-beam and lower links pivoting slightly about the crossbeam's mounting points, thus inducing a small amount of passive rear wheel steering, which may result in significantly improved handling.
When the Jaguar components are re-used in other vehicles, the differential is often rigidly mounted to the chassis, different radius arm configurations are used, and the passive rear wheel steering effect is lost.
[8] It has been fitted as a modification to a number of other vehicles, including the following: Jaguar made several fundamental changes to the design of the IRS for the new XJ40 model, launched in 1986.
The fixed-length driveshaft as the upper suspension link remained, but the lower wishbone became a fabricated steel box section with a much wider base.
In 1993 on late XJ40 models, the attachment of the lower wishbone to the hub carrier was changed to use a bolt with eccentric head, enabling the rear toe-in adjustment that was not possible before without bending the arms.
