IIRC the "968" castor mounts are recommended regardless of other changes simply because they have a LOT less rubber in the mount compared to the original (even as late as the S2) so much less deflection in the mounts without significant increase in noise or harshness compared to a "solid" type mount. Not sure which 4 bolts Waylander is referring to - if these are the two eccentric bolts and two plain bolts which mount the hub to the strut - then I'm not sure that change is mandatory. As per the Porsche bulletin copied below, you do need to change the two eccentric bolts that pin the rear of the control arm to the mount (and 4 nuts as these eccentrics are threaded on each end). As per Waylander - these part numbers may not be valid any longer but hopefully will get you to the upgraded parts.
Also some info about using 65mm offset wheels on the front...
ARTICLE BEGINNING
TECHNICAL SERVICE BULLETIN : 17 INCH APPROVED WHEELS & TIRES
Model(s):
1987-On Porsche 944 (with M30 option) 1987-On Porsche 944S (with M30 option)
1987-On Porsche 944 T (with M30 option)
1988 Porsche 944 Turbo S
1989 Porsche 944 Turbo
1989-On Porsche 944 S2
Group: 4
Bulletin No.: 9303
Date: September 28, 1993
SERVICE INFORMATION
Concern: Installing 17" Porsche wheels on vehicles previously equipped with 16" wheels.
SERVICE PROCEDURE
Installation Information
1. Front and rear fender well lips must be reworked and/or checked for adequate tire clearance. See Fig. 1.
2. Suspension travel must also be checked. Parts such as brake lines, hoses and brackets must have adequate clearance.
3. New caster eccentrics, rear mounts and nuts must be installed in the front control arms. This change is necessary due to a change in caster specification on vehicles equipped with Porsche 17" wheels. The specification for vehicles equipped with 17" wheels is 3'-15'-45. See Fig. 2.
4. Vehicles must have a rear stabilizer bar.
5. When adjusting vehicles to new caster specification, all alignment values should be checked at that time.
6. When summer tires are used on vehicles with 17" Porsche wheels, snow chains cannot be used. If winter tires are used, only snow chains with Porsche Part Number 911 361 924 00 may be used.
7. Tire pressures for front and rear 17" Porsche wheels is to be set at 2.5 bar (36 PSI) at approximately 20'C (68'F).
8. When using this rim and tire combination, a 17mm spacer plate must be installed on the rear wheel hub. The customer must be informed that if the emergency wheel is needed, the spacer must be removed.
9. Not for Cabriolet vehicles.
APPROVED WHEEL & TIRE TABLE
Tire size Rim size Offset Position Note
225/45 ZR 17 7.5 Jxl7 AH 65mm Front Summer tires
255/40 ZR 17 9 Jxl7 AH 55mm Rear (See installation information A through G.)
225/45 ZR 17 8 Jxl7 AH 52mm Front Summer tires
255/40 ZR 17 9.5 JX17 AH 68nm Rear (See installation information A through I.)
205/50 R 17 7.5 Jxl7 AH 65mm Front Winter tires
225/45 R 17 8 Jxl7 AH 52mm Rear (See installation information A through G.)
NOTE: When using this rim and tire combination, a 17mm spacer plate must be installed on the rear wheel hub. The customer must be informed that if the emergency wheel is needed, the spacer must be removed.
PARTS INFORMATION TABLE
Description Part Number Quantity
Spacer Ring 951 331 611 02 2
Wheel Bolt 904 341 671 00 10
Wheel Nut 999 182 003 36 10
APPROVED WHEEL PART NUMBER TABLE
Size Offset Part Number
7.5 Jxl7 AH 65mm 965 362 124 05
8 Jxl7 AH 52mm 965 362 126 01
9 Jxl7 AH 55mm 965 362 128 00
9.5 Jxl7 AH 68mm 965 362 128 05
SUSPENSION PART NUMBER TABLE
Suspension Parts
Part Number Quantity Required
1. Rear Mount 951 341 023 00 2 each
2. Eccentric 951 341 431 02 2 each
3. Nut (torque to 100 Nm) 900 910 115 02 4 each
END OF ARTICLE
