17" wheels and M030 suspension

[schmedes1]

I did the searches and did not come up with the exact answer I was looking for...

The feedback on the forum(s) made it clear that if you have a 951 designed for the 16" wheel, you don't just go slapping on a set of 17 - 18" wheels without some front suspension geometry mods.

Here is the question: If you have a late model 951 (not 968) M030 suspension and want to put on 17 - 18" wheels, do you need to install the castor mounts (95134102301) and eccentric bolts (95134143102) to make things right in front?

Too many opinions on this topic, need expert information.

[nynor]

as long as the offset is the same, what is the difference in the wheels, other than the diameter?

[Techno Duck]

Larger wheels put more stress on the suspension components. Everything i have read in the past says that Porsche says you must use the 968 style caster blocks when running a 17 inch wheel. They do not recommend using a 18, though plenty of people do it.

I do not think the bolts are different and you can reuse the old ones.

[nynor]

interesting... i have 17's on my car and i am pretty sure it is stock, with rebuilt A-arms, or whatever. please educate me a bit: what part is the 'caster block'?

sorry for the thread hijack, but i think the original question is getting answered along the way!

[schmedes1]

nynor... no worries!

Can someone else chime in on reusing the eccentric bolts (they cost $66 ea on Pelican)?

[Techno Duck]

I reused the stock eccentric bolts when i switched to the 968 blocks.

The caster block is the mounting part on the rear of the control arms. Its the part that connects the rear control arm to the chassis of the car. The 968 blocks have significantly less rubber.

[schmedes1]

Thanks Jon!

[Razorback1980]

Hey Jon,

After you switched, did you notice a handling difference or a tire wear difference? It's definitely easy to see that the 968 would have less give.

Thanks

[Techno Duck]

I changed many things when i did the caster blocks, so any difference i felt is subjective. Rebuilt balljoints with the longer balljoint pins, new front control arm bushings, new sway bar bushings and i lowered the front a little more since i had the longer ball joint pins.

I will say that nothing i have driven grips as well as my car .

Those are not the same caster blocks i took off my car actually, those are from my friends car with about 65k miles. Mine looked about 100x worse.

Did you get my email about the turbo stuff?

[Razorback1980]

Yes, I did...thanks for the email.

I also appreciate your sharing information on this. I think we are going to 17" inch wheels and hadn't thought about the different blocks.

[Techno Duck]

For those wanting to know, the part # for the 968 caster blocks is 951.341.023.01

I believe the older style blocks are NLA and these supersede them.

Cost is about $78 each depending where you shop.

[ae1969]

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,t 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 94.@ JX17 AH 68nm Rear (See installation information A through I.)
205/50 R 17 7;-i 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 1 82 003 36 10


APPROVED WHEEL PART NUMBER TABLE

Size Offset Part Number

7;-i Jxl7 AH 65mm 96536212405
8 Jxl7 AH 52mm 96536212601
9 Jxl7 AH 55mm 96536212800
91.@ Jxl7 AH 68mm 96536212805


APPROVED TIRES AND SIZES (SUMMER VERSIONS) TABLE

Size Makes

225/45 ZR 17 Front Bridgestone Expedia S-01 Nl
255/40 ZR 17 Rear Continental Sport Contact CZ 91 NO
Pirelli P700-Z NO
Yokohama A 008P NO
Michelin MXX 3 NO or MXX NO Pilot SX


APPROVED TIRES AND SIZES (WINTER VERSIONS) TABLE

Size Makes

205/50 R 17 89 H M&S Front Bridgestone WT05
225/45 R 17 90 H M&S Rear Continental TS 750
Pirelli winter 210 Performance


SUSPENSION PART NUMBER TABLE

Suspension Parts

1. Rear Mount

Part Number Quantity Required
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
------------------------------

[Razorback1980]

Hey Alex and/or Jon,

If I put the larger wheels on, would I need to take this bulletin to the alignment shop because of a change in the caster specification? I am guessing the alignment shop would probably have no way to determine that it changes unless I point it out to them.

[Techno Duck]

I suppose it would not be a bad idea. I personally run a more aggresive alignment on my car due to its auto-x and street usage so i just tell them to set everything more aggressive. I can do this because the place i go to knows 944's well and know what works.

I think really the most important thing is to take it to a place that is familiar with a 944. I would say 9 out of 10 local in town shops do not have the tool needed to adjust toe in the rear. Any place like this will more than likely not know how to align the rear correctly. Ive taken it to one of those places before and they had no idea how to adjust anything in the back. The front is nothing special.

An alignment from a Porsche or Euro shop that is familiar with a 944 will probably run about $100-150. Well worth the money knowing it was done right. You can usually find places familar with a 944 by checking your local PCA region and seeing what places offer tech inspections for DE's or just browsing the local PCA magazine.

If the car is street only, the factory alignment specs should be in the computer. Just tell them what caster settings you want along with that.

[david c.]

Is the 968 caster block upgrade/supercede applicable to cars that came with 15 inch wheels?

If the originals are NLA, I guess that any replacement for any car, now, will have to be to th e968 style?

[Techno Duck]

I am 99% sure only the 968 caster blocks are still available. If you look at the difference between the two the 968's really are superior and i would bet the cost difference is not very big if they are still available.

[david c.]

I'm just wondering if this is another part that I should replace before having my car realigned.

[Techno Duck]

Im pretty good at spending other peoples money. They are only $140-150 for both. Whether or not they actually make a difference is subjective, but less rubber in a suspension is always good.

[vnarma]

Careful folks. Early 968s had a different castor block and was not approved for use with the 17" alloys. They werre very similar to the regular 951 If a 968 had the 17" package, or the M030 Package it had the later style castor mounts. The last year of the 968s I believe all cars had the 968 M030 castor blocks.

[schmedes1]

Originally posted by vnarma
Careful folks. Early 968s had a different castor block and was not approved for use with the 17" alloys. They werre very similar to the regular 951 If a 968 had the 17" package, or the M030 Package it had the later style castor mounts. The last year of the 968s I believe all cars had the 968 M030 castor blocks.

Can you tell me the specific part number for the late 968 M030 castor block? The only number I can find is 951.341.023.01