marc abrams

Again, thanks everyone for your responses. Although the semi trailing arm suspension system may not be the best suspension system, By the positive responses, I'm now accepting of the fact that Porsche's semi trailing arm suspension system is very good. The rear suspension not performing to my expectations is part my fault, part lack of 15 inch performance tires, and part not understanding that a NA 944 is a grand touring car. With the exception of a wheel alignment, I will need to make some personal choices in respect to accepting it for what it is or making changes to increase the chassis performance. Marc

V2Rocket

big part of the problem as touched on by our Romanian friend is the complete and utter lack of performance 15" tires in the correct size (aside from the outrageously expensive Pirelli P6000).

marc abrams

Spencer, in your opinion, is the P6000 worth the price of admission?

V2Rocket

don't know, never used or even seen one in person.
but $250 per tire is nucking futs any way you look at it.

marc abrams

Got it.

924srr27l

You can change to a slightly smaller tyre size profile, a 60% Sidewall as opposed to the 65%, same width.

205/60/15

These are good, V rated.

http://www.ebay.com/itm/2-BRAND-NEW-...JXaXjw&vxp=mtr

R

harveyf

Hey Marc,

Thank you for your contrition Next time bring up something more tame like K&N filters! But just maybe there is a little bit of life left in this thread.

You got me to thinking. In an article I did years ago I checked the camber gains for the front suspension and came away impressed.

https://newhillgarage.com/2012/06/11...ension-camber/

I have just come back from making a similar experiment on the rear suspension of my street/track car. I removed the wheel and put a jack under this lower shock mount. I raised the car until it just came off the lift. This represents as much compression as I could get and simulates the loaded tire in a corner. Then I gradually lowered the jack. At each data point I checked the slope of the half shaft and the camber at the hub. Note that on a street car, you would probably expect zero camber somewhere around the point where the half shaft was level. Mine is set up for the track so with the half shaft level I show about -2 degrees of camber.

So the interesting point is that with a pure trailing arm suspension, with the hub/road wheel hard mounted perpendicular to the half shaft and based on the rule of complementary angles, the camber would pretty much exactly track the slope of the half shaft. Half shaft sloping upward (from the tranny) by 3 deg would give you 3 deg of negative camber. But in the data, this clearly doesn't happen. The camber change is a small fraction of the half shaft angle change. This probably oversimplifies what is going on but again, you can see that the setup used on the 944 does a pretty good job of managing camber change as the car rolls.

Half shaft Slope__________Camber
Negative Sign suspension__Negative sign is
compression, Positive_____top of wheel
Sign is droop____________tipped inward

-4.8............-3.0
-4.0............-3.0
-3.0........... -2.8
-2.2........... -2.6
-1.2........... -2.3
-0.4........... -2.1
0............... -2.0
0.7..............-1.9
1.9..............-1.6
2.7..............-1.3
3.7..............-1.1
5.2..............-0.9

Note: someone please tell me how to get this text editor to recognize blank spaces! Without having to put in the dots and dashes.

BTW get one of those digital levels. Best $100 I ever spent.

J1NX3D

late dash. 1986MY, Nov 1985 build date.

924srr27l

Ok so longer laterial wishbones and wheel offsets in the Et50's etc...


R

J1NX3D

no the '86's were still early offset 23.3mm. 87's got the ABS late offset.

I have 3 sets of late offset wheels from my 968 I can't use lol.

924srr27l

Oh I think us European's had the square dash upto 85.5, and all 86's are Oval dash.


This goes back to my thinking then that the early 944 has the same wishbone length as the 924 but the wheel offset et23 jacks out the rim to fit the arches, and this changes the scrub radius, motion ratio and camber angles (I think)


With this in mind maybe with no rear ARB and the 20mm front is why it rolls too much... ? only as I mentioned the skinny narrower track width 924 was ok with no rear bar and a 21mm front.


R

MAGK944

I think you are getting yourself confused. The "oval" dash and the "wishbone" or a-arm longer length appeared at different times. On the 944 the oval dash started late 85, the longer wishbone started in 87. So some 85 models (referred to as 85.5) and all 86 models had oval dashes and shorter wishbones.

The other changes on the 944 are the change from steel to aluminum wishbones/arms at the front and rear which also happened in 85.5, and the ABS option which coincided with the longer arms in 87.

Once you have learnt this there will be a written test and a practical test. The practical test is in four parts, rebuild a torque tube, do the belts/water pump/foes, change the rod bearings and reindex the torsion bars. Once completed you will be inducted into the 944 hall of fame! GL

924srr27l

Yeah you've solved the mystery then why I had an oval dash 86 car which had the et23 wheels, and another one I had 87 had the Et50's, I just thought (No longer!) the dash changed at the same time as the wheel offset / A Arms... !



This also confirms why the 924S feels better than the early 44's

I've had all the above work done, (Torque Tube / Belts / Rod bearings / T-Bars ) over 14 years and with 8 transaxle cars (924 / 944)
but not by me! This is all work which is far better done by professionals
with the right equipment and years of experience and NOT something I would entertain doing myself in my garage..












R

marc abrams

Porsche should have used the DeDion suspension system instead of the trailing arm suspension system. The DeDion suspension system is far better.

V2Rocket

^depends how far you're letting it move.

if you look at more modern sporting P-cars (boxster/cayman, 996/997/991) they all still use Mac struts because they are inexpensive yet effective, and largely adjustable to suit particular conditions.

funny enough, the only cars that get wishbones all around are the Panamera, Cayenne-pepper and Macadamia-nut