Adding Rear Stabilizer

[djnolan]

I have a stock rear stabilizer bar I want to install on my 87S. It looks like an easy bolt on, since all of the brackets and mount points are in place on the car.

I notice there are some adjustable eccentrics on the drop links.

I wonder what needs to be done when installing it to make sure it doesn't affect the alignment or cause a binding in the suspension travel?

[flash968]

the eccentrics in the rear are for ride height and camber. no adjustment is needed if bolting on a sway bar, as long as you realize that what you do to the rear should be compensated for in the front. if the car didn't have one on the front, and you add one in the rear, you should increase the size of the one in the front to balance it. failure to do that can easily result in oversteer.

[murrayg]

The eccentric is different for models with fitted rear sway bar and those without. The SB arm actually bolts to this eccentric. If it doesn't have a stud for the SB, just replace it with the eccentric for the SB fitted model. No adjustment is required as long as you don't loosen any other bolts on the drop link. I think that's what you were asking??
As far as balance goes, these cars understeer from the factory. The rear bar will reduce the understeer, with no other changes in the setup. It would have to be a massive rear SB to put in an oversteer situation. Overall, great addition to your car.

[djnolan]

From what I have read, the sway bar is the stock size and is matched to the one on the front. So I was referring to how to adjust the drop link bolts. There is a small eccentric in the sway bar drop link (shackle) bolts. I was not planning to adjust the large eccentric on the rear control arm. (pardon the untidiness, planning to clean up, replace bushings if available, , etc)

[flash968]

it doesn't necessarily take much to create oversteer. heck, i can do it to most any car with just tire pressure change. as an example, merely going from the 1st hole to the 3rd hole on an M030 equipped 968 will change it from mild understeer, to tail happy. granted, you are starting with larger bars.

on a 944, if you are running the OEM tire sizes, you may not notice this as much. however, if you run low profile tires, sway bar changes can make a bigger difference, just as can alignment changes.

definitely a good addition, as long as you make sure you balance things out, and are prepared for the results.

the single biggest handling and cornering improvement will be made with a good 4 wheel alignment, including ride height set, and should be done with any suspension change like this.

[murrayg]

So I was referring to how to adjust the drop link bolts.

Bolt it on and drive it away. The eccentric doesn't adjust the SB, just ride height. Don't loosen anything else, and you're good.

This is being made into a bigger deal than it should. The rear sway bar is an option on your car. Porsche will add it or delete it with no other changes. Adding it will flatten the body roll on turns, with no other effects. It certainly won't make your car oversteer.

[flash968]

i guess my first questions should have been "what is the size of the front bar, and what is the size of this bar?"

all things being equal, it will flatten the car in moderate speed turns, but not without other effects. in all situations except dead straight, it will add effective spring rate to the rear corners. this can easily cause power oversteer on a dip (which is different than regular oversteer).

depending on camber angles, it is extremely easy to create oversteer in these cars. like i said, i can do it with just some tire pressure change.

if you don't feel oversteer when adding a rear bar and not matching the front, it is likely because you just aren't driving fast enough.

as an example, i had to go up to 31.75mm in front to balance out against my 22.25mm rear. the 30mm front was not big enough, and the tail came swinging out with the slightest twitch. the same was said when i had the 30mm up front and went to the shortest hole on the 19mm.

of course, none of this showed up at speeds below 80, or in turns less than .75g. most people never see turns with a load over .75g the whole time they own a car, so it's very common not to experience oversteer.

it's still a good thing to add. just get a good alignment, including ride height, and truly enjoy the benefits.

[djnolan]

Wow, .75Gs. The gulleydeckers should be able to handle that but I better budget for some fresh rubber.

[flash968]

lol - i'm looking forward to seeing what i am cranking up in the new targa gts. it has a g-force meter on it.

[cockerpunk]

alignment plays a major role in oversteer/understeer tendencies, rear toe being the biggest one. the 944 has pretty poor rear suspension geometry which leads to toe out all the time, everywhere, under almost all suspension motion. rear toe out will push the car into oversteer easier than any other single modification.

also keep in mind, on an open dif car (like most of these cars are) adding rear bar, will cause the car to pull up an inside wheel easier, and thus, will limit your power down. as a general rule, on an open diff car, run as little rear bar as possible. in fact, on any RWD car, run as little rear bar as possible.

[djnolan]

Originally Posted by flash968

i guess my first questions should have been "what is the size of the front bar, and what is the size of this bar?"

The front stock bar is 21.5 and the rear is 18mm.

[flash968]

it's interesting that the combination changes so much over the years, starting out with that one, then moving to a more traditional larger bar up front relative to the rear, and then reverses back again, and then as soon as you get to the 87 model it returns back to the traditional setup.

please note there is an error when you get to the 968

[The Glademister]

I've looked at that chart a lot and it's really helpful but what's up with the newtons on front springs?
For example - 1985-1991 944T (M030 opt) 3250N
When you convert 3250N = 730.6291 lbs. using this...
Convert newtons to pounds - Conversion of Measurement Units
That just can't be right???

[flash968]

lol - yeah - those numbers never worked for me either. i've found a LOT of stuff in clark's that isn't right. still a decent resource, but definitely not perfect

[Jfrahm]

Newtons over what distance? Probably not an inch. Per 100mm i't be about 180 in/lbs

[The Glademister]

Originally Posted by Jfrahm

Newtons over what distance? Probably not an inch. Per 100mm i't be about 180 in/lbs

That sounds about right. I just put springs off a '86 951 with M474 option on my '82 931 and they feel a little less than 200 lb. springs.

[flash968]

the stiffest spring used on these cars (except for the cup cars) is 160 lbs/in (28n/mm). the M030 springs are also the same rate, but progressive.

the weight of the car will dramatically affect how stiff the spring "feels".