Night Rider

What is a standard set-up on a 1991 Turbo S?

Mine is 26.8mm front and 16mm rear.

Should it not be 18mm at the back?

I am thinking of going with 968 M030 pack where the front is 30mm and the rear is 19mm anyway but if I would only upgrade the rear to 18mm what would be the effect? More oversteer?

Thanks.

Jason @ Paragon Products

Sounds like it's not a US spec car, but in the US the 88 Turbo S used 26.8 on the front and 18 on the rear. The 89 Turbo (S spec) used 26.8 on the front and 16 on the rear.

badass951

Less oversteer, more understeer.

johne

Umm, are you sure he would be increasing the fronts anti-sway more than the rear. This would increase the front's grip more than the rear. Thereby adding oversteer.

John

badass951

Yes, I am sure. More understeer, not more oversteer!

Danno

"Umm, are you sure he would be increasing the fronts anti-sway more than the rear. This would increase the front's grip more than the rear. Thereby adding oversteer."

Sway bars do nothing to improve overall grip. They just determine the front/rear split of the lateral weight-transfer due to cornering. So the stiffer end gets more of the weight-transfer than the other end. The end with the more weight will end up overcoming its tyre-grip and sliding earlier.

So a stiffer front bar will cause the front end to slide earlier than before, thus more understeer.

Night Rider

Why did porsche change it? To make car less tail happy? Does it feel different?

Night Rider

So Danno to upgrade to M030 pack means;

less body roll,

same grip,

but snappier back end?

DanR 1201

However, if there is less body roll and consequently less camber change, the extra weight transfer due to the stiffer bar can be more than offset by the improved grip. One of those things where suspension tuning often ends up as a black art inspite of the science.

Waterguy

Yes and yes. The increased torque of the 944S2 and the combination of torque and standard LSD on the 951S makes it easier to induce throttle oversteer, by accident in the case of an inexperienced driver. I think Porsche responded by setting up more understeer in the suspension; they made the change early in the 1989 model year. I have the stock suspension with 26.8/16 mm bars and I understeered like a pig during the last autocross. Softening the front struts helped a bit. I can still induce throttle oversteer at DE days, however.

Asarus

Hi Night Rider,

You have the genuine setup for a 1991 951

The rear sway bar was 18mm for 1988 Turbo S and 1989 951. It changed to 16mm in mid-89 model year.

BTW, a 1991 951 cannot be called a Turbo S but a Turbo. The "Turbo S" model is the limited edition in 1988 (only). Since 1989, the 951 is just called "944 Turbo" even if the 1989 951 is almost the same as the 1988 Turbo S.

Danno

"So Danno to upgrade to M030 pack means;
less body roll,
same grip,
but snappier back end?"

Well, there's multiple factors going on here and what we are doing is juggling them all to be optimised. DanR is right on. Typically the stock car is set up such that we have lots of body-roll and the bars are set up with understeer. What this means is that the front wheels will reach 100% of their grip-limit while the rears may be at only 75%. The roll also causes positive camber-gain on the outside tyre; another reason the front tyres slip first and cause understeer.

There are multiple ways we can improve grip. One way is to stiffen up the front end to reduce body-roll using stiffer springs or a front bar. Both ways will increase lateral-weight transfer to the front wheels, but it's more than offset by the increased grip from a flatter contact patch. So you may end up with a sliding at 100% grip in front with only 65% in rear, but that 100% in front will be higher than before.

Then even better is to get stiffer springs & sway-bar in the rear as well. Now we can split more of the lateral weight-transfer to the rear tyres. If we juggle our bar-sizes correctly, we can end up with a situation where both front and rear tyres hit 100% of the grip-limits at the same time. This 100/100% grip limit will then be faster than the 100/75 or 100/65% split we had before because now we're getting the most from both outside tyres.

With the reduced body-roll, we also get more grip from the inside tyres as well since they're flatter now. So we actualy still have the same total grip as before, since that's just based upon how much weight is on each tyre, but we're balancing the weight transfers such that no one tyre is overloaded compared to the rest.