Brunhilde needs new tires to go to Amelia Island. She's an 86.5 with 7 inch rims in front and 9 inch in the rear. Current setup is 225 front and 245 rear and Brunhilde has LSD so this combination gives me more understeer than I like. I am pretty much stuck with 225 on the front and 235's will fit on the rear but the 245 is a better fit for the rim width.

If I go with the 245 in rear, what can I do to get the car more neutral? Tire pressures are an obvious answer but running 65 psi in the rears to make the car loose seems kind of dumb. Therefore, I am also wondering if Ott links on the rear sway bar or other relatively cheap mods will be effective.

Your input is appreciated.

Thanks

 

With 7x16 front wheels you are very limited options wise. You might try finding some stickier rubber for the fronts like the Toyo rubber but whether such are suitably legal remains to be seen. The Louie links were intended for folks to simply turn up for a track day and in a matter of seconds set the rear links to the stiffer setting to move the balance a bit to the rear but have never tried such on skinny rubber. You can also experiment with front camber a bit- try 1 degree maybe 1.25 degrees .

Bottom line 225 section up front is just too skinny compared to the potential performance of the 928.

 

Many variables at play here, and it brings up the age old adage coined by Jim Bailey: "The best performance upgrade is making sure everything is functioning as the factory intended" (paraphrased, I don't have the exact verbiage).

What kind of shape are all the control arm bushings in? See these threads:
https://rennlist.com/forums/928-foru...-bushings.html
https://rennlist.com/forums/928-foru...cker-bars.html

How are the shocks? Which springs are you running? When was the last alignment? Where is the ride height set to? What tires are you running now, how old are they? What tire pressure do you typically run F/R?

Before someone feels the need to point it out, yes I'm fully aware the 928's are known to understeer. But before one jumps down the rabbit hole of upgrading / modifying the suspension, best to make sure everything is 100% first.

 

Wheels are 17 inch. Shocks and springs are original (Boges). All bushings are original, all appear to be as intact as they can be for their age. Car is a documented 42k miles to the extent that matters. Tech inspections prior to DE revealed no issues, to the extent that matters. Car last aligned 2019.

My belief is that the original tire setup was 225/16 all around. Later Porsches that serve as our sources for 17" wheels are staggered.

Assuming I replaced all the bushings front and rear, would the stagger promote understeer or is the width difference negligible on a 928 with all new bushings?

 

I have an 86.5 "S3" with 16x7 fronts running 225/50s and 16x8 rears running 245/45s Yokohama Advans. I also have 928 Motorsports Konis Coilovers. The car still understeers; however, when I replaced the Droplinks with Hans-Otto ones for both front and rear, the car feels more neutral now in corners and tail rotates nicely around. Turn-in is also sharp and more responsive to input. I chalk this up to newer bushing and "bigger bar" set up configuration of the Droplinks.

 

Sounds like your car is in good shape. Over the years I've seen a number of cars (not necessarily 928's) going in for an alignment only to find something relatively simple like a failed bushing. I'd get some feedback from those who've done the full replacement, and possibly ponder the rebuild Weissach rocker. If that's wiggling around your rear toe is going to be wonky during a turn but probably be fine on the alignment rack.

I like methodically testing things. I've talked to a couple local 928'ers about buying a Durometer to test bushings before replacing them all like @Dundertaker did here:
https://rennlist.com/forums/928-foru...l#post17093310

Is this understeer you are trying to correct only on the track or on the street too? What are your tire pressures and where is your ride height set (stock or lower).

The Ott drop links are so easy to install it wouldn't hurt to pick up a set and play with them.

 

I am really feeling the understeer on the track and skidpad and I am not a good enough driver to judge whether it was induced by my incompetence or really came from the car. To me, it seems like it takes a lot for the rear to break loose and it comes on pretty suddenly.

Ride heights are set to factory spec. Tire pressures are factory spec 36 front 44 rear.

I'm going with the 245 rear as I don't really have a choice and will try the Ott links on the rear which can fortunately be installed at something close or identical to stock.

 

If you have 44 psig in the rears and you still have chronic understeer then something is a bit suspicious whatever it is. I would suggest that 44 psig is for when you have a "large" passenger or two and a suitcase full of concrete in the hatch. Run around with a solo driver and that rear pressure and you will invariably find that the centre of the tread wears out quicker because of the ballooning effect and the relative lack of grip should negate the natural understeer. That Porsche set the RDK sensors the way they did is why many folks [myself included] chose to defeat the system so they could run with a more realistic 33 psig or thereabouts.

The driver also has a role to play in this as applying too much lock will cause the front wheels to lose traction as will "not enough" throttle. On an autocross event we had over here many years ago I saw a Dutch chap wreck the front rubber on his 997 in a matter of minutes. Of course he blamed everything except himself even though it was perfectly clear that the front of his car was "bunny hopping"- not saying that is the problem here [just to be clear] but driving style and expectations can impact perceptions. A given car with a given setup can only go round a bend at a specific speed and a good driver optimises that but there is only so much that can be had without modification.

That you have a 7 inch front wheel of that style tells me you have a set of wheels that were never intended to be fitted to a 928. As I recall my GTS original front wheels were 7.5 inch affairs and I found a 235 section made a useful improvement. Indeed the GTS 7.5 inch front wheel could take up to a 245 section. Mate that to a 265 on the rears and you would probably be in good shape.

If you really want to be serious about handling the car begs for a 255 section up front but then you need the wheels to carry such. At the moment I have 265's all round and normally use a 285 or 295 on the rears but there was nothing available locally.

 

Yes, I have wheels that were never intended for use on a 928.

 

I've never run that much tire pressure in a 928. I typically aim for 32/34 with most setups.

FWIW the Corvette's I used to help setup for track days would go out on mid 20's psi cold and come back in the low 30's. This is very dependent on tires of course, but just an example of changes in hot / cold at the track.

You should have a friend stand at the nearest point off the track to check your pressures as soon as you exit the track. Even better to take tire temperatures.

My most recent track setup was 235/40-18 & 265/35-18 and I cannot say I really had issues with understeer, but I'm not the most experienced driver. But then again I'm also running stiffer springs, Koni reds, with a ride height and front wheel offset some claim will make any 928 dangerously unstable even at parking lot speeds. So what do I know?

I haven't been on the track in a while, but my next setup will have 10's all around with 265's.

 

Hacker do you need a set of 18 x 10 wheels with 265 tires I might have a deal for you

 

The early 928's had a bit of a tendency to understeer.

After the infamous Porsche 930 Laguna Beach lawsuit, Porsche went back through the designs and made absolutely sure that every street car had "ample" understeer. Limited slip designs were altered, suspensions were changed, slightly, to increase understeer. Proportioning valves were added to ABS systems, so there was never enough rear brakes to allow the rear end to rotate, even in the wet. By the time the front suspension was redesigned for the 1987 models (which the 1986.5 cars got), the cars had noticeable understeer. Add in a limited slip and it gets worse. Lower the car much below the 173mm specification, in the front, and the cars will go pretty straight when you turn the steering wheel....requiring a bit of a lift to get them to "turn in". Add some additional rubber in the rear, on some wider wheels and the cars absolutely "plow". You virtually need to remove your foot from the throttle to get the cars to "turn in".

There's a couple of simple things you can do to reduce understeer, which I would be happy to share with you, on an individual basis....quietly.
Send me an Email at GregBBRD@aol.com and I'll toss a little bit of "light" your way.

 

On the 86.5, the factory recommended tire pressures are 36 front, 44 rear, exactly as Otto is running. For the street, my car prefers these numbers. I have not tracked my car, but my autocross friends (non-928) report running very unstock tire pressures for autocross.

 

I installed drop-links at all four corners years ago. Fixed the push. Now the front-end dives in to the apex nicely, with rear following the front. MUCH better. Stock handling was characterized by the front not feeling like it wanted to steer into the corner, not like a typical "push", more like the nose would point wide of the apex all through corner. Weird. My previous car was a 2nd gen RX-7 Sport that handled like a go-cart, so needed to fix the 928. Gotta say that, although heavier feeling, the 928 handles better than my 997.

 

That's exactly how my 928 felt after adding the Hans-Ott Droplinks. Better/sharper turn ins and rear rotates more nicely in conjunction with the front.