sstrickstein

My 84 has a set of 17" turbo twists on it. Since I've had it I've run the 225/45-17 front and 255/40-17 rear with Dunlop Dz102's. I just did some reading and found those tire sizes associated with the GTS in later year production. I see that the factory recommended that car run 36 lbs air pressure all around. The car like mine with the 16" rims had a different setting of like 32 front and 36 rear. Any suggestions here? On the same thread I read that rim sizes over 17 were not recommended for the 928 as cracking and bolt loosening in the hub could occur. Not that I'm in the market today but does that sound right? And can an 84 928s even fit 18" under the wheel wells without modifying

The Forgotten On

I run 18s and you've seen them at Sharktoberfest a few weeks ago. You just need the correct front offset and tire size.

Try to stay as close as you can to 65 offset, 60 et still works and was the lowest offset factory used on the 928 and can be used without any issues, but 50 et ( found on many turbo twists) can cause tramlining.

I put 245's in the front and they rub a bit on the fender when going over large bumps at speed when turning, but never on the inner fender wall unless you go over a large bump on max wheel lock.

If you put 235's or even 225's on the front you shouldn't have any problems with that.

Also 18 inches is the max you go so you can still drive without knocking your fillings out from the lack of sidewall.

Just be sure to get a quality rim so you don't crack them. Panamera rims are relatively inexpensive and readily available, they are BBS and made of strong alloy, something many aftermarket rims lack.

They also have one of the best offsets (59 et) you can get for 18 inch rims that will fit on a 928.

Many people also run carrera III's on S4's without any issues.

Also, unless you drive on extremely rough roads constantly, I highly doubt you will crack a hub.

Good luck with your decision on your rims.

sstrickstein

With the setup I have now I feel the ripples of the road. I can only imagine what the guys running 19" panamera wheels feel!

Alan

While larger diameter wheel itself is larger - the overall wheel with tire diameter shouldn't vary by very much (or you will have speedo issues & more).

Larger diameters give you a wider range of widths - so it will usually be an issue of offsets and wider widths that will determine fit issues.

Less rubber profile to correct for bigger wheels indeed means you will rely more on suspension for ride comfort. The wheels also become relatively weaker as they get bigger for the same construction - so you will need to be more careful around potholes & curbs.

Alan

76FJ55

The base model Panamera wheels are 18", which are the Panamera wheels that are commonly being used on 928s. I have the 10 spoke Panamera wheels on my 85. there are also 5 spoke Panamera wheels in 18". The Panamera wheels are 18x8 ET 59 front and 18x9 ET43 rear and fit on my 85 S with no mods or rubbing. I'm running 235/40 front and 265/35 rears.

sstrickstein

To redirect this thread. What I was more interested in was tire pressures people that run 17" rims are running.

MainePorsche

After trials with different pressures, I finally went with 36 all around for my 17" Cups. Holds when aggressive, yet nice enough for long drives. Each will have his own depending on likes, and driving styles.

Rich9928p

I run 38 PSI all around on my GTS. That also keeps the RDK happy.

Rich
'93 GTS Cover Girl
'87 S4
'79 5-speed rescue
'79 5-liter Euro track beast

FRporscheman

Start with a pressure, and check your tire wear after a few months. If the center is more worn than the edges, then reduce the pressure. If the edges are more worn than the center, then increase the pressure. If one edge is worn, then you need an alignment.

If the whole tire is bald, then you have a lead foot.

WallyP

'90 GT w/ 17" - I have run 32 psig all-round for years. Street only- good handling, good ride, even tire wear.

Bilal928S4

I agree with Wally. The new tires need less pressure in my opinion. On my 90S4 with original 16" wheels & original size tires I still run the recommended (high) pressures to appease the RDK gods 36psi front & 44psi rears.
The wear is not bad, just near the end of tire life the center is slightly more worn then the outsides indicating over inflation, but not by a whole lot.
On my 89 without RDK & 17" wheels I run 32psi all around and have had good results so far, with about 6K miles.

joejoe

32 psi on kuhmo 275/40 and 225/45

RKD in OKC

Get an IR temp gauge. Start at 36 all round, cold. Drive around 15 to 20 minutes to heat up the tires. Stop and immediately measure the temperatures across the tread. They should be same. If center is hotter, too much pressure. If center is colder, add more. After setting pressures this way, let tires cool overnight, measure pressures. That is where your cold tire pressure needs to be set.

Typically higher pressures are needed for higher speed highway and lower pressures for more aggressive turning. With 18in 235/275 my autocross cold pressure is 28F 30R. Around town is 34/34, Highway road trips is 36/36.

sstrickstein

So here is my IR temp readings 5 minutes after parking at work this am. readings are from outside, middle, inside. This is running 36 lbs cold. My commute is 25 miles highway and 2 miles city.

Left Front: 98,98,98.5
Left Rear 99,99,83
Right Rear: 94.5,94,84.5
Right Front 94.5,95,87.5

dr bob

I've had 17's for years, with Pilot PS-2's. After some experimentation, I'm at 32 rears and 34 fronts for 'normal' driving. The fronts get the extra to help with the outside-edge wear during brisk cornering. My next alignment will include a little more negative camber in the front, something these particular tires seem to like.

Your tire temps should be taken immediately on stopping after brisk driving. Five minutes after commuting-drive means temps have evened out a lot across the tread. And, while the IR gun is convenient, you really do need a contact thermometer to get an accurate read on rubber temps. The pro's use a temp gauge with a penetrating probe (same as 'needle') to read temps 1/8 to 1/4" (or more) into the rubber.

Regardless of all that, I recommend that you measure and record tread depth regularly, using a simple tread depth gauge. I have a logbook in the car with pretty much the whole history since I've been the caretaker, with the tread measurements recorded along with everything else that's been done to the car. Tracking treadwear is an easy way to decide on inflation pressures, identify alignment and other suspension wear issues, etc, before more serious tire damage/wear happens. This after chewing through a set of front tires in just a few thousand miles following an expert commercial alignment. Besides the three-point measurements on each tire, I also log ride height changes, since those so directly affect alignment and ultimately tire wear.

My two cents...