SharkSkin

OK, I have a 78 928 with 16" phone dials. It needs tires soon, and I've been browsing around and found wheels on ebay, with & without tires. I've heard that my rims can rub against the brake caliper on hard cornering. True? If so, that alone is reason enough to replace them. If this only applies to cars that have been retrofitted with non-stock brakes, I am interested in the details, but it means I can wait perhaps until the set of tires after the next set before I make a change.

So, with respect to wheels, I'm looking for specifics here(yah, I know... damn engineers). What is the "correct" offset for this car? I mean offset as measured from tread center to hub face. Other measurements like hub face to inner edge of rim may be useful too, if rim width is accounted for. Ideally I'd like a set of polished slotted 17" rims. I've seen sets of various widths & offsets, mixed width and same width sets, and I've seen various spacers for sale. Can someone summarize the tire/wheel compatibility issues, purpose of spacers, etc or provide a pointer to some place that summarizes the things I need to know when buying used rims? For example, can I just slap on a set of Boxster rims/tires, or are there issues? What stock rims can I put on the car and fill up the wheelwells while preserving the stock offsets? My general engineering sense says that I should get wheels with the identical offset(measured tread center to hub face) as what I have now because then the suspension geometry, bearing loads, etc will all remain "as-designed". I assume this matters on the rear as well because of the Weissach(sp?) setup. Maybe this assumption doesn't bear out in this case for some strange reason?

Also I'd like recommendations on tires. The best tires I've ever had were the Pirelli P6 from the mid-80's, on a 510. They held on better in the rain than BFG T/A's did in the dry. They were incredible, and lasted quite some time. Second best, on my first-gen Z-car, were Yokohama A-509's. Neither of these fine tires are available anymore. I now have Yoko ES100's on the Z, and they are excellent in the wet and somewhat less grippy in the dry than the A-509's. Trouble is, I don't think they have an appropriate speed rating for the 928. I've looked at the Yoko AVS and it seems up to the job, but since this is an entirely different car I thought I'd ask the board about their experiences.

I live in Silicon Valley, so anyone from the area will know the driving conditions. Page Mill, Highways 1, 9, 35, 17,92, etc If you're not from the area, what I'm looking for is something that will be good for tight, twisty roads but will still work well in the wet, whether it be rain or the odd sheet of water running across the road in the apex of a turn. It also has to be a tire that I can take on a 3 to 8 hour trip without driving me crazy from trying to follow all the grooves in the road.

Oh, one more thing. I plan to take the car to Porsche and try to get the free replacement of aluminum ball joint brackets. Does anyone know if they are still doing this? Also, I'm assuming that it's best to do the alignment on new tires, though some shops say otherwise because they mount the alignment gizmos to the rim. However, my fronts have been wearing unevenly and I'm afraid that this might be an unwanted factor during the alignment process. With the inside edge worn down the load on the suspension will be different than with a new tire to some degree.... the question is, to what degree and does it matter?

Thanks in advance...

S

GlenL

S,

Please be aware that wheels have been discussed extensively. Check the archives and there's a great write-up at www.landsharkoz.com The bottom line is that the front wheels need a really big offset (65mm) and no other Porsche needed that. Don't worry about the brakes unless you get larger ones.

I've got those new Yokos. Like them and they're W rated for 168mph.

SharkSkin

Actually I didn't find a thing on tires at that link. 928gt.com had some good stuff though. Couldn't find anything of substance on how Porsche handles the ball joints.

Anyone have any thoughts on my question above re: alignment and worn tires?

Thx

LT Texan

Amazing, it's the first link on the page.

http://www.landsharkoz.com/tt/ttwheels.htm

SharkSkin

DOH! wow.... I looked right past that somehow...

V-Fib

Club Sports and New Yoko's, a hard to beat combo. IMHO



Anthony Tate
79/928 Silver Metallic
(Club Sports/Yoko's of course)

SharkSkin

I was actually looking at 17" wheels, maybe these: http://www.928gt.com/Wheels-Tires/W-mmc2T.htm

Or these: http://www.928gt.com/Wheels-Tires/W-MMcup.htm

But I can't find a good close-up pic. Are the Club Sports available in 17"? 928gt.com shows them only in 16". I'm curious about weight of the above linked items compared to real GTS wheels, and I want to see better pics. Ideally I'd like to see a straight-on pic from the rotation axis, and one 45 degrees away from that, and large enough to show detail.

I'm not one to scrub the curb, but if it DOES happen I prefer a wheel that won't get ground up. I sent an email with the question about weight and a request for pics to 928 Specialists, and am waiting for them to get around to sending a reply.

Also I called PCA and they said there is no recall or tech bulletin of any kind for my 78 car. I really think they should cover the ball joint replacement, but it seems that they are in denial.

S

Ed Scherer

Well, here's a closeup (well, it will be if you click the small version below) of the Cup wheel. I got these for my winter wheels three years ago.



There's a few more photos at this page that show the same wheels.

BTW, some points about the cup wheels.

• they're practical -- easy to clean due to smooth surfaces and no real crevices
• good aesthetic match to 928 (in my opinion) -- convex spokes are good match to 928's convex body

Definitely not as much appeal as my Kinesis Supercups for my summer wheels (again, IMHO), but more practical if you don't want to spend time cleaning around details like exposed bolts on a three-piece wheel.

SharkSkin

Yeah, those cup rims are beauties. But.... I see that you once had slotted rims on the car... I don't suppose you have those waiting around for a buyer, do you? I've been looking all over for a set of slots, 9" & 7" set, painted(original) or chrome.... all I find are dinged rims or rims that have been painted blue, red, etc. and curb-scraped. I suppose it wouldn't be a big deal to recondition a set if I could get them cheap, but they have to be true and free of dings or deep gouges.

Second choice would be a set of cups, now that I've had a close look at them. From info on your site I found the manufacturer of the wheels... they don't really mention that on the 928intl site ... I see now it's Mille Miglia. I'm not so worried about weight now. This concern comes from my Z, which came with AR Libre copies, which turned out to be significantly heavier than the originals. Anyway, whenever I get sick of looking for slots I'll probably be calling 928intl.

Thanks for the info!

S

Ed Scherer

Yeah, I've still got the original anodized 7-slots. They're the original 7x16 fronts and 8x16 rears (were there ever 9x16 slots?). Sitting naked (no tires) in an attic. As I recall, in good shape. If you're interested in them, I could take photos of them and post them. Yeah, I'd sell them. I'd need to look at them again and do a little research to determine what a reasonable asking price.

SharkSkin

Ed, if you're willing to take a look at them and post a price, I am definitely buying wheels soon and will seriously consider what you have to offer. Take your time though; for various reasons I will not be able to make a move on this until late next week at best. Also, I still have sort of an internal debate going over the potential handling gain vs ride quality trade-offs of 16" vs 17". The ability to run 255's on the rear seems like very little gain over 245's, and I'm not yet convinced that the 1/2" difference in sidewall is going to make a huge difference in cornering except at the extreme limits of traction, and even then it would probably amount to fractions of a second on a track. I'm not looking to build a race car, though I will definitely push the envelope.

What are your thoughts on 17 vs 16? Have you had any particular tire in both sizes, and if so can you share your observations?

Thx

S

Ed Scherer

OK, I'll see if I can snap some pics during daylight over the weekend. It's been a couple of years since I've seen them, so I don't remember details (like exact condition).

Probably can't help you there. Here's the combos I've run:

• Dunlop SP8000 225/50 on front 7x16, 245/45 on rear 8x16, stock suspension
• Bridgestone Potenza S02-PP 255/40 on front 9x17, 265/40 on rear 10x17, Bilstein/Eibach coilovers and adjustable sway bar drop links
• Bridgestone Potenza S03-PP 255/40 on front 9x17, 265/40 on rear 10x17 (same suspension as previous)
• (winter) Bridgestone Blizzak LM-22 225/45 on front 7.5x17, 245/40 on rear 9x17

I've intentionally stiffened up my ride, and I like it that way. You might not. If you can arrange it, I'd see if you can drive a few other people's sharks before making your decision.

One thing I've found is that my confidence level in my shark (especially when pushing it hard and close to the limit) and my ability to control it is greater than anything else I've ever driven when running on good "max performance" tires like the S02s/S03s.

Oh... another question you asked was about wheel weights. I remember research this a long time ago. Google search for "wheel weights" or "wheel weight database" (things like that). You can quickly turn up some nice databases like:

MySportsCar.com Wheel Weight Database

Hope this helps.

Marc Schwager

Replace the ball joints before you dump a bunch of money into tires! Then do the tires, wheels and alignment etc. The ball joints are a real safety hazard. They fail catastrohically with no warning.

Of course it is important that your wheels look good so you can admire it when the left front detaches from the car on Hwy 280 at 112mph and goes sailing past you :-)

SharkSkin

Funny Marc.... reeeeal funny... I'm aware of the risk... I'm going to get all of that done with the old tires.... they're crap, and I don't mind grinding them off a bit(the 10+ mile run between replacing the ball joints and getting it aligned). What I may end up doing is put the parts on, get it aligned, put the new tires on, drive till it settles, then get the alignment checked one last time.

Something just bugs me about getting an alignment on tires that are unevenly worn. IMHO the forces acting on the suspension are different with tires that are unevenly worn, and will result in a different "set". Whether the impact of this is even measurable in practical terms, let alone significant, is the part that I don't know. Following the steps I mentioned above will get me the answer to that question, since I can't seem to find the answer elsewhere.

Ed, I looked again at the pre-sale pix on your site, and to me it seemed like the rears stick out a bit more than I would expect for the width.... do you happen to know if the rear hub flanges are further apart on your '90 than on my '78? 928gt.com lists stock offset for '90 at F-65/R-52.3.

Thx,

S

Ed Scherer

Sorry, I don't know.

BTW, with the talk about alignment and tires, I just happened to go through this routine this week with another vehicle (minivan, yeah, I know, I've got the practical side of my life to deal with, too). Had some significant front-end suspension problems that got fixed, then had an alignment, tires were old and really bad (including a slipped belt, or so I was told).

Anyway, suspension work and alignment was done on Monday. Tires were replaced today (Bridgestone Turanza LS-T) and tire place did a free alignment check (it was close but not perfect). Close enough for me. Tracks perfectly.