ferik

Hi all,

I have a 993 WB, with SSR wheels (which you can see a picture of below). When I bought it, it came with tires that are now probably 10 years old:

Pirelli PZero Asimetrico
* 225/40 ZR18 No 3
* 295/30 ZR18 No 3

I am looking to buy a new set of tire. The 993 is my daily driver, I occasionally Autocross (3-4 times a year) and am hoping to do 1-2 DE next year.

I was thinking about buying Dunlop Direzza ZII but they don't seem to make it in those sizes. And even those might have been overkill for my usage pattern, I am not sure.

What would you guys suggest?

http://www.flickr.com/photos/frenchguy/8344588798/http://www.flickr.com/photos/frenchguy/8344588798/ by http://www.flickr.com/people/frenchguy/, on Flickr

BGLeduc

I would probably head to Tire Rack and see what exists in the size you require under the Extreme Performance category.

I personally have used Bridgestone RE11, and Yokohama AD08 on my Cayman S. They held up very well in mixed AX and DE use. They are also very street-able.

Those, plus the Kook RS3 are the only Extreme Performance tires in the sizes I use.

There is a new BFG (the Rival) that is the current "must have" tire among SCCA Street Tire drivers. And also a new RE-11a, plus a soon to be released updated AD08.

Brian

kjchristopher

Where do you live? What climate do you experience?

sjfehr

I'd do BFG Rival. Put 245 up front and 295 in the rear. Will be a little taller, but the grip will be worth it. alternately, you can do ZIIs with 285 in the rear. Either would be excellent for autocross, DE and daily driving.

burglar

As KJC alluded to, the sticky extreme tires (Rivals, Z2, RE-11a) get a little iffy both in deep standing water and below ~50F or so. They also wear pretty fast, ride a little rougher, and are noisy.

But they are super duper sticky in both the dry and lightly wet, and are relatively inexpensive.

ferik

I live in the North East of the US. In Boston. I am wondering if those tires you guys recommend are a little extreme for my light autocross and even lighter DE use.

burglar

Only you can answer that. Everything is a trade off, where are willing to give up? I've DD'd The Z1 and Z2 for the last 4 years in the 3 good seasons only. In winter, I swap. I love 'em, but I also autocross almost every Sunday. I also swap to r-comps for DE days. Wife isn't pleased with the stacks of tires and wheels, but what can you do?

I've never used them, but a lot of autox people that also street their cars use the Continental Extreme DS as a daily. They happen to make excellent wet autox tires, so it's a great way to bring a set of rains without really buying a set of rains. Looks like a bunch of sizes are on sale at tire rack for pretty sharp prices, maybe you can find a set of sizes that wouldn't freak out your awd?

ferik

The Z2 are not available in my size. Neither are any BFG from what I can see.

I don't really understand what size I can use beyond the one of my current tires (225/40 18 & 295/30 18)

Amongst the available in those sizes:

Kumho Ecsta SPT ($670 for the 4)

Michelin Pilot Sport PS2 (more than double the price at $1436)

and Sumitomo HTR ZIII, Hankook Ventus V12 evo K110, Toyo Proxes R888, etc (http://www.tirerack.com/tires/TireSe...earDiameter=18).

sjfehr

Don't get too hung up on those specific two OEM tire sizes. That's just what Porsche installed on your car at the factory, but there are a wide number of tires that fit your wheels; the tire sizes I suggested would fit your car and give slight benefits in performance. Note: Porsche specced out tires, pressures and alignment that cause our cars to always have safe boring horrible understeer. Increasing front tire size and pressure help dial that out and give the car more balanced performance, as does extra negative front camber. If you want to be fast at autocross and the track, you need to get away from some of the street stuff.

ZII and Rival are both top-tier autocross tires that work good (but not great) as DD. From what you're saying, you might be happier with a tire that works great as a DD but merely good for autocross. Michelin PS2 (or it's replacement, PSS) is probably the best, but pricey. Sumi HTRZIII is as good as the PS2 at autocross/DE and very nearly as good as a DD for much cheaper. All these are summer tires and will not work as well in cold temps (at/below freezing) and DEFINITELY not in the snow. If you want to drive in the snow, you're looking at all-seasons (at a minimum), which will suck horribly for autocross and DE. Better off with a 2nd set of wheels and dedicated summer/winter tires if you go that route.

ferik

Thanks for the advice. I do have winter tires (Blizzak on their own wheels) that I use in the winter so I am looking for only above freezing solutions.

Seems the Sumitomo HTR Z III would be a fine choice then. I might go with that.

When you say that I shouldn't get hung up on the current tires on my SSR wheels, what parameter can change and by how much? I am guessing they have to stay 30/40 and 18 but maybe the width can varry? I don't know how that works.

knfeparty

The Rival is not a good choice for any DD use. They come from the factory at minimum tread depth to meet racing regs and are bad in the wet. Pilot Super Sport is worth it unless you need an all-season. Those tires are both extremely quiet and comfortable as well as high-grip and can take a beating heat wise. They do "talk" quite a bit compared to Dunlop Direzza star specs but I highly recommend them.

burglar

Here is a neat link:
http://www.miata.net/garage/tirecalc.html

For tires, the first number is width in mm. The second is aspect ratio, or how much of a percent of the width is sidewall. Because of this, even though your front are 40 series and your rear are 30 series, they both have almost the exact same sidewall height, and therefore overall diameter - they are only 0.5% different.

I know you have to stay with a pretty close diameter tolerance on AWD cars to keep the center diff happy. A quick and dirty Google search came up with a 2% max difference for a C4, but please to not take this as verified info. Perhaps a better question to ask to other C4 / C4S owners.

According to Tire Rack, the OE size on your car is 225/40 & 285/30. That's a 1.4% difference. In those sizes you have plenty of choices - the Conti DW, RE-11, Z2, and more.

You can go wider or narrower on either end, but you need to match overall diameters within the Porsche specified tolerance, make sure the tire is approved for use on the rim width that you intend to use it on, and that they fit in your wheel wells without rubbing. Not the easiest game to play. Best to follow the trials and errors of others before you.

Just clicking around, 245/35 and 285/30 are 0.1% different, and you should have zero speedometer error to boot. More front rubber and about the same rear rubber might help make the car less pushy, it that's something you are after. There's 3 pretty decent tire choices in those sizes that seem like they would fit your intended use. If you have the appropriate wheel widths, and they fit under your fenders, might be a nice upgrade.

kpl

This is on my stock 2003 C4S that I daily drive and put about 20 AX days per year on it, with average about 12/runs per event. I consistently place in the top 3 in a very competitive class in local PCA events.

Tires used were stock sizes except for the Kuhmo XS and Falken's which were 235/40/18 & 315/18/30.
>Kuhmo SPT: 15K mi, took several runs to get enough heat into them to begin working well. Taking a lot of pressure out helped.
>Sumitomo HTRZIII: 12K mi, like the SPT's they took several runs to finally get enough heat into them to begin working well, and taking a lot of pressure out helped. The fronts wanted more negative camber but I don't have the adjustment to do that.
>Pirelli PZero: These came on a set of wheels I bought, stock take offs. Just horrible all around, street and AX. Took forever to get any heat into them.
>Yokohama AD08: 12Kmi, took just 1 run to get warmed up, then were good for 3-5 runs before overheating (~10min rest between runs).
>KuhmoXS: 12K mi., similar to the Yokohama's, a bit stickier and I thought better feedback.
>Falken 615K: 10K mi., similar to the XS's but noisier feedback.

I liked the Kuhmo XS's the most but whenever I'd try to order them the rears were always on backorder. I'd like to try the Rival's next.

Alignment specs from the print out of the last check:
Front:
Camber: -0.7/-0.7 deg. (max I can get stock)
Toe: 0.08/0.08 deg.
Rear:
Camber: -1.5/-1.5 deg.
Toe: 0.14/0.13

If you don't AX a lot then the rear camber will be too much and you will prematurely wear out the insides of the rear tires. You'll probably want to run no more than 1deg otherwise.