Wheel size change 2004 C4S Cabriolet

I really want to get new wheels to upgrade the look of my 2004 C4S. With that, I'd like to know 1) Is it possible to change from an 18" wheel to a 19" wheel? 2) Specifically, can I use the 2011 19" turbo wheels/size and fittiment for my 2004 C4S cab? Really not getting the offset verbiage 3) What are the pros and cons of such a move as far as ride quality, handling ...?

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Yuo're going to get a lot of responses saying the ride quality will go down with 19" wheels. With that short of a sidewall there's just no way to avoid it, the ride will be rougher and you'll be at higher risk of bending wheels from hitting potholes, etc. To understand the wheel dimensions and how they affect fitment, try this site: http://www.willtheyfit.com/

Ride quality is certainly impacted by wheel diameter, but suspension is just as important. My 997 with 19" wheels had better ride quality than my 996 with 18" wheels. I don't think the 997 turbo wheels will fit the 996 C4S properly due to offset differences, but I could be wrong. Perhaps it could be corrected with spacers. Porsche never sold a 996 with 19" wheels, so there's not an official recommendation for this diameter from the manufacturer. You'll need to get advice from somebody who has actually converted to 19" wheels. As I'm sure you've seen here in the forums, the C4S is sensitive to diameter differences between front and rear wheels/tires. If you have too much variance, then the front differential will be damaged. If my memory serves me correctly, then you need to have less than 3% difference between front and rear wheel/tire construct.

I went up from 18�s to 19�s and have no issues. Love the look and the ride. But I have a lowly C2 so take it for what it is. Don�t get discouraged by everyone flaming 19�s.

The 996 AWD system only functions properly when the front tires are larger (have less rotations per mile) than the rear tires. I wish it wasn't so... Keep that in mind when searching for your new tires.

Circumference is the biggest thing you have to watch out for - and that will come down to tire sizes. I have 19s on my 4S (previous owner installed them) so I can't comment about a change in ride quality. You can look up the stock offsets for your wheels, determine if you have factory spacers, and then so some math to compare the offset to your proposed new wheels. From there you can quickly decide if you need spacers for an exact match. In my case, I have 8mm spacers all around and that puts the front and rear within 2mm of factory offset. Cheers Charlie

The size difference per my current vs. the new will be a diff of approx. 5 to 6mm front and back (meaning closer to the strut). I can only assume that may cause a rub on certain turns and tire/rim damage. Is 5 or 6mm that much of a difference...to make a difference? Also, I am making these assumptions for my wheels front 8.5 and rear 11, correct?

997tt wheels will fit on a 996 c4s, but chances are the diameters aren't quite right. Some guys run them with no issues, but some warn to change the tire sizes to more correctly suit the awd system of the c4s (turbo awd is the same so you can ask the turbo guys also). FWIW I'm running 315/25/19 and 235/35/19 on my 996tt. It's the proper difference between the front to back tires as noted before... the problem is there's only 3 choices of tires for 315/25/19's... and none of them are all that great.

For tire size you can go to TireRack.com or 1010tires.com and use their calculator. I went to 19's for a while and went back to 18's due to the harsher ride and a complaining wife, LOL. The 19's did look good though.

There’s a set of OE 997.1 turbo wheels for sale for $500 right now on the 997 turbo board. They need to be refinished, but it could still be a really good deal on a set of OE wheels.

I'm in the same but opposite situation. My newly acquired c4s came with 19s and will go to 18s at some point in the near future based on the difference in unsprung weight and ride quality compared to my buddy's c2 on 18s.... it is significant. The main reason for the change in ride quality is based on the height of the sidewall. 19's need a lower profile tire (shorter side wall, meaning less cushion) in order to keep a similar overall diameter to the stock 18" overall diameter (wheel + tire). I'm pretty sure stock sizes are: Front 225/40 ZR 18 N3, 18 X 8 with 50mm offsets Rear 295/30 ZR 18 N3, 18 X 11 with 45mm So look to strap on 19's with the same geometry (overall height, width and offset from the hub). This can be achieved in a number of ways and can be verified here. http://www.willtheyfit.com/ I've been experimenting with wheel/tire combos for eons with BMWs. And similarly a few mm one way or the other does make a difference based on the tolerances with which these cars are built.

Same; 19 x 11.5 rear , 325/15/19 and 19 x 8.5 front , 235/35/19

I purchased my car with 19" wheels and ran those for a few years before dropping back to stock. The car had a Techart coilover suspension (similar to PSS9) and PS2 tires. It wasn't good though. I had to be really careful entering driveways and speedbumps, but the biggest problem was bottoming out the suspension when hitting depressions in the road at highway speeds. The second biggest problem was having to slow way down for railroad tracks. I moved back to stock 18" wheels and am much happier. But I found the issue wasn't really due to sidewalls (I was running the same profile tire in both cases) or the additional weight. The problem was the 19" wheels made the car 1/2" higher. And to compensate most people (including myself) lower the car but at least the same amount. The rough handling comes from the significant reduction in suspension travel. I'm convinced that if you switched to 19" wheels but kept the car at the same height the ride quality would be fine. But the body roll would be noticeably worse...