mtl911sc

Another thing to consider is the car really should be lowered at least a bit w/ 19's, to avoid looking "jacked up" and emphasizing the fender gaps.

So in my book, if going to 19's you need to factor in the cost of new springs (and make sure they match well to the stock shocks, unless you swap it all for coilovers).

Hey, anything I can do to help you spend your money on mods, I'm right here ...

quickxotica

From any rational performance/engineering perspective, 18's are better than 19's. Note that all the highest performing 996s from the factory had 18's (GT2, GT3, Turbo S, etc).

The 19's are just for bling unless you are driving a 997 (which was redesigned specifically to work with 19's).

rajeshr

I've heard this quite a few times but I don't understand what "redesigned specifically to work with 19's" means!

Assuming that the 19's don't incur a weight penalty compared to the 18's (i.e. the weight of the 18's and 19's is roughly the same), what would the issue be?

450knotOffice

Thinner sidewall maybe? More of the rotating mass further from the hub? I've wondered the same thing, actually.

Pac996

I'm running 19" turbo wheels and no spacers. Car came set up this way. I don't think it rides rough. 235/35 front and rear 275/30. When it needs tires I'm going to 295/30's in the rear next time. No problem with tracking just want more rubber back there.

frankfast

I just got a set of Carrera 18" wheels (the car has 17" now) that I bought on Ebay. They are off a '08 and can't wait to get them on. I decided that there was too much bling for me associated with aftermarket wheels, especially 19", and that the BBS were the most appealing. I was afraid of aftermarket quality. I also live on dirt roads where potholes abound. I can't believe the price of center caps. Anybody got any around with the Porsche crest (colored) that they are not using?

2K7TTMIA

I agree, NB 996 here and no probs with 19's and the ride is not rough. Pac996, are your rears 19 X 11 ? I would say definitely step up to 295/30's. the 275/30's were almost identical to the 255/40/17 OEM tire heigth; ( 25.49 vs 25.03), so I initially went that route. but they looked terrible on a 19 X 11 rear wheel. 295's are 0.93 inches taller than OEM 17's, which equates to a 2.2 mph difference on the speedo. But they look a heck of alot nicer on the 11inch wide rim. I vote for 19's. rotating mass be damned ...upgrade the brakes...

nick49

I think this is it. And more critical is tire mass further from the center of hub. The rotating mass as it is moved further from center stresses all the suspension components to a greater degree. These components further work the chassis or unibody at and beyond their points of attachment.

For this reason on early Boxsters, '97 and '98, I believe, the factory warned adamantly against fitting 18" wheels. In '99 and beyond the Chassis was stiffened to handle the added stresses incurred with the 18" wheels.

450knotOffice

Makes sense.

rajeshr

If the total diameter of the wheels & tires are kept the same between 18" and 19" (and you usually do this to keep the speedo accurate), does a minor redistribution of weight along the radius really affect it that much?

On previous cars, I've run +1 wheel and tire combos that were significantly lighter than the stock combo. If this is the case, is there still an issue?

quickxotica

19's will work on a street-driven 996 obviously, as many here can attest. It's just that the chassis and all the suspension parts were designed to work with 18's, so I believe (and I think this is the majority consensus) that 18's will work even better (again just speaking from a performance/engineering perspective).

Slap on a set of quality 19's and your car will still function, especially if they are light & strong. But I suspect factory engineers prefer to keep things conservatively within their own design parameters, and 19's with their lower profile tires (to maintain the same total OD) will necessarily have less sidewall flex, less lateral deflection and less bump compliance than 18's and will therefore trasmit greater forces to the suspension parts and attachment points than 18's. Tootling around town this makes no difference, but if you are operating at the limits of the vehicle, the forces involved *may* come close to exceeding (or surpass) the intended design thresholds of the stock suspension components. I don't know what the weakest link is, but there are forces acting on all the suspension bushings, the eccentric bolts used to align the car, etc, all of which have specs intended to cope with the softer 18" wheel&tire combo.

Full disclosure, I am not an engineer. But annecdotally, in 10 years of attending PCA track events I cannot recall ever seeing a 996 running 19" wheels on the track. Maybe there is a reason.

redridge

I think there is a reason why mostly all Porsche wheels are flushed to the hub (minimal lip), most of the stress going around the corner is directly distributed to the hub, while wheels with a lip puts stress on more on the lip instead of the hub.... I believe this and the lower sidewall is the reason why the 19" setup I mounted was very jumpy and lowered my PSM threshold... they do look cool but, after awhile, you want performance back.

nick49

It's a difficult question to answer, being that we are speaking in general rather than specific terms. Weight wise, how much is "minor"? And, how much is "that much"?

To answer your questioin another way, If looks trump everything else, and you favor the 19s, go with them. If optimum handling, responsiveness, braking, accelerating and agility are more important than bling, I'd choose the 18"

Now, probably the difference on the street would be quite subtile to most all except those most in tune to what's going on. To an experienced driver that tracks his car at or near the limits, the differences may become quite or even very apparent. To maximize performance, often weights are measured in grams and lengths in thousanths or millimeters.

Hope this helped.

ROK

18s for the track. 19s for the street.

I've read here from searching that wheel bearings go bad on stock wheels, stock setups... since there are less folks running aftermarket, haven't come up with very many 19" issues just from running 19s. No scientific studies done so pretty much just like anything else on the internet, go do so at your own risk.

TTJunkie

1. Are there any technical reasons for not moving to the 19" wheel?
Yes, your shocks are set for the extra padding of 18" tires and the weight of cast wheels.
But, you can keep the same aspect ratio by increasing the tire diameter, or you can get new shocks and much lighter wheels.

2. What are the recommended sizes (without spacers)? Is there anything special I need to pay attention with regard to offsets? I currently run 295/30/18 on the rear and 225/40/18 on the front.
Best C4S sizes:
18" 335/30ZR18 on 12x18ET45 rear, 245/40ZR18 on 8.5x18ET40 front (GT2 wheels with oversized tires)
19" 325/30ZR19 on 11.5x19ET44 rear, 255/35ZR19 on 9x19ET53 front (requires PSS10 or similar suspension)
I have run both of these on a C4S with no rubbing using Pilot Sport PS2 tires and minor rubbing in front using R-888 Proxies.


3. Is there a difference in performance? I know that when I recently increased wheel size on my Jeep from 15's to 19's, the gearing ratios were completely out of whack!
Be very careful here, more than 3% offset in front-to-rear diameters will confuse both PASM and ABS. You don't want these systems confused on the track!


4. What else am I missing?
19" wheels provide sharper turn-in.
Lighter wheels provide smooth, agile control.
18" tires are more forgiving.
Light 19" wheels and tires with a good racing suspension will make your car smoother than heavy 18" wheels with a stock suspension.
Avoid two and three piece wheels, they can leak.
The lightest (non-carbon-fiber) wheels are Champion RG5 (21 pounds rear, 17 pounds front)
Stay away from run flats! they're about 6 pounds heavier.