TomFromCT

One of the reasons I ordered a non-S vs. S car was because the 18s come standard on the non S. I was interested in having a bit larger sidewall for ride comfort as well as to minimize wheel damage due to potholes, etc.
In my opinion, the recent trend to larger and larger wheels has everything to do with bling and little to do with performance. Not that there's anything wrong with that. But if larger wheels and smaller sidewalls were performance enhancements, why wouldn't racing series such as Formula 1, ALMS, and Nascar all be moving in that direction? While I don't know the exact tire specs that these series use, visually they all have significantly larger sidewalls and correspondingly smaller wheels than a P-car with 19s or 20s.

rfedele

Just traded in my 05 997S for an 07 997. The ride difference from the 19s to the 18s is noticeable. Interestingly in addition to the 18s being more comfortable, the 19s had an annoying habit of following road imperfections (on poor roads). The 19s also seemed a bit jittery in comparison on hard turning, but slightly better steering feel.

On another issue - the power diff isn't noticeable to me between the 997S and 997, although I haven't broken 4K RPM for the break-in.

lwilkins

I've owned 2 street 964 Turbos with 18" rims (a 3.3 T and a 3.6T), and a 996 and an M3 also with 18" rims. when I got the first of these, I was warned about potholes flattening the tires. Now 8 years later driving almost all the time on the 18's, I've never had a single flat tire due to a pothole or road irregularity.

My 2005 base 997 has 19's and I've owned it for about 6 months, and 5k miles. Although I do watch the road, I'm not as paranoid as I was when I first got my 1994 3.6 Turbo in 1999.

The pothole risk seems often repeated, and little experienced, in my opinion. Pretty easily avoided by looking ahead far enough.

And I absolutely love the handling as the car now is. I might love it as well with 18's but the handling is splendid.

H20NOO

I'm a big fan of lighter wheels, brakes and unsprung weight. YES - 18" wheels fit over PCCB's with ample clearance (see pics below 235/40/18-F 315/30/18-R). I don't know if that would be true on a GT-3 or Turbo since they have a larger front PCCB rotor (with aluminum rather than stainless steel hats) than the 997S PCCB, a fact I wasn't aware of until I saw a set.

With respect to weight, it's not just the savings but where that weight is. Even if an 18" and 19" wheel weighed exactly the same, the 18" would provide a performance advantage because the weight is concentrated closer to the axis.

The tire tread is very heavy and lives at the extreme periphery of the wheel/tire package. The area between the tread and rim is filled with air or nitrogen so it is nothing. The next item of mass contributing to rotating mass and gyroscopic forces is the wheel rim and the part of the center that supports it. The further you can move that weight toward the wheel axis, the less torque is required to accelerate it, less power required to brake it, and less gyroscopic forces working against turning it.

If you had a 20lb 6" steel cube and a 20lb bag of sand mounted in the center of a turntable, which could you speed up and decellerate more quickly? Of course, the one that has less mass pushed out to the edges. That's why many of these SUV's running 24" wheel packages, often weighing 100lbs or more (per corner!) are downright dangerous. The brakes are usually not up to the task but also, the wheel bearings, power steering, ball joints, suspension and other equipment were not engineered to overcome the extreme gyroscopic and kinetic forces of such a package.

In terms of performance benefit, one pound of rotating mass removed from wheel, tire or brake is equal to 6-8lbs of static weight reduction in the car. It depends where it comes from, thus the range. A 5lb weight reduction in brake rotor has nowhere near the benefit of a 5lb tire weight reduction due to where that mass is, relative to the axis. So, saving 20lbs in tire weight should be the performance equivalent to taking 160lbs out of the car (like losing my kid brother in the passenger seat). Saving 20lbs at the brake rotors might be more like taking 120lbs out of the car (insert funny remarks about wives/girlfriends here).

adfsouth

H2, how much do those carbon fiber bad-boys weigh?

H20NOO

The front wheels (18x8.5) weighed in at 15 pounds, 12 ounces, the rear wheels (18x11) weighed 18 pounds, 5 ounces. The manufacturer claims they are 14lbs but that's not the case on the set I received.

Still the lightest wheel on the market to my knowledge and as discussed in previous post, very lightweight at the rim, where it counts the most.

MC

Edgy01

Mounted up with rubber what is the F R weights?

Hartley

We all know a 20" wheel weighs more than an 18" wheel of the same design. Anyone weigh the tire differences between an 18" and 20"? Wouldn't the lesser sidewall of the 20" help save some weight?

Very few of us track our cars or are good enough drivers that any of this would make real difference to, drive on whatever makes you happy.

rfedele

I checked tirerack a for PS2, they are basically the same weight. The larger diameters only get heavier as they get wider. I didn't expect that.

H20NOO

Wheelenhancement weighed them before tires were mounted and provided the figures above.

I weighed them on a bathroom scale with tires mounted when they arrived at my home but my scale doesn't indicate fractions of pounds. The rears were 49lbs and the fronts 39lbs. The Lobster Claws with a well worn set of PS2's weighed 56lbs and 45lbs, respectively.

MC

meaker

I read in a wheel mag, that it was only about 1 pound less on average for the 20 over a 19 tire.. Though the 20 in wheel is going to have the weight out farther from the axes then a 19 wheel.... I personal like the looks of a 20 but worry more about the less sidewall give, then weight..

H20NOO

www.tirerack.com is a great resource for these things. Here's a link to the Michelin PS2 specifications including weights:

http://www.tirerack.com/tires/Spec.j...irePageLocQty=

MC

adfsouth

Wow...very light indeed. Btw, sweet avatar

meaker

Thanks, I did read a mag that was devoted to wheels and tires. They printed that tires were on average 1 pd. less... I would more believe Tire rack specs page then that mag..

Le Chef

If the 997 was designed to run on 19's then why does the base 997 run on 18's? If the argument was really about engineering then surely both models would run on 19's?

Chris Harris (Autocar and GTPurely Porsche) reckons that the best 997 (excluding GT3 I would guess)is the base car with 18's, -20mm sports suspension + LSD, and PCCB's.

It's a shame this setup is not an option in US.

I drove one of the salemen's Cayman with PCCB's back-to-back with one with steel brakes and the difference in ride is definitely noticable. I think with that in mind and the longer life they offer over steel that they might actually start to make real sense.

Now all we need are some interesting lightweight 18" wheel designs to buy...