In the last few days I've noticed a few questions here and elsewhere about how 20" wheels / tires run. I've offered my opinion that they will run rougher than the 19s, just as 19s run rougher than 18s, and on. Because these responses are buried in threads not really offering comparison between the wheel and tire sizes, I thought I'd write this up.

I guess I never understood that part about "looks" and 19" wheels (now 20"). The car is a Porsche and I'd thought people bought them for performance. Larger wheels perform worse than the wheels the car is designed for. The 997 platform (or any modern performance based car) works best around an 18" wheel. How did we get to 18 from 17? Larger brakes and so the wheel had to grow. The 19s are heavier (tire + wheel), harsher (less sidewall to soften impacts), power robber (higher rotational / unsprung weight), and more expensive (if 19" tires are so much more than 18s, how much are 20s???). And, who is looking at the side of the car as it goes by and does any owner care what they think anyway? I can understand an individual color - where the whole car is transformed to what the owner likes (such as my Cobalt Blue) - but wheels?

A major issue to me in a performance based car is rotational mass / unsprung weight and how it sucks up HP / TQ. Why are racers constantly looking for the lightest wheel and tire package possible, which leads them to 18s for a 997? Because every pound saved at the wheel / tire (especially on the outside) improves performance. It takes more HP / TQ to spin a 50 lb wheel / tire package than it does a 40 lb package. The 18" track wheels / tires I'm looking at will be 38 lbs front and 43 lbs rear and the unsprung rotational weight savings are going to help make my 997S very quick.

When the 997 first came out I "complained" about the standard 19" wheel. I thought 18" should be standard (235/265 on base, 235/295 on 11x18 rear for the S) and if people wanted to pay for 19s, then let them. A Porsche engineer told me that within the company there was disagreement. The engineers wanted 18" wheels and tires because they are optimal. But the marketing department, especially with the US in mind, wanted 19s for the Bling Effect. When the company smells money guess who wins (not the engineers).

There was a great video I found a few years ago (can't find it again) of a Japanese Porsche racer that was the "top guy" in the East. Porsche had him take out the 997 and the 997S on the track in that order. He loved the 997 and it's balance... When he took out the 997S he loved that too even a bit more (power and brakes) and the only complaint he had was the 19s. He said "Why did Porsche put 19" wheels on this car - it would be faster around the track and drive less harsh with the 18s..." and in his conclusion he reiterated - the 997 platform should have 18s for optimal performance and the improved ride would be a bonus.

As to the looks - A set of 18s on a 997S with the red brakes looks "correct" proportionally to my eye. Purpose built like all of the pieces fit together properly. The 19s (which came on my car) makes the brakes look undersized. I could only imagine how small the brakes would look with 20" wheels. If looks and proportion are what people are interested in, I would think more people would be shopping for aftermarket 18s instead of 19s or 20s.

Heavier + Less Performance + Harsher Riding + More Expensive + Making brakes look undersized = Quest for smaller and lighter 18" wheels

 

Agree 100%. 18" on the 997S is a better choice. Now I have to buy another set of wheels to have a decent and less expensive selection of track tires. I guess Posche isn't immune from the Bling factor; disappointing.

 

1) yes, some people do look at the cars as they drive by (or parked just as well) and some owners do care how their cars are viewed. that is why there is such an enormous market for secondary wheels (tire rack, wheel enhancement, etc).

2) 19" in a porsche oem design is hardly bling

3) some owners out there don't drive their cars on a track so it really doesn't matter...those that do buy 18" wheel sets.

4) i really don't think it's a concern for many.....haven't run across too many people not opting for 19" or 20" wheels because of proportional issues....

 

Then, it is what, exactly? I guess Porsche marketing folks would call it responding to market demand. And unfortunately, that is probably true. I guess we'll be seeing 997's jacked up on 22" wheels before long.

Sorry, don't mean to argue about it, but I can't see it as anything else. 18" wheels have plenty of brake clearance, and the available 18" tires offer everything from mushy sidewalls to jarringly stiff, so ride quality can be whatever you want, with better wheel protection from potholes, and with a more affordable tire. I guess I'm just irritated at having to incur the extra expense of additional wheels, when it seems so unnecessary.

 

The trend started years ago. In the beginning, pretty much only performance oriented enthusiasts bought Porsches. Then the marketing department realized they could sell more cars if they made it softer and with more features that catered to the mass market. Clearly, the guy that gets a loaded-up 911 variant with 20" wheels is not driving on the Ring or going to DEs...

 

I agree with the marketing department I like 19" wheels and I will put up with all the down side they bring. This is just one guys opinion on 1 paticular subject. I could go into the story about opinions but I'm sure you Renn listers heard it before.

 

There is always lots of discussion about 18 v 19 v 20. What are the correct width and offsets for 18 inch wheels on a 997 C4? Also tire sizes? Thanks.

 

Interesting, but this is in conflict with the book I read last year that talked of the development of the 997. They chose the 19 inch wheel as a departure point, but not for the 'bling factor' as you indicate. As far as the size of the brakes vice wheel size I can barely get 18 inch wheels on my car. (I ordered the PCCBs). I even looked at my old 16 inch Fuchs forged alloys against the hub area and I couldn't even get close to the hub because of the massive calipers. I believe in putting the best possible brakes you can on a Porsche as it can mark the difference between staying on the road or track and not. With Porsche upgrading brakes wheels have to follow. Contrary to many manufacturers of performance automobiles (BMW comes immediately to mind) I have found that Porsche keeps up with tire needs by putting what is needed to extract the most out of the automobile. When they were beginning the work on the 997 from the 996 they started with 19 inch wheels, and soon found that they were tearing up the stock 996 suspensions. That suspension could not keep up with the forces generated by the 19 inch wheels and tires. Every casting had to be redesigned and recast. This was not well received by the Porsche bean counters, as they were hoping to simply use the 996 suspensions in the 997. As it worked out the car is head and shoulders over the 996 in handling.

I'd be curious to hear from you where you heard that the engineering staff endorsed the 18 inch wheel as a jumping off point for the 997. It's in direct conflict with this other source that I have.

On another point, I imagine that most of the Japanese pocket rockets out there on the boulevards today are blinged out with 19 and 20 inch wheels and their owners have no clue about the danger they are imposing upon the rest of us when their suspensions are simply not built for that level of stress. With Porsche, at least I feel that they did their science projects up front to support the design and subsequent manufacture. It took me awhile to adjust mentally to 19 inch wheels but have become a believer, starting about 8800 miles ago.

 

The 997 represents the first change in the overall diameter of the wheel since the 911 was born. Wheel sizes have increase while sidewalls have decreased.

The 997 was designed around an 18" wheel. Suspension geometry had to be changed to permit 19" wheels which marketing had requested. Marketing won out over engineering.

My 18" BBS LMs arrived today for track duty this summer.

 

I think your statement that merely suspension geometry had to be changed to permit 19 in wheels is a vast understatement. What's your source?

 

I also read a book on the development of the 997 and there was a section on the new wheels and tires. I believe the decision had more to do with wanting to increase tire diameters 5% than specifically wheel sizes. However, whether the final decision was engineering or marketing, I must admit I am pleasantly surprised at how well the 19" wheels and tires work on my new C4S. The ride, looks and handling are all improved over my 2004 C4S.

 

Well, this is very interesting. I would think the only wheel/tire considerations would be, enough space for the intended brakes, and a wheel/tire combo that is within some design parameter for OD, weight, and stiffness. The last three factors could be met with a variety of wheel diameters it seems, probably from 17" to 20". Although it would require some serious sidewall design for the extreme sizes to work. So, I guess I remain skeptical of any engineering need for a 19" wheel. And that is really all I question. I don't know of any engineering advantage of the 18", just don't see any need to change it. But, you have obviously done more research than I , which I respect. And if I had an equal selection of 19" tires, I'd be a happy camper.

 

My base car had 18s standard, and after 15k miles I bought a set of 19" Carrera S take-offs for street use, keeping the 18s for the track. I have plenty of track years under my belt, and to be honest, other than replacement cost there really are no detrimental effects with the 19s on the street. The factory recommended pressures for the 19s are lower, which maintains the ride quality, and wear is actually better with the 19s' recommended pressures.

I, too, read somewhere that the car was designed around 19s. I'm sure that's the case, being standard on the S, GT3, GT3RS, Turbo, I'm sure the GT2. Very few 997s are delivered with 18s. IMO, all 997 variants looks perfect with 19s, and for those who will never take their cars on the track (which is, what, 99% of owners?), they are just fine. Yes, some of it may be marketing; that nth degree of perfomance may be lost with 19s...but the aftermarket is there for those that don't want them. Porsche is breaking sales records with the 997...they know what they're doing.

 

Interesting thread, especially since it was started at 4:59 a.m. Hard time sleeping, Ron?

I personally like the look of a 19" wheel, and don't have a track near me so I can't track the car anyway. The potholes around here make me wish I had my old Fiat Spider's 14"/75-series setup!

As an aside, I believe CART rules require 15" diameter rims (rear) with 27" diameter tires (rear).

 

look at the rennline ones... they are sporting the 20's as well as the techart turbos...... i think if you're not going to track, go 20's it looks so much nicer filling out the wheel well perfectly... but if you're going to track your car, go 18's and as light as possible...