dntlvet

That was foe a HPDE weekend!

Laguna_Dude

I wonder if one can purchase the cups parts. not having hoosiers may be a deal breaker for me.

MileHigh911

Someone on RL tried hoosiers with this car and didn't like them..............Not sure where I read it.

utkinpol

So in an essence to bring 991 gt3 back to cup origin we look at toe link install after removing gt3 gizmo for rear steering, usual set of proper dogbones and arms with steel monoballs and calipers? Are struts on cup car same exact model as on gt3 or they have different sitting dimensions? So far what i saw turned my opinion about 991 gt3 180 degrees. If they indeed made most of parts swappable it is just great news. If cup calipers can be also a direct swap, well, it is really good news.

Now, what about steering in front? How big of a task is to ditch gt3 steering and swap it with cup? Or is it same exact system in cup car like in gt3?

utkinpol

Sure you can. Motorsports division sells it all, or no cup car would last more than 2 seasons.

paradocs98

Thanks for your hard work--very informative! A few thoughts and questions:

• The choice of 20" wheels on the street car intrigues me. The cynic in me says that Porsche chose 20" wheels as more of a nod toward fashion trends, and not performance. This disappoints me. I think this because the Boxster and Cayman S come with 20" wheels, which are clearly too large for such a small car. The brakes get lost in those giant wagon wheels, but they sure have 'bling.' Porsche probably felt that, if the Boxster and Cayman had 20" wheels, the GT3 certainly had to have them as well, especially if they're pitching this new car to more of a mainstream audience.
• So, then, did Porsche first decide on 20" wheels as a design parameter, and then just designed suspension components with the knowledge that they had plenty of clearance available? Or did the suspension design and rear steering mechanism, etc., come first, which necessitated a 20" wheel?
• Similarly, the brakes. It's telling that drilled rotors are used on the street car, while the Cup car has slotted rotors. Slotted rotors have been proven time and time again to be superior on track in race applications, but they have less of a 'bling' factor than drilled rotors. So once again Porsche makes a design/equipment decision on the street car for a nod to mass appeal, rather than for pure performance.
• Are the changes made to the suspension of the Cup car purely based on the need to fit an 18" wheel, as mandated by many of the race series, or are the changes primarily based on improving the street suspension to make it more fitting for track use?

Once again, thanks for all the info!

utkinpol

If 20" or 19" racing sliks would perform better than 18" slicks all racers would be on 20".
19" is still workable as hoosier makes them. As of 20" racing rubber - good luck waiting for it.
But it probably not going to be cheap to swap whole rear axle to cup parts. Not impossible, but pricey. But it probably will make sense to ditch street upright, calipers and centerlock andnput cup parts in. A lot of people did it on 997 rs cars same way, as well as all dimensions seem to be same, frame is same it is probably all double.

Would be nicer of course if upright swap would not be needed. It definetely adds a lot of complexity.

Zucc

I thought that the cup cars ran 18" to comply with the rules, no?

Mike in CA

^^Correct.

Also my understanding is that larger diameter wheels have a greater effect on the size of the contact patch than a similar increase in tire width, which is also limited by other factors. In addition to being able to clear larger brakes, larger diameter wheels allow for more rubber in contact with the road. I think these reasons, more than bling, are why all performance car manufacturers are going to larger wheels.

Zucc

Mike, makes sense, thanks.

paradocs98

Is this accurate, though? I don't think that a larger diameter wheel, per se, creates a larger contact patch. It's more likely that, all other things being equal, a larger diameter wheel will be associated with a lower aspect ratio / shorter sidewall tire. It's this shorter sidewall that leads to less tire rollover and crisper, more responsive handling. But within reason--a 23" wheel with a 15-series (aspect ratio) tire on a Porsche would be ridiculous. This setup would be heavy, with hardly any compliance. All that unsprung weight would compromise acceleration, braking and handling. In fact, I wouldn't be surprised if performance is already starting to get compromised at a 20" diameter. I really think it's fashion and marketing dictating these choices. Porsche is in the business to sell cars more than anything else, and Porsche knows that wheels are a significant aesthetic part of cars these days. The general public (including a good portion of Porsche customers) thinks that larger wheels = better performance. They like fancy wheels, and the bigger the diameter, the easier it is to showcase the aesthetics of the wheel. Same thing with Ferrari and the 458.

I was VERY impressed when I saw the new-generation Viper at the NY auto show a couple of years ago: 18" wheels up front, and 19" in back. A nod to performance first, and bling second.

Want further proof? What diameter wheels do the highest-performing race cars in the world run on? 13" for F1.

Tre

I've read this discussion multiple times across different car forums over the years. So I'll start with the question I ask myself...is the GT3 a road car first and can be used for HPDEs, or a track car designed to be street legal? I use the same logic in the world of motorcycles too.

Next, manufacturers have gone up in the choice wheel diameters over the last decade for sure. But why? One can always use the bling factor as an excuse because of the impression that manufacturers are trying to please the crowd that chooses big wheels with low profile pothole busting tires. But what is the real reason? Until designers AND engineers provide inside, proprietary input, we're all left to speculate.

As for going with a 19, or even an 18" option, can one simply go with smaller diameter rotors and associated calipers/braking system? I'm sure there are smaller packages very capable of stopping a ~3200lb vehicle. How does the Z06 and Viper manage to fit their traditional 18f/19r setup? They've been running that combo for a long time without clearance issues.

Also, why have racing series consistently stuck with the 18" ceiling? I'm sure it's not strictly for performance because many of these same series limit hp despite the road going counterparts having much more. Is it to limit the playing field among different engines (ie, V6-V10)? Is it because some smart engineer calculated that 18" is the apex of performance given the aforementioned hp ceiling requirements?

As for the F1 analogy, it's tough to compare their use of 13" wheels given how unrealistic it is to put those cars in the same discussion. I've seen many low riders sporting 13s and I can't say they were performance oriented cars.

I'm just trying to think outside the box here.

MayorAdamWest

You apparently did not actually read the original post...

Tre

I did, and was completely inline with the discussion until paradocs brought up the "bling" discussion again.

The OP stated that another issue was due to the Brembo kit. Does the whole shebang (cup parts included) need to be swapped, or could the braking system alone be swapped to make 18s work? I went through the same a$$ pain in '09 when I got a GTR and there was nothing in the 20" segment outside of the experimental 20" R888s. So came the months of talking with others on 19" options that would fit the brake systems. Fortunately the market caught up and more options became available.

In the end, I'd like to know if swapping for cup parts is really necessary. Maybe for now?

wanna911

Larger diameter wheels do in fact create a bigger contact patch. That is the one and only benefit. With smaller wheels though you can control more with the design of the tire sidewall stiffness. You also begin to affect the suspension geometry and limit lower rise heights unless you run rubber bands for tires. The larger diameter wheels raise the outboard mounting point unless you shorten the tire height. Not to mention weight. Bling is a part of today's car market.

I have said and still contest that Porsche put the 20's on for bling and to prevent the use of slicks. They further designed the suspension to make it impossible. Looking at the pictures makes it hard to argue that they couldn't have put that control arm mount up higher. Someone would have surely take their car straight to the track and put slicks on without reading the manual otherwise.

Drilled rotors always have been about bling. They cool better yeah, but for maybe a couple of stops until they get all clogged up with brake pad material.