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The 918 hasn't been a great success, it's a good way to recover sunk R&D money.
Agree the 918 hasn't been a great success. It's taken Porsche much longer than expected to sell all 917 cars.
However, by now hasn't Porsche sold >80% of the available 918s and so recouped their R & D money?
Can anybody explain why it would need a bigger rear wheel than front?
Increased footprint length for increased grip. Quoting myself from earlier in the thread:
The change to 21s is going to be driven primarily by grip. It's not an accident that as cars get more powerful the tire diameter tends to go up. Think drag racers, funny car, top fuel, even F1 for some extreme examples. Part of the reason is to extend the length of the contact patch, which does improve grip, particularly at speed, where friction usually drops off.
The best "tire models" include speed, because rubber's friction is also a function of how long it's in contact with the road. This is because it's a viscoelastic material, meaning "flows" into the roughness of the road to grip, and as speed increases it has less time in contact with the road to flow. By increasing the OD of the tire you increase the length of the contact patch, thereby increasing the time the rubber has to flow. A long contact patch also reduces the slip angle a tire operates at, increasing the tires responsiveness in the process.
Porsche themselves have used progressively larger diameter rear tires- the RSRs, for example, for half a decade used a tire over an inch taller in the rear than the Cups to increase grip. Unfortunately in motorsports wheel diameter has been frozen by rules at 18" for nearly two decades to limit costs, so an increase in sidewall height was required to get this larger OD, slowing the rear tire's response. This leads to a number of undesirable traits that must be countered, including slower turn-in and both transient and steady state oversteer. It would be far better to run a short sidewall and get quicker response.
Porsche seemed to prove this by winning Le Mans with 20" wheels before they were banned, but they aren't banned on the street, so as power and grip climb to ex-Le Mans levels it's no surprise we're seeing larger wheels. It is heavier and more expensive, the large, low profile tires requiring more segments in the multi-piece tire molds, costing more to make. However on a high power car that both needs the grip and has the horsepower to spin big wheels you should see better overall performance for those penalties.
Unfortunately in motorsports wheel diameter has been frozen by rules at 18" for nearly two decades to limit costs, so an increase in sidewall height was required to get this larger OD, slowing the rear tire's response. This leads to a number of undesirable traits that must be countered, including slower turn-in and both transient and steady state oversteer. It would be far better to run a short sidewall and get quicker response.
Interesting. OEM diameter with my 997 and Cayman is 19", and I've wondered how performance might be (adversely) affected by using 18" wheels with higher-profile tires.
http://www.motorauthority.com/news/1...acelift-report
Considering that it would be very difficult to increase HP reliably on the RS without Turbocharging, the earlier hints from PAG that their may not be any further GT2s, the existence of Turbo Inlets in the rear
fenders of the RS Track prototypes, most of the new German car's Engines (including Porsche) going to Turbocharging - even for the lower HP Engines, the better fuel efficiency of Turbocharged Engines when used on the street, and MB introducing a true 500 HP competitor to the 911 - Personally I believe the new GT3RS will be Turbocharged - and I further believe our N/A enthusiasts will eventually accept a Turboed RS as they have the addition of PDK. I believe that is the only way to achieve a substantial performance improvement over the present outstanding GT3. If the RS is introduced at Geneva in March, production cars are unlikely to be available until 3-6 months later and will be 2016 Models. I also believe they may incorporate some of the hybrid Electric technology of the 918 using Electric Motors to generate even
greater HP and Torque. I can't wait!!!!
http://www.motorauthority.com/news/1...acelift-report
Considering that it would be very difficult to increase HP reliably on the RS without Turbocharging, the earlier hints from PAG that their may not be any further GT2s, the existence of Turbo Inlets in the rear
fenders of the RS Track prototypes, most of the new German car's Engines (including Porsche) going to Turbocharging - even for the lower HP Engines, the better fuel efficiency of Turbocharged Engines when used on the street, and MB introducing a true 500 HP competitor to the 911 - Personally I believe the new GT3RS will be Turbocharged - and I further believe our N/A enthusiasts will eventually accept a Turboed RS as they have the addition of PDK. I believe that is the only way to achieve a substantial performance improvement over the present outstanding GT3. If the RS is introduced at Geneva in March, production cars are unlikely to be available until 3-6 months later and will be 2016 Models. I also believe they may incorporate some of the hybrid Electric technology of the 918 using Electric Motors to generate even
greater HP and Torque. I can't wait!!!!
http://www.motorauthority.com/news/1...acelift-report
Considering that it would be very difficult to increase HP reliably on the RS without Turbocharging, the earlier hints from PAG that their may not be any further GT2s, the existence of Turbo Inlets in the rear
fenders of the RS Track prototypes, most of the new German car's Engines (including Porsche) going to Turbocharging - even for the lower HP Engines, the better fuel efficiency of Turbocharged Engines when used on the street, and MB introducing a true 500 HP competitor to the 911 - Personally I believe the new GT3RS will be Turbocharged - and I further believe our N/A enthusiasts will eventually accept a Turboed RS as they have the addition of PDK. I believe that is the only way to achieve a substantial performance improvement over the present outstanding GT3. If the RS is introduced at Geneva in March, production cars are unlikely to be available until 3-6 months later and will be 2016 Models. I also believe they may incorporate some of the hybrid Electric technology of the 918 using Electric Motors to generate even
greater HP and Torque. I can't wait!!!!
I've heard from a number of sources that it will be 4.0 and NA introduced in Geneva will US slots starting in June. I've also heard from a couple that it won't have RWS.
I 100% agree with the rest of your comments - everyone will quickly forget about N/A when they improve the sound and have hybrids/FIs with stupid amounts of torque.
everyone will quickly forget about N/A when they improve the sound and have hybrids/FIs with stupid amounts of torque.
I think you are wrong. Cars already have HP and torque coming out of their ears. What they lack is lightness. There will soon be a change in the direction/priorities in the sports car market. Or at least I hope so.
I hope they fine tune the look of that wing a bit for the production model. The squared off winglets are a bit too much. Don't like the solid wing supports either when they are Cup car tall.
I think you are wrong. Cars already have HP and torque coming out of their ears. What they lack is lightness. There will soon be a change in the direction/priorities in the sports car market. Or at least I hope so.
Actually, PCars lack lightness - other manufacturers have gone that direction PAG seems to have gone the other way by adding size to the latest 911 and Cayman, which was somewhat offset by lighter weight material.
Hopefully I'll be able to tell you where my Cayman 3.8 racecar ends up weight wise next weekend, but I still expect it to be significantly heavier than something like an Exige V6 Cup R.
I'm surprised to see that the RS has steel breaks. I thought it came with ceramics...
The wing is a bit too much for my taste. I'm sure it drive awesome though. But that look isn't going to compete with the 458 speciale. IMHO
10-11-2014, 10:46 PM
