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Originally Posted by lakatu
Thanks st-anger for the new section. I really like the idea.
I have been trying to comprehend the impressiveness of the CGT lap time (7.28 8)) and the decline in lap times for 911s in general over the years on the NS. I started out thinking why is it so hard to make improvements to lap times. To answer my question I started thinking about the physics that are required to improve the performance to lower the lap times. I have a few ideas but in some instances they don’t seem to make as much sense as in other instances. I was wondering what other Porsche fanatics thought about these ideas and what everyone’s thoughts are as to what has been the single biggest contributor to lower these times i.e. power/ weight, improved braking, suspension refinement or tires. I think to some degree the answer is improved power/weight but that is just my opinion. However, I think the answer is much larger than that as I hope is obvious from my examples.
Here is what I have come up with. When you look at lap times and performance increases there obviously isn’t a linear relationship. For example, an increase of power/weight ratio that is 2x doesn’t result in a lap time that is ½ the original. After looking back through some old physics books I notice that circular motion, and acceleration formulas are all directly proportional to the square of velocity. My assumption is that during a lap of NS the driver is constantly accelerating, braking or cornering and that to improve the lap times the forces required to improve the times would have to increase as the square of the change in velocity.
Let me use an example. In a prior post I have shared that I have seen a posting of a 1987 911 by Auto Bild with a lap time of 9:22. I calculate this is an average speed of 132.5 km/hr. Porsche drivers in the MKII 996 posted a time of 8:20 which is 150.0 km/hr or a 13.2% increase. Based on my simplified assumptions, I figure to increase average lap speed by this amount would require 1.132^2 or a 28% increase in the forces of acceleration, braking and turning. That seems to check out because I calculate that the power/weight has improved 24% and the lateral acceleration 13% and I’m not sure about the braking. Obviously all these forces would not have to increase in the same proportion acceleration could increase more say that braking or lateral acceleration.
However, when I use an other example the GT3 RS vs the CGT I get average speeds of 160.6 km/hr and 167.4 km/hr respectively or a 4.2% improvement. I calculate this would require a 8.7% improvement in accelerative force. That doesn’t seem right because the power to weight ratio of the GT3 RS is 4.65 kg/hp while the CGT is 2.29 kg/hp or a 50% decrease. Based on this I would have expected to see a larger improvement in the CGT’s time relative to the time of the GT3 RS.
So maybe there is a breakdown in my assumptions that the driver is always in a state of changing the speed of the car or in other words is always accelerating. If this were the case and at times the NS driver maintains a constant velocity the physics laws governing acceleration wouldn’t apply and other factors maybe working to change lap times.
For example, while I haven’t seen the NS I have heard reports that the surface conditions are challenging and I figure that a suspensions ability to remain controllable while absorbing bumps and imperfections maybe a limiting factor. What I mean is that a driver may not be able to continue to accelerate because the cars suspension is not able to maintain stability at faster speeds and the car would be in a state of constant velocity. Therefore, some of the improvements in average lap speeds may not be due to an increase in the generating forces but the refinement of the suspension to deal with road irregularities allowing faster speed through those sections.
I might be alone here, but I find this discussion interesting and any feedback would be helpful. I figure it is possible that I am completely wrong in my application of physics or there maybe other factor occurring that I haven’t even thought about. Any thoughts?
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…well, really some nice thoughts, i´m especially glad that you´re dealing with all this already quite professional, i´ve gone through your calculations a bit, also through your thoughts and you are basically on the right way… i´d say on the chassis/suspension side there´s quite some scope left, definitely on the factory cars, on the other hand the tuners are quite near the limit, there´re special NS suspensions mainly from “Bilstein” undriveable anywhere else but bloody effective on NS but a good setup for NS is nearly an impossible task, quite some compromises have to be made, again we can´t compare NS with a regular race track like HHR…
so suspension is not the limit on NS these days, sure it´s at the limit, but EVERY single part is at it´s absolute limit on a fast lap on NS, IMO the main influencing factor are still the tryes…
so acceleration, grip lateral g´s are mainly limited because of the tyres, we tested that excessively with more or less three manufacturers for our Porsche models, Michelin, Pirelli and Conti, nowadays Michelin and Pirelli only, but now we could start an endless discussion, as you know Pirellis were significantly faster on NS but again we can´t equip a car with the tyre XY only because it´s 20sec faster on NS, it should be driveable, especially in the wet which is a key point for our sports cars, they should be driveable every day, for shopping, in the city, but also on the track, so it´s always a huge compromise.
again we have to talk about the tyres when we´re talking about increasing forces, for the suspension/chassis forces up to 2+ g´s are no problem, but the tyres have to deliver this performance as well, on all the different surfaces… and that´s the point again, sure with racing slicks we can drive whatever g´s but this is not the task of a Porsche or sportscar in general, as i said some time before only very very few ppl will ever explore the potential of their e.g. CGT or GT3RS, even i have to try hard after driving Porsches for ~ 20 years now…
personally i only know 2 guys who can really push any Porsche to its limit: WR and Roland Kussmaul…
in the end it´s a bit hard to characterize NS on theoretical physics, as well as CGT and GT3RS, they seem to be on quite the same performance level but the RS is not even close to the CGT…