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      10-25-2007, 10:37 PM   #68
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Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

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Wrong again

Originally Posted by gbb357 View Post
Me driving a Lexus has got nothing to do with this. I for one is a huge BMW fan as well. The point i'm making is your making a conclusion or assumption right away that Lexus is under rating the IS-F just base on it's performance without even having any real data is ridiculous. And just because you have used a formula to estimate the performance and come up with some data, all that is is an estimation. The real data is what the car will do on actual driving condition, no formula will come up with a better result than that. Now in terms of the figures that Car and Driver came up with, everyone knows that those numbers can change anytime. As a matter of fact, 4 different 0-60 times have been recorder so far for the IS-F that has quite huge discrepancy. Edmunds being the worst at 4.8 secs, Motor Trend at 4.7 and Automobile at 4.6. I just posted and showed you an actual dyno and yet your still arguing that the IS-F is underrated. Reading is fundamental. Everyone knows that the wheel hp is usually around 20% less than the crank hp. Calculate 416hp at 80% and you'll get around 330hp which is close to what Automobilemag came up with in their dyno test. Just because you don't like the results and it favors Lexus, does not mean it's not correct. I could care less if you "dogging" Lexus, but don't be such a fanboy about it. BMW makes some of the best cars out there, but that does'nt mean they're the best at everything.
We have all of the real data we need to determine if the car is under rated. We know the torque curve, transmission ratios, tire sizes that really about covers it all except for all the smaller subtleties of parasitic losses. I have indeed used "formulas" to model/simulate the car but it is much more than just formulas or ratios - it is physics. Phyiscs is the most predictive and exact science we have. Its "humble" formulae can predict things as small as subatomic particles to things as inconceivably large as red giant stars, things going as slow as an ant or as fast at light. If you doubt that physics and engineering can make accurate predictions based on sound principles and numerical techniques we simply can not have a debate. Do you know how much physics and engineering, formulae and simulation are used to design every car we drive, including yours.

Furthemore it is not true that a formula can not beat actual test data. This may sound unbelievable but think about it for a minute. How much variation do we see in real world testing. Just look at the performance figures thread where we track M3 and competitors performance on this board. In real world test it is impossible to precisely control all variables (temperature, pressure, tire conditions and inflation, individual car to car variations, driver skill, equipment accuracy, etc. etc., we could go on forever here). just look at the real spread of any performance spec of a car from a number of sources! What really matters is an average number and some idea of the statistical spread of those numbers. With simulation you should be able to get a good average number, and sometimes when clever, you can even simulate the distribution of results. Scientists do this regularly - one common technique here is called Monte-carlo analysis and guess what - it simply "works".

I am encouraged that you are tracking the IS-F numbers well enough to have observed this effect. These pieces of data will help me to compare my simulations to an average data point rather than the possible outlier point I noted in my first point.

Your comments that the wheel hp is 20% less than the crank is a drastic over simplification. The parasitic losses in a vehicle are from a few main sources, some speed dependent and some rpm dependent, other yet still temperature dependent. Losses come from friction, air resistance, bearing losses (friction) tire heat dissipation, etc., etc. An accurate quantification of these losses is essential in any simulation. These parameters are generally well known and modeled. Using a fixed number here, say 20% is just as bad as talking about peak hp and not the entire torque across the whole rpm range. It will tell you some things but by far not the entire picture. Note my previous posts showing how CarTest takes all of this into account!

If you would have read my posts more carefully you would see I have never once "dogged" Lexus. I am thrilled (yet very suprised) the car is performing as well as it did in the C&D test. Competition is simply great for everyone! If you take any time to read some of my posts here on this forum you will see I am quick to ciriticize the M3 and BMW as well as sing its praises. I just am not a fanboy.

I am not sure how many times I have to say it (adding a point here actually and refining a bit) but this is my conclusion. One or more of the following are INCONSISTENT:
1. The C&D performance figures acurately representing the average or even the peak performance of the car
2. The weight of 1690 kg
3. The reported hp and torque figures
4. The dyno results

This has nothing to do with brand loyalty, fanboy-ism, favoritism, bias, or any such thing. The "facts" as they are reported to us JUST DO NOT ADD UP. The C&D results for the car are too good given the specs and knowledge we have on it.