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Originally Posted by CanAutM3
What about the results from Rototest that show drivetrain losses in the 6-10% range for the E9X?
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I had secretly hoped that wouldn't come up, but not for this reason. These guys use the same (bizarre) definition of a loss as simply stated vs. observed. I think they didn't want to get into the politics of under/over rating. This admittedly bizarre definition is exactly the one we have been telling others here in this thread are nonsensical, which they are... That being said, I believe they can and sometimes do directly test for drivetrain losses.
Quote:
Originally Posted by CanAutM3
Aren't "auxilaries" or "ancillaries" losses included in SAE and DIN power ratings nowadays?
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Good question, not sure.
Quote:
Originally Posted by CanAutM3
Isn't 5% a bit much for drive wheel hubs and axles?
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Perhaps. The numbers I have provided are a result of many different sources, including technical papers, curve fitting (CarTest vs. observed results), CarTest defaults, Gillespie's book, etc. Getting this type of information precisely is not easy! The good results I have obtained with CarTest vs. real world always include the particular (default) number as I have never adjusted it.
Quote:
Originally Posted by CanAutM3
As for tire losses, there seems to be a discrepancy in the number shown here and the one used in the top speed thread. To calculate top speed, the losses of all four tires needs to be considered. However, to establish losses on a 2WD roller type dyno, only the loss of the drive axle needs to be considered (2 wheels). Yet 30hp is used in both scenarios.
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Good observation. In short, the 30 hp figure is more accurate than the somewhat rough estimate used in the thread I linked to prior.
If you want to calculate any real world performance in a sim, you must count losses for all wheels. If you want to make a correction of some sort for a 2WD roller dyno you should use 1/2 of the total vehicle tire losses, but of course at the given effective ground speed at peak hp in that gear, not at Vmax! This loss will be considerably less than 30hp since it grows non-linearly with speed. For example at Vmax in 3rd gear in an E92 M3, the loss for the rear wheels only is only about 5 hp. The number here of 30 hp is taken directly from CarTest and I have verified that the approach of CarTest is based directly on a common formula and posted on that methodology prior (pretty sure you were involved in that discussion). The M3 and M4 results will also differ due to the vehicles weight difference.