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Originally Posted by CanAutM3
This is probably the most likely explanation. True losses are very complex and difficult to model. The equations we have quoted so far all consider drivetrain efficiency as a constant applied to transmitted torque, which is far from reality. A portion of the efficiency varies with speed and another varies with torque. For example, the viscous losses in a transmission are still present even if no torque is transmitted.
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I don't fully agree. Losses are both in the real world, in CarTest and in my spreadsheet simulator, speed dependent. Even the most basic ideal damping loss we learn about in Differential Equations is a speed dependent linear loss (sliding friction, damper losses, etc). Furthermore manufacturers even quote things like transmission and diff losses as a percentage. Yes losses in general are from a lot of small complex effects but the overall approximation of them being a percentage and scaling with speed or rpm as required is a pretty good model. No it's not accurate that all trannies or all diffs have the same loss but again the errors from such an assumption are not critical in an overall accurate performance prediction. That approximation will cause some vehicles to be slightly under predicted and others over depending on if the efficiencies of the components are all in total better or worse than the nominal values.
You certainly don't need to be reminded of this but all of these things being user controlled inputs, along with CarTests ability to do sensitivity studies are overall points that make simulation incredibly insightful and useful.
Quote:
Originally Posted by CanAutM3
I would not have expected that doubling the FD while halving the gear ratios to have an impact on optimal shift points. The resulting relationship between the car acceleration and engine angular acceleration remains the same and the ratio between gear ratios also stays the same.
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I would. Look at the basic tractive force equation again here are both Nf and Ntf terms. Again probably not a large real world change in the rpm predicted but it is an effect and it is simply missing in CarTest.