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Old 12-10-2008, 04:00 PM   #12 (permalink)
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same thinking

Originally Posted by MetroMPG View Post
Do you know if the same thinking applies to losses in the CV/universal joints, potential brake drag, and differential/transaxle resistance - strictly for the purposes of calculating RR?

Good idea. Currently you can lump that into the "engine efficiency" figure in the calculator, if you're working backward from a known MPG at a certain speed.

Still some refinement to be done, for sure. Thanks for the feedback Phil.
Darin,the SAE likes to limit RR to the tires only,as an independent variable. When official testing is done,brake drag is checked for,and eliminated before the testing cycle(so it isn't included in the methodology,although we definitely need to be aware of it). With respect to bearings,ring and pinion,C-V joints,split-driveshaft center support bearing perch,pin-bearings in U-joints,dust seals,transmission/transaxle/transfer-case,oil,grease hydrodynamic losses,these are all contained within Mu,the mechanical -efficiency value of the driveline.

Hoerner uses 90%(1950),CAR and DRIVER have used as low as 80% when discussing their Maxda RX-7 at Bonneville.SAE says 95% for 1/2-ton pickup.

We could use some current good numbers for these values.CVTs are supposed to have horrible efficiencies which cancel out much of their benefit.

Perhaps GOOGLE can provide some up-to-date and accurate quanta for us to use.Anyone lurking could jump on this one and help out.

I'll check back should I have any revelations.Thanks for all you do,Phil.
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