Hi,
If you get a chance, check my work?
I used the following from the EPA table:
- Target Coef A (lbf)
- Target Coef B (lbf/mph)
- Target Coef C (lbf/mph**2)
Using the chart, we would expected the same rate per second of fuel burn going horizontal.
~18hp @80 mph "Prius hatchback"
~18hp @67 mph "CMAX"
~18hp @67 mph "Prius v"
For example, our 2010 Prius gets ~39 MPG at 80 mph:
Now back of the envelope, we can estimate the CMAX/'Prius v' MPG by scaling for the slower speed ASSUMING the fuel burn rate per unit time are identical:
~33MPG = 39MPG * (67/80) ::@67 mph
The owner reports:
- 38MPG @65mph
- 33MPG @70mph
Close enough for my work.
The power vs speed chart of the CMAX shows rolling and aerodynamic drag consistent with the "Prius v". I've included the "Prius hatchback" for reference yet this is the EPA ratings:
City Hwy Model
47 47 CMAX
44 40 Prius v
51 48 Prius hatchback
What this means is any vehicle with coefficients listed in the EPA tables can have a power vs speed graph. Then if one has their own MPG vs mph chart, one can estimate the expected performance.
Your posting gave me the clue needed to do the power vs speed chart. The rest is simple math:
Quote:
Originally Posted by Old Tele man
The "EPA testing" process begins with the manufacturer: (A) doing "coast down" tests to find a "road load hp (RLHP)" number for the vehicle. Then, they (B) come up with a supposedly equivalent "test load hp (TLHP)" for the dynomometer they used. So, errors in A propagate into B and so on...
The two equations:
RLHP = (A + BV + CV^2)/7.5 ...A,B,C coefficients for "road"
...where:
V = mph
A = lbf
B = lbf/mph
V = lbf/mph^2
TLHP =(A + 50B + 2500C)/7.5 ...F0, F1, F2 coefficients for "test" dyno
_V = 50 mph
F0 = 36.62 (rolling force)
F1 = 0.1461 (rotational force)
F2 = 0.01869 (aero force)
...example from GM data submitted to EPA:
TLHP = (36.62 + 50(0.1461) + 2500(0.01869))/7.5 = 12.1 "test" hp @ 50 mph
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Thanks,
Bob Wilson