Tire Diameter Change In Fuel Log?

[Blue Angel]

Tele, what are "engine revolutions at 50 mph"? I can't seem to figure out what that's those numbers are actually representing... something dependant on gearing and tire size?

What is the other model that has a manual transmission and 215/55-17 GoodYears?

[gone-ot]

It's EPA-speak (ha,ha), one of the EPA's 'test' parameters, N/V Ratio -- RPM/MPH, ie: engine RPM (N) divided by vehicle speed (V) of 50 MPH, where the "key" is knowing that EPA assumes 50 MPH vehicle speed!

For example, consider the Eco automatic with final drive ratio (FDR) of 3.53:1 and 6th gear of 0.74:1, where N/V = 34.9. Thus: 34.9 = (XXXX rpm / 50 MPH), so XXXX = 1,745 RPM (engine) at 50 MPH (dyno test speed).

...and, continuing this "numerical" exercise, then:

MPH = [ 60 / (G × A)] × [ RPM / rpm ]

50 = [60/(0.74×3.53)]×[1745/rpm] ...so, rpm = 802 rev-per-mile

...where:

MPH = vehicle speed.
RPM = engine speed.
rpm = tire revolutions-per-mile.
60 = conversion constant, minutes-per-hour.
A = axle (Final Drive) ratio.
G = gear (6th) ratio.

Thus, any tire/rim combination having tire rpm ~ 795-805 will all be "close enough"!

Addendum -- Sorry, that second 17" wheel/tire was a typo error.