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You're definitely high with your Cd estimate. I'm sorry that I cannot trace this to a reliable source, as it's simply a number that comes to mind (certainly less than reliable these days!) for the 122... use .40 as the Cd and I'll bet you're going to be very, very close. The 122 is aerodynamically cleaner than you might imagine. As a matter of fact, I recall some 70's racer talk (prolly originating from the guys at IPD) indicating the 122, despite having slightly more frontal area, generated a little less aero drag than the 1800. That would mean of course, it had a lower Cd.
Finally, I haven't looked at the calculator mentioned in detail, but it appears the results are calculated to total lbs of drag. Once you have the Cd right, you should come up with a total drag of something in the neighborhood of 115 to 120 lbs at 60 mph for the 122. Again, this is total drag, aerodynamic and rolling resistance combined. To be exact, 117 lbs is the average of 4 separate Road & Track road tests of various 122's between 1959 and 1965. The R&T data was measured (I've forgotten the details of how... they quit reporting it as part of the road tests in the late 60's), as opposed to a theoretical calculation as I recall. There appears to be reasonable scatter in the data, ranging from 111 to 124 lbs for the 4 tests. Anyway, given that number (or possibly a couple pounds less... you're undoubtedly on radial tires, the R&T cars were not), you can probably reverse calculate to arrive at a reasonably accurate Cd.
And BTW, Road & Track seems to have always come up with 20.9 square feet as the frontal area for a 122. I believe this was simply width times height times a fudge factor of 0.8 IIRC.
Gary L
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1971 142E ITB racer, 1973 1800ES, 2002 S60 T5
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