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Old 05-04-2020, 03:39 AM   #31 (permalink)
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Originally Posted by 2000mc View Post
Have you tried testing with a scangauge or other similar device? Measuring to .1mpg should give you around 7x the resolution for an insight vs kmph.
When i tried testing wheel covers my results kept trending upwards, which I think would have been lost along with any result, if not for greater resolution.
Do you have thoughts as to why in this more recent test, windows down produced 101kmph from a baseline of 103.5, while in an earlier video showed 98 from a baseline of 104?
I have a full MoTeC data logging system. I can measure mileage to basically whatever resolution I want at whatever frequency I want. But I don't think short-term mileage testing tells you anything much.

I think the problem with both short term mileage and coast downs is that the test occurs over a period. Any change at any point within that test period will give you an error. A change in yaw angle, a gust of wind, etc. With throttle stop testing, you just get to that speed and then it holds. It's a settled, single number recorded at that point.

Yes, I have a very good idea at the reason for the change in maximum speed with the windows down this time. It was dead calm. The other test, it was blowing a gusting crosswind.

Finally, I think that chasing maximum resolution is the wrong fundamental approach. I don't think any on-road testing (including acceleration, etc) has the repeatability to require high resolution. In those circumstances, high resolution gives you a false sense of data accuracy. If I can't see a change of well over 1 per cent (and usually higher), for me the aero modification is not worth pursuing.

(The parallel is performance testing. A few decades ago I used to run dozens and dozens of stopwatched 0-100 km/h road times on my cars, doing runs after every modification. Say the car was typically doing 0-100 in 6.4 seconds. I'd want to see 6.2 seconds as the average of the runs before I figured I'd made any improvement. That's 3 per cent.)

Last edited by JulianEdgar; 05-04-2020 at 06:00 AM..
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