[wmjinman]

RiderofBikes,

During my past life as a land surveyor, I picked up a few concepts in my 27 year career. While maybe not "scientifically rigorous" statistics-wise, we had many methods for ensuring our results were good. We hardly did anything without checking it. If we measured a distance, we'd measure it twice. If we'd turn an angle, we'd turn it twice (or more). Same thing with elevations. The concept of "closing the traverse" is to make sure that when you come back to where you started from, your measurements in your notes ALSO say you came back to that same point. Same thing with "closing a level loop"

When I read Metro MPGs article on "proper testing" with the "A-B-A" method, it made perfect sense to me as a surveyor. So while maybe not statistically rigorous, I think three "sets" of data can tell you something IF they're consistant. The first one gives you a number. The second one gives you a comparison. Then the third one confirms (or disputes) that your set is consistant.

For example, you make 3 "A" runs (two way, of course) and get 40.2, 40.1 and another 40.1. Actually, that would be 6 runs, since these are all the averages of the "out and back". But I would personally be very satisfied to go away thinking the results were 40.133 or whatever it comes out to. (actually, 40.1 taking "significant figures" into account). However, if the runs were 40.2, 41.8, and 33.4, I'd want to do some more, because the spread was so great.

Doing two-way runs is EXTREMELY important because it automatically averages-out so many error factors. Grade, wind, etc. If one-way is bad because it's not level, doing it the other way will compensate because it's not level, but in the opposite direction. Same thing with wind. (within reason, of course - doing it on a hill so steep you have to go up it in low gear and brake on the way back down obviously won't give you good results.)

But back to the surveying, my wise old bosses introduced a concept called "does it LOOK right?" A newer member on the crew once tried to stake a new property line out into the street. The boss said, "It doesn't matter how powerful your calculator is, we KNOW that property line doesn't go out into the street". So if a set of three runs "looks good" (tight grouping), then I'm happy with it. But if it's "all over the place", then we need to do more until we figure out where it should be.

Anyway, sorry if this is a rant, but for me, I don't (usually) need more than a few runs to be able to determine what I want. For example, yesterday I did 3 out & back runs in the "A" configuration. Two-way averages were: 30.95, 30.95, and 30.80. Overall average of 30.90. I considered this "good", since the maximum spread was only 0.15 mpg. Then I folded the mirrors back to see what the result would be. Two way averages were: 30.95, 31.05, and 31.05. Overall average of 31.02. When you round off for significant figures (ScanGauge only reads to a tenth of a mpg), you get 30.9 vs. 31.0, or one tenth of a mpg gain by folding the mirrors.

(I did do a final "A" run with the mirrors back out, that came out at 30.65. Not sure why it was so much less than the first 3, but at least I knew the "B" test going up wasn't because "conditions" went up). Including that with the 3 original "A" tests still only shows the mirror fold as less than 0.2 mpg gain.

In my mind, I got the answer I was looking for: "It helps, but precious little". Considering the lack of rearward visibility and potential attention from the cops, I think I'm leaning towards "not worth it". To me, that's all I really wanted to learn from that test. I also learned that same day that adding about 10 more psi of air to my tires seems to be good for 1.3 mpg!!! Now there's something that IS worth it!!!!