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Old 10-16-2012, 12:58 AM   #82 (permalink)
wmjinman
Master EcoModder
 
Join Date: Oct 2012
Location: Carson City, Nevada
Posts: 612

Jimmy - '00 GMC Jimmy SLT
90 day: 21.18 mpg (US)

The White Gnat - '99 Suzuki Swift
Team Suzuki
90 day: 51.87 mpg (US)
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RiderofBikes,

Yeah, I think I "get" what you're saying, too. And you're absolutely right that we had "tolerances" in our surveys. Oftentimes we'd turn 2 "sets" of angles (direct and "reverse" with the instrument), and if they were within 8 seconds of angle, we were "good". If the spread was more, we'd do another one. Now, in the winter, especially, when the frozen ground might be melting under the tripod foot (or feet) as we're turning the angles, the results might "climb". Like, the first set might be 21.2, the second one 29.9. That's over 8 seconds, so we'd do another. But what if it was 31.3? That's well within the 8 second "window" of the second angle, but why was the first one so low? In other words, it kept climbing. What we would like to see would be a third one in between the first two. So in the winter time, what we'd do is go check the sights and re-set the "gun" (the survey instrument). In the summertime, if we were set up on the "oil" (asphalt pavement), the feet could actually sink in if it was soft enough. And watch out if one foot was in the sun and the other two were in the shade (or any combination like that!!)

So I'm very aware of outside influences. And like you say, just because raising the air pressure in the tires 10 psi in the summer gives you 1.3 more mpg, you can't automatically assume it will work exactly the same on a different car, or with different tires, or at a different time of the year. Although, I think it's safe to assume from this that it will probably yield an improvement of some sort. Of course, another variable is the pressure you're working with. Chances are, raising it from 15psi to 25, will probably yield even better results than from 45 to 55. And I would suspect (assuming it's even possible) that raising it from 90 psi to 100 would probably benefit LESS.

Even now, I'm wondering if folding the mirrors in is more "worthwhile" at higher speeds? Because the wind drag probably isn't as severe at 50. If I did it at 70, I wonder if the savings would go way up? So I see your point that to REALLY KNOW, it takes a lot of data.

Also, I re-read part of this whole thread, and see MetroMPG was primarily talking about the kind of testing that should be done before trying to "separate people's money from their wallets". And, yes, I absolutely agree!! back to my mirror test, just becasue on one day, at 50 mph, my Jimmy "only" got 0.1 (or 0.2) mpg better and I'm thinking maybe it isn't "worth it", certainly wouldn't take that as "sufficient evidence" to start selling rearview TV cameras and trying to convince people to delete their mirrors. Uh, wait - that doesn't make sense. What I mean is if the mirror folding had looked like it helped a LOT on that one test, I wouldn't decide that it helps a LOT on ALL cars at all speeds.

These tests of mine were also in Washoe Valley, elevation 5200 ft. The air is a lot thinner up there than where 90% of the population lives nearer sea level. So my suspicion is that the aero forces are LESS significant in Washoe Valley. But it's near where I live and where I drive, so whaddam I gonna do, right?

Last edited by wmjinman; 10-16-2012 at 01:03 AM..
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