Ok, latest observations, my round trip to Monterey is about 390 miles, when I drove my beater Prius it took about 8.5gallons, it died last year so now I’ve bought a Kia Soul (finding any new car in the past year was a challenge and used were selling for more than new, I found this kia new just off the boat for msrp)
the Kia would do the trip using using 11.8 gallons, first hour was loaded with all of my gear and the next 2+ hours or middle 4+ for the whole trip was loaded with all of the gear for two divers. Friday after the trip the car took 10.2 gallons. It’s was hot and the a/c was on the majority of the time. I already drive fairly conservatively and try to keep it at 70 most of the time but sometimes I find I’m doing 85 just to stay in the flow.
I bought these with the magnetic base so I could move them around, this is how I’ve tuned them and when I’m coming off the hill (live in the Sierra foothills) I used to see the onboard MPG clock show about 39 mpg, as it doesn’t take a lot of gas going mostly down hill. The last trip it showed about 48mpg, this I believe is due to these little bumps making my box on wheels slip through the air a bit easier.
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here you can see I’ve clocked in the outer 3 on each side, this improved things another 10% or so
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Going through a soft touch type car wash doesn’t disturb them but the outer ones got moved with a run through a regular car wash with the more aggressive brushes, didn’t knock them off but did move them but being magnetic it’s easy to remove them before such activity or just put them back in place.
I know it’s seems like snake oil but I think these actually include some snake.