100 mpg sustained @ low 40's mph (with 20 km/h / 12 mph tail wind) - Page 2 - Fuel Economy, Hypermiling, EcoModding News and Forum

MetroMPG · 04-13-2009, 12:14 PM

Yup - average continues to drop after the car is stopped on my SGII ver 3.15. Thanks for the info, Andrew.

Posted an FYI on the subject: Mini test: how ScanGauge calculates average speed

Tango Charlie · 04-13-2009, 02:51 PM

Yup, I've noticed that with my Scangauge, too.

I said it before, and I'll say it again; I just love a good tailwind!

Frank Lee · 04-13-2009, 04:18 PM

Speaking of winds again, your first thought would be that the odds of encountering a tailwind are the same as for a crosswind or a headwind... but they're NOT!

For example, when I venture out of town, I typically go due West, and I typically go in the afternoon or evening. The prevailing winds are out of the NW. So, I get to fight quartering headwinds almost every time. OK, so you think, oh well, I sort of get to make up for that penalty with quartering tailwinds on the way back... NOT SO! Because after the sun goes down, oftentimes the winds die down too. For me it's a net loss situation. Someone who had the opposite route from mine would have the luxury of more often than not getting tailwinds!

wagonman76 · 04-14-2009, 12:23 PM

Yep, the chances of getting a direct tailwind are not so great, because of all the other directions the wind could be coming from.

I first learned about dealing with headwinds and tailwinds from an RV forum. They had a really nice spreadsheet to determine how much power was required to maintain a certain road speed, based on expected grades, wind speed/direction, and the frontal area/weight of your rig. Along with weight distribution calcs. Amazing how fast my 175HP van topped out with my 16 ft camper.

They always said headwinds hurt more than tailwinds can help. Which makes sense, because the power needed to deal with wind goes up exponentially with wind speed. Add a headwind and the power needed goes out of sight. Add a tailwind and the the power needed goes down but not really that much.

Metrompg, I just remembered you installed a kammback. I wonder if that kammback was helping, acting like a parachute to help the tailwind push you along.

MetroMPG · 04-14-2009, 12:38 PM

The Kammback definitely helps - but not as a parachute! (Unless I was driving below 20 km/h, the apparent wind would always be coming from the front, or quarter).

Frank: I have been known to plan trip times for just that reason (stronger wind during the day, lighter/absent in the evening/morning). When I do testing, I often do it in the evenings.

wagonman76 · 04-14-2009, 01:01 PM

Yeah, now I think about it, it couldn't act as a parachute. That's cool that you have noticed an improvement with it.

Frank Lee · 04-14-2009, 03:54 PM

When my schedule is flexible and I'm looking at fighting a gale-force headwind, I'll delay the trip.

elhigh · 04-14-2009, 05:01 PM

Dang....

Maybe if I replace my 195/75R14s with bicycle wheels, swap in a 3.15:1 rearend, add a Kammback and a full bellypan and drive at a steady 26mph, I could imagine my vehicle getting 60. That's wild fantasy territory. But 100? I mean, even in a Metro that's just awesome.

Frank Lee · 04-23-2009, 10:18 AM

HA!!! Got 22 mpg with the F150- BEST EVER in 15 years! (Previous best was 21.75, way back when the truck was new.) Yah- kinda a short fill but not a ridiculous one (5 gallons). Not a fluke though- next 250 miles look to be on track for 20 or so (haven't filled yet). I credit the wind which was at times an xwind and at times a tailwind; no cooling fan, ribby tires aired up high, E50, good temps in the 50s and 60s, and of course good driver technique.