My brother's thoughts on ecomodding/hypermiling
 

Hi All,

I have had an ongoing e-mail conversation with my brother Wayne, who is off at college. My last e-mail to him was about motorcycle aerodynamics.

He currently drives a Chevy AstroVan and just had to drive from my hometown back up to school.

I thought his comments about it were interesting. They cover economics, drafting, aerodynamics, coasting and other subjects of interest to us.



Here are his comments:

"When driving back to Stout, i had my display set to MPG, and realized I was getting horrible gas mileage.
Then I noticed I was also going 73 mph. So I slowed to 68... and it went from 18 to 23. Then i slowed to 63 and it went to near 26. I set the cruise control, and touched nothing for 2 hours. Cars had no problem going around me, and i never had to slow for someone else.

I stopped and bought a Hardees six dollar burger meal, and at a trip of 250 miles figure the meal was basically free and still saved another $6 by slowing down. Free lunch accomplished.

Later I was able to slow to 56 on a county hwy. and didnt notice any savings... below 55 my fuel economy got worse.

At one point I did manage to draft a greyhound bus for a few miles.. I was getting 29 mpg at 76mph. Damn hard to catch it though, and at 20' kinda scary... the drafting was super obvious though. I slowed down microscopically to get back away, and the second I was too far back, I lost speed like crazy and mpg cut in half.

Also have been playing with hypermiling in Menomonie. A powerglide kinda game. First power up to a best guess speed, and then glide as far as you can. Not doing it for fuel economy, just for fun. My record so far is 0.6 miles coasting and gliding into my parking spot (its kinda downhill, but hey thats part of the game). So much better at guessing what other cars are going to do and when lights change... also how to hit a turn going just the right speed.

If I can find the right speed, 1.1 miles is possible in neutral."

8 MPG for 10 mph. Pretty easy FE gain. Tell me again way the National speed limits is not 55?

Is he a convert now or do you think he'll be back to "normal" driving? Does he have a scan gauge?

pretty cool.. yeah i drove my jeep grand cherokee todatits got a 318 v8 and sucks fuel , but its got a MPG gauge... 10mph can suck some serous fuel.. the best 55mph flat cruising mpg i can get out of the jeep with full time 4x4 is 27mpg.. guess that not to bad with a 318 v8..

I agree with your brother its kind of a game in a way.. a challange that just helps the bottom line.. Cool story

I didn't realize the mpg gain drafting was so high, but 20' at 76 mph is way too close to be safe.

My girlfriend went from 31mpg to 41mpg in her Impreza wagon by drafting trucks about 50% of 250 mi. I haven't measured the effect in my Ranger. What I do is pull forward until the wind noise changes.

Has anyone had a problem drafting to close? The only issues I can see is that if the truck blows a tire or kicks up something, then you have no time to react.
The only other habit you need to do is, follow the truck if it swerves abruptly, you have to assume its avoiding something, and you can not wait until you see it to react.
You should be able to react and slow down faster than any draftable vehicle but obviously you need to pay more attention.
Also if you have a crosswind you may be able to draft in the next lane over without tailgating.
Ian

Typically if I'm drafting, it's a decision to slow down and follow the truck. So, I check to make sure there is no traffic in front of the truck before pulling in behind it. That takes care of most of my concerns. I have no particluar illusions of being able to react behind the truck. My future aero car will have cameras mounted like antennae (sort of F1 style) so I can see around taller traffic.

Let's see: You can drive a Chevy Astrovan at 63 mph instead of 73, and go from 18 mpg to 26. Or you can drive a Honda Insight instead of the Chevy, and go from 26 mpg to 70.

Now tell me, which of these has more effect on fuel consumption? So why are people still talking about 55 mph speed limits (Which were tried before, remember?), and not building vehicles with decent fuel economy?

PS: And notice that the improvement was going from 73 to 63, but not going slower. So why 55 as the limit, instead of 65?

I noticed HUGE gains, upwards of 10-12mpg, from drafting a semi and that was at 70mph. I usually get 36mpg on the highway at 62mph, I was getting 10mpg over that at 8mph faster which means if I had been still able to go 62mph, it would have been more like 15mpg savings. When I draft though, I'm super super cautious about it. Not only is following too closely illegal, with the ability to cost big bucks in fines from local police (believe me, I know first hand). When you're following a truck too closely, you have the usual dangers of not seeing what's ahead, not seeing what's around, not to mention a little thing called "retread" that is likely to fly off the tires at any moment. When I'm back there, I try to give myself about half of what would be considered the "safe" distance from a vehicle moving at the speed I am traveling. So, say I'm going 70mph behind that truck again, I stay about 3 and halfish car lengths back. This, obviously doesn't work if your only going 20mph because 1 car length is just flat out too close, but, 3-4 car lengths still gives a pretty decent FE gain while giving you enough room to see decently around a truck and time to react if something happens (and for those who say, no it's not, I have been able to avoid one blown tire already just by paying attention to the way the truck behaves and watching for unusual wheel wobble).