I did a search and looked through the FAQ but didn't find what I was looking for. Assuming level interstate and no traffic to draft, what is the optimal speed for good FE? My gut reaction is "as slow as possible" to avoid friction and drag, but some engines are more efficient in certain RPM ranges. Has anyone experimented with different cruising speeds above 55 to see what's best?

 

I think GaryG has that table on cleanmpg.com, among other excellent FE data and tips there:


http://www.cleanmpg.com/forums/showthread.php?t=350

 

Hi Brady

In a article I wrote for CleanMPG.com http://www.cleanmpg.com/forums/showthread.php?t=350
I did a steady state speed test for Wayne Gerdes for a presentation at Hybridfest a few months ago. The test was conduced for both cruise control and without at speeds of 30, 40, 50, and 60mph.

In addition, I have gotten up to 70.3mpg driving max EV between 25-35mph Pulse and Glide. Hope to break my record this winter when it cools down here in Florida.

GaryG

 

Thanks for the info! Interesting what a drastic dip the FE is between 50 and 60mph. It's usually pretty dangerous to drive less than 60 on the expressways of Chicago, so maybe I'll modify my route for more side streets. After about nine tanks I'm pretty pleased with my results but this is my first tank of trying some of the techniques I've read about here.

One more question... about how far back can you be from a semi and still get a good draft? I don't have the NAV or a SG so it's not easy to tell.

 

I read that you can still get decent draft 150ft back. That seems too far to me.

I've been keeping ~3 cars length in between (i.e I would be the 4th car or about ~75-100ft) and seem to be getting good draft without the trucker getting peed at you. Although I'm not sure if I'm gettin good draft or that I'm just going slow since the trucks go slow.

 

Brad Berman interviewed me last year for that article you must have read at Hybridcars.com. He sent me drafts to correct and I corrected that 150ft distance, but he left it in there, I think for liability reasons. Forget drafting 150ft if you want any benifits.

For a good draft, a one second delay is great, but you are taking chances. The recommended distance for most State Highway Safety Dept. is no closer than two second behind the car in front of you. With a two second delay, people are cutting in front of you and you have to constantly back off their tail to get back to the two second rule. Most of my drafting is one second to one and one half seconds.

If you are in moderate traffic, most people drive one second behind each other to prevent being cut off every few minutes anyway. Generally, truckers don't mind that distance because they know someone will cut between you and him if your further back anyway. However, when you have an open road and your that close, some truckers will get mad. What I do is watch my Scangauge instant MPG reading for the most distance and still get decent draft. This is a another good reason for having KAM fuel trim. Most of the time, that is an acceptable distance to the trucker.

One other point while we are talking drafting, is a cross wind. Sometimes there is to much turbulance due to a cross wind behind a trucker and drafting there does not help. What I do is move to the edge of the lane oposite the direction of the cross wind or even to the right or left lane behind the trucker. Of course, this is provided it is safe to do this and not effect other traffic.

BTW, if you don't have a scangauge, you can get instant MPG readings from your dash econ readout by resetting it, same with the navi.. This is what I used before I got my scangauge. I have the same feature in my '02 EB Explorer and use it all the time also.

GaryG