What's Better?
 

I do about 12 miles of mostly highway driving to work everyday. I try to keep the speed down around 55 to 60 mph. A lot of times though I can get behind the big trucks on the way, but most of them like to run between 65 or 70. Should I pull in behind and draft at 65 or 70? or do I just maintain my 55 mph in the slow lane?

Slow down, drafting is not recommended.

What's wrong with drafting? It seems to me like it might be the best aeromod we can make.

Yeah, but it's not that safe, particularly in heavy traffic if someone is close behind you. You can always slow down much faster than a truck, but the person behind you can still jam your car under the wheels of a trailer.

On the upside, you can draft somewhat effectively surprisingly far behind a truck.

Agreed. Zero-drafting or what I call it "death" drafting is not recommended even though there are gains with it. The problems as mentioned are safety, lack of forward visibility and at those speeds some cars may not be able to negotiate the distance safely.

Better method would be to use distance drafting or at least give some distance (3-4 seconds) if you're going at highway speeds. Obviously it really depends on the situations but from what I've read and experienced it's just safer to give yourself some room and you'll still get some benefits of a lead blocker.

Also with HM, you're better off going slower or less than 60 (depending on your car) due to aerodynamics and the engine gearing. I know with my Scion she's very frugal at 50mph. :D

I know there has been a lot of negative press with HM and death drafting and when Wayne Gerdes (who coined the "hypermiling" term) says "NO DON'T DO IT - NOT SAFE", I gotta agree with the man. Plus there are other ways to squeeze the petrol that don't put you or other drivers at risk. Oh and welcome! :)

Here's a topic that addresses the issue of drafting:

also when drafting at close speeds you would be tailgaiting and wouldn't be using your gasoline as efficiently, you would be focused on staying close.

I never draft unless I'm lucky enough to find a semi going the same slow, constant speed. I stay 3+ seconds behind. It has only happened twice in my life.

well with me, I drive 55-60 until a semi passes me, then i follow them. If i just drive 60 and don't draft my truck downshifts going up hills. If i draft at 55-65 it doesn't downshift. And when drafting i will speed up using the same amount of throttle. I don't ride their back doors too close, usually a semi-trailer length. I feel it's safe. I have 3 seasons of circle track racing in my experience, and the front end only had a few bumps to it, and i drove hard in the division.
I think it's all about how comfortable you are behind them

Guys I understand the dangers of tailgating, but what I'm asking is what is more fuel efficient- 2 to 3 second Semi truck drafting at 65 or a steady 55 on my own?

I think it depends on a lot of factors. How good your car's aerodynamics are, whether there's a head or tail wind, the type of semi you're following. I think the only way to really tell is to do it in a car with a sensitive fuel consumption display, but that still wouldn't tell how your car will do.

Even with the Insight, "drafting" (by which I mean being behind a semi at what is standard separation on California freeways) sometimes gives me a 30-40% jump in mpg, but other times doesn't seem to have any effect at all.