Drafting Works

Took a trip to Miami for the new year. And yes, I'm quite mad that I'm back in 30 odd degree weather, when the coldest temps I saw for a week was 50 (with highs in the mid 80's). Yes. I'm a weeeee bit upset about that.

Anyway. I own a 1997 Z3 2.8 with the infamous "dancing fuel level indicator". For those unfamiliar with this "feature" it is simply that the fuel level indicator will point to "empty" for miles upon miles and then decide to pop up to whatever level your fuel is actually at. Perhaps it will hold that for a day, and hour. a second and then drop back to empty. The "low fuel" indicator does work so you'll always know when you actually have, oh, about one half gallon left. But before that happens, well, when the needle does the dance, or stays at empty, your guess is as good as mine.

So, how do I know when to refuel? Well THIS model has the on board computer that will tell you how many miles you can go before empty. during my years of ownership I have discovered that when it says 75 miles left, you've got a quarter tank. In the case of a Z3, that's about 2 gallons. We're going to get to the drafting bit in a minute.

So on my way down to Miami, the computer told me I had all of 100 miles left on the tank I had. So I passed on the gas exit that was upcoming. No sooner had I passed the exit than the computer did what I call "The big drop".

You see, on occasion the computer discovers that it was well, wrong. To my dismay 100 miles dropped to 90 in the space of one mile. 80, 70, 60, soon followed. Shall we say I let off the gas. NO help. 50-40....46. And on came the "low fuel" light. I was not happy.

Fortunately I was near the next exit where I could refuel.

See my usual rule is 75 miles to go or 1/4 tank. Whichever comes first. But when the needle is asleep and the computer decides to go into freefall, well..You better hope there is a petrol station nearby. Right.

So on the way back home I hit the magic 100. Fortunately the needle was working. But I wanted to make it to Fayetteville NC so I pulled in behind a semi. Oh look....miles to go is INCREASING! I must have gained an expected 20 miles before I decided to not press my luck and pass Fayetteville.

I decided that for the remainder of the trip, whenever I found a truck or large SUV traveling at least 15 MPH over the posted speed limit, I would tuck in behind it. I knew how close I needed to be because in the "vacuum" created by the huge vehicles ahead of me, I could no longer hear wind hitting the cloth roof.

Let me tell you. I have NEVER. Ever. had my expected miles go above 360. The computer reported 404 miles. I did a quick calculation and found that while drafting at various illegal speeds my car was seeing a nearly 30% increase in efficiency.

Of course there is a major downside to this method of saving fuel. Had any of the vehicles I was behind crashed or otherwise stopped short, I was certainly...dead.

See the safety reasons for not tailgating are as follows: firstly you have space to come to a stop or engage in evasive maneuvers. Secondly you can actually see what the vehicles in front of the vehicle you're behind are doing. Often I brake before the person in front of me does, because I can see that the people in front of him are braking or doing something silly. When all you can see is the tail of the truck in front of you. There are no warnings.

But all that said. If you desperately need to make an exit and you have allowed that "low fuel" light to come on (I don't recommend that), Do pull in behind a truck. 30% more distance from what you have left.

PS: I know some wanker is reading this and saying "just drive slower". Look you. The idea here is to make time AND be fuel efficient.