To draft or slow down?

[racertim]

Originally Posted by PaleMelanesian

75mpg - 50-60mph P&G

That means gas from 50 to 60, off the gas 60 to 50, repeat?

[palemelanesian]

That's right. Shift into Neutral for the glide part. Pulse at medium-high throttle. Is yours an automatic? Leave the engine running for the glide. If it's a manual, you can shut it off and then clutch-bump to start it back up.

[theholycow]

Originally Posted by racertim

What do you recommend that I try differently then? I was cruising steady behind the trucks at 1 sec at 70mph on average.

Back off. It's definitely more beneficial for drafting and for safety/courtesy to stay back at least 2 or 3 seconds.

[GasSavers_RoadWarrior]

Oh there is a thing that happens that might make drivers suppose that drafters are causing extra drag...

If you move in close behind a vehicle from another lane, slide across behind it, while you're coming across you collapse the vortex on one side of the vehicle, as you come over, this causes the forces to be imbalanced and the vortex on the other side is still causing drag force... so... a sensitive driver may feel something that feels like a tug as the vehicle moves across behind him, this is not extra drag, but merely uneven relief of base drag vortex pressures.

[1993CivicVX]

Originally Posted by theholycow

In group bicycling and auto racing, drafting helps both the puller and the drafter. I can't say for sure it works that way with hypermilers drafting trucks, but I don't know why it wouldn't.

Okay, this is what I originally thought! (oddly, I actually forgot I thought that until I read this.) Someone had told me it drags the puller to be drafted and this was such a surprise to me I internalized it. (my brain operates in odd ways.)

I think people assume that it would create more drag on the truck because it's benefiting the car, and TANSTAAFL...but in this case, here's my guess as to how it helps the truck: Normally, the truck has to burn fuel to pull that vacuum behind it. The car fills part of the vacuum, and aerodynamically becomes part of the truck and is a sloping the rear piece instead of the truck being cut off flat. I'm no aerodynamics expert, so this is all conjecture.

Yeah, this is what I used to think. I like this idea more, I think I will reassume it in my thinking.

[1993CivicVX]

Originally Posted by PaleMelanesian

The Civic has TERRIBLE highway gearing. But I've done some great numbers using Pulse&Glide combined with a 2-3 sec draft - upper 50's mpg at 70mph average. The aerodynamic benefit is still there, it's just that the high gearing masks it.

I would propose P&G has more benefit over steady state in a car with bad highway gearing. Because the pulse is going to happen quicker (and thus shorter amount of time with the engine using gas) and the bad gearing will be more a benefit for the pulse than a detriment--as compared to the detriment it is for highway steady state.

In other words, if you have a car with close gearing (and thus a "short" final gear), use it to your advantage by employing more P&G and less steady state driving.

[1993CivicVX]

Originally Posted by racertim

Wow.... I haven't checked the thread in a few days and there are million posts!

I supposed I had a good first question!

Anyways, I updated my mileage log with my tests between drafting and slowing down. I managed to get a couple MPG better by slowing down. I think I will do another test to see if the results are confirmed.

It's been a stimulating and learning experience

[theholycow]

Originally Posted by 1993CivicVX

In other words, if you have a car with close gearing (and thus a "short" final gear), use it to your advantage by employing more P&G and less steady state driving.

That describes my car, and one of the main things I dislike about it. Once I am satisfied with my skip-shifting experiments, I will either try P&G or drafting.

[palemelanesian]

I agree entirely.

[1993CivicVX]

Originally Posted by theholycow

That describes my car, and one of the main things I dislike about it. Once I am satisfied with my skip-shifting experiments, I will either try P&G or drafting.

If I had your gearing in my VX I'd be getting better mileage around town and I would be saving my clutch. First gear is so tall I have to keep the clutch in much longer than you do in first, unless I want to rev the engine a bunch. I'm going about 25mph in 2nd gear before I hit 2000rpms.. means i spend a lot of time at higher revs around town because the gears are so far apart. Granted I make up for these losses on the highway, but my friend's 2 door DX coupe of the same generation as my VX had the nicest gearing for slower driving. This is the only pet peeve I have with my VX. I hate having to use the clutch to accelerate from less than like 7mph. In my friend's DX coupe, you barely needed the clutch at all.