Drafting vs. P&EOC
 

On a four hour drive today I contemplated the gas benefits and drawbacks of drafting a semi versus pulse and glide with engine off coasting. I was P&EOC'ing from 50-65 and the semi was going about 62. I don't think I was saving any gas by maintaining 62 behind the semi, but maybe at lower speeds drafting would be more efficient than P&G? I also did a little EOC while drafting but that was difficult because I would slow down and lose the slipstream.

What's for sure is that other drivers (except the semi driver) are less annoyed at drafting than P&G. [tangent]I've been thinking there should be some way to quickly let people know what P&G is so they can just pass and get on with their lives instead of tailgating and passing aggressively. I considered putting a "<-- PASS ME" sign on the rear window with masking tape but never ended up doing it. [/tangent]

Also it's a possibility that I will be driving from Detroit to Calumet, MI (570 miles) for a rally race in two weeks and I'm wondering if drafting my friend's VW Quantum will make up for his self-imposed speed of 75mph, versus setting the cruise at 60mph without drafting.

What do you all think about this? :)

PS- sorry for the scatterbrained post

http://www.nekegu.com/personal/TestCar.jpg

:thumbup:

Rick

Sven7: I think that you'd have to draft that VW pretty close @75mph to greatly improve on what you'd get by cruising or P&Ging around 60mph. I personally wouldn't sacrifice safety for so little. You could decrease the global fuel consumption (your's and your friend's) by either towing one of the cars or having him follow you at your self-imposed 60mph.

Rick: Is that your's? So cool:cool:

Indeed it is, and thank you! The Cabrio died this summer though, so these days the sign's on the back of the CARDIS.

Rick

I rarely find a truck moving slow enough to make it worth the effort. also at highway speeds I find that DWL works nearly as well and is not as tiresome to keep up.

Cool! That's a good idea; I just didn't know what to say on it. Will probably try to make one. Thanks :cool:

I talked to him about it and if I'm going in the caravan I'm going to have to do 75mph like the other three cars. It's a 10 hour drive so that 15mph difference amounts to about 2 1/2 hours difference in the whole trip time. In those extra two hours we could be mountain biking in Copper Harbor :thumbup:

So i guess the question is, is it worth trying to catch the slipstream on a 10 hour drive? How much would it affect MPG? Keep in mind he'll have two mountain bikes on a roof rack- that probably makes a difference in turbulence. If I get 5mpg better I'm willing to draft him.

I was just showing you're not alone in trying to find the answer. :)

I suggest the largest-font, easiest-to-read, most quick-to-comprehend sign you can conceive. I think the best bets are the really simple ones like RESEARCH VEHICLE - PLEASE PASS (whoever did that one, please weigh in). But I'm paranoid, and I can imagine some idiot whipping by me on a double yellow, nearly buying the farm in a head-on, and then suing me because "His sign said to pass!"

You'll notice TEST CAR and PASS are in the largest font. The former's to send a message that something out of the ordinary's happening (e.g., I'm going slow) and the latter suggests a course of action. The "okay to pass when safe" part is for my peace of mind (see above). I doubt most bother to read the rest (if they even can from a distance), but as a whole it makes a good conversation starter at the pumps and elsewhere. Which helps spread the word and maybe change mindsets.

Back in the day, I had a lot of people sit behind me for miles and then finally whip past me. My theory was they figured nobody would willingly drive the speed limit :turtle: so there must be someone ahead with a radar gun. Then after a few miles they'd realize that wasn't the case, and tear off in frustration over having slowed down for nothing.

Once I added the sign, I had a lot less of that; people would either pass fairly quickly, or fall in behind me (maybe using me as an excuse to go slow themselves, I dunno).

The sign also helps when I run interference for other slowpokes. Yesterday it was somebody on a motorcycle doing 50 :eek: on a 70MPH interstate! That's slower than I would choose to go (in fact it seems downright dangerous), but I was worried the poor guy was gonna be fatally rear-ended. I matched his speed about three or four seconds back to deflect faster traffic for him; I'd rather people curse me out and go around both of us than be on top of a 25 MPH slower motorcycle before they realize what's going on.

The 45 MPG I averaged on that run was just a nice karma-based bonus. :D

Cheers,
Rick

I was drafting a flat deck semi with a low load doing 90 kph on the highway for about 20 kilometers and the mpguino was reading between 80-120 mpg , for me P&EOC gets around 60-70 at that speed.
This is the first time drafting has worked for me, I was approx 3-4 car lengths behind which surprised me , I always thought you needed to be right up close.
I had my drivers window open an inch or so and as i was approaching the semi it was buffeting,then it all of a sudden stopped and the mpg shot up, so I stayed behind and enjoyed the run.
Disclaimer .. do so at your own risk

Just the kind of thoughtful discussion I was hoping for (a little bit OT I guess but that's fine)! You're describing just the things I run into when driving on the interstate. I usually coast down to 45 and up to 60 when possible, but watch my mirror and will prematurely start a pulse if I see someone approaching very fast.

I just made this up in Photoshop
http://farm7.static.flickr.com/6178/...1f546b3b_z.jpg
OK TO PASS! by Tyler Linner... drinking the Kool Aid, on Flickr

But your comments are making me think it should just say

MPG TEST - OK TO PASS

It's classic graphic design- portray the vital information as quickly and clearly as possible. And yes, it helps with the on-lookers when the car is parked. I regularly go to car meets and other events and many people wonder why my car looks so "silly". Apparently the "45 MPG" sticker on the back is not clear enough? :confused:

Anyway thanks for the help.

Very interesting. Does anyone else have experience (numbers) with this? I've been wondering how far back I can be and still feel the effects. It's interesting that having the engine on constantly while drafting could be more efficient than P&EOC.

I'm too poor to buy an MPGuino or anything so I'm relying on theory, experience and you guys to exceed that magical 45mpg mark! (Technically only 0.5mpg away but I rounded up hehe)

Edit: Here's version 2.

http://farm7.static.flickr.com/6169/...74bd9b10_z.jpg
&lt;&lt; MPG TEST &lt;&lt; OK TO PASS by Tyler Linner, on Flickr

Seeing how this is your discussion thread, you're probably safe in going off topic a little. :p I think your original "tangential" judgement is probably closer to the truth than "off topic" anyway. We don't usually get to pulse and glide "in a vacuum," and respecting other drivers and minimizing disruptions is, to my mind, a vital aspect of the technique.

I think both of your sign ideas look great! I like how you turned the sign itself into the arrow. And using the whole bumper is probably a good idea. Getting that oncoming driver's attention as quickly as possible has to help.

I was telling a friend the other day that, when doing this kind of stuff on the interstate, one sometimes spends as much time watching the rear view as looking ahead. People aren't expecting out of the ordinary things, and I think the monotony of the highway lulls many into a less attentive state. Like you, if I see someone coming up on me rapidly, FE goals go out the window and I accelerate to reduce the speed delta before they get to me.

Sorry I can't contribute much to the "on topic" aspect of this thread. Drafting never seemed to make much difference to the Cabrio (I think because it was so small and short). And I've been trying to hold a constant speed with the Versa for other tests, thus haven't had many chances to try drafting with it. Plus with both being A/T, pulse and glide doesn't offer me as much benefit. (I'll NICE-ON P&G through a 25 MPH neighborhood at the end of my homeward run -- a 40 MPG trip average will plummet if I drive it at a constant 25 -- but that's about it.)

Cheers,
Rick