To draft or slow down? - Page 16 - Fuelly Forums

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Old 05-10-2008, 03:01 PM   #151
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Quote:
Originally Posted by monroe74 View Post
For me, the essence of this technique is that I avoid any throttle setting other than about 70%.

But this kills my lean burn, right? Because lean burn generally works only at relatively low throttle settings, right?
I'm not well studied in lean burn strategy, but the ECU goes to open loop/pre-set ratio tables on most cars (supposedly) at much closer to WOT, I'm guessing 95% open throttle. If I'm wrong I could probably be saving more gas than I currently am, so I'd like to know too...

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Originally Posted by mkiVX View Post
i have tried all sizes of tires. nothing works better then the 165/70 13
people on this board think that skinnier tires like the 155 80 13 will get you better mpg
what they dint realize is that they are over all taller and require more push of the pedal to get going...
the best tire i have bough up to date are 165 70 13 sumitomo htr t4 at 60 psi
165/70 has a 115.5mm sidewall. 155/80 has a 124mm sidewall. That's nearly a whole centimeter, probably about 3/8 of an inch if you prefer that type of measurement. It's not a huge difference. If you do less stop-and-go then it might be better.

More important is rolling resistance. You might be surprised to know that a wider tire is going to have less rolling resistance, all other variables being equal. Here's why: Contact patch is simply pounds against PSI (Pounds per Square Inch). If you have 500 pounds on a tire at 50 psi, your contact patch will be 10 square inches. Now, a wider tire's contact patch will be wide, while a narrow tire's contact patch will be long. In order for the narrower tire to get that contact patch, more of its sidewall has to bend/deflect, and that's where your rolling resistance comes from.

I learned that in rec.bicycles.tech where rolling resistance is VERY important. A common myth is that the narrow tires on road bikes have less rolling resistance...but in reality, if you can get the same tire with the same compounds and same pressure ratings in a wider size it will have less rolling resistance -- at the cost of aerodynamic drag, of course.
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Old 05-10-2008, 07:56 PM   #152
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What should be done...

The government should start a research project for automated platooning. There have been lots of research on the reduction of CD caused by platooning (drafting) - it's old news. Also, the price of fuel is too high and the benefits from platooning are too promising. Now what needs to be done is: 1. A standard for communicating between car ECUs the necessary information to allow safe automatic cruise control 2. Testing and verification of ensuring safety under several different driving scenarios. 3. Have the car companies produce a limited number of cars equipped with automatic cruise control hardware. 4. Build and open a new platooning-only highway system that is a few dozen miles long. 5. Then when the concept is thoroughly tested, some initial problems are corrected, and this concept becomes more popular begin to expand this new highway system until all cars are platooning-enabled.

The possible benefits of automated cruise control systems don't just include the 40% drag reduction and reduction in fuel consumption due to the decrease in traffic congestion, there will be improvements in safety, less brake wear and damage to body panels, etc.
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Old 05-10-2008, 08:09 PM   #153
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I was thinking of starting a new trend on the highways by making a bumper sticker that says: "Form a train in the slow lane!"

I was also thinking of maybe, as a warning to others, having a bumper sticker that reads: "This car employs the P&G method" --this is a good sticker because it's gets peoples' attention "what's the P&G method?" The smart people will figure it out when they see me driving like a yoyo. This would go well next to the "Gassavers.org" bumper sticker, which I have yet to order. Not sure what I'm waiting for.
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Old 05-10-2008, 08:51 PM   #154
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holy: "95% open throttle"

Could be. That's what I've heard in various places.

I'm having a hard time figuring out where open-loop starts on my VX. I just started using a DMM to monitor the mixture, and I see it goes from very lean to fairly rich if I move the throttle from, say, 20% to 70%. Then it increases to very rich if I open the throttle 100%. So it's hard to tell where open-loop kicks in. Then again, maybe it doesn't matter. But it's still perplexing to decide if I should try to maximize lean-burn, or try to minimize pumping losses. These goals seem mutually exclusive.

Last tank I did great with large throttle openings, and P&G, even though this meant I was mostly not using lean-burn.

Next I'm going to try to monitor what my injectors are doing. Maybe that will shed some light on the puzzle.

I think having a wideband sensor actually makes it harder to tell when open-loop begins. I think an ordinary O2 sensor in closed-loop mode behaves in a distinctive way, with the voltage oscillating. Then there's an abrupt transition to open-loop, and the voltage becomes relatively steady.

With a wideband sensor, the voltage is relatively steady all the time.

Someone please chime in and correct me if I'm wrong.

Very interesting point about tire width. Thanks for explaining that.
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Old 05-10-2008, 08:58 PM   #155
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Another thought on intentional drafting groups, well two thoughts.

Motion sensors that work with cruise control to amintain distance.

A yellow warning light that informs drivers behind you that you are coasting or decelerating in gear.

No light engine power engaged
Yellow light coasting or decelerating without brakes
Red light brakes applied

This would allow the car behind you to anticipate your glide and do the same.

regards
gary
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Old 05-10-2008, 09:13 PM   #156
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"Motion sensors that work with cruise control to amintain distance."

Toyota has offered something like that since 2001:

http://www.carbuyersnotebook.com/arc...as_dynamic.htm
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Old 05-10-2008, 10:46 PM   #157
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You see, a lane change in and of itself is more dangerous than staying put.
Because of the blind spot, a lane change involves always a slight risk of collision.
But, tailgating isn't the solution either.
I mean if someone wants to follow 2-3 seconds behind, fine by me.

But as for rigs, a lane change carries considerable risk.
There is always a chance someone is in the blind spot, and the bigger the vehicle the larger that spot becomes. You really have to study your mirrors and hope you're right, these things are 75 or 80 feet long, something like 3-4 times longer than your car.
Not to mention, a rig's tire is big enough it will roll right over top of a car, literally.

Drive anything trailered sometime, even a car with a homemade one,
or towing a boat, you can see it then.

So...
My rules are even simpler: Pass in the first available lane.
I don't care, left or right, either one.
Not to get into a tiff of lane switching, it's a matter of if someone is already in a lane that has nothing but open space in front, why should I move out of my lane so they can get in it just to pass?

See around here we got 3 and 4 lane highways and there's no other way of doing it, I'm not moving 3 lanes over and that's all there is to it because with 100 cars in a mile of space there's no telling anymore who is faster, who is slower...
So by the time I get on a 2-laner my mind's already set that way... Just pass in the open lane and be done switching.

Because it's this thing about slow and fast...
Well excuse me but if the speed limit is 65 and I'm already doing 70 just how FAST did the other driver want me to go?! 10 over around here is ticketable for sure.
So am I the slow vehicle now?
Fine, and they're in the technical slow lane doing 72...
So, they're going to get over, behind me, force me to get over too.
Then they pass me, and then they get over in front of me?
(Half the time they cut me off too).

I saw it in Europe...
I know it's the law there, fine.
But it makes little sense to have two cars switch lanes a total of three times when not 20 seconds ago they could have just kept on going and the faster car passed the slower one ooops in the open lane...

Oh well.
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Old 05-11-2008, 04:36 AM   #158
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Quote:
Originally Posted by 1993CivicVX View Post
bumper sticker that says: "Form a train in the slow lane!"

a bumper sticker that reads: "This car employs the P&G method" --this is a good sticker because it's gets peoples' attention "what's the P&G method?" The smart people will figure it out
would go well next to the "Gassavers.org" bumper sticker
Realistically, people will never figure it out. The gassavers.org sticker might help a couple people, though when you go to gassavers.org the forum isn't really conspicuous enough.

I still can't figure out this one that I saw on my commute:


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Originally Posted by monroe74 View Post
But it's still perplexing to decide if I should try to maximize lean-burn, or try to minimize pumping losses. These goals seem mutually exclusive.
That's a decision that has to be made for a few FE strategies, and the way I make it is first by which is more practical, and second by which is more comfortable. For example, if I'm on a busy highway P&G is not practical but drafting is.
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Old 05-11-2008, 07:02 AM   #159
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"That's a decision that has to be made for a few FE strategies, and the way I make it is first by which is more practical, and second by which is more comfortable."

Good point. Sometimes the strategies are mutually exclusive. But I also want to take into account which strategy is more powerful. Maybe there's a big difference, and then I'll mostly ignore the weaker strategy.

I could imagine various experiments that might indicate that one strategy is much more powerful than the other (maximize lean-burn vs. minimize pumping losses). Trouble is, I'm starting to think those experiments haven't been done (I hope someone can tell me I'm wrong).

Maybe this is not surprising, since there aren't lots of lean-burn cars out there. Just the VX, HX, Insight, and the first-gen Civic hybrid, as far as I know.
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Old 05-12-2008, 08:03 AM   #160
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Open loop: from the Scangauge, mine goes into Open above about 95% load.
Bump-start: you should do a quick up-down bump in high gear (5th) and then choose your driving gear. It's much much much smoother that way.
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