Some hypermiling techniques illegal in my state!

[cfg83]

basjoos -

Originally Posted by basjoos

Why is coasting "very dangerous" and why would coasting a modern car make someone lose control? That accident is more likely the result of someone not paying attention to their driving. There is very little difference in the driving characteristics between coasting with the clutch depressed and "coasting" in an overdrive 5th gear with its limited amount of engine braking, other than when coasting, you have a 1/4" sec delay in releasing the clutch to get power to the wheels from the engine. With an automatic, coasting is a little more dangerous since you have a 1 to 2 sec delay before getting power back when going from "N" to "D". But most of these anti-coasting laws pre-date the appearance of the automatic transmission. They date back to the early years of automotive history when friction wheel braking on most cars was very poor and you mainly used engine braking to control speed on the downhills. They were implemented after a number of accidents were people crashed after coasting their cars downhill out of gear and got up to a speed that was beyond the ability of their primitive friction brakes to slow and engine braking was taking too long to get the car slowed down before they wrecked.

I agree with this because the engine response in 5th gear is very minimal. I think for manual shifting, I would have to pop into a lower gear ASAP to avoid a burgeoning accident.

How's this for a compromise? Make it part of the suggested "rules of thumb" that driving in Neutral also require that the driver have their hand on the shift knob and their foot on the clutch pedal at all times.

Now, this is still a gray area. If I am on a steep downhill for an extended period of time, especially on the Grapevine (the 5 freeway in California), I will be in gear and use my engine braking because I can't see my brakes lasting all the way down that hill.

This is actually the one part of gas saving techniques that is the biggest change for me. I have always engine braked. It's been one of the "fun" parts of stick driving for me because it is part of "engaged driving". These days I am very conscious of when the old me would engine brake and I kinda miss it. But I still know it's there when I need it, so I guess that's ok.

CarloSW2

[cfg83]

Ted -

Originally Posted by Ted Hart

If you've ever driven in the Smokey Mts. and seen the runaway truck sand traps on most of the downhill stretches...you'd appreciate engine braking. Get caught in "N" with thousands of pounds behind you! ... and hot (faded) brakes...and you'll pray for the next sand trap...to be empty!

Just like the Grapevine. Where it says "trucks use low gears", I will always stay in gear (until the near-bottom of the hill, where I can pick up some free speed).

CarloSW2

[Silveredwings]

Originally Posted by Spule 4

Coasting is very dangerous and illegal in much of the US, a friend's father is nearly paralyzed due to someone doing this and loosing control of the car and hitting them head-on.

However, some cars do it, mostly two strokes of the past, for very obvious reasons!

How exactly did this happen? I'm really curious. Was the driver just allow his car to go way too fast for the conditions and thereby lose control of the car? Was lost power steering the problem? If so, the difficulty of steering is usually inversely proportional to the speed. Or were power brakes an issue?

[Silveredwings]

It's a mystery to me as well. Normally when in gear, the car is limited to whatever speed the drivetrain will give you. Hills can still increase accelleration regardless of the gear, but it seems to me that some may think that with the drivetrain out of the picture, the car can freewheel to a higher speed.

If that's true then the problem is excessive speed, not the mechanical configuration of the driving apparatus. Speeding is already against the law. What does the coasting-in-neutral law buy us? You can get into plenty-o-trouble in that respect with the engine IN gear.

Now on mountain roads, I'd rather use engine braking anyway because it saves brakes AND the ECU shuts off the fuel flow w/o even killing the engine. In fact, since I don't use an engine kill, I use coasting in gear almost anytime I need to decelerate more than about 25 yards, but I coast out of gear when I want to go farther w/o the engine being above idle. Driving conditions determine which method is optimal.

[rh77]

Stuff like this is "only illegal until you get busted" -- meaning, unless they have a really good reason otherwise, law enforcement will not pull you over for it. If you have a broken windshield and got pulled over for speeding -- you're likely to get 2 infractions out of the deal.

But in this day and age of 20+ the speed limit, being "normal operation", I don't see too many cops having a problem with coasting -- or even knowing that you're doing it. Millions of people break the law every day by speeding. These "buried statutes" can be taken with the seriousness of the citizen and the enforcer.

RH77

[GasSavers_TomO]

Originally Posted by theclencher

Stupidest thing about it is MN doesn't even have any hills!

Amen to that! On my trip to Worthington, I coasted a total of 2.5-3 miles out of 407. and that was from the three big hills on trip.

[Spule 4]

Originally Posted by basjoos

Why is coasting "very dangerous" and why would coasting a modern car make someone lose control? That accident is more likely the result of someone not paying attention to their driving. They were implemented after a number of accidents were people crashed after coasting their cars downhill out of gear and got up to a speed that was beyond the ability of their primitive friction brakes to slow and engine braking was taking too long to get the car slowed down before they wrecked.

Exactly. I have cooked the brakes on some cars even with automatic in my time too. I guess a W123 body Merc with OEM brakes was a primative car?

[Spule 4]

Originally Posted by Silveredwings

How exactly did this happen? I'm really curious. Was the driver just allow his car to go way too fast for the conditions and thereby lose control of the car? Was lost power steering the problem? If so, the difficulty of steering is usually inversely proportional to the speed. Or were power brakes an issue?

Yes, yes, and ah....yes. Happend in the gas crunch 25 years ago by some nuts trying to "save gas" and they lost it.

[cfg83]

Silveredwings -

Originally Posted by Silveredwings

It's a mystery to me as well. Normally when in gear, the car is limited to whatever speed the drivetrain will give you. Hills can still increase accelleration regardless of the gear, but it seems to me that some may think that with the drivetrain out of the picture, the car can freewheel to a higher speed.

If that's true then the problem is excessive speed, not the mechanical configuration of the driving apparatus. Speeding is already against the law. What does the coasting-in-neutral law buy us? You can get into plenty-o-trouble in that respect with the engine IN gear.

Now on mountain roads, I'd rather use engine braking anyway because it saves brakes AND the ECU shuts off the fuel flow w/o even killing the engine. In fact, since I don't use an engine kill, I use coasting in gear almost anytime I need to decelerate more than about 25 yards, but I coast out of gear when I want to go farther w/o the engine being above idle. Driving conditions determine which method is optimal.

Is this fuel flow cut-off feature unique to your car or is this something that is true of most cars?

CarloSW2

[Silveredwings]

Originally Posted by cfg83

Silveredwings -

Is this fuel flow cut-off feature unique to your car or is this something that is true of most cars?

CarloSW2

It is definately not unique to my car(s).

I know there have been discussions about this in threads here. I believe that most EFI cars now do this. I recently divested a '99 bmw and a '97 passat that both did it. What appears to happen is that when the gas pedal is not calling for any 'throttle,' and engine is exceeding about 1500-1600 rpm for about 2 seconds (because of clutch-out coasting), the ECU decides that it doesn't need to send any fuel to the injectors to keep the engine above idle rpm. I've seen evidence of this in both instantaneous as well as averaging mpg instrumentation. If I slow down so that the rpm drops to about 900, or if I put the clutch in and let the rpm drop, the ECU steps in and resumes idle fuel flow so the engine doesn't stall. BTW, it's assumed that the engine and cat converter are both warmed up.

I use this extensively and it gets to be a strategy game deciding which mode I want to be in: clutch-in coasting, or clutch-out coasting. Each has a distinct advantage depending on what I need to do with my speed and momentum. I tried killing the engine in the passat at times and I didn't think I got as big a return for the effort so I returned to these 2 modes of coasting (I also had some odd problems with my engine).

I hope that helps.