Hypermiling

[Leggy1]

No, not at all, the engine's effect on braking is additive. If you're at the point where you're using ABS you're in deep crap anyway, especially if your instructor's in the car

Yes in normal situations. But you have the greatest amount of stopping power out of gear.

And emergency stops had to be practised

On the topic of hypermiling, when I was a learner, I drove my parents VW Touran TDI several times. On a long trip I got an average of 60mpg, not bad for a 140hp people carrier. The claimed combined mpg is around 45. Just by being sensible (not slow) really helped.

 

[TenEightyOne]

Yes in normal situations. But you have the greatest amount of stopping power out of gear.

And emergency stops had to be practised

On the topic of hypermiling, when I was a learner, I drove my parents VW Touran TDI several times. On a long trip I got an average of 60mpg, not bad for a 140hp people carrier. The claimed combined mpg is around 45. Just by being sensible (not slow) really helped.

No, you have the greatest amount of stopping power in gear. Take a look at sports formulas and see how many disengage the clutch to brake; I'll bet it's a total of none.

And the Touran TDi 1.9 was a 60mpg engine on the motorway iirc, the engine was in a lot of vehicles. The combined mileage includes urban, not so good.

During the emergency maneuvers testing they make you engage the ABS while performing emergency stops to let you see how it works.

That would be during an emergency stop. Naturally you stop the vehicle in neutral unless you're in an old person's car with automatic gears. That's completely removed from normal braking, you're implying that you disengage gears during braking outside the emergency-stop manoeuvre.

 

[Tornado]

No, not at all, the engine's effect on braking is additive. If you're at the point where you're using ABS you're in deep crap anyway, especially if your instructor's in the car

Cars with front and rear unassisted drums on modern tires can still lock the brakes from speed. Engine braking is additive, but the hard limit still remains the tires.

 

[MatskiMonk]

Most learner cars didn't have ABS when I passed my test

edit: also, what's with all this, "what if you need emergency power!" when coasting stuff?

I have to change gear to get any kind of kick, and even then it's normally after a couple of seconds of waiting for the turbo to wake up, get out of bed, brush it's teeth, put it's shirt on and turn up for work.... it's no longer to knock it back in gear from neutral ?

 

[Bopop4]

No, you have the greatest amount of stopping power in gear. Take a look at sports formulas and see how many disengage the clutch to brake; I'll bet it's a total of none.

Only reason they don't go out of gear is because it would upset the balance at high speed when they let the clutch back out. On a bike the clutch is designed so that it can freewheel.

That would be during an emergency stop. Naturally you stop the vehicle in neutral unless you're in an old person's car with automatic gears. That's completely removed from normal braking, you're implying that you disengage gears during braking outside the emergency-stop manoeuvre.

I let the car roll to a stop in neutral yes, but if I need to brake hard I still have that capability.

 

[TenEightyOne]

Only reason they don't go out of gear is because it would upset the balance at high speed when they let the clutch back out.

Nope, otherwise they wouldn't change gear at the same time.

 

[Bopop4]

Nope, otherwise they wouldn't change gear at the same time.

What? That makes no sense. They change gears to be in the powerband for the next turn. They can't go down too fast or they'll lock the rear, too slow and the sudden jump through the gears will cause the rear to skip around.

In a road driving situation, there is plenty of power to lock the wheels with the car freewheeling.
To say otherwise is blind.

 

[Leggy1]

And the Touran TDi 1.9 was a 60mpg engine on the motorway iirc, the engine was in a lot of vehicles. The combined mileage includes urban, not so good.

Our car is the 2.0, less economical than the 1.9, and it's a 2007 car. 54mpg at the higher speed test. I thought I got a decent figure considering the environment and it's usual economy of 50-52.

 

[TB]

Take a look at sports formulas and see how many disengage the clutch to brake; I'll bet it's a total of none.

If you want to make a claim, don't ask us to look up your information for you.

Naturally you stop the vehicle in neutral unless you're in an old person's car with automatic gears.

You can stop bad mouthing automatics any time.

 

[TenEightyOne]

What? That makes no sense. They change gears to be in the powerband for the next turn. They can't go down too fast or they'll lock the rear, too slow and the sudden jump through the gears will cause the rear to skip around.

In a road driving situation, there is plenty of power to lock the wheels with the car freewheeling.
To say otherwise is blind.

Yes, I understand how changing gear at the wrong time is bad, I think we can accept that most of us in here can actually drive a car

What you said was;

Only reason they don't go out of gear is because it would upset the balance at high speed when they let the clutch back out.

Then you said

What? That makes no sense. They change gears to be in the powerband for the next turn. They can't go down too fast or they'll lock the rear, too slow and the sudden jump through the gears will cause the rear to skip around.

So how are they letting the clutch back out for gear changes? As you say yourself, changing down through the gears has to be done with the right ratio at the right time (not difficult, I think you'll agree) but you imply that letting the clutch out imbalances things.

I'll clear it up for you; engine braking is part of the deacceleration. If it were the case that braking in neutral was even equally efficient then professional drivers would do it - it's a lot easier on the engines for a start.

However that isn't the case; engine braking is a normal accepted part of slowing a car down, you accuse me of blindness but I genuinely think you have something to learn.

If you want to make a claim, don't ask us to look up your information for you.

I wonder if you're mistaken; his claim was "you have the greatest amount of stopping power out of gear", I'm actually refuting that claim. My response was that he'd find no sports formulas where neutral braking of the type he describes was normal. He won't, but I can't look up things that don't exist

You can stop bad mouthing automatics any time.

Not bad-mouthing them, the way old people drive is very different as are their requirements. I have nothing against automatic cars but they're less fuel-efficient and have a weird lever... would they be relevant here?

EDIT: Apology; I am being tongue-in-cheek about autos, but I don't think they represent normal/average driving

 

[Leggy1]

I wonder if you're mistaken; his claim was "you have the greatest amount of stopping power out of gear", I'm actually refuting that claim. My response was that he'd find no sports formulas where neutral braking of the type he describes was normal. He won't, but I can't look up things that don't exist

But they're less fuel-efficient

For modern, ordinary road cars with ABS, the car will stop quicker out of gear. Sure, that may well be different in race cars with downforce and sticky tires and no ABS, but race cars are less relevant.

Oh, and modern automatics are more economical than manuals now.

 

[Tornado]

I'll clear it up for you; engine braking is part of the deacceleration.

A very minor part.

If it were the case that braking in neutral was even equally efficient then professional drivers would do it - it's a lot easier on the engines for a start.

Actually, professional drivers don't do it because when you are racing a car you have to worry about brake heat effecting stopping capability, and engine braking mitigates that to a decent degree. Has absolutely nothing to do with the maximum braking ability in normal daily driving unless you are driving a full size GM car from the 1960s down a mountainside.

However that isn't the case; engine braking is a normal accepted part of slowing a car down, you accuse me of blindness but I genuinely think you have something to learn.

No, you really are pretty blind if you think engine braking can work independently of the tires.

I wonder if you're mistaken; his claim was "you have the greatest amount of stopping power out of gear"

I know you're mistaken, since Bopop wasn't the one who said that in the first place. What Bopop said is that "in neutral you have just as much stopping power as normal". Which has been true for pretty much every normal passenger car in the past... let's say 25 years.

 

[Bopop4]

Yes, I understand how changing gear at the wrong time is bad, I think we can accept that most of us in here can actually drive a car

What you said was;



Then you said



So how are they letting the clutch back out for gear changes? As you say yourself, changing down through the gears has to be done with the right ratio at the right time (not difficult, I think you'll agree) but you imply that letting the clutch out imbalances things.

I'll clear it up for you; engine braking is part of the deacceleration. If it were the case that braking in neutral was even equally efficient then professional drivers would do it - it's a lot easier on the engines for a start.

However that isn't the case; engine braking is a normal accepted part of slowing a car down, you accuse me of blindness but I genuinely think you have something to learn.





I wonder if you're mistaken; his claim was "you have the greatest amount of stopping power out of gear", I'm actually refuting that claim. My response was that he'd find no sports formulas where neutral braking of the type he describes was normal. He won't, but I can't look up things that don't exist



Not bad-mouthing them, the way old people drive is very different as are their requirements. I have nothing against automatic cars but they're less fuel-efficient and have a weird lever... would they be relevant here?

EDIT: Apology; I am being tongue-in-cheek about autos, but I don't think they represent normal/average driving

I did not say that you have more braking power, I said that you can stop just as fast.
As Tornado said, the limit is the tires, has been for some years now.

You shift down at equal times when racing because to do it all in one go with the clutch in would create problems when letting the clutch out as you enter the corner. As the rpms change the amount of engine braking changes and that actually makes it harder to maintain max brake force, but that is a small price to pay for having to try and rev match up 8000rpm.

Edit: This is about street driving, where you can stop in neutral just as quick as if you were gear.
I would never go into neutral in a race because it isn't as fast, but on the street it saves fuel.

 

[TenEightyOne]

For modern, ordinary road cars with ABS, the car will stop quicker out of gear.

Source required

Oh, and modern automatics are more economical than manuals now.

The devil's in the definition; normal (or "traditional") auto boxes still aren't, newer auto boxes (that change like a manual, but automatically) are.

@Tornado...dangnabbit.

@Bopop you didn't say that... @Leggy1 you did and I disagree , @TB it still wasn't me who made the claim

You shift down at equal times when racing because to do it all in one go with the clutch in would create problems when letting the clutch out as you enter the corner.

The same when driving a normal car, of course, you're explaining how-to-actually-drive

 

[Bopop4]

The same when driving a normal car, of course, you're explaining how-to-actually-drive

Absolutely not, if you're at the point where you're going that hard then it's dangerous.

 

[TenEightyOne]

Absolutely not, if you're at the point where you're going that hard then it's dangerous.

The basic skills are the same though, millions and millions people change up-and-down gears all day without blowing their engines - the difference when racing is the speed you're doing it at. That doesn't mean most people can't learn to do it much more quickly if required, of course.

 

[Bopop4]

The basic skills are the same though, millions and millions people change up-and-down gears all day without blowing their engines - the difference when racing is the speed you're doing it at. That doesn't mean most people can't learn to do it much more quickly if required, of course.

That's missed the point by so much I'm not even sure how to respond.


Ignoring the trolling, has anyone done any aero mods to their cars? I was experimenting with a grille block but I think an under tray would be feasible if made out of coroplast.

 

[TenEightyOne]

Ignoring the trolling

"Trolling" based on your claim that you freewheel on public roads believing it's somehow better/safer and that you think one brakes equally (or maybe even better) in neutral. You also claimed to have tested this (extensively in fact) but have produced no data so far that I can see.

 

[niky]

Just completed an eco-run... and... man... should've been a technical advisor on this one.

They did all the usual things wrong. First, the trip was very short. Which means fuel use was tiny. Which means that the team that had the foresight to shake the air bubbles out of the tank got an ungodly "40+ km/l" on the first leg, because they had less air bubbles shake to the top of the tank at the end of the run.

Then, of course, they relied on the brim method, and didn't control engine and car condition during each fill, which meant that two teams in another division achieved "50 km/l" as the fuel pumps primed before the second fill... dumping two to three liters of overheated fuel back into the tank. (when the car heat-soaks, the fuel in the rail reaches boiling-hot temps. Which means that when you start the car again, the fuel temp sensor goes into panic mode and forces the car to dump the whole load back into the tank...)

And lastly, no in-car judges to control what the contestants did... so AC off, EOC, drafting... all the regular tricks were doable for those who wanted to do them. Which is what I did on the second leg, pissed at myself for forgetting to cheat on the first leg... beating the guys who got the 40+ km/l on the outbound leg (the shaking trick only works on the first fill-up... after that, shaking the car will lower your score).

I meant from a control point of view more than anything, the time taken to select the gear and apply the throttle to get out of trouble is critical.

And the maths of coast-saving is questionable too.

Nope. It isn't.

For those who actually test (and teach) fuel economy on a day-to-day basis, we understand that coasting in neutral is almost always the best answer. (and by almost, I mean 99% of the time)

This is because momentum is more precious than saving a scant few cc's when the injectors cut off.

This is why many modern automatics will automatically coast in neutral whenever they get the chance.

Of course, it won't save you fuel if you don't adjust your driving. If you lift off at the exact same point every time, whether you're in-gear or in neutral, then you're simply wasting momentum, and those extra milligrams of fuel count. But if you adjust for the longer coasting distances, you will save. Because it costs more fuel to regain momentum than you lose while coasting in neutral. Engine braking, even at very low rpms, is a real momentum killer.

Professional hypermilers would laugh at the guy's assertion.

Yes, the computer doesn't handle coasting very accurately (typically 5% optimistic... but when you coast, it can be up to 30% off), but tank-to-tank numbers don't lie.

-

The real hang-up against coasting in neutral is the assumption that you won't have enough vacuum to brake... which isn't true, and that you won't be able to accelerate out of trouble. Unless you're a Subaru owner who's... OMG... just avoided a falling tree in the snow by doing a Scandinavian flick transitioning into a glorious four-wheel drift while pinging off the limiter... no. It's not an issue.

Also, in-gear, with some of these new automatics, you will not be in the proper gear in less time whether you're starting from neutral or a coast-down gear. It still takes half-a-second (or even a full second) for the car to find the gear. And that's not counting the delay in throttle response, as new electronic throttles delay full throttle to prevent momentary lean conditions, for emissions purposes.

And the way most people drive, holding a higher gear until they're nearly at a stop, means that they will still need to downshift if they need to suddenly accelerate... which is not any different from the person in neutral... who is, as said, coasting earlier and going slower.


-

And as for braking: Speaking as someone who's been performing instrumented testing on car brakes for the past five years, and who finished nearly 180 instrumented brake tests just this month... engine-braking doesn't do squat.

Gear in or gear out, the car will stop in the amount of time it will stop. Under full-on, emergency braking, it doesn't matter if you're in neutral or revving the engine to 10,000 rpm in first gear after mistakenly downshifting three gears too many. And if you blow the engine and it seizes, braking distances get very long, as locked tires don't really stop very well. (Something we've seen over the past few years, as well).

You can't get much more emergency-braking-ish as a full-on, two-feet on the stop pedal, panic stop from 62 mph. And our results show that the driver who performs perfectly rev-matched downshifts while standing on the brake doesn't stop any quicker than the guy who simply hits the brakes. After the first twenty or thirty times we tried this, in cars from FWD econoboxes to RWD sportscars, we simply stopped trying to downshift and engine brake and simply concentrated on hitting the pedal. The V-Box doesn't lie.

Except when it's cloudy out.

Gets even worse in low-speed accidents on the road, as those same emissions regulations that cause throttle delay cause throttle over-run when you lift off the throttle, and sometimes throttle surge when the engine detects that it is about to stall, which means engine-braking doesn't start when you think it should. (Ford Ecoboosts are particularly infuriating in this regard)

 

[Tornado]

"Trolling" based on your claim that you freewheel on public roads believing it's somehow better/safer and that you think one brakes equally (or maybe even better) in neutral

There is nothing questionable about the claim that panic braking while free wheeling will provide the same stopping distance as braking while in gear. I've put my car in first a couple times, one of which was just to see what it would do when I let off the gas. It for damn sure didn't stop faster than all those times I panicked stopped from 70 soon after I bought it to try to clean the rust off the front brake discs, and since the ABS went crazy each time I know it wouldn't stop any faster if I had it in 2nd at 6200 rpm instead of 4th at 1800.

 

[Zenith]

Engine braking is not additive in an emergency stop!

If the tires are slowing down at a rate greater than what the engine naturally wants to decelerate at, then the brakes must slow the driveline in addition to the chassis.

A is the rate the engine wants to decelerate.

B is the rate the brakes want to slow the driveline and chassis.

When A=B, a gentle brake, the brakes are neither helped nor impeded by the rotating driveline.

When A<B, the brakes must apply a braking load to the driveline because the driveline is connected to the wheels and wants to decelerate at rate B. The extra braking force required can be thought if as A minus B.

This becomes true in an E-stop.

There's a reason they say "both feet in!"

@niky post is also killer. By far the most useful post in this thread.

 

[Bopop4]

Just completed an eco-run... and... man... should've been a technical advisor on this one.

They did all the usual things wrong. First, the trip was very short. Which means fuel use was tiny. Which means that the team that had the foresight to shake the air bubbles out of the tank got an ungodly "40+ km/l" on the first leg, because they had less air bubbles shake to the top of the tank at the end of the run.

Then, of course, they relied on the brim method, and didn't control engine and car condition during each fill, which meant that two teams in another division achieved "50 km/l" as the fuel pumps primed before the second fill... dumping two to three liters of overheated fuel back into the tank. (when the car heat-soaks, the fuel in the rail reaches boiling-hot temps. Which means that when you start the car again, the fuel temp sensor goes into panic mode and forces the car to dump the whole load back into the tank...)

And lastly, no in-car judges to control what the contestants did... so AC off, EOC, drafting... all the regular tricks were doable for those who wanted to do them. Which is what I did on the second leg, pissed at myself for forgetting to cheat on the first leg... beating the guys who got the 40+ km/l on the outbound leg (the shaking trick only works on the first fill-up... after that, shaking the car will lower your score).



Nope. It isn't.

For those who actually test (and teach) fuel economy on a day-to-day basis, we understand that coasting in neutral is almost always the best answer. (and by almost, I mean 99% of the time)

This is because momentum is more precious than saving a scant few cc's when the injectors cut off.

This is why many modern automatics will automatically coast in neutral whenever they get the chance.

Of course, it won't save you fuel if you don't adjust your driving. If you lift off at the exact same point every time, whether you're in-gear or in neutral, then you're simply wasting momentum, and those extra milligrams of fuel count. But if you adjust for the longer coasting distances, you will save. Because it costs more fuel to regain momentum than you lose while coasting in neutral. Engine braking, even at very low rpms, is a real momentum killer.

Professional hypermilers would laugh at the guy's assertion.

Yes, the computer doesn't handle coasting very accurately (typically 5% optimistic... but when you coast, it can be up to 30% off), but tank-to-tank numbers don't lie.

-

The real hang-up against coasting in neutral is the assumption that you won't have enough vacuum to brake... which isn't true, and that you won't be able to accelerate out of trouble. Unless you're a Subaru owner who's... OMG... just avoided a falling tree in the snow by doing a Scandinavian flick transitioning into a glorious four-wheel drift while pinging off the limiter... no. It's not an issue.

Also, in-gear, with some of these new automatics, you will not be in the proper gear in less time whether you're starting from neutral or a coast-down gear. It still takes half-a-second (or even a full second) for the car to find the gear. And that's not counting the delay in throttle response, as new electronic throttles delay full throttle to prevent momentary lean conditions, for emissions purposes.

And the way most people drive, holding a higher gear until they're nearly at a stop, means that they will still need to downshift if they need to suddenly accelerate... which is not any different from the person in neutral... who is, as said, coasting earlier and going slower.


-

And as for braking: Speaking as someone who's been performing instrumented testing on car brakes for the past five years, and who finished nearly 180 instrumented brake tests just this month... engine-braking doesn't do squat.

Gear in or gear out, the car will stop in the amount of time it will stop. Under full-on, emergency braking, it doesn't matter if you're in neutral or revving the engine to 10,000 rpm in first gear after mistakenly downshifting three gears too many. And if you blow the engine and it seizes, braking distances get very long, as locked tires don't really stop very well. (Something we've seen over the past few years, as well).

You can't get much more emergency-braking-ish as a full-on, two-feet on the stop pedal, panic stop from 62 mph. And our results show that the driver who performs perfectly rev-matched downshifts while standing on the brake doesn't stop any quicker than the guy who simply hits the brakes. After the first twenty or thirty times we tried this, in cars from FWD econoboxes to RWD sportscars, we simply stopped trying to downshift and engine brake and simply concentrated on hitting the pedal. The V-Box doesn't lie.

Except when it's cloudy out.

Gets even worse in low-speed accidents on the road, as those same emissions regulations that cause throttle delay cause throttle over-run when you lift off the throttle, and sometimes throttle surge when the engine detects that it is about to stall, which means engine-braking doesn't start when you think it should. (Ford Ecoboosts are particularly infuriating in this regard)

Please come over and drive my car for an hour, I'll bake you cookies!

 

[TB]

I wonder if you're mistaken; his claim was "you have the greatest amount of stopping power out of gear", I'm actually refuting that claim.

Fair enough. 👍

EDIT: Apology; I am being tongue-in-cheek about autos, but I don't think they represent normal/average driving

Manuals might be the norm in Europe but they are very much in the minority in the US (apparently 6.5%). In my 20 years of driving, three out of eight of my cars have been manuals (Omega (A), Blazer (A), Neon (M), Grand Prix (A), Pilot (A), Civic (M), CR-V (A), 124 Spider (M)) and of my friends and family, I am an anomaly (quiet! ) for that ratio as many have never owned a manual or, in the case of my mom, even know how to drive one. While it might be "normal/average" there, that statement doesn't apply everywhere.

@niky - Fantastic post.

 

[EF12345678]

Manuals might be the norm in Europe but they are very much in the minority in the US (apparently 6.5%). In my 20 years of driving, three out of eight of my cars have been manuals (Omega (A), Blazer (A), Neon (M), Grand Prix (A), Pilot (A), Civic (M), CR-V (A), 124 Spider (M)) and of my friends and family, I am an anomaly (quiet! ) for that ratio as many have never owned a manual or, in the case of my mom, even know how to drive one. While it might be "normal/average" there, that statement doesn't apply everywhere.

I can second @TB's post. Even our trucks down here in Texas are automatic. I've never been in a manual car either. The closest thing to manual my family has is my Grandparents Explorer with SelectShift.

 

[niky]

Please come over and drive my car for an hour, I'll bake you cookies!

My pulse-and-glide EOC sucks. I hit 27.5 km/l combined on that leg, but I think I left another 5 km/l on the table because I didn't concentrate on my DWL on the acceleration portions, and my target speed (60 km/h) was too high. But I wasn't aiming to set records, I just wanted to win that leg.

-

If you pay my plane ticket, I will make you a duct-tape body kit. I'll even throw in some duct-tape pin-striping, as a bonus.

 

[GT Pro]

Does anybody know a good way to calculate the time threshold beyond which a given engine ought to be turned off at a red light, drive-through, etc, both in regards to saving fuel and reducing emissions? Guestimates from 3-to-10-to-30 seconds are often made, with no real attempt to incorporate starter motor replacement or engine-size, cylinder-count and engine age into consideration.

Because my car is pre-OBDII (1992), apparently the only way to really get a good, active measure of mileage is via a device called an MPGuino, but I am not sure if that would work in my car.

 

[niky]

Typically it's between 30-60 seconds... and it will depend greatly upon how effective the starter motor is. Older cars use more gas to start than newer ones.

I suppose you could splice an IV bottle full of gas into your fuel line and test it out that way.

 

[motortrend]

With a stick-shift car, don't shift into neutral to roll to a stop.

Think of it this way, when the car is rolling to a stop in gear, the engine is kept running by the momentum of the car. There is no fuel needed.

When the car has the engine in neutral, the engine is supported by itself. It has to idle.

You're right, though neutral is more useful on downhills where you want to maintain speed.

I'm not a hypermiler at all, my car is rated at like 15mpg and I'm getting something like 14 (has to do with the 3.62 rear too). I do a WOT pull in 2nd at least once daily (not to redline) and generally have some fun and waste some gas, however if I'm coming out of green light and up to a red one I go up to ~10mph below the limit (so as to not hold up traffic) then throw it into neutral and coast to the next red light. Some people pass me and some inpatient ones even go around me but we all end up at the same place at the same time. Apart from that when I'm driving normally I throw it into N for all downhills, check for upcoming traffic in front, and in general look for what is going on as far as possible to take the best decision that requires the least gas. Like I said though, that's definitely not most of the time.

 

[Bopop4]

Averaged 50mpg this trip, so close to rolling over the 1000km mark.

 

[niky]

1000 km a tank? That would be well impressive!

You're right, though neutral is more useful on downhills where you want to maintain speed.

If the downhill is steep enough and you've got an electronically-controlled engine and are not turning it off, keep it in gear and let the DFCO (deceleration fuel cut-off) do its magic.