Quote from tristancliffe :

He was pointing out that even with aerodynamic drag alone, your car will slow down faster than you claim, as your car doesn't have a Cd of 0.25.

Why not? An Audi A2 has a Cd of 0.25, and that's not far off the shape of my car. A Pug 308 has a Cd of 0.29. Given my car has a smaller area than both of these, I don't see why a Cd of around 0.25 is impossible?

Cd has nothing to do with frontal area.

The Yaris is, from memory (you can look it up if you like) around 0.3 - 0.35.

And even if it IS as low as 0.25, then that's aero alone. Without any engine braking. If you honestly think that lifting in gear at 160km/h drops you 1km/h/s then you are mistaken or lying.

Quote from tristancliffe :

And even if it IS as low as 0.25, then that's aero alone. Without any engine braking. If you honestly think that lifting in gear at 160km/h drops you 1km/h/s then you are mistaken or lying.

True, at speeds like that you will see a quite fast drop in speed from aero alone, even with a car that has a low frontal area and drag coefficient.
I didn't consider we were talking about speeds this high Remember that drag force goes up exponentially with velocity.

squared, but ok.

(x^2 is squared, e^x is exponential)

Oops sorry yeah, it increases with the square of the velocity

Quote from tristancliffe :

Cd has nothing to do with frontal area.

The Yaris is, from memory (you can look it up if you like) around 0.3 - 0.35.

And even if it IS as low as 0.25, then that's aero alone. Without any engine braking. If you honestly think that lifting in gear at 160km/h drops you 1km/h/s then you are mistaken or lying.

Mk1 Yaris (I'm assuming Mk2 is very similar, maybe smaller Cd but bigger A): drag coefficient of ~0,3 and frontal area around 2,1 m^2 -> total drag = 0,63..

Add to that the rolling resistance, there's no way to slow down so slowly unless resting ones foot on the accelerator.

I see this as one of those arguments that will go on forever and even of dodarfella does realise he is wrong he isn't going to admit it now.

But for fun, to give an example of engine braking, I've almost been ejected through he wind screen by dropping a cog from 4th-2nd as I was slowing form 30MPH for a tight corner and forgot to rev-match. Because the revs stayed the same in each gear the lack of motion in the engine caused huge mechanical resistance which slowed the car down so violently the bottle on the back seat went flying.

Or there is a nice hill a stones throw from where I live. Last time I went down it I was in a 207 and found 3rd gear kept it at a constant 32MPH, so once at the bottom I could stick it back into 4th and carry on my way. If I left the car in 4th or put it in neutral for that hill, I'd have to have the brakes on the whole way down and that is piss poor driving. And hardly mechanically sympathetic.

Quote from P5YcHoM4N :

Or there is a nice hill a stones throw from where I live. Last time I went down it I was in a 207 and found 3rd gear kept it at a constant 32MPH, so once at the bottom I could stick it back into 4th and carry on my way. If I left the car in 4th or put it in neutral for that hill, I'd have to have the brakes on the whole way down and that is piss poor driving. And hardly mechanically sympathetic.

That kind of sums up my current opinion on engine braking;use it for keeping speed under control or as a slight assistance, not full on slowing down.

Quote from P5YcHoM4N :

Or there is a nice hill a stones throw from where I live. Last time I went down it I was in a 207 and found 3rd gear kept it at a constant 32MPH, so once at the bottom I could stick it back into 4th and carry on my way. If I left the car in 4th or put it in neutral for that hill, I'd have to have the brakes on the whole way down and that is piss poor driving. And hardly mechanically sympathetic.

Quote from speed1 :

That kind of sums up my current opinion on engine braking;use it for keeping speed under control or as a slight assistance, not full on slowing down.

Which is exactly the right technique. Full control, little wear, little fuel wasted (if any), and as much safety as one can muster controlling a tonne of steel at several meters per second. The trouble is, when people get told "Engine is for going, brakes are for slowing" they only see black and white, and don't realise that with rules of thumb like that there are degrees between the two.

Maybe if you told the same people "Power sells motors, torque wins motor races" they'd demand to buy a car from a dealer that somehow produced 300hp but no torque, on the basis that torque is only for racing... These people are idiots. They won't like being told they are idiots, but it needs to be done, and they'll just cause more ignorance if you don't.

i'd say the idiot is the one who says "power sells motors, torque wins races" which to an ignorant person sounds like "the car you'll buy doesn't need to have power(torque), only torque(power)".

sounds like if you said "your computer doesn't need a graphics card if you don't play games" without giving the important detail that it is a "good/expensive" card that he doesn't need. that isn't exactly what you're supposed to say to someone who isn't very knowledgeable.

and in the end, if someone does not have the smarts to understand the underlying mechanics, it is better to tell him "when going down a hill, go slower than you would go on a level surface and use your brakes to keep a steady speed" instead of "when going down a hill you need to determine the optimum gear, revs and ratio of engine brake to foot brake, based on inclination, curvature, the brakes' performance, your engine's braking so as to drive safe, keep the brakes from overheating, keep the engine from overrevving..."

my 0.02

In the UK the advice is "when going downhill, select a lower gear to assist controlling your speed". It works, and it doesn't confuse many people. Using the brakes on their own will, one day, kill.

Quote from george_tsiros :

and in the end, if someone does not have the smarts to understand the underlying mechanics, it is better to tell him "when going down a hill, go slower than you would go on a level surface and use your brakes to keep a steady speed" instead of "when going down a hill you need to determine the optimum gear, revs and ratio of engine brake to foot brake, based on inclination, curvature, the brakes' performance, your engine's braking so as to drive safe, keep the brakes from overheating, keep the engine from overrevving..."

It might be because I happen to live in a country full of mountains, but what is so hard to understand at "when you're going downhill, keep it in gear or you're dead"?

To the original question (poll is less then useless): test have found out that full throttle to the desired speed and then holding a steady speed yields best economy (actually full throttle and coasting down saves more but you'll get into trouble with law enforcement pretty soon with that)...

I did laugh at the idea that engine braking (in normal driving) causes wear so excessive that it's best avoided where possible!

So what, it's straight into neutral everytime you want to slow down, no simple lifting off the throttle in 4th gear (for example) and gently decellerating?

Ridiculous. If your engine genuinely cannot handle a few thousand rpm driven by the wheels then you already have problems. I think someone said the engine would require 4 times the work if you "use" engine braking? What the hell?

I think I'd rather not have to change pads and discs so often and accept that I inflict some wear on the engine simply by driving it.

Next we'll hear that it's best to get out and push your car to a couple of mph before attempting to engage the clutch because the wear inflicted means you'll have to replace the clutch every 4 months.

To be honest it was quite funny to read some posts in this thread. Man can learn few things

I think the best way to check what is most economical is to check the car`s computer with current usage to see few times what is best in each time.If you need for example suddenly to accelarate in the uphill with the highest gear the fuel consumation will be very high but thats the fact everyone knows hopefully.

To the neutral discussion. I admit I do that few times but mostly on the flat road not in dowhnill. As someonebody said it gives you more control and I totally agree as it saved me a life once. I was going downhill and suddenly from the side road went a car. He did not notice me otherwise he would not do that stupid thing. I was too close to be able to break or only avoid. It would not help so I had to put my foot on the gas when avoiding. I am not able to imagine how I could save me life when I would have to put the gear on. Even 1 second mean few meters especially going downhill. It can be matter of death or life. For me it was probably.

Cheers

Quote from bbman :

It might be because I happen to live in a country full of mountains, but what is so hard to understand at "when you're going downhill, keep it in gear or you're dead"?

you say that while quoting me... but i never said to disengage any gear. in fact, i said to do keep it in gear.

You're right, I misread that...

Something else I've never understood, why put it in neutral in the first place? Clutches arent that hard to hold down and (I'm comparing it to every other manual transmissioned cars that I've driven, and what I've been told by a few people now) my CR-V has a fairly heavy clutch (thanks in part to wear; its a fairly heavy, underpowered car with around 100k miles on it that 3 or 4 people have learned on).

the clutch, under normal operating conditions, is to be used at two times and at twose two times only.

to get the car in motion and to bring the car to a stop.
and change gears.

i say it in such a serious tone because i've seen people using or abusing the clutch in many cases where it is completely unecessary. (waiting at an uphill intersection, while cornering at low speeds,... ... well, just those two i remember now)

(of course i am not implying that "put it in neutral instead of pressing the clutch". stay in gear, foot off the clutch. if you don't need to be pressing the accelerator, put your foot above the brake. the cases where immediate braking will be required in an emergency are like 1000 times more probable than immediate acceleration)

Quote from speed1 :

Something else I've never understood, why put it in neutral in the first place? Clutches arent that hard to hold down and (I'm comparing it to every other manual transmissioned cars that I've driven, and what I've been told by a few people now) my CR-V has a fairly heavy clutch (thanks in part to wear; its a fairly heavy, underpowered car with around 100k miles on it that 3 or 4 people have learned on).

Two reasons: The clutch plates might not disconnect entirely, so you're wearing them out without even knowing it, and maybe more probable, you can always slip off the clutch - telling the police that the accident happened because you didn't want to put it in neutral will make it pretty hard to plead innocent...

And you might think they aren't that hard, but just try to press the pedal with your right foot for a change...

Quote from bbman :

And you might think they aren't that hard, but just try to press the pedal with your right foot for a change...

Aint that the truth. Or similarly, try braking with your left foot when you are use to driving a clutch. Weirdest thing was when I realized how easy it was to left foot brake on the computer in sim racing in comparison to left foot braking in a real car. In a real car, I would dang near split my lip open on the steering wheel if I would left foot brake.

Left foot braking in the car, completely unnatural. Left foot braking on the computer, completely natural. Perhaps its my 15 years of forktruck running at work that it seems natural on the computer because the pedals of a forktruck are quite similar to a 2 wheel computer pedal set.

Also try not to forget that you have little springs on your clutch that keep it in place. By keeping you clutch depressed excessively you will stop the springs being springs and you'll get a shit ton of clutch slippage.

Only if your clutch is seriously out of adjustment. Most clutches (and relevant clutch systems) avoid the springs from being over compressed beyond their safe working range, so the springs shouldn't be over stressed just by pressing the pedal, even for extended periods of time.

Of course, if you change the clutch, or a part of the clutch system, to something non-standard then you might get into problems if you don't correct the problem.

I've been playing with master cylinder sizes on my racecar to get a clutch I like (I don't like soft, progressive race clutches, but hard on/off clutches), and the amount of fiddling we've had to do to the clutch pedal stops, pushrod lengths and pivot positions is far more than the actual work of replacing parts of the hydraulic system.

Like I said before, by law, the car must be in gear at all times. Shifting is the only time that you can be in neutral. Which means that you CAN be pulled over if the cop behind you sees through your rear window that you are in neutral, not first at a stop light. Plus, what happens if that truck behind you cant stop in time. You probably arent going to be able to get it in gear fast enough to avoid being rear ended.

Indeed, my driving instructor says you must always be ready to pull off even if it looks like you wont be for some time.

Quote from tristancliffe :

Only if your clutch is seriously out of adjustment. Most clutches (and relevant clutch systems) avoid the springs from being over compressed beyond their safe working range, so the springs shouldn't be over stressed just by pressing the pedal, even for extended periods of time.

Ah, I must have been misinformed.

Quote from 5haz :

Indeed, my driving instructor says you must always be ready to pull off even if it looks like you wont be for some time.

Mine told me the opposite. When a stop becomes a wait, take the car out of gear and pop on the hand brake. Although that is a personal thing, he didn't mind if I didn't bother with the gears as long as I did put on the hand brake.