Hypermiling.....Is it worth the effort?

[HarryMann]

Same as driving through narrow streets in 2nd or 3rd instead of 4th or 5th, more control, more braking quicker if something should happen, more acceleration quicker if its needed

[Nicola&Tony]

Why is this in the Alternative Fuels forum (a genuine question . . . I'm not "having a go" at anyone!) ?!

Tony

[Llamapup]

Why is this in the Alternative Fuels forum (a genuine question . . . I'm not "having a go" at anyone!) ?!

Tony

Fair comment. I was hoping to take advantage of the Alternative Fuels writers' enthusiasm and knowledge for fuel efficiency to help shed some light on the subject. I thought it would just get lost in the mix in the general section.

[HarryMann]

Fair comment... it is Alternative (use of) Fuel

Everyone has their pet theories and way of driving for best economy, some are theoretically based others are from practical experience.

Some say you should lug up hills in a high gear with a large throttle setting, others that you should use a lower gear and lower throttle setting...

One thing is sure: diesels and petrols vary enornously in driving technique. Diesels don't suffer the pumping loss inefficiencies of throttled ottos! Which means that a petrol (Otto) is not an efficient engine when producing low power, whilst diesels having no throttling restriction are more efficient across a wider range of power settings, e.g. less sensitive to driving technique.The modern intercooled, turbocharged Tdi diesel has capitalised on this, and IMHO is a remarkable piece of engineering, and when married to an aerodyamic marvel like some modern saloons, can give 40~50mpg almost regardless of driving style at quite high speeds.

The modern answer to petrol engine economy improvement is of course to match the engine characteristics to the car and reduce weight. Smaller petrol engines fare better as they then have to be driven at higher throttle opening, reducing the pumping losses. Modern hybrids take this further by changing the Otto cycle, such that compression/expansion strokes are not symmetrical within the engine, cutting the inlet stroke short - which seems wrong. But then further combine this with electrical generation so the engine can run at its best throttle setting and speed regardless...

Techniques: First gear used to be called an inertia gear, just to get rolling, and then second gear was engaged to do any acceleration... now this is in vogue again, get it in 2nd pretty quick, get the clutch up and engaged and then use the engine's torque to accelearte fairly briskly but not madly, then short change up into 3rd... as when you are doing very low speeds, the miles per gallon obviously is suffering.

Safety and economy tend to conflict, as you want a low gear fro car control and higher gear fro economy when in urban areas. Go for safety, points on your license or a crash will generally cost you a lot more than slightly better fuel economy over more than one year!

This is relevant too

[mikey9]

Excellent stuff Harry- and I (just about) understand the explaination And it may help (I probably - wrongly - try to drive the van like I drive a modern Tdi...)

I can't help thinking the "extremely high fuel price" stories are a bit over the top.
I heard yesterday someone complaining that their staff were having to spend £60 - £80 per month on getting to work and this was making them struggle. With an increase for petrol from £1 to £1.10 this is only a 10% increase meaning they were previously spending £54 -£72 per month.

Compared with the cost of many other things - the 10% increase isn't as big a deal (how much has your Gas, Lectric and Heating Oil gone up in the last year).

It seems that "Fuel Price" stories get far more media coverage and than they justify (in the scheme of things).

[..lee..]

if coasting down hill out of gear means you are not fully in controll of the car think of this.

see hazard jump on brake and stop or

see hazard jump on brake then realize you are still in gear think about depressing the clutch depress clutch and then stop.

i wish the people who invent this bull **** would realise that some people can actually drive.

they`ll be telling us next its not safe to change gear whilst we are driving.

sorry rant over.

lee.

[HarryMann]

Don't think it's got much to do with needing to jump on the clutch or not...

It's surely the fact that there is a constant and fairly consistent and even ratardation limiting runaway speed when in gear, even before the brakes have to be used. Dipping the clutch at the last moment or so, is no great brain teaser, and actually 'stopping' is not always necessary, just slowing for a hazard... vehicle 'definitely' under a lot more control when in gear on overrun IMHO

[andysimpson]

if coasting down hill out of gear means you are not fully in controll of the car think of this.

see hazard jump on brake and stop or

see hazard jump on brake then realize you are still in gear think about depressing the clutch depress clutch and then stop.

i wish the people who invent this bull **** would realise that some people can actually drive.

they`ll be telling us next its not safe to change gear whilst we are driving.

sorry rant over.

lee.

I agree when it comes to modern cars, everything is sorted for the driver anyway by ESP, anyone that loses control with ESP should not be driving.

[..lee..]

harryman agree with your comment, its just the comment on it being illegal wound me up so was forced to rant.

on the way to and from work i often freewheel as i`ve noticed a slight improvement in economy doing this, i`ve only been doing it recently and on the slight inclines that i do it and at speeds of less than 30mph i notice little or no difference in controll to traveling in 5th gear.

[HarryMann]

If we all had regenerative braking systems installed, wouldn't it be great down those hills, getting some fuel back rather than heat...

Hydrogen fuel for nothing

Beeb Radio 4 programme on this 2 days ago... maybe will try to find it on 'listen again'

[andymacdonald30]

Don't think it's got much to do with needing to jump on the clutch or not...

It's surely the fact that there is a constant and fairly consistent and even ratardation limiting runaway speed when in gear, even before the brakes have to be used. Dipping the clutch at the last moment or so, is no great brain teaser, and actually 'stopping' is not always necessary, just slowing for a hazard... vehicle 'definitely' under a lot more control when in gear on overrun IMHO

This theory is fine if you drive a 50-ton truck or a very old car
The brakes on a 50-ton truck obviously need every bit of help they can get
So out of gear down hill is a big no no
The engaging a low gear on a down hill road is only for extreme hills or very long descents where the brakes may overheat due to prolonged use
In 20 years of HGV1 driving I have only come across a hill that warranted this action
Once or twice
Old cars have brakes that are not overly efficient so again out of gear situations are a no no as well

But modern cars have brakes that are powerful enough to pull a car up from 100 mph and not struggle

Taking into account modern brakes it does not matter if the car is in gear or not for then to work
But if you turned the engine off and use the brakes a couple of times you could use up the vacuum in the servo
Thus rendering the brakes unable to work at the efficiency they are designed for

So I believe that the coasting down hill law is really outdated and of little use in today's world with modern cars and brakes

Only a personal opinion but one I firmly believe in

But for fuel saving tips
The best one is keep your tires up to the correct presure for up to a 10% improvement
And do not try to beat the boy racers away from the lights (tempting as it may be )

Andy

[lloyd]

Our van's brakes are just adequate, and as such being in gear is needed on some of our hills. There are many hills that we go down that the gearing we are using requires braking to keep our speed down. Here in the southwest there are many.. including Telegraph, King's Ash, etc.. and many on Exmoor dropping into the coastal villages are examples.

I'm not saying we need to use gearing like a 50 ton lorry, but do need some engine braking on some grades... and is why the law says to stay in gear. Also, if in gear and engine dies, it's still turning over keeping power steering, brake booster, etc. working. Ever try stopping without any vacuum in brake booster? ... Or loose your power steering and/or brake booster in many modern vehicles and see how hard it is to steer / brake.

Many of the things I do in the name of fuel economy are hard to explain on paper because there are so many variables involved (incline, traffic, slick vs dry roads, etc) that require different techniques. You would have to ride/drive with me to learn/understand when they are safe and when not.

Have to agree with Andy on the boy racing away from lights. The less the engine works, the better the mileage. Try following a lorry for 50 miles vs the way you normally drive as it will amaze you how much better your mileage will be.

[andymacdonald30]

Yes I have had that pleasure
Trying to stop without the servo assistance
A drive belt snapped on a transit I was in
There were more skid marks on the inside of the van that there were out side

To gain better fuel mileage in my T25 I have fitted a Peugeot engine
1.9 n/a diesel approx 42 mpg. Normal driving
I want to fit in the 1.9 TDI pug this has been quoted as being able to get 45 mpg

But in my T4 2.5 tdi I have fitted a fuel catalyst from Broquet and this, I have proved on other vehicles, to improve fuel mileage by up to 10 %
http://www.broquet.com/" onclick="window.open(this.href);return false;

Andy

[damongrounsell]

Whats wrong with coasting, I've certainly done it, and I'm pretty sure it saves fuel
example
on my way to work 1.0 nissan micra 2000, go up hill slow, cars pull ahead, on way down hill slip into neutral and coast, car wizzes down hill till terminal velocity of car on hill is reached, 60mph in micra with one passenger, and I stay at that speed till the bottom, then put onto 5th and keep on going at a staedy 50-55mpg.
I drive 35miles to work there and back every day and saving fuel is my only joy. If anyone can explain why you have less control of the car just because there is less resistance to forward movement I'd be happy to change my practice. Modern brakes with ABS are perfectly capable of stopping a vehicle. Only the past generation of cars 2004 since stop delivery of fuel to the engine whilst going down hill.
Of course in a T25, not great brakes, higher mass and no ABS then the engine inertia acts as a form of ABS causing the wheels to keep spinning and not locking up increasing control. So in a T25 i'd recommend against the practice.

Big positive impact on fuel consumpion is over inflated tyres, but that ofcause comes with less grip and a thus increased breaking distances and decreased lateral grip too.

P.S. a well polished car should get higher mpg too, although this is perfectly safe the effect is minimal.

Damon

[HarryMann]

The reasoning is along the lines that:

a) Should your require to accelerate rapidly to avoid an accident, you can immediately (the right pedal can be the best one to use in some situations to avoid a colllision), just as valid as the middle one;

b) while removing foot from right pedal and to middle & braking (0.3~0.4 sec at a critical time) the car already starts slowing;

c) the transition from free-wheeling to braking is a sharper transient for the suspension attitude than from neutral or trailing throttle to braking (more apparent in the wet);

d) the inertia of the driveline and coupled engine rotating components act as 'smoothing' to wheel braking acting in an anti-skid manner (quite apparent on potholed and rough or wet roads);

e) the right pedal is a steering control as well as a power control (when in gear). When the tyres have any appreciable slip-angle, changes in throttle can alter the car's direction & subsequent track quite substantially... and is used often intuitively by experienced drivers to maximise cornering and avoidance maneouvres.*

Provisos
for c) & e) ... very modern sophisticated suspension geometry somewhat negates this, but not totally.
for d) ...providing the brakes are quite powerful enough in the first place, which they are designed to be in most post 60's cars when in good condition
... very modern vehicles with anti-skid systems and sophisticated suspension geometry negate this effect (to some extent or other)

d) is demonstrated by the braking distances for Syncros Vs 2WD T25s, the former is shorter due all 4 wheels being coupled to the transmission.

* Driving a slalom course through cones (obstacle avoidance) cannot be accomplished free-wheeling (if you lay them out down a hill for instance) with anything like the accuracy and speed that can be demonstrated when gear engaged and using throttle control - IMHO

** Gear engaged and power and brakes together (left foot braking), whilst predominantly a rally technique, also indicates that suspension, weight tarnsfer and wheel control under braking and especilly combined braking and turning gives noticeably superior maneouvrability when transmission is coupled.

*** All Advanced Driving organisations (CAMDA, IAM) as well as the Police Advanced Driving Instruction course, always teach 'Gear for the speed, speed for the hazard' - that is, as low a gear as puts the engine in it's normal working range (mid-speed) for the roadspeed - for maximum car-control, especially pertaining to hazards (predominantly today, almost everywhere!). They never condone free-wheeling, for the above mentioned reasons...

**** It is now known that a lot of back-road and urban accidents by inexperienced drivers, occurs due to the wrong (too high, thinking mpg not control) gear for the situation, with the car not under full control, steering and speed-wise. That is, it is obvious that speed control by an on/off switch (the brake pedal) is not as steady as when engaged to a spinning engine - and the car can run away in excessively high-gears, with higher thinking and reacting distances being covered than when in a lower gear. A higher gear is more near to a 'free-wheeling' situation than a lower one.

== That said, constant energy driving driving (slow up fast down like you say) if traffic flows and safe speed allows, is a good technique for fuel consumption reduction. In a modern car with idle fuel-cut-off and mimimal light throttle consumption down hills in high gear, there probably is little difference in using a neutral throttle than actually free-wheeling down the hill ==