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Discussion Starter · #1 · (Edited)
I'm talking about coasting in a car, but there's no reason why you can't do it on a bike (although they seem to have a lot more drag).

From the day I started driving, it was always drummed into me that "coasting is a no-no". Coasting for those that don't know, or are from foreign shores, is taking your car out of gear, or pushing the clutch down, and using the momentum or a hill to continue moving.

Well, as I've matured, vehicle technology (brakes in particular) has advanced, and driving test rules have changed (so new drivers now stop in 4th gear to save the planet) I do a lot more coasting in my car. In fact, there are regular stretches of road that I use, where I easily can roll for quite a few miles, for example on the A22 from Colemans Hatch to Forest Row (all gently downhill)

I was always told that rolling in neutral, or with the clutch down, gave you less control over a car, especially if you needed to suddenly brake. Well with modern strong ABS brakes and all sorts of other gizmos in cars, is this still the case?


So, in your eyes, am I being foolhardy, a tightwad, or is there mileage (pun intended) in my cost saving frugalness??


Your learn'ed opinions please!!!


[EDIT: I thought I'd mention I drive a diesel 2004 VW Golf, which I can easily get 50mpg out of, OR, if I drive like an old granny and do a bit of coasting, can eek out over 60mpg]
 

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Craigypops
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Discussion Starter · #3 ·
I wouldn't do it personally.

What if you pick up a good bit of speed and put it in the wrong gear?

If you just dip the clutch (as opposed to taking out of gear) you just let the clutch up, and you should still be in the right gear you originally built up to speed in.
 

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Bob,

I'm sure you'll open a tin of worms with this one, sit back & watch, by the way did you get the computer thing sorted ?

For me personally, it's a dangerous practice, goes against the principles of driving, & what happens if or should you be involved in an unfortunate rtc.

It doesn't have to be your fault, but you have no control & little reaction time to respond to the potential problem & effectively no control of your motorised vehicle whatever size it may be.

There could be a legal implication I assume too, especially in the litigatious world we now live in.

As Craig mentions no engine braking either.

So I'd say "NO" you are being a tight wad mate.


I drive a Volvo V70 diesel, & get over 60 mpg driving a 60 mph on a run. . . .
 

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Bob - I would think that as long as you are driving to the speed limit, not causing any hindrance to other road users, and generally aware of other traffic around you...........then you can pretty much do what you want.

If you adjust your driving to suit the vehicle you are in - I don't see a problem. An ancient car on drum brakes is going to need much more time to brake once your brain has reacted to any input and told your feet to brake, than any modern car. Just think how differently you drive your 'truck' over the Golf.

Coasting in a modern car is an excepted way of saving fuel - IIRC I was taught to go down through the gearbox when coming to a junction or slowing down, whereas now its dip the clutch, coast under braking, and then when stopped select new gear ready to move off again.

Take a look at Hypermiling - if you really want get serious about it

Anyway - in your case Bob, it's all irrelevant - you should stop driving like 'Miss Daisy', treat the loud pedal as a switch;)..............and if you get rid of all that crap you're carrying around in the boot you'll double your economy :D:D

 

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Craigypops
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I only passed my car test a few years ago (I did my bike before my car) and I was taught to go down through the gear box when approaching a roundabout/junction etc, it would feel very strange to just dip the clutch and use only brakes? Do the same with the bike, can't imagine just pulling the clutch in and braking without going down the gears...



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Discussion Starter · #7 ·
..Just think how differently you drive your 'truck' over the Golf.

The truck requires wearing binoculours, or 24 hours written notice of red lights ahead!!.


..and if you get rid of all that crap you're carrying around in the boot you'll double your economy :D:D.

Oh man, you've seen all the $hite I carry around then! A boy racer I occasionally work with thought I'd had lowered suspension fitted, until he saw all the tools and junk in the boot!



P.S. I only coast where conditions allow; so generally on traffic free stretches of road.
 

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I don't personally see the peoblem with coasting but don't do it myself, however, while coasting the vehicle is using fuel as it's ticking over (unless you are foolish enough to turn it off....), while on the overrun modern vehicles cut fuel completely so the engine is effectively "off" & not using fuel but it's also slowing the vehicle down so will require throttle sooner than a coasting vehicle.
Which is the most fuel efficient is anyones guess.
I'm sure someone infinately cleverever than me could work out some formula to give an answer!

Personally, I'm not going to lose sleep over trying to save .02ltr of fuel every tank :)

Phil


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Discussion Starter · #9 ·
Personally, I'm not going to lose sleep over trying to save .02ltr of fuel every tank :)

Phil




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BUT, lots of little can equal a lot. Any saving is better in my opinion. What I save rolling two miles, surely drives me atleast a mile further on a tank?
 

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What I save in not fretting over this sort of thing is well worth the few extra pennies though. ;-)

(For me it's no use anyway, one doesn't save much coasting off offramps in this otherwise pancake-flat land.)
 

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Craigypops
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BUT, lots of little can equal a lot. Any saving is better in my opinion. What I save rolling two miles, surely drives me atleast a mile further on a tank?
Without having any figures or statistics in front of me, I'd say that's bollocks Bob... I reckon it would amount to a few quid a year, at best. You're already going downhill so will be using a very small amount of fuel if using the throttle compared to the fuel used to tick the engine over when coasting, just can't see that it's worth it to be honest. :)



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Discussion Starter · #13 ·
Without having any figures or statistics in front of me, I'd say that's bollocks Bob... :)

Is that a technical term Craig!?!?!!?!?!? :laughing3:

Well, you MAY be right, I suppose I'll never know without a proper scientific study BUT, I've driven a few of the roads so many times that I've tested the theory as much as possible with the onboard VW compooter, and it does actually make a difference. Rolling or freewheeling, does actually seem to make a difference to driving with a very small amount of throttle, which you have to do as no throttle would definitely see the inirtia of the engine/gearbox slow the car down.

I'm sure the VW computer probably isn't that accurate, or possibly might even lie to make their cars look good, but it does have me convinced.

I rest my case!
 

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Work quiet, is it Bob? :D

wouldn't be advisable to coast in my automatic tractor.

Done it on the bike in France when I was running on fumes.....:confused:
 

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Some cars used to have free-wheel devices Saabs pre GM 2 stroke and the V4s and some German 2 stroke cars (Auto Union DKW).
 

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Can someone please explain the "in gear to improve emergency braking" argument? Most cars nowadays can stop so quickly that you'd have to push the clutch in as soon as you press the brake pedal, so engine braking is negligible or non-existent. There's certainly insufficient time to go down through the gears. And anyway the tyres can handle only so much decelleration so adding engine-braking won't help. I'd rather concentrate avoiding the obstacle!

(Indeed I've heard of drivers accidentally pressing the accellerator instead of the brake and crashing harder as a result... but that's rare.)

Regarding the economy angle, as Phil (Pigugly) says, modern FI engines use less fuel on the over-run than coasting. My trip computer shows zero fuel consumption on the over-run, but perhaps 150 - 200 mpg when coasting. When rolling down a very gentle slope, you may be able to maintain your speed when coasting, though, so I can see a small financial advantage there. Otherwise no.
 

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As Dod pointed out Saab and Wartburg two strokes from the '60s/70s used freewheel devices to allow coasting. This was because the two stroke engines were using a premix lubrication system and on long downhills where the throttle was closed they would get virtually no fuel and therefore very little oil. I have been working recently for Mercedes in Milton Keynes and was told that the stop/start system fitted on the C220 diesel saves a tankful of fuel in 3 years of ownership. But I found the delay between lifting my foot off the brake and hoping the engine starts before hitting the throttle as I try to join a busy roundabout too nerve-racking. I'll just turn it off and pay the extra to know it will accelerate when I need it.
 

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BUT, lots of little can equal a lot. Any saving is better in my opinion. What I save rolling two miles, surely drives me atleast a mile further on a tank?
Yep, I agree. Any saving is good but then how much fuel is wasted due to hideous "environmental" devices fitted to modern vehicles - cats, egrs & dpfs then there's the subsequent failure of said devices.....
Don't get me started on that lot or the fact that modern diesels can be more temperamental than an '70s petrol car. All in the name of the environment :D:rolleyes:
It's a crazy world.

As for rolling 2 miles giving you enough fuel to power you a mile, that's the million dollar Q.
I still reckon there won't be much saving by coasting, over a modernish engine on the overrun using zero fuel for a lesser time.

Phil

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