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Freewheeling
J Bonington Jagworth
on 15 April 2008
Those of you with teeth as long as mine may remember cars (mostly Rovers, IIRC) that had a 'freewheel' option, which was effectively a one-way clutch that allowed the engine to drive the wheels, but not the reverse. This meant no engine braking, but allowed the car to coast whenever you took your foot off the throttle. This was for economy purposes, so I wonder it hasn't been resurrected now we are supposed to be worrying about our carbon output.
I assume it was abandoned for safety reasons, but we have much better brakes now, and AFAIK, Rovers were never regarded as worse than any other make in that regard - better, if anything.
As a footnote, I would mention that 2-stroke cars, such as the Wartburg, also had it, because driving the engine fast on a low throttle setting (which meant little lubrication) would have seized it pretty quickly. I rather enjoyed mine, especially when I tried to describe it to the then Mrs JBJ, who when I mentioned a free wheel, wanted to know which one it was...
I assume it was abandoned for safety reasons, but we have much better brakes now, and AFAIK, Rovers were never regarded as worse than any other make in that regard - better, if anything.
As a footnote, I would mention that 2-stroke cars, such as the Wartburg, also had it, because driving the engine fast on a low throttle setting (which meant little lubrication) would have seized it pretty quickly. I rather enjoyed mine, especially when I tried to describe it to the then Mrs JBJ, who when I mentioned a free wheel, wanted to know which one it was...
Comments
Manatee on 15 April 2008
Our Saab 96, although a V4 4 stroke, had the freewheel. A hangover from the 2 stroke version as you say.I remember telling my wife what a good idea it was, and that it would save fuel. Then I actually tried using it in hilly West Yorkshire. The rate at which it picked up speed downhill was terrifying, and long descents were a major threat to road safety with the ever-present fear of brake fade and fluid boiling. The little T handle that operated the freewheel was returned to its previous position very quickly and not disturbed again.
Bilboman on 15 April 2008
Forgive my ignorance, but how does a freewheen mechanism actually work? I simply cannot visualise or understand tthe workings. A layman's guide to freewheeling would be most appreciated if any BRs can help !
Number_Cruncher on 15 April 2008
>>A layman's guide to freewheeling would be most appreciatedwww.gmnbt.com/freewheel_technology.htm
J Bonington Jagworth on 16 April 2008
Not sure that counts as a layman's guide, NC! :-)The simplest example I can think of is that on a bicycle - when you pedal, the wheel gets driven, but when you stop pedalling, the bike carries on. In the car version, the engine idles when you take your foot off the gas/accelerator, irrespective of your speed or gear, but drives again when you put your foot back down. If you can live without engine braking, it makes a lot of sense.
Number_Cruncher on 16 April 2008
Mmm, I grant you that the English style is somewhat opaque, but, the vital bits are there!
Lud on 16 April 2008
In the days of carburettors freewheeling was economical. With modern electronic petrol engines the overrun in fifth or whatever your top gear is called is more economical still, using no fuel at all unless you are going quite slowly.
J Bonington Jagworth on 16 April 2008
"somewhat opaque":-)
Wikipedia has quite a good summary:
en.wikipedia.org/wiki/Freewheel
MichaelR on 16 April 2008
This was for
economy purposes so I wonder it hasn't been resurrected now we are supposed to be
worrying about our carbon output.
Becuase when using zero throttle a modern fuel injected car cuts off fuel supply and uses zero fuel.
grumpyscot on 16 April 2008
My 1971 Saab 99 had the freewheel - got 40mpg out of it (even though it had the awful Triumph Dolomite-based engine)! Terrifying going downhill, but great that you only had to use the clutch when moving off from rest in 1st gear. After that, you only had to back off the throttle a little to change gear.
Billy Whizz on 16 April 2008
JBJ, Lud and MichaelR have your answer.In a fuel injected car, when your foot is off the accelerator pedal and the revs are over about 1200 rpm, there is no fuel being used. As the revs drop below 1200 some fuel may start to be added as the anti-stall kicks in.
With most (all?) carb engines you always had some fuel being supplied.
Edited by Billy Whizz on 16/04/2008 at 08:48
jc2 on 16 April 2008
Many late carburetted cars were fitted with a "decel" valve which did the same as modern injected cars.
Saltrampen on 16 April 2008
To Confirm what BW says with modern cars, just watch the reset mpg on computer when going downhill with foot off pedal, it normally goes to 99.9, ie no fuel or virtually no fuel being used.When accelerator is renegaged can sometimes feel a very slight (almost unnoticable) jolt from engine.
pleiades on 16 April 2008
I once had a very second hand 1948 Bristol 400 which had a permanent freewheel on 1st gear only - no idea why and certainly not for economy. In fact I found it a bit of a pain creeping in traffic as when freewheeling and then accelerating the engine revs always caught up with the roadspeed with a bit of a jerk leading to fears of bursting the mechanism.A later 1959 AC Ace-Bristol I had the same 2-litre engine/gearbox (uprated from 80 upto 125 old fashioned bhp) and had no freewheel which IMHO a good thing in a car with a decently high 1st gear giving 40mph at 6000 rpm
Mind you don't torque convertor automatics more or less freewheel in D?
J Bonington Jagworth on 16 April 2008
"decently high 1st gear"That's probably why your older one had it - selecting first by mistake would have done a lot more damage!
Billy Whizz on 16 April 2008
>goes to 99.9,only because there are no extra digits in the display to 100+ mpg!
>ie no fuel or virtually no fuel being used
I understand it is really zero fuel - perhaps they should display the infinity symbol although most drivers these days would probably not know what it meant!
Edited by Billy Whizz on 16/04/2008 at 10:45
Cliff Pope on 16 April 2008
Is that true? I had one - it had a V4, with a counter-rotating crank balancing shaft. I thought it was very reliable and pretty nifty.The Dolomite I thought had a straight four, half of a Stag V8 as they used to say, and had similar problems to the Stag - barely adequate cooling, susceptibility to corrosion.
I agree the free-wheel was frightening. I played with it once then never again.
Cliff Pope on 16 April 2008
Sorry, that post is out of place. It refers to the Saab post earlier.
FotheringtonThomas on 16 April 2008
when using zero throttle a modern fuel injected car cuts off fuel supply and
uses zero fuel.
However, you can't "freewheel" anywhere near as far.
jc2 on 16 April 2008
"Leycock de Normanville" overdrives had a freewheel built in.
jc2 on 16 April 2008
And no-one has mentioned that with a freewheel,you could change gear without the clutch!!
s61sw on 16 April 2008
You don't need a freewheel to have clutchless gear changes - I do it all the time. Up shifts are relativley easy, down shifts take a bit more care, and I've never managed it from second to first.S6 1SW
Cliff Pope on 16 April 2008
"Leycock de Normanville" overdrives had a freewheel built in.
Not the ones I've experience of. I've a J-type in the Volvo, and the Triumph has an A-type. Interesting if earlier ones had this facility.
moonshine {P} on 16 April 2008
This is the exact point that most people fail to understand - well done FT!
The distance travelled is as important as the fuel used.
Billy Whizz on 16 April 2008
How would your freewheel system work in a fuel injected car? If it disconnects from the engine braking effects to allow a further distance it would also allow the engine to drop to idle which would then require fuel to be supplied to keep it running which defeats the purpose.I suppose the engine could switch off and restart when required... just as they do in certain Golf, Polo and Mini models.
Can you explain to me just how much freewheeling you want to do in today's traffic?
J Bonington Jagworth on 16 April 2008
"how much freewheeling you want to do"Virtually every time I lift off! Bear in mind that we tailor our driving to the behaviour of the car, so engine braking quickly becomes part of the anticipation. Would you rather have a fixed-wheel bicycle? :-)
J Bonington Jagworth on 16 April 2008
>However, you can't "freewheel" anywhere near as farExactly! You've still got the engine braking, which you may not want or need.
jc2 on 16 April 2008
Why not just put the g/lever into neutral???
Mapmaker on 16 April 2008
>>allow a further distance it would also allow the engine to drop to idle which would then>>require fuel to be supplied to keep it running which defeats the purpose.
Well no. For an engine idling at 700 rpm uses less fuel than the kinetic energy required to keep it turning over at 3000rpm when it would otherwise be freewheeling at 70mph.
Billy Whizz on 16 April 2008
Mapmaker, do you have any maths with that?JBJ, do you have an instantaneous MPG readout in your Mazda? I had a lot of fun with this in a Corolla hire car I had for a month & 2000 miles.
moonshine {P} on 16 April 2008
Here's something I posted a while back in another thread
-------
here are two key facts:
1 - A modern car will use less fuel on the over run if left in gear
2 - A car will coast further if left in neutral due to absence of engine braking.
here's some very crude maths to try and explain. Lots of assumptions in here, I'm hoping someone may be able to help with some more accurate figures, but regardless of the figures and accuracy it should illustrate the point.
'In gear'
Travel for 1 mile up hill, using 0.1 litres of fuel. Travel downhill for 0.5miles (due to engine braking) but use no fuel. Distance travelled is 1.5 miles using 0.1 litres of fuel.
Miles per litre = 15
'In Nuetral'
Travel for 1 mile up hill, using 0.1 litres of fuel. Travel downhill for 1 mile (due to no engine braking) but use 0.02 litres of fuel. Distance travelled is 2 miles using 0.12 litres of fuel.
Miles per litre = 16
-----------
The above will only work for certain situations, so reading the road ahead is always the most important bit to get right. For example, if you are going to have to stop at the bottom of the hill then it's better to leave the car in gear.
J Bonington Jagworth on 16 April 2008
"Travel for 1 mile up hill..."But the figures would be more advantageous to freewheeling on the return journey, I think.
I realise we're not talking about great untapped resources here, but I was curious that the green lobbyists don't appear to have discovered it yet. Perhaps I should keep quiet.
J Bonington Jagworth on 16 April 2008
"JBJ, do you have an instantaneous MPG readout"I'm afraid not. I have a spreadsheet, but I try not to use it while driving.. :-)
madf on 16 April 2008
I had Rovers with freewheel : 16, 75 - both with drum brakes and a 110 with no freewheel but iirc overdrive and disk brakes.All of them were heavy(1.5 tonnes) and when the freewheel was set to work , it would significantly improve fuel economy on hilly roads: up to 10% from c 22 to 24mpg. But the drum braked ones were prone to brake fade on long hills.. and the smell of smouldering brake linings and brake drums glowing red is horrible as is the feeling of pressing further and further down on the brake pedal and nothing happening.
I emphasise these were LONG (1 mile +) hills such as found in Scotland or the Lake District or parts of Wales...or the Peak District.
Changing gear without using the clutch was good for slow moving traffic.
In reality I used freewheel very little due to the braking system weaknesses. I don't regret its demise.
For a different era when roads were relatively empty.
Hamsafar on 16 April 2008
My last car had a one way clutch in the autobox, It was a diesel automatic, diesels tend to have more engine braking than petrols. It was great. You could lift off so far before traffic lights and coast along with hardly any loss of speed. In Sports mode, it was disabled, and slowing down with engine braking occurred. Using the freewheeling made for excellent fuel economy and a quiet and relaxed ride. The petrol version of the car didn't seem to have this feature.
J Bonington Jagworth on 16 April 2008
"The petrol version of the car didn't seem to have this feature."Interesting that the diesel did. I'd rather assumed that Health & Efficiency (aka H&S) had squashed it, but I was hoping it might return under the superior force of the green lobby...
Lud on 16 April 2008
I've posted this before, but forty or fifty years ago in my hitchhiking youth when HGVs in this country were governed to 38mph maximum, drivers used to freewheel downhill to reduce their journey times and have a bit of fun. I particularly remember a smart, matching Tate&Lyle sugar tanker and trailer going through East Anglian small towns at 60 or 70 in the dead of night. Tremendously sporting, although what might have happened in the event of a severe booboo doesn't bear thinking about.
Cliff Pope on 16 April 2008
>> when using zero throttle a modern fuel injected car cuts off fuel supply and
>> uses zero fuel.
However you can't "freewheel" anywhere near as far.
We've had a thread on this subject. Number Cruncher, I think, pointed out that there was still engine compression and friction, both of which are eliminated in true free-wheeling.
Lud on 16 April 2008
That is certainly so CP, but it is also the case that my early-90s Escort 16v runs very freely in top gear on the overrun at speeds between 30 and 50mph, surprisingly so. Indeed when I had a metal-to-metal situation in one of the front brakes a while back and tried to drive 55 miles without using the brakes in earnest, I found even changing down to fourth and third on the approach to roundabouts didn't check speed much unless I just touched the brake pedal short of causing any noise.
J Bonington Jagworth on 16 April 2008
"still engine compression and friction"And air pumping, unless the valvegear is disabled too.
The original argument against freewheel devices was that of inadequate braking and/or fade. That hardly applies now, so why not make it an option again? It's pretty simple, mechanically, which lead me to wonder if there was any other reason.
Apologies if it's all been debated before.
Pug Eyed on 16 April 2008
I too had a Rover 75 (the Cyclops model) purchased for 30 pounds in 1969, when both I and the car were 18 years old. It was operated by a knurled knob under the dashboard in the middle of the car, which my friends used to play with to see what it did. I wasn't particularly worried about the fuel comsumption, with Jet Premium costing 4/11 per gallon (5.5p per liter) and didn't use it much as the Tank needed all the braking power, including engine braking) that was available.I'm slightly ashamed to say now that it's main use was getting the back wheels to spin at 30mph: freewheel at 40, put the car into second, wait till it slows down to 30 and then floor the accelerator. By the time the revs matched the speed and the clutch engaged, the torque was enough to lay rubber tracks on the road with suitable screeching sound effects. Oh happy days!
Suprisingly, nothing broke in the transmission or drivetrain but perhaps unsurprisingly, the the engine died during a thrashing down the M1 from Manchester to London. For all that I know, the car might still be in Newport Pagnell Services car park.
Harleyman on 16 April 2008
I have to confess that I use "angel gear" quite frequently with my old 1963 GMC pick-up truck; since it's also fitted with "mandraulic" steering and has no brake servo there's less risk in coasting with the engine turned off altogether, also the brake lights work independently of the ignition switch. I do reserve this behaviour for main roads with long straight descents though; given that she averages about 14 mpg overall any fuel saving at all is a bonus!As for engine braking, the beast has a 5-litre V-6 engine (yes it is the original one) and a 3-speed column change. Let us just say it provides excellent retardation!
Edited by Harleyman on 16/04/2008 at 22:53
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