Out of curiosity I tried foot off the throttle engine braking glide vs freewheeling. I had anticipated that foot off would consume no fuel but in my car that is not the case.My A2 is petrol converted to lpg and maybe the ecu is programmed differently but here are the results. I drove an identical two runs on the same stretch of down hill road near where I live and used an Elm327 with Torquelite on my phone to measure the instant kilometers per litre being used. On the first run engine braking from 60mph the km per litre were about 32-35 indicating fuel was being consumed albeit at a low rate. On the second run freewheeling the km per litre showed 85 to 90 and the car glided further maintaining speed. Quite a difference unless the elm327 readings are rubbish. I was careful to try this with no traffic about so safe to do.
Freewheeling vs foot off throttle
- Thread starter Welshboy
- Start date
Little Dog
A2OC Donor
Free wheeling is naughty.
Hangs head in shame.
dj_efk
A2OC Donor
Think (as always) there has been a thread on this before, although the LPG angle adds a new dimension.
The conclusion was freewheeling is indeed more economical if you don’t wish to slow down (for example on a straight fast road going downhill when you can clearly see ahead for a considerable distance and there are no hazards etc. ahead); however if you will need to slow or stop when going downhill (e.g. when travelling towards a roundabout), then engine braking is better.
I still don’t understand why freewheeling is dangerous - when arguing this I have yet to see a logical scenario that makes sense whereby the car not being in gear puts you in danger, other than complete and hence near-impossible simultaneous foot and hand brake failure.
The conclusion was freewheeling is indeed more economical if you don’t wish to slow down (for example on a straight fast road going downhill when you can clearly see ahead for a considerable distance and there are no hazards etc. ahead); however if you will need to slow or stop when going downhill (e.g. when travelling towards a roundabout), then engine braking is better.
I still don’t understand why freewheeling is dangerous - when arguing this I have yet to see a logical scenario that makes sense whereby the car not being in gear puts you in danger, other than complete and hence near-impossible simultaneous foot and hand brake failure.
I do not understand the numbers I got. If we assume my car does 45mpg at 60 mph which is 3000 rpm then converting to litres it becomes about 15km per litre at 3000 rpm. Freewheeling is about 850 rpm which prorata equates to about 55km per litre unless the extra load of pushing the car normally explains the difference
steve_c
Grumpy OAP & A2OC Donor
It's not that dangerous - plenty of cars have been sold from new fitted with freewheels over the years without there being any issue. However, freewheeling does increase the load on the brakes, and drivers need to be aware of that.
My main car from 1966 to 2005 was a Saab Sport which had a freewheel and it never seemed to be any sort of problem.
dj_efk
A2OC Donor
Right - agreed. I’m not sure the increased load on the brakes I do not think is the reason behind the doom-mongering by the wider automotive community on this subject however.
Erlingtheyounger
Member
As does the a2 in 1.2 form! No doubt it plays a part in its parsimonious performance. How bigger part is hard to tell but my guess is it’s not insignificant.
Thank you for the info. I looked it up and the 1.2t shares the same engine gearbox as the vw lupo.- from Wiki---In ECO mode, the clutch was disengaged when the accelerator pedal was released for maximum economy, so the car freewheels as much as possible, with the clutch re engaging as soon as the accelerator pedal or brake pedal is touched.In July 2001, a Japanese economy driver, Dr. Miyano, used it to set a new world record for the most frugal circumnavigation of Britain in a standard diesel production car, with an average fuel economy figure of 119.48 mpg or 2.36 L/100 km.
As 1.2TDI owner, my car does freewheeling by default, and a little tap on brakes makes it switch to engine braking mode if needed.
I sometimes drive on a slope where is allowed 70km/h and car maintains that speed with clutch disengaged, using maybe 0,7l/100km. But if i put it in gear, i either use 1,2l/100km to maintain speed or start losing speed. Since i need to slow down at the end, i'll use engine brake when not bothering others by doing so, but if it were elsewhere, freewheel would win.
More i freewheel, nicer numbers i see at the end. Mostly use cruise control for convenience. But since there is noticeable difference, i'll disengage it on longer downhills or where it is better to roll while nearing a stop, slower area etc...
Very noticeable at city speeds and traffic in lower gears, but i'm not a city person much. If eco mode is off and driving without freewheeling, it feels like handbrake is on and you constantly need to apply gas where you could usually roll without care...
Best to use both as situation dictates. Too bothersome to do so in standard car for me, but 1,2 makes it very easy to use both variants.
You can even start rolling by releasing gas pedal, switch to engine brake by tapping brake pedal and resume rolling by tapping gas. All in one go with one foot... Even switches gears down for you while engine braking
Edit: While braking it is in gear or switches into gear if braking is started while freewheeling. So break wear is the same in this case.
I sometimes drive on a slope where is allowed 70km/h and car maintains that speed with clutch disengaged, using maybe 0,7l/100km. But if i put it in gear, i either use 1,2l/100km to maintain speed or start losing speed. Since i need to slow down at the end, i'll use engine brake when not bothering others by doing so, but if it were elsewhere, freewheel would win.
More i freewheel, nicer numbers i see at the end. Mostly use cruise control for convenience. But since there is noticeable difference, i'll disengage it on longer downhills or where it is better to roll while nearing a stop, slower area etc...
Very noticeable at city speeds and traffic in lower gears, but i'm not a city person much. If eco mode is off and driving without freewheeling, it feels like handbrake is on and you constantly need to apply gas where you could usually roll without care...
Best to use both as situation dictates. Too bothersome to do so in standard car for me, but 1,2 makes it very easy to use both variants.
You can even start rolling by releasing gas pedal, switch to engine brake by tapping brake pedal and resume rolling by tapping gas. All in one go with one foot... Even switches gears down for you while engine braking
Edit: While braking it is in gear or switches into gear if braking is started while freewheeling. So break wear is the same in this case.
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Erlingtheyounger
Member
@Welshboy when I’m next in Tenby you’re very welcome to have a go in mine. This was the return this evening on the way back on a round trip from Gloucestershire to Eurodisney fully loaded. My wife made me fill up when we got off the Chunnel but the DIS indicated 75 miles left. Not bad from a 34L tank
datsundrew
A2OC Donor
60s Saabs freewheelEd on the over run, I dont think they had a reputation for being dangerous. Its down to the driver and awareness of the conditions.
This is what the Highway Code says about 'coasting'
I suspect cars with built in freewheeling devices are exempt because the car is designed to responds normally to all the controls
Cheers Spike
Rule 122
Coasting. This term describes a vehicle travelling in neutral or with the clutch pressed down. It can reduce driver control because- engine braking is eliminated
- vehicle speed downhill will increase quickly
- increased use of the footbrake can reduce its effectiveness
- steering response will be affected, particularly on bends and corners
- it may be more difficult to select the appropriate gear when needed.
I suspect cars with built in freewheeling devices are exempt because the car is designed to responds normally to all the controls
Cheers Spike
steve_c
Grumpy OAP & A2OC Donor
Freewheeling is not illegal. It follows on from this that cars built with freewheeling devices require no exemption. Regardless of whether one is freewheeling or not, it is important to maintain proper control of the vehicle. That's all that needs to be said on this.
G
Guest 4123
Guest
Having to put the car into gear may mean that you are not in complete control of the car and may pay heavily for that. Cars such as a 1.2Tdi go back into gear immediately the accelerator or clutch are touched.
RAB
PlasticMac
Member
G
Guest 4123
Guest
Aren't you confusing two issues? Cars that freewheel automatically also select the correct gear automatically. Manual gearboxes don't.
RAB
PlasticMac
Member
G
Guest 4123
Guest
I would have thought so. Certainly the 1.2Tdis are. The only other that I know of is the XL1.
RAB
hydo14
A2OC Donor
Newer Audis with DSG boxes (and the ZF's found in the 2017 onwards A4-A6) also allow coasting by disconnecting the clutch, they do this when you have the drive select set to economy.
My S3 has it but I have found the feature very hard to get used to as its a relatively heavy car so will accelerate pretty quickly if on any incline and it does this every time you lift off the accelerator requiring you to dab the brakes to get engine braking (which I would find confusing if I was in a car following).I find that I need engine braking a lot more than I need to coast so don't find myself using this feature much except when motorway driving.
This system works a lot better in the 2017+ A4 as it is linked to the sat nav and therefore intelligently chooses whether to coast or engine brake based on approaching a speed limit reduction, junction, sharp bend etc.
My S3 has it but I have found the feature very hard to get used to as its a relatively heavy car so will accelerate pretty quickly if on any incline and it does this every time you lift off the accelerator requiring you to dab the brakes to get engine braking (which I would find confusing if I was in a car following).I find that I need engine braking a lot more than I need to coast so don't find myself using this feature much except when motorway driving.
This system works a lot better in the 2017+ A4 as it is linked to the sat nav and therefore intelligently chooses whether to coast or engine brake based on approaching a speed limit reduction, junction, sharp bend etc.
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