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Prius Mpg Re-Visited


barrycoll
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I had a meeting near Oxford this week, and checked TomTomlive traffic before leaving Nth London....it all looked clear, but things changed quickly, and the A 406 and then the start of the M40 became a stop-start nightmare...

By the time I reached a clear M40 I was very late indeed, and decided to give the T Spirit some solid welly....so it was foot the the floor doing a very old fashioned 85-90 mph for a good 35 miles, and reduced my losses to 15 minutes.

And interestingly, when I finally pressed the Off button, the mpg recorded 52 mpg, which was amazing

On the way home at 6pm, the traffic was just ghastly, but finally in my driveway, I was rewarded with 72.9 mpg....even more amazing!

I also have a Roof Rack on the car at the moment, which must be beneficial rather than harmful!.....maybe because they are 2 aero bars both pushed almost touching one another to the very back of the roof like a giant spoiler! But in this position I can again open the glass sunroof

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Yeah, it's a bit weird ain't it? I've been finding a similar thing.

I normally drive around 63mph but lately have been bombing along at 70-ish mph and the mpg hasn't really dropped (If anything it's been higher?! :eek:)

I can only assume it's some combination of the engine running hotter (And thus more efficiently), and me having less acceleration/deceleration cycles since I can just sweep past e.g. HGVs at the same speed rather than accelerating past them from 63mph and then dropping back again.

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The logic doesn't hang together, as pushing through the air resistance is unavoidable, and the main 'problem'

On the other hand, when traffic bunched up, and a glide type accelerator pedal was called for, 100mpg stayed showing up even at 80/90mph.

Interestingly, despite being flat to the floor for long periods, I was also constantly being passed by long strings of cars and vans......nobody else was doing 52 mpg though!

In my panic to get to my destination, I had forgotten that I was still in Eco mode, and that the amount of accelerator travel seemed quite enormous......making the car feel gutless. So now I must try this 'experiment' again, switching out the Eco, and seeing what the final mpg is, hopefully without losing my licence

Has anybody else tried Power setting as a M-way option???

And what does it feel like?

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Air resistance is a major factor, but changes in speed (i.e. acceleration) expends a lot more fuel. I'm not sure how efficiency changes with engine heat; Generally hotter engine = better economy but I don't know by how much.

In my case, I'm becoming increasingly convinced that sticking to 70mph uses less fuel than going from 63mph to 70mph and back again repeatedly. Driving at 63mph all the time would be more efficient but I can't stand overtaking HGVs at 63mph as I'm terrified I'm going to get a 70mph+ Audi up the **** :eek:

I'd be interested to hear how you get on too tho'! The Prius has a nice sleek shape so hopefully the air resistance isn't as big a factor!

The overtaking thing is depressingly normal. Even at 70mph I find people are still flying past me as if I was doing 60mph and I'm sure if I was going even faster, a lot of people would still be flying past overtaking me!!!

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An aerodynamicist on another group once pointed out that the drag factor matters most when pointing directly into headwind.

A partial headwind which effectively comes at you from say 45° to the right or left (taking into account the speed at which you are driving) will see a very different shape of the car, and he suggested (admittedly from his experience rather than substantive testing) that this could have a much bigger impact than no wind or a direct headwind.

It sounds plausible, but of course is only opinion, not fact. However, over the last 12 years/300,000+ miles in Hybrids, one thing I've found is than on a longer journey where one tends to monitor fuel consumption, there's no obvious consistent correlation between road & weather conditions, average speed, general level of acceleration etc. and the resultant fuel consumption as displayed on the car.

Often, on journeys I'd expected to do particularly well, that has been the case, but sometimes the opposite results. Other journeys where I'd expected to do badly, I haven't always!

Now, I keep a database on my phone of every single refuel, and I record the displayed mpg for the tank full (using Trip B for that purpose), and the calculated figure is almost always 3¼-4 mpg worse than the computer figure, so I generally knock about 3½ off.

Yesterday, I did a trip to Bedfordshire from the Norfolk coast, and filled to the brim 7 miles after leaving home (120.7 p/liter at Asda!). I'd used cruise control extensively, it was 13°C when I left and returned, reaching 19°C during the day, with little or no wind and dry roads. I cruised at 60-65 on the clock where permitted, at the speed limit or 1-2 mph above on the clock in lower limit zones, accelerated with the bar towards the right end of the ECO part of the ECO gauge (I can always see it in the HUD). When I got home I'd driven 261 miles in the day, of which about 15 was local driving in Bedfordshire. The trip computer showed 70.9, so say about 67½ true. There were no holdups at all, just 8 miles of 40 limit through the A11 Thetford Forest road works. A/C was on all the time, climate set between 18-20.

On some journeys I'd have seen 73-75 mpg on the computer on a journey this good, but I have seen just 65 once or twice.

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I dont know whether other folk have been watching "SPEED, with Guy Martin" on C4, where this amiable nut case is trying to break the 24 hour endurance record for riding a tandem bike (with a chum)

It was explained to him that overall, 90% of effort goes into overcoming wind resistance, 7% from internal bike frictions, and 'just' 3% from rider input.

So the slippery Prius, travelling at 70 mph, "sees" an apparent wind of 70mph on a no wind day, that it has to overcome, uncomplicated by side, or tail winds.

After that statement, it all gets too complicated, with possible low friction M-way surface, tyre pressures, engine temperature, cruise control parameters, traffic conditions etc that it starts to "do my head in" as a friendly yoof might say

But just why my Roof Rack didn't knock at least 10% 0f the mpg is another quandry......are aero bars that efficient??

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It says something that the world record flat cycling speed is only 83.13 mph (133.78 km/h), while the record following a pace vehicle with a wind deflector is an amazing 167 mph (268 km/h) (I guess they didn't use a Prius as the pace vehicle!).

source: http://en.wikipedia.org/wiki/Cycling_records

In my heyday, I could hold 25 mph on my racing style bike on a calm day/level road for an hour or so - these days I have joggers pass me occasionally when I'm on my electric-assisted bike!

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Doesn't Tesco and/or Asda petrol have higher concentrations of ethanol in it? Hence why it's cheaper but also why your economy was down a little. It's said it's about 10% loss of mpgs on the US forums. Some over there actively seek E0 petrol in States that still have it.

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The British record is set by the one and only Guy Martin

( The British [27]absolute speed record was set by Guy Martin in 2013 pedaling at a speed of 112.94 mph behind a modified racing truck.)

It was on softish sand, and the rubbish thrown up by the truck's tyres nearly killed him..................good viewing though

Falling off the bike at that speed would have been like hitting a brick wall of the wind resistance outside the trucks rear end.......not to mention hitting the ground!

25 mph on the flat, for a whole hour, is pretty stirring stuff Pete....must have been at least 6 months ago

Are you suggesting Grumpy, that Shell Nitro, or similar, would by a similar token, take the car further per litre?

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Doesn't Tesco and/or Asda petrol have higher concentrations of ethanol in it? Hence why it's cheaper but also why your economy was down a little. It's said it's about 10% loss of mpgs on the US forums. Some over there actively seek E0 petrol in States that still have it.

I'm not sure, but I won't touch supermarket fuel personally, I can tell the difference in dads car when he fills at Tesco and I fill it at Shell.

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Doesn't Tesco and/or Asda petrol have higher concentrations of ethanol in it? Hence why it's cheaper but also why your economy was down a little. It's said it's about 10% loss of mpgs on the US forums. Some over there actively seek E0 petrol in States that still have it.

Prior to March 2013, the UK allowed up to 5% ethanol to be added to unleaded fuel, and this blend is known as E5. In March 2013, the Motor Fuel Regulations were amended to allow a blend of up to 10% ethanol, and this fuel is known as E10.

In the States, tests have shown that E10 is 3-4% less economical than E0 (0% ethanol).

There is EU legislation in place which makes pump labelling of fuel containing more than 5% ethanol mandatory -

‘UNLEADED PETROL 95 E10 Not suitable for all vehicles: consult vehicle manufacturer before use. BS EN 228’.

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So if E10 fuel was 3-4% cheaper than E0 fuel then the fuel economy (pence per mile) would be the same. Is there a way to find out what the E number of the fuel you are buying is?

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Doesn't Tesco and/or Asda petrol have higher concentrations of ethanol in it? Hence why it's cheaper but also why your economy was down a little. It's said it's about 10% loss of mpgs on the US forums. Some over there actively seek E0 petrol in States that still have it.

Prior to March 2013, the UK allowed up to 5% ethanol to be added to unleaded fuel, and this blend is known as E5. In March 2013, the Motor Fuel Regulations were amended to allow a blend of up to 10% ethanol, and this fuel is known as E10.

In the States, tests have shown that E10 is 3-4% less economical than E0 (0% ethanol).

There is EU legislation in place which makes pump labelling of fuel containing more than 5% ethanol mandatory -

‘UNLEADED PETROL 95 E10 Not suitable for all vehicles: consult vehicle manufacturer before use. BS EN 228’.

Maybe Asda and Tesco have 5% and other offerings are 2.5% or 0%?

And do they legally have to state what you displayed or can they just get away with "Unleaded Petrol BS EN 228"?

Appreciate links to confirm.

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For E10 fuel, they have to include the above message on pumps. But the labelling requirement doesn't apply to E5 - so it is quite feasible that certain brands could contain nearer to 5% ethanol and other brands less.

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This is from a BMW forum re ethanol....



Having read this, I also read that Honest John recommends Nitro + Super Premium for his father's Prius!



Posted 15 August 2013 - 05:42 PM




This is what I find particularly shocking:



"Blending
Ethanol with the petrol is the final act that the fuel company
undertake. It is added only when the fuel is in the tanker, ready to be
delivered. This is because if added sooner than this, the Ethanol would
attack the storage tanks in the fuel depot. It is for this reason also
that Ethanol can’t be transferred along piplines with the rest of the
fuel (it eats them too). It has also been known to damage the storage
tanks in service station outlets and these need to be modified to
contain Ethanol fuel. "



http://www.groups.tr...nol-update.html



And it seems that E5 petrol is already commonplace, espcially for 95 octane. This information is not necessarily current though.



BP Ethanol
is added at 5% to unleaded petrol at all sites across the UK. BP
Ultimate (super unleaded petrol) does not have Ethanol added, except in
the South West of England.


Esso Ethanol
is added at 5% to unleaded petrol at most sites in the UK. Esso Super
Unleaded petrol does not contain Ethanol, except in the South West of
England (Devon & Cornwall)


Shell
Shell has repeatedly refused to answer the question. It is therefore an
assumption only, that all Shell petrol should be considered to contain
5% Ethanol.


Texaco Ethanol is added at 5% to unleaded petrol. Texaco Super Unleaded petrol does not contain Ethanol.

Total Ethanol
is not added to any Total fuel (including standard unleaded petrol).
Except in the North West and South East of England.

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Why does super unleaded have ethanol added in some parts of the country and not others?

Does the price change to reflect the cheaper ingredients?

update:

Have just read the article and noted

This information was correct at the time of asking…Feb 2011

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