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Thursday
May172012

73.9 MPG

I posted this picture on Twitter on Saturday evening after a 120 mile drive across the UK. It was taken in the Toyota Prius I own, and I posted it because I was pleased to have used so little petrol on such a long journey. Just in case you haven’t seen the Prius dashboard before, it’s saying 73.9 mpg on a 120.2 mile journey at an average speed of 41 miles an hour.

The first tweets I got back where, 41 mph! That’s so slow, no wonder!

I didn’t have the space or patience to clarify the difference between average speed and highest speed. The route I took was about 80% A roads, the speed limit on an A road is 60. I didn’t break the speed limit but I didn’t slow other cars down. On the short sections of motorways I used I stuck at exactly 70.

The weather was fine, the route was across the eastern half of England, from Gloucestershire to Lincoln, so the last half of the journey was very flat. Hills make a lot of difference and where I live it’s all hills.

Of course the post gleaned the usual reaction from diesel drivers, the ‘I get 238 mpg going up hill pulling a trailer in my 3 ton diesel SUV’ nonsense.

I was told by someone that they got 85 mpg in a Skoda Octavia 1.9 diesel. Impressive, if true, but then I started to think. He posted no pictures and the most cursory of searches reveals 100’s of Octavia drivers saying 60 mpg is very good, and when they have compared actual fuel used in comparison to the readout on the dash, it’s more like 57 mpg.

It’s then I realised that a very easy thing to do on Twitter is say exactly what this individual had said, essentially ‘my dad is bigger than yours.’ It’s barely one step on from 8 year olds in the playground.

I know it’s pointless enraging the diesel heads but I’m also a little immature sometimes. The original post was not meant to goad, I was just impressed that I’d done such efficient driving on such a long journey. But goad it did, the usual rash of ‘but the Prius batteries are much worse than a diesel engine’ and all the normal nonsense I’ve grown immune to.

One thing we can all be sure of, what the readout says on a modern cars dash and what you are actually getting are only loosely connected.

Last year I drove a plug in Toyota Prius. This looks exactly like the regular Prius but has a higher capacity lithium-ion battery that you can re-charge from the mains. This gives the car an all electric range of a mere 12 miles, however if you forget about that, it has a quite remarkable effect on the overall MPG.

How do I know, well, judging from the cars on screen readout it was always doing 99.9 MPG because that’s as high as the standard Prius screen can go. It’s only got 3 digits.

I wanted to know exactly how much it really used. For the first time I actually remembered to fill the tank, reset the mileage to zero, drive the car, charge it when I could, and then re-fill it at the end and do a simple calculation, how much fuel had I put in, how far had I travelled.

The result was impressive. Over 412 miles of driving with 4 re-charges (it only takes an hour to re-charge) my final calculation revealed 124 miles to the gallon. This was in a prototype test version of the Prius, the full production model doesn’t come out until the autumn.

It will be a pleasure to post the MPG readouts which will be so spectacularly greater than the Octavia 1.9 diesel there really is no argument.

Also, while I’m droning on about such nonsense, the figures for the Nissan Leaf, well obviously it doesn’t use petrol but the energy equivalent, as in kilowatts of energy mean it runs at well over 350 MPG.

This is what is so hard to explain, the energy stored in the Leaf’s fully charged 24 kWh battery is equivalent to a mere one and a half liters of petrol, and on that energy the car can travel 100 miles. An electric car is a lot more efficient, but that is a very complex and difficult message to communicate.

 

Reader Comments (11)

That is a very informative blog, i have a diesel scenic but i would love to have an electric car, i have 4 grand children and i want them to grow up in a decent World, not a mad max type World. Thank you for your very interesting blogs.

May 17, 2012 | Unregistered CommenterPaul Williams

Thanks for this blog entry. Must show it to hubby as soon as he is home - he has a Prius and has encountered this sort of (unsolicited) attitude about his choice of car ever since. I am sure he will be pleased you 'share' his frustrations.
(He had a 'home made' electriccar once which was a delight - so smooth and quiet...roll on the time they are commonplace)

I LOVE his Prius - yes it has good green credentials but also i think it the most comfortable & delicious car to drive long distances that I have ever driven.

Thanks for what you do and write about Mr Llew...really helps like minded folks like us keep hopeful and feeling less isolated.
Hilary Brett
(@Mossy)

May 17, 2012 | Unregistered CommenterHilary Brett

Bragging about MPG ratings is like bragging about penis length - if there's no documentation, then it's just hot air. All guys do it, and now it's progressing to MPG.
We often show off to the world that we're achieving amazing unheard of economy, but in reality we're typically doing what the the manufacturer claimed we would.

May 17, 2012 | Unregistered CommenterGav

Here's a sweeping generalisation. Most motorists average 28 mph, as an average of their journeys. So, your average of 41 mph is actually quite high and would be possible only by avoiding most town centres and traffic jams.
Still amused by all the figures though, as my bicycle does about 20 miles to the cereal bar. Beat that!

May 17, 2012 | Unregistered CommenterPaul

I've driven big miles in an Octavia, now a 2.0 Audi A3. I still want to flip to electric or hybrid when the breakthrough car comes. Tesla for 20k, or next gen jap hybrid. I will defend the diesel mpg though, and I do think we should work machines their lifetime, hell so much energy used to get the materials out of the ground and into a car shape. The A3 does better than the Skoda on long trips. It has 6 gears and torque. = 65 or 70 mpg on motorway trips and never less than 50mpg overall with grownup driving. BUT I dont like what it chucks out...bit of a dilemma as I believe that much metal and manufacturing has to stride out for 200k miles before I contribute to the build carbon of another metal box....Now if someone designed electric heart transplant for old Audis :)

It seems that everyone has their own facts in the EV argument which makes it hard for us uninformed folk to draw a conclusion There is a lot more discussion of motives of the various parties than finding figures acceptable for all.
I say this because I find the official, well EPA, figure for Leaf mpg to be 120. While mpg for an EV is a pretty meaningless figure it is a symptom of how hard it is to understand the issues.

May 18, 2012 | Unregistered CommenterPhil J

Also I'm coming to the conclusion that I must be a computer, given how often I get CAPTHAs wrong these days!

May 18, 2012 | Unregistered CommenterPhil J

Here is someone who has crunched a lot of numbers - let the physics do the talking! It's an excellent blog that is based firmly in reality.

MPG of a human
http://physics.ucsd.edu/do-the-math/2011/11/mpg-of-a-human/
(he calculates that push bikes get the equivalent of between 160 and 290mpg)

MPG of electric cars
http://physics.ucsd.edu/do-the-math/2011/08/mpg-for-electric-cars/

Is 100mpg in a petrol car feasible?
http://physics.ucsd.edu/do-the-math/2011/07/100-mpg-on-gasoline/

May 18, 2012 | Unregistered CommenterJoe

73.9mpg is very impressive indeed. I've not had the fortune of driving a Prius yet but the possibility of numbers like that certainly makes you question diesels.

Dubious emissions aside though, diesel can be impressive. In a Greenline II-spec Octavia, with a 1.6-litre diesel, I averaged over 60mpg in a week of driving, with 65-ish possible over the up-hill-down-dale stuff of the Yorkshire Dales.

The only hybrid I've had for any length of time was a Lexus RX. Did over 40mpg around town, which is astonishing for a 2+ tonne SUV, but only 30mpg on the motorway, which isn't so impressive.

Different vehicles suit different environments, but it looks like the Prius hits a sweet spot where it's equally capable in or out of town.

@antonyingram

May 21, 2012 | Unregistered CommenterAntony

Sometimes the Prius HSI display is a little optimistic.
My record is 155.7km consuming 4.0l/100km at an average of 99km/h.
Converted that is 96.7 miles 70.6mpg(UK) at an average of 61.5 mph.

My true figure was probably more like 4.3l/100km or 65.7mpg(UK). This is based several readings of 4.6l/100km on the HSI but calculating 4.9l/100km when I filled the tank; a 6.5% error.

If Toyota offered a choice of extended battery options for its Plug-in model, it might find a real winner. If you regularly drive 200km, a 24km EV range helps a little, but an 80km battery would be great. Or for city driving, a24 km range might be ideal.

May 25, 2012 | Unregistered CommenterBradley Temperley

MPG goals are a good thing, however I have 1 bug bear.. the 'equivalent MPG' of plug-in vehicles. This figure is complete BS, it does not help the environment and is definately not an efficiency figure. You state the bigger battery is more efficient but this is not correct, it may use less petrol but how well does it use the coal that is burnt in the power stations? You also state the Nissan stores an 'equivalent amount of energy', again I must pick up on that and state that it is not correct, the equivalence is based on cost not energy.

The real problem is that electricity is too cheap, it needs to be taxed the same as fuel on a carbon basis. This will happen when petrol tax receipts are not enough to run the bloated government.

It is quite possible that it is more energy (and therefore carbon) efficient to burn fuel locally than to incurr the electrical transmission and generation losses. This is why we mainly burn fuel to heat our houses (although again this also unfairly untaxed).

I'm not against the development of the technology, there are some benefits, and it could move the evnironmental effort to the power generation industry, but we are making the problem worse (short term) in order to make it better (long term).

March 6, 2013 | Unregistered CommenterTony

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