Comparison Tests

Toyota Prius C Vs Hyundai i30: Diesel vs hybrid – which is more fuel efficient?

If you really want to save fuel which is best, petrol/electric hybrid or turbo-diesel? We compare the 2015 Toyota Prius C and 2015 Hyundai i30.

ON THE LEFT IS Toyota’s small hybrid, the Prius C (review can be found here).  On the right is our long-term tester, the Hyundai i30 Active Diesel automatic. Both represent the latest technology – the Prius has been in production for 18 years now, and the Hyundai diesel has a modern common-rail injection system allied to a seven-speed DSG gearbox (which Hyundai designed and built) which not only has more gears than older systems, but is more efficient, too.

Let the battle commence…

The vehicles

Here’s the vital statistics of each vehicle:

 CarEngineOutputTransmissionWeightLength / width / height

ADR81/02 Fuel Consumption

Urban / Extra Urban / Combined

Emissions of Co2 (grams/km)

Driveaway cost (Melbourne)
Hyundai i30 Active Diesel1.6L turbo diesel100kW @ 4000rpm
300Nm @ 1750-2500rpm
7-speed DSG1400kg4300 / 1790 / 1470

5.9 / 4.3 / 4.9

129g/km

$23,990
Toyota Prius C1.5L petrol & electric

Petrol:

54kW @ 4800rpm
111Nm @ 4000rpm

Electric :

45kW / 169Nm

Combined: 74kW / 280Nm

CVT1140kg3995 / 1695 / 1455

3.7 / 3.8 / 3.9

90g/km

$26,391

It’s not actually a truly fair comparison because the i30 is larger, over 300mm longer and 95mm wider. That accounts for its extra weight, some 260kg, but diesels are also heavy engines, even if the Prius has to cart around a battery.

The official fuel consumption figures are interesting. The Urban cycle usually has the highest consumption because it’s stop-start which involves lots of accelerating, and the Extra Urban the least because the car is mostly cruising, with the Combined somewhere between the two. The i30 follows this pattern, but the Prius does not. This is because once in cruise it cannot leverage its electric motor which, along with the battery, becomes dead weight. We have more on the format of the official fuel tests here.

Emissions comparison

You can compare Australian vehicles for fuel consumption and emissions over at the government’s Green Vehicle Guide.  Here’s the results for our two cars:

Capture

The emissions Co2 figure is how much carbon dixoide, in grams, is emitted during fuel consumption testing.  Petrol and diesel engines perform quite differently in this respect and there is no easy soundbite to answer which is better or worse.

In brief, diesel engines use less fuel per kilometer than petrol, so advantage diesel. If we then look at the various types of pollutant emitted by internal combustion engines (both petrol and diesel) then diesels do better than petrol, except in the case of particulate matter (tiny particles of soot) and nitrogen oxides (NOx) emissions which “can cause a range of adverse health effects” according to the Guide.  

However, every new generation of diesels is improving (as indeed are petrols). The latest Euro 5 standards are particularly tough, as are California’s emissions laws. This is why you see only modest power and torque improvements from new engines, because all the development effort is going into making the engine clean which tends to reduce power and torque. So in many ways if the carmakers can get the same engine outputs from a new, clean engine as the older, dirtier one that’s a win.

About the Prius…

The Prius is a hybrid petrol-electric. This means it has two engines, one petrol, one electric. The basic principle is that the car converts what would have been wasted energy through braking or deceleration into electric energy which is stored in its battery, ready for re-use. Braking energy is harnessed only through the front wheels, not rear. The Prius also works as a pure electric vehicle (EV) at slow speeds, not using the petrol engine at all.

The modes the Prius can run in are:

  • EV (Electric Vehicle).  Propelled only by the electric motor.  Works only up till around 40km/h, and will take the car up to 2km.  On the flat.
  • Petrol – the petrol engine only powers the car.  The petrol engine may also run a generator to recharge the battery at the same time.
  • Combined – the car is driven by both the petrol and electric engines at the same time.

Toyota call this Hybrid Synergy Drive.  In practice, the Prius will prefer its electric engine at slow speeds, the petrol at higher, it’ll take every chance it can to recharge its battery, and will use both electric and petrol engines when it needs to accelerate.

The Prius transmission is a CVT, which we have fully explained here.  Briefly, a CVT is a ‘gearless’ transmission which allows the engine to remain precisely in its most effective rev range. That’s why Toyota don’t quote how many ‘gears’ the Prius has.

About the i30…

The i30 has the latest turbo-diesel technology. I could fill a book writing about it, but take it as read if there’s something new and cool, the i30’s engine has it. Briefly though – the diesel engine has a variable geometry turbocharger which means the turbo changes configuration so it works efficiently across all rev ranges, and it is common rail which means microscopic droplets of diesel are very precisely metered into the engine under extremely high pressure, all computer controlled, again for maximum efficiency.

The i30 also has a DSG gearbox, which means Direct Shift Gearbox. This is a very efficient automatic transmission that doesn’t have the friction losses of a normal automatic gearbox (one with a ‘torque convertor’), shifts very quickly and has seven gears so the engine can spend a lot of time in its most effective rev range, not too dissimilar to the CVT in that respect, but where the CVT has an infinite amount of gears the DSG has seven.

The one thing the i30 is missing is stop/start tech which turns the engine off when the car comes to a halt, and instantly restarts it.

Diesel vs petrol

Diesel engines are more efficient than petrol engines – you go further on a litre of diesel than petrol. This is because there is more energy in a litre of diesel than a litre of petrol. However, diesel engines are heavier not only through their inherent construction, but because they have turbochargers and intercoolers.

The test

The test route started with Part A: 50km of busy Saturday morning suburban traffic; then Part B, another 90km of faster suburban roads and freeways, again in fairly busy conditions. The total distance was 140km, the maximum speed was 100km/h, average speed was 54km/h and the total time was 2 hours, 35 minutes.  Of that, 25 minutes was spent stationary.  

Capture2
Graph of speed vs time – vertical axis goes from 0 to 100km/h

Both vehicles were unloaded, with tyre pressures set at manufacturer’s recommended. We brim-filled both tanks at the start of the test and at the end because you cannot rely on the consistency of the automatic click-stop even at the same servo on the same pump. Aircon was on in both cars, and ambient temperate was between 27 and 30 degrees. Both cars have Eco modes, and both are a total waste of time for reasons I will explain later in a later post, so neither mode was enabled. Both vehicles were warmed up before the test commenced.

I drove the i30 in the lead, and used basic fuel efficency driving techniques, but not to the extent we cruised below speed limits, other road users were impaired, or road safety compromised. The Prius followed right behind and did the same.

The results

After Part A, the urban run, the Prius’ internal fuel consumption meter registered 3.6L/100km and the i30 4.5L/100km. While neither internal meter is accurate, they can be used for relative comparison. 

The Prius won because:

  • It switched its engine off at idle (had the i30 been fitted with idle stop/start tech this advantage would have been largely negated);
  • Is 260kg lighter (important for acceleration); and
  • Is able to store energy used to brake the car to accelerate and move later on.

The official urban cycle fuel consumption figures are 5.9L and 3.7L for the i30 and Prius respectively.   The real-world test shows a similar gap, and both cars beat their official figures with little effort from the drivers – more on why people should stop whining about the official figures is here.

Then we moved to Part B, which involved 80km/h roads (thanks Melbourne, we seem to have quite a few such freeways), less suburban driving and freeway cruising. This is where the tables were turned, as the i30’s fuel consumption crept down.  Conversely, the Prius’ edged up. The reasons are more or less the inverse of Part A:

  • The Prius had little chance to use its energy recovery systems and idle stop; and
  • The weight difference is much less important in cruise than acceleration.

At the end of the rest we had the following results:

Final resultsDistance & timeIndicated fuel use (L/100km)Fuel used (L)Actual fuel use (L/100km)Official combined cycle figureTotal emissions (1)
Hyundai i30 diesel auto140km / 2hr 35m4.25.523.94.9 18.06kg
Toyota Prius C hybrid140km / 2hr 35m3.75.293.83.9 12.06kg

Analysis

Here’s what we learned based on this test. Obviously different conditions will produce different results, but nevertheless the conclusions here are pretty sound for the average driver.

  • Hybrids do not make financial sense. You pay a lot more to buy a hybrid and the fuel consumption savings are minimal at best. The only time a hybrid makes sense is when you do a lot of stop/start driving below an average speed of 50km/h, and even then you’d need to do a lot of driving, an infeasible amount (see below), to get back the thousands of extra dollars you pay for a hybrid over the same-sized conventional car. Once you’re rolling, a modern diesel is more efficient – we need to allow for the fact the i30 is a bigger car than the Prius, and yet it very nearly matched it for fuel efficiency.  I feel sure that had the i30 been the same size as the Prius it would have used less fuel;
  • Hybrids pollute less – the total emissions are pretty clear, 18 to 12. Even accounting for the i30’s extra size, that’s a win for the Prius; and
  • The combined cycle is achievable Yes, the lab-tested fuel consumption figures are not out of reach with some basic fuel consumption techniques.

Hybrids are what you buy if you are willing to pay extra to reduce emissions, or if you really want a electric vehicle mode which would be useful when maneuvering for extended periods of time in confined spaces.  Otherwise, a small, modern diesel (or petrol) makes more sense.

 

(1) how come the cars used 5L or so of fuel (which weighs less than 5kg), yet managed to produce much more weight in CO2 emissions?  The answer is that during combustion each carbon atom combines with two oxygen atoms to make CO2, and the emissions figures take this into account.  The extra two atoms make the total CO2 result around 3.7 times heavier than the pure carbon alone. What’s important is not so much the actual weight (although less is better), but the relative amount between vehicles.

Hyundai and diesel emissions

In the wake of #dieselgate, Practical Motoring asked Hyundai about ‘defeat devices’and they told us this: “We confirm that none of our vehicles are fitted with any type of software intended to manipulate regulatory emissions test results.”

The question doesn’t apply to the Prius as it’s a petrol.

How far do you need to drive to make money on a more fuel efficient car?

A long way.  Taking the i30 and Prius C at $23,990 and $26,391 that’s a $2,401 price saving.  If we use the standard fuel consumption of 4.9 and 3.9L/100km then for 20,000km per year we have $1421 and $1076 for fuel, assuming diesel is a bit more expensive – that’s $400 per year saved.

Then divide $2401 by $400 and the answer is about seven years before the extra purchase price is worth it.

That doesn’t account for higher repayments, more money tied up in a car and lots of other factors.   If you did the same calculations for diesel vs petrol you find the same thing, the extra cost of a diesel isn’t worth it.

One scenario in which hybrids make sense is as a taxi:

20151002_093836

The reason is that taxis spend a long time in stop/start traffic, and at slow speeds. The huge mileages they cover means the hybrid premium is worth paying.

A note about the Hummer and the prius…

Please don’t comment about that study which shows a Hummer has a lower lifecycle cost than a Prius. It is clickbait junk research of the lowest order that has been comprehensively torn apart in many different places so I’m not going to bother with it here.  It is also an object lesson in how people uncritically repost information that fits their preconcieved ideas.

However, like most junk research that study does have a fundamentally true premise which is that you have to look at the end-to-end environmental impact of your vehicle, not just the emissions/consumption.  In that regard hybrids come off worse than conventional vehicles because they have all the normal parts but an extra engine and battery. How much worse? Depends on the vehicle, and whether or not it’s worse overall also depend on your usage in real life.


14 Comments

  1. Jacques Pretorius
    October 7, 2015 at 1:33 am — Reply

    Wow that is excellent fuel consumption for the Hyundai considering the weight disadvantage. Excellent on par with any diesel technology. Bluemotion eat your heart out. Hyundai doesn’t need fancy badging like vw. No stop/start so no imagine if Hyundai install all this fuel saving techniques, it would be most frugal diesel in 1.6 range

    • October 7, 2015 at 8:13 am — Reply

      To be fair most of the carmakers have the same tech, so another modern diesel with a DSG gearbox could be expected to do as well as the i30. We might get a few together and see which one fares best…

  2. petey53
    October 12, 2015 at 7:29 pm — Reply

    Actually the Prius c has fewer moving parts and is more reliable than a Hyundai turbo-diesel. It has no separate starter motor or alternator — components that often fail in older cars. Its elegant electronic CVT is simple and very reliable. Batteries usually last the life of the car. It may take 140000 km to save its price premium with lower fuel costs, but the car can easily last twice that distance, so there would be a saving if you keep the car. Plus it is significantly cleaner to operate.

    • October 13, 2015 at 8:20 am — Reply

      I don’t think reliability will be a problem in either case. Note: for these two cars the Prius warranty is 3 years, the i30 is 5.

      If you run the Prius long enough there will be a saving (provided that you drive in a way which allows the hybrid to work). 140,000 @ 20k km/year is 7 years, so quite a long time. That doesn’t allow for the fact that you’ve spent extra capital cost. Also, the i30 is bigger than the Prius c so not a direct comparison but as we had the cars to hand we did the test.

      The major advantage is the cleanliness, and in city crawling life would be so much better for everyone if all cars were such hybrids. However, that’s not a financial justification to the hip pocket of the buyer, and therefore many buyers will not care.

      • petey53
        October 13, 2015 at 8:34 pm — Reply

        Here’s another way to look at the extra cost. If you fully financed both vehicles for 7 yrs at 7%, the Prius c payments would be $432 more per year than the i30. But you say it saves you $400/yr in fuel. So it seems to me it’s pretty much a wash and if you drive more than 20000km per year or fuel prices rise, the Prius c is the cost winner, even over 7 yrs — after that you keep on saving. I agree the i30 is a bit bigger, but the Prius c still beats it in rear legroom so, for 4, it should be just as comfortable (I have never sat in either car).

        • October 13, 2015 at 9:14 pm — Reply

          Possibly….but that does assume 20,000km per year which for a city car is a lot. There’s also resale too. The i30 has more room than the Prius c all round. A better comparison would be Yaris to Prius c, both the same size, but the Yaris is a *lot* cheaper. There are definitely cost scenarios where a hybrid makes sense, but it’s not in every case.

          Exactly the same applies to diesel. The typical extra premium paid for diesel in small cars is not generally worth it.

          • petey53
            October 14, 2015 at 11:06 am

            The 20000km/yr assumption was yours. It is less than I drive. For a one-car family doing commuting and some inter-city trips it seems reasonable. For purely urban driving, the break even point is only 69500km, or less than 5 years at 15,000km/yr. If both cars are fully financed for 7yrs at 7% the Prius c would save $86 every year vs the i30 until paid off, then $520/yr after that. We don’t know the resale value of a 5 yr old Prius c yet but I suspect it will be very good, probably better than a dirty diesel. Versus a Yaris, an urban driver would pay only $68/yr more in net payments for a Prius c and after paying it off would save $724/yr in fuel. Buy the car you want, but for many drivers, a Prius c can make good economic sense vs either a diesel or a conventional petrol car. Plus it scores very well on both the Australian greenhouse and air pollution ratings.

          • October 14, 2015 at 5:00 pm

            A Prius *may* make economic sense. It is by no means a definite and very dependent on not only mileage, but the types of miles. My 20,000km figure was quite generous as the latest stats are that Aussies drive 14,000km per year. I suspect for city cars that figure is even less. So for lots of urban driving a Prius may well make economic sense, otherwise it is unlikely. This is borne out by the extensive use of hybrids in the urba taxi industry which is exactly that use of high mileage, low-speed where hybrids are most cost-effective.

          • petey53
            October 14, 2015 at 6:00 pm

            I’m willing to leave the economic arguments at that. I do want, however, to correct the impression you leave that a Prius c is only beneficial in city driving. Its extra urban fuel usage still beats the auto diesel i30 handily (3.9 to 4.3 l/100km). Toyota’s Hybrid Synergy Drive does more than turn the engine off at stop lights and drive electrically at low speeds. The inclusion of an electric motor allows the Atkinson cycle petrol engine to be optimized for efficiency instead of power and torque. The CVT transmission allows a very high gear ratio at highway speeds and the electric motor can add torque when needed for passing. Taxi drivers appreciate the fuel efficiency but also the reliability and low maintenance of Toyota hybrids. I have 275,000 km on my Prius and I have never had to replace the brake pads, due to the regenerative braking. Rather than increasing the mechanical complexity with turbos and complex transmissions, Toyota adds reliable, maintenance-free electrical and electronic components. It’s a good design for a dependable, clean all-purpose vehicle.

          • October 14, 2015 at 7:22 pm

            Peter appreciate your experience and views, all comments of that nature are welcome.

            On test, we found the Prius not do do well in cruise. Its fuel consumption actually increased over the urban, whereas the i30 was the reverse. The figures you quote are from the Extra Urban cycle which actually includes a fair bit of stop/start and isn’t representative of a true cruise.

            The brake pads are interesting…I need to replace them on my Toyota 86 every few weeks. I can see how they would last longer on a Prius!

          • petey53
            October 14, 2015 at 8:07 pm

            I didn’t know that about the Australian test cycles. I’m in Canada. In my case I figure I saved about $1000/yr in fuel with my 2004 Prius compared to a 2004 Mazda 3. The Prius was much more expensive in Canada at that time but I have made up the difference. My friend’s Mazda 3 died on a busy highway in a dangerous situation. My Prius is going strong. I have even added a backup camera and parking sensors to it easily for under $100.

  3. October 13, 2015 at 8:23 am — Reply

    We will shortly post a comparison of hybrid vs non-hybrid costs to see how far you need to drive in order to pay back the additional purchase cost of a hybrid.

  4. Happyd00d
    February 20, 2017 at 4:39 pm — Reply

    I won’t mind either diesel or hybrid for money saving commute, there is a hidden cost on diesel cars that this article forgot to mention, which is a DPF, a very expensive wearing item in most(if not all) turbo diesel car. a diesel car will need one of this replace sooner or later depending on where it is driven. and a DPF cost thousands of dollars to replace.

  5. Horace
    August 12, 2017 at 6:51 am — Reply

    The regular Prius is great if you have babies. If you are out with your wife and kids and the babies are asleep, you can leave them in the car with an adult with the car on. The engine will only start up every once in a while to recharge the batteries, and the HVAC will be on the whole time. You can’t idle a car engine for longer than a couple minutes in some countries legally and even for those that are legal this will definitely kill your fuel consumption.

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Robert Pepper

Robert Pepper