At 70mph the Hyundai Ioniq travels 25%  further than a Nissan Leaf on a unit of electricity…

I had the opportunity to compare my Leaf (Mk1.5, 2013) to our new Hyundai Ioniq today. In an attempt to make it a reasonably accurate test, we used 2 different speeds, 50 and 70mph, with a GPS speedometer to remove any speedometer inaccuracy. Because of traffic we had to use two different roads; an A-road for 50mph and a motorway for 70mph. Both had average traffic levels and it wasn’t easy to keep a constant speed. We kept away from other vehicles as much as possible, to try and avoid any slipstreaming benefits. We did runs on the same road in two directions, to remove the effects of hills and possibly wind, although both roads are quite level. We used no heating and cruise control to keep the speed constant. The weather was damp roads, a temperature of 7 to 12C. All of what follows assumes these conditions. Add in a headwind or lower temperatures and the range will fall, warmer weather will improve range, up to a point.

Two of the aero measures on the Ioniq: slots direct a jet of air around the front wheel. The small front grille opening is controlled by a flap (behind it) to open only when necessary.

Speedometer accuracy

With 16″ Goodyear tyres about one-third worn, the Leaf speedo was just over 10% fast. 56mph indicated is actually 50mph GPS, and 77 indicated is 69-70mph GPS. Not too surprising, the Leaf does have a reputation here!

The Ioniq was on new tyres and was around 5% fast. 54 indicated was actually 50mph GPS; 74 indicated was 70mph GPS.


Averaging over a few miles and in two directions, these are the figures reported by the cars computers:

Leaf (2017 measurements, no heating)

50mph (actual) = 5.0 miles/kWh

70mph (actual) = 3.25 miles/kWh

Ioniq (2018 measurements, with heating)

50mph (actual) = 6 miles/kWh

70mph (actual) = 4.2 miles/kWh

These figures are in line with the EPA highway test results, which rated the Ioniq as 122mpge and the Leaf 100mpge, a 22% difference. The EPA highway test peaks at only 60mph, and averages 48mph. So I’d expect any differences between the cars to be a bit less in the EPA tests, than at a steady 70mph.

The efficiency of the Ioniq at 70mph is impressive and means you can realistically cruise at this speed for 100 miles if traffic permits, or more in summer, with a 15 mile buffer. Realistically I find it’s almost impossible to average a speed of more than 64mph however, which means the real range is slightly higher.


What does this mean in day-to-day driving?

For equal economy, at a real 70mph in the Ioniq, the Leaf needs to travel at about 60mph. That’s 15 minutes quicker over 100 miles (completely theoretical- as a Leaf 24 battery isn’t big enough to do 100 miles at any realistic speed!)

In terms of range, any Leaf driver will have noticed the benefit in slowing down, to eke out more miles from the battery. I’d certainly rate the Leaf as a great day-to-day car and commuter, but not a motorway car. On the motorway at 70 that would give my 5 year old car (now with 18.5kWh) a range of  barely 60 miles. The Ioniq, on the other hand is quite happy on the motorway and even in winter will do 110 miles. Does any Leaf driver really sit on the motorway at 77mph indicated though?

The comparison with a Leaf 30 is interesting too; at true 70mph, the Leaf30 has up to 90 miles range, the Ioniq 120 miles.

The Leaf figures apply to all Leafs including the 2018 model; as battery sizes and weights increase the efficiency will drop slightly but in theory should only be noticeable in hilly or stop-start driving.

It’s interesting that the difference in efficiency I found roughly matches the relative sizes of the batteries fitted to the current Ioniq 28 (~28kWh useable) and the new Leaf 40 (probably ~37kWh useable).

The much anticipated 60kWh Leaf, assuming similar aerodynamics to the existing cars, could have a 60*3.25 = 195 mile range. The lower efficiency compared with a Model 3, or maybe a larger battery Ioniq, will be even more obvious. Whether people will pay for a car that’s still a sub-200 mile motorway car is yet to be seen. Ultimately supply plays a big part- and that includes batteries as well as cars.

And the Kona? Well, the EPA rate the Kona as 108mpge compared to the Ioniq’s 122mpge, that’s a 13% advantage, and a little more advantage at speeds as high as 70mph since the test only includes speeds up to 60mph.

All this makes me realise that we need a new metric for electric cars, battery size alone doesn’t tell you enough.

Summer 2019 – motorway efficiency revisited

I used a regular 20 mile route to estimate the real efficiency of the Ioniq at 70mph. In theory this is an easy test, drive 20 miles and take the speed and display miles/kWh. There are some significant errors however, and I’ve tried to capture these. I used no heating or air-conditioning, or headlights. Although there are hills, the start and end points are at a similar elevation.

Run 1: westerly, with tailwind, 24degC, average 60mph (due to traffic), 5.3 miles/kWh displayed

Run 2: easterly, into 15mph headwind, 13degC average 70mph, 4.4 miles/kWh displayed

Errors? I checked the 70mph figure using the time it took for the trip, and the displayed battery percentages and hence the percentage used. 14% of battery (81 to 67%) which corresponds to 4.2kWh and a higher efficiency of 4.7miles/kWh. That’s an 8% higher figure, which could be partly accounted for by the worn tyres. Even when new, I noticed the speedo was reading 5% high.

Either way, you’ll get more than 4 miles/kWh at a real 70mph even into a headwind.

3 thoughts on “Leaf vs Ioniq energy efficiency real-world test

  1. Good report Si, onward and upward it seems. I wonder if electric will eventually suffer the same seasonal price hike that fossil fuels do. Dad


    1. I believe diesel is more expensive in winter because of heating oil demand. No sign at the moment that there’s any seasonal variation in electricity. However we can expect pricing to vary in future depending on time of day, and eventually the effect of weather on renewable electricity generation. For now I’m happy with “fuel” costs at about a tenth of a 40mpg ICE car!


  2. Yes, that’s the first thing you notice when driving the Ioniq after the mk1 LEAF – miles per kWh. The Ioniq is far more efficient. Then there is the increase in interior space, lots of leg room and a huge boot / trunk on the Ioniq.


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