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Toyota’s Prius has been known to be the most fuel-efficient vehicle in the U.S. market for years and the automaker has kept that title with their 2016 Prius Eco. Well now it’s time for the Prius to step down because the Hyundai Ioniq hybrid’s Blue model is now the most fuel-efficient hybrid in the United States with a combined rating of 58 mpg.

When CarAndDriver asked Ioniq project members how they achieved this feat, they were directed towards a few design key points.

The engine runs lean and has the same thermal efficiency as the Prius at 40%. What pushes the Ioniq ahead is the engine’s long 1.35 stroke-to-bore ratio which keeps thermal mass to a minimum. To increase combustion efficiency, a 2900-psi direct-injection system.

Then there’s the battery portion of the hybrid and Hyundai’s battery-control strategy. They didn’t say much regarding this matter aside from claiming that their control algorithm is better than a competitors even if the same lithium-ion batteries are used.

Very little torque lost in translation thanks to the Ioniq’s dual-clutch automatic which has a torque-transfer efficiency of 95.7%, thus providing owners with better fuel economy and a closer connection to the powertrain.

Aerodynamics plays a large part as drag can increase a vehicle’s fuel consumption. All Ioniqs have a 0.24 coefficient of drag thanks to underbody shielding and brake calipers pistons retracts slightly. Hybrid and plug-in-hybrid models have additional grille shutters and the Blue models are equipped with special aero-optimized wheels.

Weight reduction is another way to increase fuel economy and the Ioniq lineup was put on a diet of aluminum hood, liftgate, and suspension components along with 54% high-strength steel for the core body structure.

Combined, these features managed to deliver the most fuel-efficient Ioniq the United States has ever seen.
 

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Thanks for this. I read the linked Car and Driver blog. Mentioned was that the US Ioniq Blue model had a lighter weight dash pad, trunk mat, and carpet. If the same in European cars, that might explain some of the complaints of road noise as well as the mixed reports.
 

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It's good to see this, and the blog is a good read. I hope this isn't bait for people to start trashing each other's cars. The only thing remaining to address is reliability, and only time will tell.
 

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Even though it sounds very optimistic, I do not think that an Ioniq would beat the latest Prius in MPG's nor in the comfort round (sound proofing). But, somebody would need to do a fair an objective test.
 

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I acknowledge that it is only natural to compare the new Ioniq to the Prius, even Hyundai has made that point .... but I'd like to see the day when the Ioniq stands or falls on its own. In my mind, it is not a comparison between the two vehicles because I will not own a Prius until there are serious changes in the exterior and interior design. I suppose that will be another four years?

I have been reading and watching for article about the Ioniq for over a year now. I have my disappointments in what I have read for sure. I do not like the color choices; I do not like the fact that the 15" wheels are available only on the basic vehicle, that also has the least insulation; I'm really hesitant about the belt driven starter............

But I like the looks (from photographs, not having actually seen one); I like the transmission (not actually having driven one); and I like the warranty. My problem is, with Prius "off the table" and questions about the Ioniq ..... I have nothing else on my short-list. I'm not interested in any GM car; I can't afford a BMW or Tesla; and dislike the Leaf's looks even more than the Prius.
 

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Once again, Stirfelt, you've penned a masterful summary of my own feelings, with the exception that, if I'm EVER able to pull the trigger on an Ioniq, I plan to go for the bigger wheels regardless of mileage and ride penalties. Also, the belt-driven starter (is that definitively known? I thought there was still conflicting information out there) doesn't bother me.

Great summary, though!
 

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Even though it sounds very optimistic, I do not think that an Ioniq would beat the latest Prius in MPG's nor in the comfort round (sound proofing). But, somebody would need to do a fair an objective test.
Within limits, those objective tests have been done by reviewers in Europe and the Prius does better. I posted a video of such a test from the Netherlands (and posted the numbers) a few days ago in the review thread.
 

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Also, the belt-driven starter (is that definitively known? I thought there was still conflicting information out there) doesn't bother me.
Yes, it is. If you look at pictures of the engine, you can see it. Links have been posted in other threads about the different kinds of "power split" designs. I've read them, if not completely understood them, but both designs have advantages and disadvantages.

In terms of parasitic transmission losses, the dual clutch beats the Prius's planetary gear system, on the highway anyway.

One thing is a complete flip of highway versus local mpg. The Prius mpg rating shows better mpg around town than highway, and the Ioniq/Niro is just the opposite. So as a general principal, the Prius design (and the many similar models from Ford and Toyota) does relatively better around town, and long distance drivers do better with the Ioniq hybrid design.

That is not saying that one design is better than another, or that the Ioniq does better in real life against the Prius, just that both designs are valid and not inferior when specific use is considered.
 

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Yeah, the reason the Prius is rated better in urban as opposed to highway driving, as far as I know, is because in stop-and-go traffic you get more energy back through the regenerative braking. I can observe that effect in my own Prius, which usually indicates in the mid- to high-50 MPG range when I'm driving in town but in the mid- to high-40s on the Interstates.
 

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Both designs rely heavily on regenerative braking for their mileage gains over non-hybrids for both urban and highway driving. It is more that the belt driven engine starts do worse in urban settings with efficiency losses from the belt operation versus a no-belt start in the Prius.
 

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Urrr, I'm not sure you are correct yticolev. From what I understand .... the Ioniq does not have regen brakes (at least in the hybrid). One advantage is the brakes on the Ioniq feel like the brakes on non-hybrid vehicle, whereas the brakes on the Prius do not .... like when braking and encounter a slick spot, or a pot-hole. The first time it occurred to me it scared me that the brakes were failing.

sundayt you are very complementary, and I appreciate that. Actually, I am not sure where I stand on the 15 vs 17 inch tires. Never having seen the Ioniq, appearances may change my mind. Actually, I read that the plug-in hybrid has 16 inch tires. That might be a compromise.

The belt driven starter worries me. I have read that the belt is a maintenance item that must be replaced at regular intervals. The belt has been described as thin. How thin? I owned a car with a belt driven overhead cam and it was never a problem. I may well be concerned about nothing significant at all, but the ICE on a hybrid starts numerous times in each outing.

I am hoping that my interest in the real Ioniq will support my interest based on photographs. Where we live will favor the highway advantage of the Ioniq. Very little stop and go driving; lots of 35-55 mph cruising. I was able to achieve mid 50's mpg in my 2010 Prius with regularity (summer and more ideal conditions).

One final point ... several writers fault the Ioniq for 10 plus seconds from 0-62 mph. I recall in 1955 when Chevrolet introduced the V-8 engine. The magazines touted that it would accelerate from 0-60 mph in 10 seconds flat. WOW. The Ioniq video's and writers frequently speak about how good the performance fels with the 6 speed transmission vs. CVT. Hopefully that will be my experience when I actually get to drive one.

A question that I have that will need to be resolved: I owned an Acura. V8, plenty of horsepower. Driving with a steady foot along the interstate, it would downshift at every slight change in elevation (where crossing another highway or railroad). It aggravated me that it would not go over the slightest incline without downshifting. I own a straight shift, and drop down to a lower gear only when going up a mountain.

Time will tell.
 

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We are all learning. But all hybrids capture energy from braking.

The belt is very thin (and very wide). I've read that there is no scheduled replacement and that the expected life is 60 to 80 thousand miles. The photo I saw looks like it is an external belt, which would make it easy to do a visual inspection whenever the mood strikes, and likely an easy home replacement as well (you will probably have to get a tow with no way to start the engine though).

If your Acura had a 6 gears or more, it should downshift on smaller uphills. The more gears you have in an automatic, the easier they can design in better mileage by keeping the engine in the most efficient (or powerful if called for) gear. These gearboxes includes a much higher final drive ratio (think overdrive) that would be silly in a manual. If your manual had such a ratio, you would complain about having to downshift for the smallest inclines, and drop a couple gears for the bigger inclines. Since it is an automatic and a powerful car at that, most people wouldn't notice the gear shifts if they were smooth.

I have a large 670 cc Honda motorcycle that was designed for high mileage. And in fact, my three year average mpg is exactly 68 mpg (US) riding briskly. It has a 6 speed manual transmission and the last one is an overdrive. While it is slow compared to fast modern 650 bikes, it is much stronger than the 650 Triumph I rode in the 1970s. But if I have to make a fast pass on a two lane at 50 mph, I have to drop two, or even three gears to make a safe pass.

I prefer manuals (all I've ever owned to date) and it is frustrating to think about purchasing a fun car, like a Honda Fit, in a manual and have the EPA listed highway mpg be lower than the optional automatic. I look at those ratings and they don't make sense directly as manuals have lower transmission losses than automatics (not including dual clutch automatics like on the Ioniq/Niro). But a look at the specifications reveals that the auto has a higher drive ratio than the automatic, thus increasing highway mpg more than the transmission inefficiency. Some of this is marketing, the market for manual transmission cars is already so small in America, and they think a manual that requires so much downshifting will be even less popular. So they make manuals with top gears that don't need to be downshifted on slight inclines. Personally, I'd love a car like that that requires more shifting. Kind of the same kind of fun that driving slow cars (think original Miata or MGs) fast brings.
 

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Urrr, I'm not sure you are correct yticolev. From what I understand .... the Ioniq does not have regen brakes (at least in the hybrid).
I don't believe that is accurate. My understanding is the Ioniq hybrid does have regen braking. Emphasis on the BRAKING. Where it fails is that it does not recapture energy from coasting momentum.
 

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DaveAz,

I don't believe that is accurate. My understanding is the Ioniq hybrid does have regen braking. Emphasis on the BRAKING. Where it fails is that it does not recapture energy from coasting momentum.
I believe you're correct. From what I've read, the Ioniq Hybrid lacks the "B" setting that you can engage in the Prius to get some engine braking. Regenerative braking when applying the brake pedal, in which some electrical energy goes back to the battery, IS, I believe, a feature of both cars.
 

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But I like the looks (from photographs, not having actually seen one); I like the transmission (not actually having driven one); and I like the warranty. My problem is, with Prius "off the table" and questions about the Ioniq ..... I have nothing else on my short-list. I'm not interested in any GM car; I can't afford a BMW or Tesla; and dislike the Leaf's looks even more than the Prius.
Although not quite the MPG rating of either the Ionic or Prius, you might consider the 2017 Honda Accord Hybrid. From reading, it seems to have its act together with the drivetrain, and at least to me, the styling bests Ionic or Prius. This is the way I have decided to go.
 

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I don't believe that is accurate. My understanding is the Ioniq hybrid does have regen braking. Emphasis on the BRAKING. Where it fails is that it does not recapture energy from coasting momentum.
Not sure that is a fail, but I would prefer one pedal driving. If you want to slow down instead of coasting, just touch the brake pedal. You have to go a fair distance before the hydraulic brakes kick in. You should enjoy the EV model with paddle set regen levels. That should make one pedal driving easy.

Interesting about coasting. Perhaps some actual owners can chime in here but several reviewers of the hybrid note that manual downshifts increase the engine note, but do not slow the car. I wonder if the Ioniq/Nia have a freewheeling function without a power load, a la some 1960 Saabs (certainly the two strokes). That will make them feel different from other cars for sure.
 

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jemanner,

I looked at a 2016 Accord Hybrid last year, and the deal-breaking feature from my perspective is that the Hybrid battery made a huge hump in the cargo area floor. I assume the '17s are the same.
 

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jemanner,

I looked at a 2016 Accord Hybrid last year, and the deal-breaking feature from my perspective is that the Hybrid battery made a huge hump in the cargo area floor. I assume the '17s are the same.
As I understand it, Honda did not make a Accord Hybrid in 2016, so you may have looked at a 2015 model year. However, yes, the battery does have a hump in the cargo area, although I believe it has been minimized from 2015. It is the drivetrain which intrigues me, completely redesigned from prior years, with essentially no transmission. I haven't been able to look close enough to see if there are any drive belts. I'm hoping it is a beltless engine, as it is known the water pump and A/C compressor are both electric driven. What I really like is the conventional interior with good headroom for the rear seat passengers, and not some crazy cockpit design as in the Prius. Oh, and don't know how long it will last, but the Accord Hybrid is made in Japan, a big plus in my opinion. (Have a 2005 Toyota 4Runner made in Japan, and it has been flawless).
 
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