I assume you're talking about the plug-in version and not the EV and fuel-cell variants.

Not sure where you're getting your numbers. Clarity plug-in has an electric range of 42 miles with a 105MPGe - basically equivalent to the volt.

MPG values for plug ins are computed based on the full range of the vehicle: (EV range + gas range) / (gallons burned). I know a few Volt owners, and they basically fill up a 3-6 times/year.

I can't find an mpg value for the clarity plug-in, just a range. However, plug-ins are basically full EV's with small batteries. You have the propulsion systems for both gas and electric but with an undersized battery. Their gasoline economy suffers as a result.

When you start factoring in the EV range and averaging that 105MPGe value, then your gas mpg goes WAY up.

The Prius Prime maintains the high mpg numbers by providing significantly less range - they basically took the Prius and upsized the battery as little as possible to give meh range.

 

Most articles on the PEHV state Honda is estimating ~42mpg on gasoline alone. We'll have to wait and see what the EPA says, of course.

I'll grab some sources when I get home.

 

Then that's an improvement over the Volt, which would also account for the fact that the Volt has 25% more EV range.

The reason is the same. The Accord hybrid is simply that... a hybrid. The PHEV Clarity has the ability to go 42 miles on EV only. That's going to cost you something in gasoline efficiency.

 

The fuel cell car has: a heavy fuel cell, heavy hydrogen tanks, a lithium battery pack (for power, fuel cell output isn't great... assume much larger than 1.3kwh since the car CANNOT accelerate without it) plus electric motor. Plus the tanks have to be a space-wasting cylindrical shape.

The Accord hybrid has a gas engine with electric motor, a shapey gas tank and a 1.3kw lithium battery.

I'd like to see the specs on a non-PHEV Clarity. I bet they'd be more similar to the Accord in weight, acceleration, and stowage.

The one I'm more excited about is the full-EV Clarity "TBA."

 

Honda Clarity EV and Plug-in Hybrid Debut in New York - Motor Trend

The expected volume-seller of the series, the Clarity PHEV, replaces the hydrogen fuel cell with a 181-hp gasoline engine and a lithium-ion battery pack. Honda claims the PHEV will travel 42 miles under pure electric power and achieve an estimated 42 mpg when the gasoline engine is running. The gasoline engine will mostly act as a generator, but will occasionally help drive the wheels when it’s more efficient to do so.

42mpg for the gasoline electric hybrid, vs 48 (combined) for the Accord hybrid. They use an almost identical drivetrain as I understand it, but the Clarity has a smaller displacement engine, which should be more efficient, all else being equal.


http://www.digitaltrends.com/cars/honda-clarity-plug-in-hybrid-news-specs-performance-range/

A 17kWh battery pack stores enough juice to power the sedan on its own for up to 42 miles. When electricity and gasoline join forces, the Clarity boasts a total driving range of over 330 miles and it returns an EPA-estimated 105 MPGe. Topping up the battery pack takes two and a half hours when the pack is plugged into a 240-volt charger.

105MPGe for the Clarity vs 115MPGe for the Accord PEHV. Even running on electricity alone the Accord is more efficient.


Honda Clarity EV and Plug-In Hybrid Unveiled at New York Auto Show - The Drive

As for the Clarity PHEV, numbers are fairly impressive. A lithium-ion battery pack works in tandem with a 181 horsepower gasoline engine to propel the car, and it can even drive 42 miles on electric power alone. With the gasoline engine in play, it can achieve 42 miles per gallon, a respectable figure for the segment. Total range is predicted to be about 330 miles, putting it right up there with conventional gas-powered cars. It can be charged to full power from empty in just 2.5 hours via a 240-volt, Level 2 charger.

I believe they got the horsepower numbers wrong, but here's another site claiming 42mpg.

~

So, the Clarity hybrid has similar cabin volume to the Accord, smaller cargo space, a larger battery (but weight has almost no effect on highway economy), a downsized engine (should be more efficient!) and gets 15% worse fuel economy on gasoline, and ~10% worse economy on electricity. Seems to me that simply upsizing the battery in the Accord would make a better car. Maybe they cut some corners to hit that price point?

 

You've introduced something new. We've been talking hybrid accord, not a plug in hybrid accord. It has a "whopping" 13 mile electric range.

 

Irrelevant. The Accord hybrid and PEHV have identical drivetrains. Would an Insight get better gas mileage if it has a 5 gallon gas tank? A 20 gallon tank?

Battery size has almost nothing to do with MPGe, or MPG on gasoline alone, aside from a bit of weight. These are measures of how far the car can go on a given unit of energy.

 

You might enjoy reading about how Honda's newer hybrid drivetrains work. These are not integrated motor assist, nor are they orbital gearsets like in the Prius or Volt.

Explaining the Honda Accord's Shrewdly Designed New Hybrid System – Tech Dept. – Car and Driver

Essentially, the Clarity and Accord hybrid are both EVs, with a gasoline engine (or fuel cell) generator that produces electricity for the electric motor when either the battery gets too low, or when the demands of the motor are greater than the battery can output. In the hybrids, Honda also put in a fixed (one-speed) gear to allow the engine to connect directly to the wheels between certain speeds on the highway, to avoid the losses of mechanical -> electric -> mechanical conversion. But outside of this, the electric motor is the only thing attached to the wheels.

EDIT: You're right of course about drivetrain management, but again what I'm wondering is how Honda managed to lose 6mpg in a car of similar size when both are being run on gasoline alone, when the Clarity is supposed to be more aerodynamic, and has a smaller displacement engine.

 

Thanks for the clarification. That makes a lot more sense, and I should have figured that bit out - the electric puts out all its power down low when the atkinson is sucking wind, and it has far less oomph at peak ICE output speeds.

The 600# increase in weight and smaller ICE are absolutely going to impact city driving adversely. How do the highway ratings compare? I would expect the clarity to be about the same or a little better.

 

It's early to tell. The Clarity hybrid hasn't hit the roads yet, so we only have this ambiguous "predicted 42 (combined?)" from Honda. My experience with my Insight is that weight isn't that big a deal though, especially for a hybrid, and that weight figure I found was for the fuel cell version. The hybrid may (or may not) be lighter.

 

It's early to tell. The Clarity hybrid hasn't hit the roads yet, so we only have this ambiguous "predicted 42 (combined?)" from Honda. My experience with my Insight is that weight isn't that big a deal though, especially for a hybrid, and that weight figure I found was for the fuel cell version. The hybrid may (or may not) be lighter.

Not sure how you figure that. The Insight is one of the lightest cars ever made and plays a key role in its economy. Industry/fleet-wide weight reductions have been key to fleet mpg improvements.

A common recommendation for mpg improvement is to ensure you're not carrying around a bunch of unnecessary junk in the car - because the extra weight hurts your mileage.

The clarity requires 17% more energy to accelerate it to a given speed than the Accord. That is going adversely affect economy no matter how you look at it or whether that energy comes from electric assist or gas.

A 600# weight reduction (13%) of the F-150 when they switched to an aluminum body resulted in an 11% improvement in the combined fuel economy rating. It follows a 17% increase in weight would have a substantial fuel economy penalty.

 

I suppose we'll have to see how heavy the Clarity hybrid ends up, then - that figure is still unknown.

I've moved pretty significant amounts of weight in my car and have found that it's only when I need to keep the hatch open that there's any noticeable drop in highway economy. E.g. pulling an empty trailer vs a trailer with ~1000lbs of tools and junk in it, my economy is within margin of error, and in the city the difference is also very little so long as I'm slowing down mostly using regenerative braking.

 

I agree it doesn't quite add up. Let's compare 2014 Accord Hybrid vs 2014 Accord Plug-in vs 2017 Accord Hybrid:

https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=34395&id=33557&id=37825

It's 2014 hybrid: 47mpg, 2014 plug-in: 46mpg, 2017 hybrid: 48mpg combined. Granted 2014 plug-in has a much smaller battery pack, but 42mpg for clarity seems to fall a bit short even with the bigger heavier battery pack. I was certainly hoping for better as well.