Best (reasonable) highway speed for fuel economy.

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Timothy

Timothy

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We are in NC where gasoline has disappeared. We're headed for the mountains on Saturday, 212 miles. Our Clarity is full of gas. I filled it before the current crisis, just for this trip. We can charge at the place we are staying and we'll keep our day trips under 50 miles. I never thought that this would be one of the benefits of owning a Clarity. I have even found charging stations on the way home in case we find no gas in the next week. I believe we can make it back home, though slowly.

My question is, what is the sweet spot for highway fuel economy? Also, I believe there is a highway speed at which the ICE will directly power the wheels (which I would assume is quite efficient). What is that speed range?

Thanks in advance for your help with this. When we first bought the Clarity I think I checked this board every other day and found some great info.
 
I believe the “gear icon” showing engine drive mode will come on between 45 and 70 mph when certain conditions are met.

Best speed on the highway for fuel efficiency is the slowest you can safely maintain. I’d guess the slowest before you start causing problems for traffic is around 55 mph. Anything above that will decrease range and fuel economy in a geometrically increasing manner.
 
My wife recently drove the car on a lengthy trip at speeds generally between 60-65mph and achieved ~47mpg in HV. She doesn’t concern herself with the functions of the car, so there’s no telling how much of the drive may have been in Engine Drive Mode/Direct Drive.

EDM will engage at speeds above 45mph. I have seen it remain engaged up to 90mph.
 
I normally drive at 78 mph with ICE directly powering the wheels (Engine Drive Mode - EDM).

I get about 40 mpg in HV mode. I assume it is that low because of my 'high' speed, but I am willing to pay for gas to avoid drive time. Most of my driving is up and down hills in upstate New York.
 
ClarityBill said:
I normally drive at 78 mph with ICE directly powering the wheels (Engine Drive Mode - EDM).

I get about 40 mpg in HV mode. I assume it is that low because of my 'high' speed, but I am willing to pay for gas to avoid drive time. Most of my driving is up and down hills in upstate New York.
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I am also looking to save time. If gas does not become available in NC over the next week, I will be stopping to charge on the way home.
 
ClarityBill said:
I normally drive at 78 mph with ICE directly powering the wheels (Engine Drive Mode - EDM).

I get about 40 mpg in HV mode. I assume it is that low because of my 'high' speed, but I am willing to pay for gas to avoid drive time. Most of my driving is up and down hills in upstate New York.
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We’ve had similar results. Aerodynamic resistance is the main culprit. On the same trip mentioned previously, at speeds of 75-80mph, the car calculated ~40mpg. Actual was ~36mpg. Others have noted that the computer calculation is about 10% more optimistic than reality. EDM engaged and disengaged as conditions changed. It may have been engaged ~50% of the time.
 
Landshark said:
We’ve had similar results. Aerodynamic resistance is the main culprit. On the same trip mentioned previously, at speeds of 75-80mph, the car calculated ~40mpg. Actual was ~36mpg. Others have noted that the computer calculation is about 10% more optimistic than reality. EDM engaged and disengaged as conditions changed. It may have been engaged ~50% of the time.
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My Subaru Outback gets less than 20 mpg at those speeds. At 55 mph, I can get 32-34 mpg in the Subie. It rides high so forget about aerodynamics. The Clarity is super aerodynamic hence the bigger gap in mileage at higher speeds. The Outback is also a smaller car, both shorter and more narrow. BTW, 0-60 in the Outback is just under 10 seconds while it's about 7.6 seconds in the Clarity so I don't get better acceleration for the poor gas mileage.
 
Timothy said:
We are in NC where gasoline has disappeared. We're headed for the mountains on Saturday, 212 miles. Our Clarity is full of gas. I filled it before the current crisis, just for this trip. We can charge at the place we are staying and we'll keep our day trips under 50 miles. I never thought that this would be one of the benefits of owning a Clarity. I have even found charging stations on the way home in case we find no gas in the next week. I believe we can make it back home, though slowly.

My question is, what is the sweet spot for highway fuel economy? Also, I believe there is a highway speed at which the ICE will directly power the wheels (which I would assume is quite efficient). What is that speed range?

Thanks in advance for your help with this. When we first bought the Clarity I think I checked this board every other day and found some great info.
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The beat way to really track your current efficiency is to moniter the current power level (the tach looking dial) and strive to keep it below 25 percent, and even lower when possible. I recently did an ev range test and got the factory estimate of 47 miles before gas turned on. I was driving at 60 to 64 mph but was mo re e focused on keeping the power (discharge) level below 25 percent. When you do use hv mode try to run in with gear symbol. Be sure to push the economy mode as well.
 
PHEV Newbie said:
My Subaru Outback gets less than 20 mpg at those speeds. At 55 mph, I can get 32-34 mpg in the Subie. It rides high so forget about aerodynamics. The Clarity is super aerodynamic hence the bigger gap in mileage at higher speeds. The Outback is also a smaller car, both shorter and more narrow. BTW, 0-60 in the Outback is just under 10 seconds while it's about 7.6 seconds in the Clarity so I don't get better acceleration for the poor gas mileage.
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An Outback is a completely different vehicle. It’s AWD and has a 2.5l or 3.0l engine that runs all the time. I had a WRX for a few years and the wife drove a Crosstrek for 5 years.

For the most part, cars, in my experience, tend to get close to the stated mileage when driven in a reasonable fashion. I’m a bit disappointed that the Clarity only gets ~36mpg when cruise is set to 80mph and there are some portions that are driven slower due to traffic. My 2005 Jetta diesel managed 36mpg at 80mph and only increased to 38-40mpg at speeds of 60-65mph. Even our 5500lb 4x4 Grand Cherokee diesel gets 27mpg at 80mph and 30mpg at 65mph.

Granted, the Clarity gets better than stated mileage at 60-65, but is takes a more significant hit than any other vehicle I’ve driven when traveling at 80mph.
 
I thought I'd share my experience too. Clarity is an odd beast to me because there are a few counter-intuitive things. For example, the electric motor is the stronger, so for limited hills (i.e. not a full on mountain), I save EV charge and engage it for the 'tough hill.' The car seems to like stop and go traffic due to regen. Clarity also doesn't get an advantage on flat ground going at like 80Mph (as mentioned). Under this scenario, there's basically no opportunity for regen, just the cost of keeping the momentum.

Anyway, mountains are a favorite for me. I recently drove from Eugene to Sisters Oregon. Mountain pass about 4000 feet. The car in hybrid mode seems to always get 40mpg for me, and once I hit the top and come down, I get good regeneration. I manage this both ways capturing as much regen as possible on the down sides. Anyway, my recent trip I got 60 actual miles per gallon (not measured by the car, but just the number of miles divided by gallons of gas used measured at the pump).

Also I specifically remember a ski trip going up in hybrid mode, a little low on fuel (willamette pass). I figured in my head that while HV miles ran low, the trip home is very substantially down-hill. And, once at the valley floor there are abundant chances to get gas. So I took my chances, arriving at the ski area with low fuel. Sure enough, I regenerated EV range on the way down, and made it all the way home without needing to stop for gas. The regen down hill is amazing. The obvious bit is as you go down a say 20 mile long hill, you get X miles of EV range, but the cool part too is that the 20 miles cost you nothing. I just mean in addition to gaining range, your also simultaneously covering ground. Maybe that's a bit obvious but it continues to amaze me.
 
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Dan Albrich said:
The regen down hill is amazing. The obvious bit is as you go down a say 20 mile long hill, you get X miles of EV range, but the cool part too is that the 20 miles cost you nothing. I just mean in addition to gaining range, your also simultaneously covering ground. Maybe that's a bit obvious but it continues to amaze me.
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And now, suddenly, going down hills in an ICE vehicle just seems like SUCH A WASTE!!!
 
Dan Albrich said:
Sure enough, I regenerated EV range on the way down, and made it all the way home without needing to stop for gas. The regen down hill is amazing. The obvious bit is as you go down a say 20 mile long hill, you get X miles of EV range, but the cool part too is that the 20 miles cost you nothing.
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Technically, the 20 miles downhill, cost you all the energy it took to get up the hill. You just paid in advance. We’ll never be able to recapture 100% of that energy.

The EV range estimate after a long descent is a deceptive beast. I’ve reached the top of Siskiyou summit with EV range in the mid-40’s. Switching out of HV for the descent, EV range showed 80 upon reaching Ashland. Clearly, an inaccurate reading. If memory serves, the battery gauge increased by one bar, which is a more accurate measure of the state of charge.

Yes, the car travelled the ~8 miles without using gas or electricity and actually recovered some of the energy used to ascend the mountain. I’d estimate the actual gain in EV range at ~3 miles, based on the one bar rise of the battery gauge.
 
Keeping the math simple some deliberate rounding and convenient assumptions below.

Let’s assume you do need to get home using electric. Charging from empty will take at least 2 hours. The traction batter holds about 50 miles or about an hour’s worth of highway driving. So every 1 hour of electric driving needs another 2 hours of charging. If you stop 4 times to charge you will add 8 hours to your already 4 hour 212 mile trip for a total of 12 hours.

Fortunately you do not need to find much gas to make it home thanks to the good gas mileage of the Clarity.
 
Landshark said:
Technically, the 20 miles downhill, cost you all the energy it took to get up the hill. You just paid in advance. We’ll never be able to recapture 100% of that energy.

The EV range estimate after a long descent is a deceptive beast. I’ve reached the top of Siskiyou summit with EV range in the mid-40’s. Switching out of HV for the descent, EV range showed 80 upon reaching Ashland. Clearly, an inaccurate reading. If memory serves, the battery gauge increased by one bar, which is a more accurate measure of the state of charge.

Yes, the car travelled the ~8 miles without using gas or electricity and actually recovered some of the energy used to ascend the mountain. I’d estimate the actual gain in EV range at ~3 miles, based on the one bar rise of the battery gauge.
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As you know the reason for low ev range gain on your decent was because there was no room to store it with your battery almost full. My clarity is too smart to allow me to reach the top of the 5k ft mountain i climb. In hv mode it will use a moderate ammout (about 3 lines) in the climb. So its best to use some ev range climbing to make room for regeneration in the decent.
 
neal adkins said:
As you know the reason for low ev range gain on your decent was because there was no room to store it with your battery almost full. My clarity is too smart to allow me to reach the top of the 5k ft mountain i climb. In hv mode it will use a moderate ammout (about 3 lines) in the climb. So its best to use some ev range climbing to make room for regeneration in the decent.
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The EV range gain on the descent, as stated, was actually tremendous. From mid-40’s to 80. I’ve reported on this trip previously in another thread. It was the tail end of a single day, 700 mile trip with 3 fuel stops. The starting EV estimate at the beginning of the trip was 62 miles and the battery gauge had dropped 4 bars upon reaching the final summit.

I suspect that the BMS limits regenerative charging to something close to a 1C rate. So, the ~10 minutes of descending may have added ~2kWh’s of charge to the battery. I ballpark 1 bar at 1KWh, or ~3 miles Those are rough numbers. It is possible that the gauge was about to lose a 5th bar at the summit or that it was about to add a 2nd bar at the bottom. Being down 4 bars isn’t nearly full in my book, and we know that the car only dumps excess regen under moderate to heavy braking after coming off a full charge.

Can you clarify what you mean by “my Clarity is too smart to let me reach the top of the 5K ft mountain climb”?
 
Landshark said:
Technically, the 20 miles downhill, cost you all the energy it took to get up the hill. You just paid in advance. We’ll never be able to recapture 100% of that energy.
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Totally true, but [except for the extra battery weight] you'd pay that fee on the way up with a gas car too, but the extra energy would just be transformed into heat in your brakes. At lease we can get some of it back.

Top tip. Buy your car from a dealer at altitude and live at low altitude. The dealer wont charge it, but at least you will get the initial charge on the way down for free (/s)
 
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