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My wife and I just got back from a 4,516 mile road trip in her 2018 Clarity Touring PHEV. We drove from Denver to DC to New Hampshire to Philadelphia and back to Denver. For anyone asking if the Clarity is a good car for road trips, the answer is definitely yes. It's not perfect but it's pretty close.

I drove the entire way, setting the adaptive cruise control (ACC) anywhere from speed limit plus 2 to plus 5. What I discovered is the following:
  • Eco mode will get you from zero to speed, eventually, but is really useful for reduced speed following in construction zones. As a side, last winter I discovered ECO mode is also useful in stop and go traffic in snow and ice conditions as it doesn't try to accelerate hard enough to break traction.
  • Normal mode will accelerate at a reasonable rate, being somewhere in the mid range for all vehicles for acceleration
  • Sport is useful in rolling hills on two lane roads - this is very definitely the smoothest mode on these roads.
The following distance controls are really nice. I use the longest distance in construction zones and on two lane roads where I want to give myself as much reaction time as possible. I use the shorter distances on the interstate. Just pay attention to your speed as the car is usually very smooth at deceleration when coming up behind someone.

The ACC has a serious flaw - it can't reliably see white vehicles during the daylight hours as in I was running about 50 feet behind a white semi trailer and the car didn't show it even saw the truck. I had a couple of other instances where the system didn't see a white SUV in front of me as well. All driving was done during daylight hours so night time wasn't the problem. Honda uses Lidar and two Teslas using Lidar have run into white vehicles now, one collision being into a white semi trailer on a sunny day. Lidar apparently cannot reliably see white vehicles.

In the owner's manual there is a warning that long high speed descents may overheat the ACC system. It handles them fine so I'm not sure where Honda tested this. I've done long high speed descents in the Colorado mountains and now in West Virginia and Pennsylvania. The ACC never overheated.

Lane keep assist (LKAS) is useful in two situations. The first is when dealing with a heavy cross wind, such as when crossing the eastern plains of Colorado and the entire state of Kansas. LKAS is also really useful on the curvy interstates in West Virginia. The car follows the highway reasonably closely making it feel much lighter to steer. It handles turns to the left better than to the right, so I'm assuming the solid white line is easier to follow than the dotted lane dividers and yellow solid lines on the left. When driving on a straight road without a cross wind LKAS and I fight over the steering wheel. Also, turn LKAS off in construction zones or any other narrow lane situations as it gets hopelessly confused and continuously triggers the lane departure warning. The other thing I dislike about LKAS is that it won't let you use the entire lane. For example, when passing wide load trucks you want to be as far to the left as you can and LKAS really dislikes this, even though you're still in the lane.

These two driving aids make driving the Clarity all day much less tiring when used properly, but neither is 100% reliable and both have a lot of work to become that reliable. Thus you still must pay attention to your driving.

While this car has the built in navigation, I used Google Maps and Android Auto for this purpose. I'm much more familiar with this system and it works in my 2017 Volt as well.

One of my biggest concerns was running out of battery under extended high load situations such at high speeds in a headwind or long steep grades. To avoid this I tried to remember to switch to HV mode as soon as I entered the highway. On the eastbound leg across Colorado and Kansas, I discovered HV mode doesn't regenerate power as fast as it's used and the car was very low on battery by the time I exited I-70 in Topeka. Anytime I was on slower highways (60 MPG or lower) I used HV Charge to get ready for the next high speed road with either anticipated head winds or serious climbs. HV Charge sucks down the gas significantly faster than HV or normal/no battery. As a result I recommend you don't use HV Charge unless you really have to. I also noticed the car is more aggressive in maintaining the low battery SOC buffer once it reaches two bars than while there is still battery left. I was able to charge in West Virginia, DC, and New Hampshire so I didn't drive the entire way on gas. The overall MPG for the trip was an estimated 42.8 MPG, assuming I used about 2.5 gallons from Limon, CO to home this afternoon.

My trip through Pennsylvania took us on secondary roads. In HV mode (no battery), this car absolutely can't find a gear at 35 MPG when driving through hills. In EV mode it has no noticeable gear searching but when the ICE is propelling the car it searches like crazy with the engine RPMs constantly going up and down.

Before we went I had the tires rotated and the oil changed. At 3100 miles into the trip I received an A 0 1 alert for oil change, chassis lubrication, tire rotation. I suspect it was really for the tire rotation as we couldn't reset the tire rotation when this were done. However, I refuse to believe the A 0 portion was anything other than Honda trying to lighten my wallet with an unnecessary oil change. I reset the maintenance minder at the next stop and reiterate how stupid, paternalistic, and wallet lightening this system is.

The Clarity PHEV has an 8 gallon tank with a roughly half gallon fill pipe. I can say this with > 99% certainty. The fill pipe for most sedans is about half a gallon so I'm assuming the Clarity is the same. That extra gallon weighs about 7 lbs and Honda wouldn't be the first car company to artificially lower the size of the gas tank to reduce weight, thereby increasing the EPA City MPG number for marketing purposes. It's easy to reduce tank size by simply using a longer than normal shroud on the fuel pumps main air vent, thereby preventing air from quickly escaping up the fill pipe. (We know for a fact that Chevrolet did this with the 2011-2016 Cruze ECO Manual to reduce a 15 gallon tank to 12 gallons - the tank part numbers was identical to all other gas Cruze trims and a CruzeTalk member who replaced his fuel pump discovered the shroud difference.) I had several fill ups where the total gallons of gas in the tank was close to 8 gallons and a couple where it was over 8 gallons.

Finally, there's a special place in hell for whoever designed the trunk. Their punishment will be to fit luggage into the trunk, just to have it all disappear and another set appear; sort of like Sisyphus from Greek mythology. It's impossible to utilize the full trunk capacity without using lawn bags full of dirty clothes.
 

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My wife and I just got back from a 4,516 mile road trip in her 2018 Clarity Touring PHEV….

My trip through Pennsylvania took us on secondary roads. In HV mode (no battery), this car absolutely can't find a gear at 35 MPG when driving through hills. In EV mode it has no noticeable gear searching but when the ICE is propelling the car it searches like crazy with the engine RPMs constantly going up and down.
Just a clarification. The car isn’t “searching a gear” because there is no gear to search. It’s simply changing engine load/rpm to account for how much charge the battery/motor needs. Even if it seems like you’re running at a steady speed on a steady incline, the car may be seeing a need to dump more charge into the HV battery.
 

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Discussion Starter · #3 ·
Just a clarification. The car isn’t “searching a gear” because there is no gear to search. It’s simply changing engine load/rpm to account for how much charge the battery/motor needs. Even if it seems like you’re running at a steady speed on a steady incline, the car may be seeing a need to dump more charge into the HV battery.
The end result is exactly like driving any automatic transmission - the engine is revving up and down with no change in power to the wheels. All automatics have a speed where they do this. It appears the Clarity PHEV's speed is 35 mph.
 

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The end result is exactly like driving any automatic transmission - the engine is revving up and down with no change in power to the wheels. All automatics have a speed where they do this. It appears the Clarity PHEV's speed is 35 mph.
The effect you describe when driving an automatic transmission automobile is due to the fact that a gas engine doesn’t develop much torque at low rpm. It tries to stay at low rpm, however, when under low-load situations like driving steady state on a level road. Any little thing which causes an extra load to be imposed on the engine then causes the transmission to downshift to a lower gear to obtain the extra torque necessary to meet the load. A hybrid vehicle is much different, though. An electric motor has plenty of torque over a wide rpm range so there’s no need to shift gears with a transmission. However, the gas engine still runs to charge either the electric motor, the hybrid battery, or both. Being an internal combustion engine, it deals with the same problem of not developing as much torque and not being as efficient at low rpms. Therefore, the computer which controls the engine will make the choice at the appropriate times whether to speed up the rpms or slow down. The result may sound the same to you but the reason is different. The speeding up and slowing down of the ICE is more likely due to a certain defined hysteresis of charging the battery.
 

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The end result is exactly like driving any automatic transmission - the engine is revving up and down with no change in power to the wheels. All automatics have a speed where they do this.
I think you are referring to a CVT which is what most hybrids have. A CVT can vary RPM with no change in vehicle speed. This can be somewhat disconcerting to new hybrid owners. That and having the engine shut off at a red light which also can be startling to someone who is not used to it.

The Clarity meanwhile doesn't have even a CVT. As ClarityDave said changing the RPM only changes the amount of electricity being produced, some of which can be going to recharge the battery thus having no immediate effect on vehicle speed.

There is an exception when the car goes into direct drive mode, where the engine powers the wheels directly through a single overdrive gear. But that only happens at steady speed so you wouldn't hear any changes in engine RPM. I can't even tell when it goes into direct drive mode other than the little gear icon that appears on the energy screen.

I had several fill ups where the total gallons of gas in the tank was close to 8 gallons and a couple where it was over 8 gallons.
I thought the Clarity had a 7 gallon tank. The most I ever put in was 6.7 gallons after driving to 0 HV miles. I haven't pushed past that but I have heard there is another half gallon or so after that before it actually goes dry. So that made me think there is maybe 7.2 gallons in total. When you put in 8 gallons how many HV miles were left?
 

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Thanks for the post. We’re planning a long drive with some hills, so I think your advice will be helpful. The fastest highway, however, will be 65 mph so I will likely only be getting the car up to 70 mpg. I’m hoping HV mode can keep up with 70. Most of the drive will be slower than that :(
 

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Discussion Starter · #7 ·
Thanks for the post. We’re planning a long drive with some hills, so I think your advice will be helpful. The fastest highway, however, will be 65 mph so I will likely only be getting the car up to 70 mpg. I’m hoping HV mode can keep up with 70. Most of the drive will be slower than that :(
I'd still keep some battery. Also, be aware that there is a 2 to 3 second delay in the ACC before it starts accelerating after a descent. Sport mode seems to reduce this delay.
 

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Discussion Starter · #8 ·
I think you are referring to a CVT which is what most hybrids have. A CVT can vary RPM with no change in vehicle speed. This can be somewhat disconcerting to new hybrid owners. That and having the engine shut off at a red light which also can be startling to someone who is not used to it.

The Clarity meanwhile doesn't have even a CVT. As ClarityDave said changing the RPM only changes the amount of electricity being produced, some of which can be going to recharge the battery thus having no immediate effect on vehicle speed.

There is an exception when the car goes into direct drive mode, where the engine powers the wheels directly through a single overdrive gear. But that only happens at steady speed so you wouldn't hear any changes in engine RPM. I can't even tell when it goes into direct drive mode other than the little gear icon that appears on the energy screen.


I thought the Clarity had a 7 gallon tank. The most I ever put in was 6.7 gallons after driving to 0 HV miles. I haven't pushed past that but I have heard there is another half gallon or so after that before it actually goes dry. So that made me think there is maybe 7.2 gallons in total. When you put in 8 gallons how many HV miles were left?
The most I've put in the tank is 7.2 gallons and this was with 50-60 miles left on the gas tank. At 42 MPG this is still 1.2 to 1.4 gallons of gas left in the tank when I made this fill up.
 

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I just had the exact same experience with ACC regarding a white car in front of me. I had Adaptive Cruise Control on in soem traffic and was coming up to a slowing white car when I noticed the car was not slowing down and I was getting uncomfortably close before I had to hit the brake myself. I was very surprised as it normally works quite well. I did notice the car was white but had not noticed if I had previous events like this in the past.

This is something Honda absolutely should investigate and notify all owners about if it is a repeatable flaw.

I am wondering is there any good reason one should use HV Charge to add more than a few miles to the EV range? I like to keep a few miles so that the battery has some reserve to assist the ICE engine in EV mode when on hills and on the highway, as well as to use in cities or in situations with stop and go driving. But does anyone know if using HV Charge adds the same number of miles to EV range as it uses up in gas range?

I suspect the transfer is not 100% efficient, so that if you are using HV Charge to add 10 miles to your EV range, you may be reducing your gas range by slightly more than 10 miles, so there's not an efficiency reason to add EV range this way.
 

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Discussion Starter · #10 ·
I just had the exact same experience with ACC regarding a white car in front of me. I had Adaptive Cruise Control on in soem traffic and was coming up to a slowing white car when I noticed the car was not slowing down and I was getting uncomfortably close before I had to hit the brake myself. I was very surprised as it normally works quite well. I did notice the car was white but had not noticed if I had previous events like this in the past.

This is something Honda absolutely should investigate and notify all owners about if it is a repeatable flaw.
Definitely repeatable. Honda uses Lidar and two Teslas equipped with Lidar have hit white vehicles while "driving autonomously". One was with the driver, who didn't notice the white semi. The other was recent and it was a car using the Summon mode so it was a low speed collission.

I am wondering is there any good reason one should use HV Charge to add more than a few miles to the EV range? I like to keep a few miles so that the battery has some reserve to assist the ICE engine in EV mode when on hills and on the highway, as well as to use in cities or in situations with stop and go driving. But does anyone know if using HV Charge adds the same number of miles to EV range as it uses up in gas range?

I suspect the transfer is not 100% efficient, so that if you are using HV Charge to add 10 miles to your EV range, you may be reducing your gas range by slightly more than 10 miles, so there's not an efficiency reason to add EV range this way.
The laws of thermodynamics clearly state that anytime you change energy form you have losses. Since HV charge turns gasoline into electricity for later use, it cannot be as efficient as HV mode by itself. The only time I know to use HV charge is if you forget to put the in HV mode after starting and you need electric power to supplement the gas engine.
 
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Great trip report. I recently took a ~240 mile (total; round trip) city to city trip on the east coast. Everything went smoothly, but I got a little uncomfortable with the HV range estimation on the way home, and stopped in at a rest stop along the interstate to top off the gasoline.

I was counting the miles down on my GPS (Apple Maps) and comparing that to the total range estimate of the car, while in HV mode with about 11 miles of EV range left (to keep that "buffer" everyone talks about, and to get us somewhere in case we really did run out of gas or the ICE failed or something).

As we were cruising down the highway going between 70 - 75 mph, we found that the distance between the car's range estimate and the number of miles left on the trip was closing fast. For example, during the early part of our trip home, Apple Maps might've said we had 100 miles left to travel, and the car might've said we had 160 miles of range. OK - that's comfortable. But I saw that distance halve in a relatively short time, to the extent that we had, say, 60 miles left on the trip, and 90 miles left of range. So the distance went from 60 to 30 -- clearly the car was over-estimating the actual range remaining.

I don't like to drive for very long -- especially knowing that I have dozens of miles to go, at night, in unfamiliar territory -- without very much gas to spare. Add to that, the fact that we couldn't be sure that any particular rest stop would be accessible and open (they can close or the road to them can be closed at night for any reason, ranging from construction to crime to COVID).

So I did the "chicken" thing, and with about 70 miles of range estimated remaining in the tank, I stopped at a rest stop Sunoco and filled up.

This isn't the first time I've encountered this problem, either. This car always overestimates its HV range. It's actually really good with the EV range, and if anything it underestimates that, but the HV range is always a good 10-30% less than it states.

Would I have made it home without filling up? In retrospect, yes, definitely. But the estimation logic doesn't give me a warm fuzzy.

2018 Clarity PHEV base model with just over 20k miles.

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By the way, this is somewhat unrelated, but people have asked for reasons to use HV Charge or to run your car in HV mode with plenty of range on the battery. Other than arguments about battery longevity, one obvious reason is if you anticipate spending time in the car idling. I do this a lot.

Example: taking a family member to a doctor's appointment. Whether near or far, I leave about 15-20 miles of EV range, because (1) most places don't have an EV charger, or if they do, it's taken; and (2) I'm going to sit in the car with the air conditioning or heat on, most of the time, and I don't want the engine cycling on and off to provide the power for it. Not only would that sound annoying, but it's pretty inefficient. The most efficient use of the gas in your tank is to drive at highway speed in direct drive mode.

Another example: if you ever get caught parking in the bottom level of a deep parking garage with a lot of people above you, for a sporting event or concert, you know it can take 1-2 hours sometimes until you can get out of there. Often, the ventilation in those parking garages is terrible, and the only way to keep yourself safe and cool is to keep the A/C on recirculating. It's great to not contribute further to the fumes in the parking garage by keeping your car in EV mode, but if you don't save any battery, this isn't possible.
 

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Discussion Starter · #12 ·
I noticed on my trip that the HV range estimate is pretty accurate up to about 65 mph. Above that it's optimistic. Also, using HV charge really sucks down the gas at about 20 to 30% faster than hybrid mode (EV without battery or HV selected) alone. On long trips I don't like to go below 100 miles on gas, regardless of the vehicle. For a pure BEV I wouldn't want to go below 100 miles on battery either. I've run into too many places where you simply can't get gas.

Great examples of where you want additional battery.
 

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I am wondering is there any good reason one should use HV Charge to add more than a few miles to the EV range? I like to keep a few miles so that the battery has some reserve to assist the ICE engine in EV mode when on hills and on the highway, as well as to use in cities or in situations with stop and go driving. But does anyone know if using HV Charge adds the same number of miles to EV range as it uses up in gas range?

I suspect the transfer is not 100% efficient, so that if you are using HV Charge to add 10 miles to your EV range, you may be reducing your gas range by slightly more than 10 miles, so there's not an efficiency reason to add EV range this way.
People who have done some informal testing say that using HV Charge mode does not seem to impact mpg very much one way or the other. It burns more gas while in HV Charge mode but as you pointed out you can then "coast" in EV mode for twenty or so miles using the extra electricity that you generated. Whether this creates a slight gain in efficiency, a slight loss, or an even wash, depends on the driving conditions. While there will be some losses due to converting energy back and forth as obermd pointed out, there can in theory be a gain from using the engine at higher RPM where it is more efficient. However another potential loss occurs due to the fact that as far as I can tell the engine will not go into direct drive mode while in HV Charge.

The main reason for using HV Charge is for the other reasons mentioned, like having some EV range when you are driving around at your destination city, or to have battery power available when climbing hills. Since HV Charge seems to be at least similar efficiency as regular HV mode, there is no reason not to use it for those purposes.
 

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Discussion Starter · #14 ·
People who have done some informal testing say that using HV Charge mode does not seem to impact mpg very much one way or the other. It burns more gas while in HV Charge mode but as you pointed out you can then "coast" in EV mode for twenty or so miles using the extra electricity that you generated. Whether this creates a slight gain in efficiency, a slight loss, or an even wash, depends on the driving conditions. While there will be some losses due to converting energy back and forth as obermd pointed out, there can in theory be a gain from using the engine at higher RPM where it is more efficient. However another potential loss occurs due to the fact that as far as I can tell the engine will not go into direct drive mode while in HV Charge.

The main reason for using HV Charge is for the other reasons mentioned, like having some EV range when you are driving around at your destination city, or to have battery power available when climbing hills. Since HV Charge seems to be at least similar efficiency as regular HV mode, there is no reason not to use it for those purposes.
I have to disagree with the assessment that HV Charge has limited impact on total range. I lost more range than HV charge added, and by quite a bit. When I added 25 miles (seems to be about the maximum), which takes about 30 miles at 60 MPH, I would loose 35 miles of total range. This is a significant drop in efficiency.
 

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I have to disagree with the assessment that HV Charge has limited impact on total range. I lost more range than HV charge added, and by quite a bit. When I added 25 miles (seems to be about the maximum), which takes about 30 miles at 60 MPH, I would loose 35 miles of total range. This is a significant drop in efficiency.
Not sure what the difference would be compared to others who say it doesn't change that much when they run the same route in either HV or HV Charge. Maybe some type of difference in the driving conditions, hills for example.

Although if you were looking only at the guess-o-meter for total range, it's not necessarily accurate because using HV charge could possibly throw off the HV prediction and thus the total miles estimate.

The only accurate way to determine a difference is by measuring actual gas consumption, which unfortunately isn't that easy. For example you start with 0 miles of EV range and a full tank of gas. You drive in HV Charge mode for 30 miles, at which point you have built up 25 miles EV range. You then switch to EV and drive out the 25 miles that you built up, giving you a total range of 55 miles on whatever gas you burned during the 30 miles of HV charge. Sometime during your 25 miles of EV driving you would need to pull off to a gas station and fill up, the number of gallons pumped will be the amount of gas that you used during the 30 miles of HV Charge. Then compare that to how much gas you would normally use to drive 55 miles.

I think the people who tested this did something similar in concept, although they drove a longer repeated route like say 100 miles, a route they do fairly often, doing one run where they used HV Charge and the other only HV. Starting each test run with a full tank, and filling up at the end after each test run to determine the gallons used. I'm not sure if they started with 0 EV miles each time but they really need to for the comparison to be accurate so that previously stored EV range doesn't affect the test. And during the test run where they are using HV Charge they need to be sure and use up all of the EV miles that they built up in HV Charge before they reach the end of the run and fill up, because if there are any remaining EV miles at the end that would skew the results.
 
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