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High speed efficiency

2545 Views 15 Replies 11 Participants Last post by Voldar, Apr 25, 2022

GeneL

Discussion Starter · Apr 16, 2022

Last night I drove from Austin to Athens TX. The first leg was IH 35 to Waco. We stopped for dinner in Round Rock. After dinner traffic was pretty light; so I played some games.

I set the cruise on 75, reset the trip meter and drove 20 miles. I got about 3.8 M/kWh. I then put the speed up to 80, reset the trip meter and drove another 20 miles. This time I got about 3.4 M/kWh.

This section of 35 is pretty new and in good shape. New smooth concrete, slightly hilly. I had the AC on but it wasn't doing much.

After charging in Waco I turned on to TX 31. This road has an awful surface. It's so noisy my wife and can't talk in the passenger compartment. I reset the trip meter, put the cruise on 75 and went 10 miles (could not make 20 because of the small towns). I was only getting about 3.3 M/kWh.

I really don't think there is much difference in the two roads other than the surface and yet efficiency was reduced by 0.5 M/kWh. Has anyone else experienced reduced efficiency due to poor road surface?

The numbers I got on 35 were pretty consistent with my experience on other high speed drives.

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Herbie Bolt

· #2 · Apr 16, 2022

I think you have a good point there @GeneL
Last night I was forced to drive a 10km run at 80km on fresh gravel, I don’t have hard numbers as I didn’t reset but the usage was horrible, where I was running 14 to 18 kw on live display it never dropped below 24 while on the gravel.

Packard V8

· #3 · Apr 16, 2022

Some have mentioned heavy rain on the road requires more power.

jack vines

Reactions: 3

roseberry

· #4 · Apr 16, 2022

I know that gravel roads require a lot more juice as I drive on them all the time. Our paved roads are what we call chip-seal, where gravel (in our case 5/8" crushed basalt) is spread out over oil and traffic gets to do the rest of the job for a week or two and then they sweep the remaining gravel to the side and voila, paved road. It's the greatest process ever for windshield replacement companies. Tires wear out quickly too on chip-seal roads because they're like extremely course sandpaper and I think the energy to wear out those tires comes from either your gas tank or your battery. Slowing down is your only defense against the noise, tire wear, and energy consumption.

Reactions: 1

Terry Hancock

· #5 · Apr 16, 2022 (Edited)

A dffferent EV, but I have seen the same in a Bolt. And that is the following: took 75 electronic miles out of my tank to go to Albuquerque from my house...with the wind at my back. It took 95 miles out of the tank to go straight back home...into the wind. Cruise was set identically both ways, and the surface was I25, which is in pretty good shape.

Reactions: 1

Packard V8

· #6 · Apr 16, 2022

Terry Hancock said:
A dffferent EV, but I have seen the same in a Bolt. And that is the following: took 75 electronic miles out of my tank to go to Albuquerque from my house...with the wind at my back. It took 95 miles out of the tank to go straight back home...into the wind. Cruise was set identically both ways, and the surface was I25, which is in pretty good shape.

A ten-mile wind ;>)

jack vines

wesley

· #7 · Apr 17, 2022

Packard V8 said:
Some have mentioned heavy rain on the road requires more power.

jack vines

Yep, I even wrote about this in the book I published last year. I usually see about 10 to 20% drop in efficiency under heavy rain and wet road.

Reactions: 2

Voldar

· #8 · Apr 17, 2022

It’s all about friction. On a smooth surface, the car needs less power to move forward than on a rugged surface. It’s only physics.

Reactions: 1

roseberry

· #9 · Apr 17, 2022

I rarely drive in the rain but I will tomorrow. Going down the gorge to Portland with the wind at my back, thankfully, and then tomorrow up to Tacoma in rain, according to the forecast.

Voldar

· #10 · Apr 17, 2022

roseberry said:
I rarely drive in the rain but I will tomorrow. Going down the gorge to Portland with the wind at my back, thankfully, and then tomorrow up to Tacoma in rain, according to the forecast.

Wind has a bigger impact than the rain. If you face rain and wind, you are in the wrong place at the wrong time, so you should just slow down speed. It’s the only thing that you can control.

Reactions: 1

Sean Nelson

· #11 · Apr 17, 2022

All you have to do is to imagine how far the car would roll if you shifted it into neutral. It seems pretty intuitively obvious to me that you wouldn't get anywhere near as far doing this on a gravel road or a wet road as you would on a nice day paved road. Same thing applies for headwinds vs tailwinds.

Reactions: 2

GeneL

Discussion Starter · #12 · Apr 17, 2022

wesley said:
Yep, I even wrote about this in the book I published last year.

Tell us about your book.

Reactions: 2

jmcbrew

· #13 · Apr 19, 2022

Internal combustion powered cars don’t see as much of a hit from these variables — wind, rain, etc — because they tend to get more thermally efficient at higher loads. This is why generators are rarely over powered. It is more fuel efficient to run a smaller engine harder than a larger engine at a lower load. EVs tend to get “fuel” economy that is more proportionate to the load.

It all depends on how you look at it, though — I had someone ask me if it is true that EVs get worse fuel economy in the winter. I told him, “no, they get better fuel economy in the summer.” He looked at me for a few seconds and replied, “well, that’s not what I heard.”

Reactions: 3

Bolticus

· #14 · Apr 20, 2022

jmcbrew said:
Internal combustion powered cars don’t see as much of a hit from these variables — wind, rain, etc — because they tend to get more thermally efficient at higher loads. This is why generators are rarely over powered. It is more fuel efficient to run a smaller engine harder than a larger engine at a lower load. EVs tend to get “fuel” economy that is more proportionate to the load.

It all depends on how you look at it, though — I had someone ask me if it is true that EVs get worse fuel economy in the winter. I told him, “no, they get better fuel economy in the summer.” He looked at me for a few seconds and replied, “well, that’s not what I heard.”

There is another factor at work here. ICE cars are only about 20% efficient, meaning a little over 19% of the energy in the gas actually gets turned into moving the car down the road. The rest is lost in heat (free heat for winter). So, ICE cars do lose efficiency going over rough/wet roads and in wind/rain, but it isn't very noticeable because most of the energy in the gas is being wasted anyway. EVs however are over 90% efficient, so changes in conditions make a noticeable difference.

Yaroslav Pasichnyk

· #15 · Apr 25, 2022

Voldar said:
Wind has a bigger impact than the rain. If you face rain and wind, you are in the wrong place at the wrong time, so you should just slow down speed. It’s the only thing that you can control.

If i'm on the road trip and face strong headwind, I usually start tailgating a truck, who pushes wind for me. I consider it more safer than slowing down on the highway.

Reactions: 1

Voldar

· #16 · Apr 25, 2022

Yaroslav Pasichnyk said:
If i'm on the road trip and face strong headwind, I usually start tailgating a truck, who pushes wind for me. I consider it more safer than slowing down on the highway.

Following a truck = lower speed anyway. If you have a truck around, that’s great. If not, lower the speed. It will not be a problem on the highways of Canada where most people drive at 95-110 km/h.

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