Horrible efficiency on recent trip.

[sotek2345]

Hello all,

Had my lighting for 3 years and many road trips now so I am used to all the things that impact efficiency, but this trip has me stumped. Relatively flat terrain, cruise set at 72 (with the some slowdowns), about 50 degrees out with minimal HVAC use, very light tail wind, and I am seeing 1.5 to 1.6 m/kWh. Usually in these conditions I am seeing 1.9 to 2.0.

I did a quick check of the aero elements up front and don't see anything obstructed and I am not getting any errors.

Any idea what else to check? I still have about 300 miles or so to go today!

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[Grumpy2]

Checked your tire pressure?

 

[sotek2345]

Checked your tire pressure?

A little lower than I normally keep it, but not very low. 40psi per tire.

 

[B177y]

Only 30 miles in that snapshot makes me think it might be warming the battery. Was it a cool/cold night? Were you able to set a departure time while plugged in?

The 1.6 m/kwh isn't unexpected for speeds over 70mph.

 

[sotek2345]

Only 30 miles in that snapshot makes me think it might be warming the battery. Was it a cool/cold night? Were you able to set a departure time while plugged in?

I wanted to show all highway miles, so this was after a bathroom / breakfast stop at a rest area. We had been driving over an hour.

 

[Grumpy2]

Since you have been driving over an hour the tire pressure should be higher than you would would normally have parked at home. Also, I don't know how accurate the truck monitoring system is.

 

[B177y]

At 70+ mph even slight variations in wind and terrain will drastically change efficiency. I just finished a 3000 mile trip (WA, ID, MT, ND) and varied from 1.4 - 2.0 at speeds in the upper 70's and occasionally at 80 where speed limits allowed. Only got my efficiency near 2.0 when I had a 40 mph tailwind (that never happens!). Kept it mostly at mid 70's to balance speed vs efficiency. Your 1.6 doesn't seem too out of spec. Keep an eye on battery percentage for charge stops.

 

[Efiddy]

On road trips, I’m beginning to think the added time savings of driving above 70 mph isn’t worth the potential additional charging time. It depends on the length of the trip of course. At 80 mph you’re burning energy so fast that you end up charging deeper into the slow zone of the pack. Unless you’re pulling perfect 110 kW averages the whole way, you don’t actually save time.

70 mph is the real-world sweet spot. It feels slower, but you make fewer/shorter stops and usually roll in sooner.

I am not happy about this. The state police however appreciate a 7000 lb vehicle sticking to the speed limit.

 

[SpaceEVDriver]

You stated you stopped for breakfast after about an hour, so presumably you started before dawn, or at least early in the morning. So… It was probably colder than 50 degrees F, given that you’re in upstate NY in November. That lower temperature almost certainly cost some energy to warm up the battery.

What was the humidity? Was there water on the road?

I run my tire pressure at about 48 PSI cold, and I check that with a real pressure gauge, not the TPMS, which can be off by more than 10%.

I typically get between 2.2 and 2.5 miles/kWh on the freeway at 72 mph in pleasant conditions. If there’s adverse weather, we can see drops to 2.0. The first part of the drive getting up to speed on the freeway or before the battery has warmed up can be lower, but it’s anomalous to the full drive (if the drive is >300 miles).

I’ve run the calculations on our ~50k miles of road trips and the sweet spot speed for time on the road is between about 67 and 72 mph. I still pass most truckers, which is annoying. I wish they’d stick to a 70 mph speed so I can draft behind them for even more energy savings.

 

[sotek2345]

On road trips, I’m beginning to think the added time savings of driving above 70 mph isn’t worth the potential additional charging time. It depends on the length of the trip of course. At 80 mph you’re burning energy so fast that you end up charging deeper into the slow zone of the pack. Unless you’re pulling perfect 110 kW averages the whole way, you don’t actually save time.

70 mph is the real-world sweet spot. It feels slower, but you make fewer/shorter stops and usually roll in sooner.

I am not happy about this. The state police however appreciate a 7000 lb vehicle sticking to the speed limit.

I have found the sweet spot to be between 72 and 74, but we have pretty good charger coverage so more frequent stops are available.

 

[Heliian]

It's cold and your tire pressure is too low. Did you precon?

What was you overall efficiency? A 30 mile snapshot isn't overly clear. Also, winds.

 

[PJnc284]

I typically get between 2.2 and 2.5 miles/kWh on the freeway at 72 mph in pleasant conditions. If there’s adverse weather, we can see drops to 2.0.

The lightning must love AZ. That's better than most seem to get. Best I've seen here in SE NC on a nice day is about 2.0mi/kWh @70mph and that was with a tailwind. Usually average 1.8/1.9. At 60, I get 2.2. Do have the Hankook AT's though but have them set to 45psi due to wearing on the outer edges at the oem recommended 36.

 

[sotek2345]

It's cold and your tire pressure is too low. Did you precon?

What was you overall efficiency? A 30 mile snapshot isn't overly clear. Also, winds.

Overall for the trip down was 1.6 over a little less than 200 miles. During a slower speed section 55 to 60mph, efficiency increased to 1.8. I will check the tire pressure as soon as I can find a gas station on the trip home later today. Maybe that it is. Never had efficiency impacts this big until it got down near zero.

Wind was very light (1 to 2 mph) and was with the direction of travel, so that wasn't it.

 

[SpaceEVDriver]

The lightning must love AZ. That's better than most seem to get. Best I've seen here in SE NC on a nice day is about 2.0mi/kWh @70mph and that was with a tailwind. Usually average 1.8/1.9. At 60, I get 2.2. Do have the Hankook AT's though but have them set to 45psi due to wearing on the outer edges at the oem recommended 36.

We get a lot of snow here in the winter (I live near one of the snowiest cities in north America). We don’t get extreme cold (the lowest I have on my home record is -15 degrees F).

For me, I think it’s a combination of a lot of experience with high-efficiency driving and high elevation driving.

For example, while I will pass, I usually don’t pass if I need to jump from my cruising speed of ~72 mph to 85 mph (for example) to safely complete the pass; I can afford to wait few minutes for traffic to clear.

Another example: atmospheric density at ~7,000 feet elevation is close to 20% lower than at sea level. Density has a direct, linear impact on drag forces (but it’s not as direct an impact on efficiency since other factors also come into play). And we usually have a much lower relative humidity (despite the high snow volume), which tends to lower atmospheric density even more.

The regular trip I take about once a month is ~460 miles and though one end of the trip is near sea level, the average elevation is 3100 feet (about 10% reduced drag). But, I do have to climb from ~sea level to 7300 feet elevation. Some sections can bring my efficiency down to about 1.9-2.2 miles/kWh. But our average is about 2.3 miles/kWh.

 

[PJnc284]

You can keep the snow. I'll take the lower efficiency.

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