[Mr. Body Massage]

Hey everyone, I'm picking up my new to me 2015 i8 on Wednesday and driving it about 1000 miles home. I've seen multiple posts saying that the trick to getting the best fuel economy on interstate driving is to set the car to hold charge at 90% in comfort mode. Is this true? If so, why would this give the best mileage?

[Coastali8]

That procedure won’t do anything on a 1000 mile interstate drive. All it will do is allow you to arrive at your destination with 90% charge.

If you run in comfort mode the ICE will fire up after the battery goes dead in about 18 miles. Then the car will run along in 5th gear the rest of the trip on the highway. If you select sport mode then you can manually paddle shift up to 6th gear and run along in 6th vs 5th. Better gas mileage will result. The ICE will be running the entire trip either way. And when you arrive at your destination the battery will be at 100% as a result of running in sport mode.

Be prepared to open the fuel door manually with the cable in the trunk when your tank is near empty after a long drive. Unless your car has had the fuel tank pressure sensor replaced. BMW will replace the sensor under warranty for 10 years.

[eswimm]

Originally Posted by Coastal i8

If you run in comfort mode the ICE will fire up after the battery goes dead in about 18 miles. Then the car will run along in 5th gear the rest of the trip on the highway. If you select sport mode then you can manually paddle shift up to 6th gear and run along in 6th vs 5th.

I know it stays in 5th gear in sport, but are you sure it stays in 5th in comfort? My impression has been that it shifts up all the way in comfort.

Over 1000 miles, the fuel savings from ~15mi of battery range is going to be pretty negligible, but if you knew you were going to be in for 10+ mi of stop and go traffic at the end of the trip, you might save 1/3-1/2 a gallon of gas by using sport in 6th gear to charge it up before switching back to comfort for the traffic.

[patsgarageonline]

The highest gear the car will drive in is 6th gear in Comfort, and 5th gear in Sport (unless you manually shift to 6th). Comfort drains the battery up to 63mph, when the ICE engine kicks in and the car will not use battery unless you floor it and eBoost becomes active on the display (with a bright blue ring), or you drop below 63mph. You can charge the car to about 10mi remaining by switching to Sport at any point in your trip, and then just switch to Comfort when you have the amount of battery remaining that you desire. Using Sport Mode increases accessory draw on your ICE engine so you'll lose some mileage but it shouldn't be noticeable on a long trip.

If you set your destination in the GPS, the computer in the car will manage the battery by charging it ahead of stop and go or city traffic so that you have enough of a charge not to constantly stop/start the ICE engine. However, I try to use Sport Mode on a trip to keep the battery over 5mi at any point so the engine is not cycling on every time I pull out with 0mi remaining. Each start is additional wear on the starter/generator and engine and I'm all about lengthening component life. I drove 750mi on a round trip and got 35mpg.

[Mr. Body Massage]

That makes sense. I was failing to see how the hold charge would increase fuel economy. Thanks!

[Coastali8]

I stand corrected.
You are correct about comfort mode attaining 6th gear and sport mode only going up to 5th on its own.
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