Why the BMW i3-REx

Drink more coffee (or that warm, brown liquid sold at filling stations.) Also, carry a wife and her two dogs.

Actually have three planned mods:

• aerodynamic tweaks - after body taper should reduce drag improving efficiency and/or speed.
• engine oil change - going 0W-20 which BMW is already planning
• transmission gear oil - change; test; change, and; test

Bob Wilson

 

I will be subscribing to their technical information site not only for the transmission oil specs but other important technical specs and layout. Then I'll follow a familiar protocol:

• get OEM oil
• change and send virgin and used oil for analysis (baseline and initial replacement)
  • removes initial manufacturing debris and clues on oil analysis
• decide what to replace it with (thinking Type WS as it is excellent)
• after 5k miles, change send 2nd used oil for analysis
  • look for oil wear pattern
• after 5k miles, change send 3d used oil for analysis
  • looking for new oil service wear

I may set up some temperature sensors to measure the changes in service.

Bob Wilson

 

If you think of a BMW i3-REx as an over-grown motorcycle, the cross country performance makes a lot of sense. The small tank size which limits single fill-up range to a little over an hour is pretty common in motorcycles. Even the optimum speed, 65 mph, and MPG, these are not far from what I remember from my motorcycle days.

Bob Wilson

 

Return trip actual arrival 1:30 AM, to photo later that morning:

• 697/16 hrs ~= 43 mph block-to-block
• 57.9 mph - while READY, speed

Bob Wilson

 

Been thinking about how to achieve long range in an EV, the BMW i3-REx in particular. I keep coming up with one solution, a trailer battery pack:

• Must connect in parallel with existing pack - avoids conversion losses.
  • same battery chemistry and density
• Mass ~= "n" existing traction battery pack
  • 60Ahr -> 72 miles
• Needs full BMS - cooling for hot temperatures and heating for cold
  • the pack is a significant investment and needs reasonable protection
• RV park charging - 208-240 VAC @40 A charger
  • DC chargers just are not available
• Reasonable lifting assist so the two-wheels don't leave it on its nice person or on the tongue
  • might consider tricycle trailer

But to make the Oklahoma trip, I would have needed 10x battery pack. This would be unreasonable.

I also considered a series of rapid-charge stations. The problem is I'm seeing typical capital expenditures of $100k. Ideally located for me, 10 stops would be $1.0m but in reality, it is a question of density and there should be one every 35 miles, half the 72 mile range, $2.0m. Suddenly, high-speed, DC charger placement looks like something that should be co-located with truck stops.

I'm also modeling different BMW i3-REx approaches including:

• 1.9 -> 2.4 gal - a software hack, it add 0.5 gal or 20 miles to REx range
  • 1 gal spare can worked perfectly adding 40 miles range, ~112 miles
• 40 -> 42 MPG - after body taper may give a 5% improvement in mileage
  • skirts and rear wheel cover might help
• dipping into EV - instead of preserving SOC, use "n%" at the end of each tank, ~5%
  • assumes full charge at destination
  • assumes navigation accurate enough
  • ~1.4% per mile or 5% ~=3 miles
    
  • use EV at the end

Bob Wilson

 

And then the REx starts up. Actually just wallet angst.

Since July 17, our JuiceBox Pro (40) recorded ~600 kWh, enough for 2,400-2,500 miles, $60.

In our 2010 Prius that would be ~46-48 gallons, ~$85-89 @$1.85/gal. Now what makes this interesting is the absence of State or Federal tax on the electricity. We've been running ~$1.85/gal locally of which $0.21 State and $0.18 Federal. When I recalculate the gasoline cost without the road tax, ~$1.46/gal or ~$67-70.

My best estimate suggests a 2016-current Prius without road taxes would have nearly identical cost per mile to our BMW i3-REx. Then the Colonial pipeline broke and gasoline went from $1.85 to $2.19.

Our BMW i3-REx electricity rates did not change with the pipeline break. In about 30 days, gasoline prices should return to normal.

Meanwhile, ~1/3d of the BMW miles are from 'free' local stores. In effect, ~800-900 free miles totally blowing away any parity with the 2016 Prius.

Bob Wilson