Why the BMW i3-REx

So we have both a 2017 Prius Prime and 2014 BMW i3-REx . . . which one to drive today:

• BMW i3-REx - best urban car, a pocket rocket with a high seating and excellent view. The power to weight ratio means point and scoot and the short wheel base parks easy. It has acceptable cross-country capability but stay near interstates especially at night as it is 80 miles per segment and carry a 1 gallon spare can.
• Prius Prime Plus - best cross country car, smooth, excellent suspension and outstanding highway MPG. Visibility is much improved over our Gen-3 and the dynamic cruise control is great. Around town, know your charging locations and shop at nearby stores. The traction battery charges ~40% or 10 miles per hour and has no fast charging. In town, it drives like a tuned-up Prius, more than adequate.

Bob Wilson

 

Source: BMW i3 plug-in hybrid recall to fix fuel-vapor problem, fire concerns

BMW is recalling more than 19,000 i3 REx extended-range electric cars due to concerns over the potential for fires to be started by fuel vapors.

The REx uses a small gasoline engine to charge its battery pack, offering a longer range than the all-electric i3 when both gasoline and electric power are used.

According to the National Highway Traffic Safety Administration, the i3's fuel-tank vent line may rub against the ribbed wire protection sleeve of the battery positive cable.
. . .​

I am so glad we have a 2017 Prius Prime that replaced our Gen-3 Prius.

Bob Wilson

 

Technical details of the recall: https://static.nhtsa.gov/odi/rcl/2017/RCLRPT-17V088-5114.PDF

Bob Wilson

 

HOME TO WORK

Preconditioning, nice cabin and 100% SOC. Got to cross-town intersection and had forgotten work badge. Added 3 miles to commute and brought SOC to 87% instead of 91%.

Work to Nashville

About 8-9 miles, the SOC reached 75% and I turned on the REx. In Ardmore, 20-25 miles at the Interstate, topped off gas tank, grabbed a burger and unsweetened tea and on the 70 mph I-65.

Now 70 mph is the REx output energy output. I had a 15 mph tailwind but had to climb the Piedmont. SOC decayed from 75% to 72% and stayed there.

Followed a 70 mph truck to Nashville but ran out of gas 6 miles short with 70 miles EV range in battery. Horrors! I continued and arrived actually an hour early.

Sweet Home

Turns out ChargePoint had put in a new, four hose charger three blocks away. At $0.84/hr, reasonable. The a block and a half away, a new Japanese style restaurant and sushi bar. Just the thing to eat a brunch before heading to a gas station and home.

Expenses

• $1.19 - top off tank in Ardmore
• $1.35 (7.161 kWh) - charge in Nashville, $0.18/kWh
• $4.98 (2.007 gal) - fill-up tank in Nashville ($2.48/gal)
• $0.72 (7.161 kWh) - charge in Huntsville residential rate, $0.10/kWh
• $4.50 (2 gallons ) - fill-up local Huntsville fuel, $2/gal Reg, $2.25/gal Premium
• $12.74 - expected gas and electricity
• 234 miles - HSV->Nashville->HSV
• $0.054 / mile

With the expense per mile, we can reverse calculate the equivalent expense using Huntsville prices:

• $2/gal Reg / $0.054/mile ~= 36.7 MPG (regular)
• $2.25/gal Prem / $0.054/mile ~= 41.4 MPG (premium)

Ouch, I was not expecting this but I did have fun driving the Bimmer. Given the measured MPG at 70 mph is 38 MPG, this is about right. I did not dilute enough of the trip energy with electricity, the cheaper fuel.

The USA default is to turn on the REx at 6% but some have found there is not enough energy to handle highway loads without limiting performance during the engine warm-up. If I wait until the SOC is ~12-18% instead of starting at 75%, then more of the gas, the expensive fuel, will be preserved, left in the tank. FYI, the SOC was ~40% when I parked.

The lesson learned is if you're blending electric and gas on a given trip, maximize the electrical usage and preserve the gas. This is not a trivial problem because loss of electrical and gas energy can be unpleasant. Time to carry a spare gallon for future runs.

Bob Wilson

 

A little math fun:

• cost_per_mile = cost_per_gallon / miles_per_gallon
• EV_cost_per_mile = cost_per_kWh / miles_per_kWh

So we can the calculate the trip cost:

• n%_gas_miles
• 1 - n%_gas_miles

Huntsville:

	model	gas_price	kWh_price	MPG	mi/kWh	$gas/mi	$kWh/mi
1	BMW i3-REx	$2.35	$0.11	39	3.4	$0.0603	$0.0324
2	Prius Prime	$1.97	$0.11	54	4.0	$0.0365	$0.0275

Nashville:

	model	gas_price	kWh_price	MPG	mi/kWh	$gas/mi	$kWh/mi
1	BMW i3-REx	$2.25	$0.18	39	3.4	$0.0577	$0.0529
2	Prius Prime	$1.92	$0.18	54	4.0	$0.0356	$0.0450

ChargePoint $0.85 for 6.6 kWh = $0.18/kWh
Gas prices from gasbuddy.com​

Well I wasn't expecting this:

• BMW i3-REx is more efficient EV regardless of Huntsville or Nashville rates, slightly.
• Prius Prime is more efficient EV in Huntsville but somewhat cheaper on gas in Nashville

This suggests we should be able to make a table of gas and electric costs that defines parity for both cars. Then select the motive fuel/energy to minimize the cost per mile. It should be linear relationship for each vehicle.

Bob Wilson

 

Got a nice e-mail from ChargePoint:

Hi Robert,
Just a heads up, your Toyota Complimentary Charging balance of $98.65 expires in 60 days. Any remaining Toyota Complimentary Charging balance will disappear at that time, and has no cash value. See full terms and conditions here.
Don't worry, you can keep using your ChargePoint card or mobile app to charge your Prius Prime after your balance expires.
We hope you're having fun driving in EV mode.
Charge on,
Team ChargePoint​

I charged the BMW i3-REx in Nashville.

Bob Wilson

​

 

I have to admit, driving the BMW i3-REx around town is a blast.

Bob Wilson

 

Electrical rate effect of BMW i3-REx, ~$20/month:

• (20000 - (6440 + 1863)) / 10 ~= 1,670 miles / month
  • 6440 miles, when bought
  • 1863 miles, vacation 700 miles each way, 463 mile delivery
• $20 / 1,200 mi ~= $0.017 per mile, out of pocket
  • $0.17 per 10 mile
  • $0.25 per 10 mile based on both free and home electrical costs (*)
  • $0.08 per 10 miles, free charging
  • ~1/3d free electrical miles
• Charging just at home, estimated ~$60/month

* - $0.10/kWh local Huntsville electrical rate

Bob Wilson

 

An opportunity missed.

Saturday afternoon, I was running errands and stopped at Whole Foods. There were two families admiring a Tesla but no one around. So I backed in and plugged-in. Then I gave them a walk around and talk economics. One sat in the car and noticed the visibility and I'd opened the rear seat doors. I was thinking about giving some test drives but my wife was waiting at home.

I regret not having the time to take them for a test ride. Unlike 2900 lbs, 168 hp, a test drive converts that into butt feel. Maybe another day.

Bob Wilson

 

Source: The Electric BMW i3: Incorrect State Of Charge Readings Causing Problems For i3 Owners

. . . look up service bulletins B61 20 16 and B61 20 17. These bulletins will instruct the dealers on how to correct the problem. You should also make sure you have software version 16-11-502 or later.

. . . There have been cases where the software update didn't work for some reason. When that happens, the dealership needs to connect the car to BMW HQ and perform a remote IRAP session. The IRAP reprogramming will definitely resolve the issue if the software update doesn't.​

Bob Wilson

 

A graphical history of a JuiceBox Pro 40:

• Up until 2017 the EVSE was at home and we only had a BMW i3-REx, maximum 31A.
• In 2017, the EVSE was at Propst where our BMW i3-REx, Prius Prime, and mystery cars could charge.

Bob Wilson

 

After a visit for the recall, I got a copy of the "Tire Tread Depth" which shows 'red' on the inner grooves:

	outer	center	inner	side	inner	center	outer	position
1	5	6	2	L(*) R	2	6	5	front
2	5	5	2	L(*) R	1	5	4	rear

* - the driver side

The service writer suggested it was the aggressive regeneration. Since the rear, center grooves are shallower than the front, that would be the signature of regeneration wear. But the 1 and 2mm inner grooves fail on all four tires. These tires have +13k service miles and the service writer reports they typically last 15k miles. Tires that were new in June 2016, 10 months ago.

Searching, I found heated, 'tire groove' tools, that have a mix of heated blades. These are typically used in competitions to improve tire performance. Prices range from $90-500 and there are different sizes and shapes, round and square. But they do not appear to have a gauge or stop to limit the depth (Oh give me a hard problem!) So this begs the question, has anyone thought to use a tire groove tool to deepen the shallow, inner groove?

The rubber profile looks OK although the driver-side, rear looks a little raised. But if this happened on our Prius, I would look at putting in shims to give the tires more camber towards the outer tread. In effect, offloading the inner tread to even out the wear. But another alternative is a wheel alignment tool and add the camber without the shim. Anyone (@ericbecky or @3prongpaul ) look at this approach, adjusting the camber to offload the inner tire tread?

Thanks,
Bob Wilson

 

Thank you!

Upon further reflection, I agree that re-groove needs to be done carefully. Rather than just hack at it, I think I'll ask for both rear tires as they seem to have the worst of it. Then I'll see if I can section and experiment. My biggest concern is whether I'll be able to get a clean-cut through the belt with my reciprocating saw and a metal blade.

I agree that the problem is the camber is off both front and back. Upon checking with Mr. Google, I plan to use the 'string plumb bob' technique to measure the camber of the existing tires. Once I have my metrics, I'll go back and discuss what we can do when they do the alignment of the new, rear tires, and let them get the first crack at 'doing the right thing.' I'll double check their work with the string plumb bob and if off, try to fix it myself without using a shim kit.

Then we'll order the new front tires and again, ask to add some camber.

I do like your suggestion of chalk testing the tire contact. The other technique I've used is tire tread temperature.

You are right that the REx is located on that side. This is also the car that had the motor mount bolt on the driver side break. No telling what the heck it was doing before then.

BTW, this car came without the tire goop and pump. The maintenance record shows it had a tire replaced which suggests it had a 'boo boo' with the original lease holder. These things can screw up other parts and one is always concerned that in an ordinary car, there might have been frame damage. I'm not ready to go there, yet.

Bob Wilson

 

Good news! A false-positive from the screening system.

I spoke with the tech and he checked the tires and he thinks they are OK. I'll measure when I get home to make sure. Then I'll do a tread-temp test. If they are even, it ain't broke.

The tech said their screening system is designed for wider tires.

Bob Wilson

 

Thanks!

You're not crazy:

So this morning, 63F, I ran at 60-75 mph on an extended commute and used an IR thermometer to measure the driver-side, rear wheel tread temperatures going from outside to inside:

87.3 1st
88.0
85.9
86.1
86.4
86.6 2nd
86.1
86.4
88.6
87.2
87.6
86.4 3d
86.2
86.3
86.1
85.8
86.8
88.4 4th
88.1
88.4
88.1
88.4
88.6
88.9
88.8​

The temperature profile shows the inner tread it doing more work than the outer tread. This is the signature of negative camber that would wear out the inner tread of the tires first. So I checked the training charts, pp. 24:

• IO1 Chassis and Suspension
  2. Axles
  . . .
  Rear axle adjustment values . . . I01 Standard chassis and suspension
  Camber ... -1 degrees 40 minutes

Now this bothers me because the outer tread has the deeper groove. The inner tread starts with the shallower groove. This leads to two hypothesis:

• The camber is wrong and should read +1 degree 40 minutes.
• The tires have been mounted wrong side out.

Regardless, it is worth sharing this information with NHTSA, Bridgestone, and BMW. I'm not terribly concerned about how this came about. But I am interested in getting serious people to start talking with each other.

FYI, negative camber (tops closer together) in theory makes a car corner better as the lateral force would tend to move the tires into a more vertical orientation. But if you're going to do that, the thickest tread should be on the inside to wear the tires evenly and get a firm grip. Our tires are the reverse and that would lead to early wear of the thinnest part.

It is not enough to have the tires mounted so the outside is now the inside. The grooves and tread pattern are critical to getting water out of the way so the tires won't hydroplane. If we become our own auto/tire engineers, we would need to quantify what happens in rain as well as on a track.

Bob Wilson