My experience with the i3 Rex on a 1200 mile trip...

[EVBob]

Greetings All,

Just wanted to share my experience with a long distance trip with the (coded) REx

My trip from South Florida to Indiana required (10) gas fill ups, (2) DC quick charges and (2) overnight L2 charges. Total weight of passengers and cargo was probably around 600-700 lbs - here is what I've noticed during the trip:
- Going at highway speeds 67+ mph with AC running on hot days on Eco Pro Mode - the REx will not keep the SOC at 75% - it will go down albeit very slowly - but still enough that it made us feel more comfortable to get DC charges when we came across one when we were between 30-50% SOC.

- Going at 60-65 mph with the AC running on eco pro - it will for the most part hold SOC - cloudy days help, since the i3 is kinda like a big solar oven with that huge windshield.

- Going at 75+ mph with AC running on hot days - if at all possible - don't do it if you can avoid it - unfortunately for the beginning of our trip, everyone was going this speed (typical South Florida traffic on the turnpike) and no trucks to "draft" could be found - this chewed away at the SOC fast.

- Engaging the REx at 75%, expect it to drop to 71-72% before the REx fully warms up and can output its Max power. If your lucky, this will happen right as your ontop of a hill and the regen combined with the REx can bring your SOC close to 75%

- The Fuel door/Vapor release system is wonky - get real comfortable with the manual green vapor release tab in the frunk. Only once did the fuel tank door open without the green tab...each time we filled up, it was 1-5 miles after the fuel was depleted.

- With the fuel "fully depleted" - I could only put in a maximum of 2.34 gallons - this is with careful pumping and filling until I could see fuel right at the edge of the fuel cap port, sometimes a drop or two trickling out...I know the systems limit the pump to have a reserve of .5 gallon/pumping out 2.4 gallons for longevity of the pump - perhaps topping up like this was unnecessary, as "overfilling" doesn't really increase range...psychologically it feels better though

- The Rex/fuel system is not 100% reliable - one time during our trip - the REx would not engage, we stopped, restarted the car a few times, REx would not start...opened and closed the fuel cap & door a few times in combination with restarting the car - was finally able to start the REx...was quite scary since we were in the middle of the trip...


Will be doing the trip back in a few weeks and compare the data


//update 07/20
The i3 was throwing drive train error message and took it to the nearest dealership - they found the fuel pressure sensor to be bad - they swapped it out and now the fuel door opens as it should without messing with the green vapor release tab every time so far.

 

[bwilson4web]

Hi,

I run our car at maximum sidewall pressure, 51 psi, and just like the Prius, it makes a measurable improvement in mileage. Given your load, maximum sidewall pressure, also ensures the maximum load capacity.

Bob Wilson

 

[EVBob]

Hi,
I run our car at maximum sidewall pressure, 51 psi, and just like the Prius, it makes a measurable improvement in mileage. Given your load, maximum sidewall pressure, also ensures the maximum load capacity.
...

Thanks for the tip!

I glanced at the TPM once during the trip - I recall the fronts were at 47-49 psi and the rears were around 49-50psi - I'll be sure to bring them all up to 51-52 psi on the trip back...

Thinking about it - I need check the tires on my gen1 insight are at 55 psi ;-)

 

[alohart]

I glanced at the TPM once during the trip - I recall the fronts were at 47-49 psi and the rears were around 49-50psi - I'll be sure to bring them all up to 51-52 psi on the trip back...

Thinking about it - I need check the tires on my gen1 insight are at 55 psi ;-)

There must be a good reason why the recommended inflation pressures differ for front and rear tires, so I maintain the 8 psi difference on our i3 and the 3 psi difference on our Insight with the higher pressure equal to the maximum inflation pressure stamped on the sidewall, 51 psi on our i3 and 44 psi on our Insight.

 

[jadnashuanh]

The higher the pressure, the smaller the tire contact area, the less traction, and the ride gets stiffer. You're also more prone to tire/wheel damage, since it can't respond as easily if the air pressure isn't as designed. Your choice. In a worst case scenario, you'll also wear out the middle of the tire faster than the edges...the belts can only hold the shape so well.

 

[alohart]

You're also more prone to tire/wheel damage, since it can't respond as easily if the air pressure isn't as designed.

It's difficult for me to understand how higher inflation pressure might result in a greater probability of tire/wheel damage. In my case, I want to reduce the likelihood that the sharp edge of a pothole could collapse a tire so much that the tire could be pinched between the pothole edge and the wheel. Increased inflation pressure accomplishes this goal.

In a worst case scenario, you'll also wear out the middle of the tire faster than the edges...the belts can only hold the shape so well.

This was true for bias ply tires, but much less true for radial ply tires. Honda Insight owners who have been inflating their Bridgestone low rolling resistance tires as much as 15 psi over the sidewall maximum pressure continue reporting tire edges wearing out before the middle area, so I expect similar results with our i3's Bridgestone tires.

 

[jadnashuanh]

When inflated to the specified pressure, the tire acts as a major component of the suspension. When you significantly over inflate it, instead of absorbing (by flexing) on those impacts, the entire tire/wheel acts more as a solid body...given a big enough impact, that force can damage the tire and potentially, the wheel and maybe even the suspension. It also makes it harder for it to conform to irregularities in the road surface, limiting its surface contact, which will decrease rolling resistance, but also increase braking distance and affect handling. Raise the pressure high enough, the tire barely deflects, and the contact patch approaches just the area immediately at the road surface - a narrow strip. The bead is only so strong, as is the wheel.

 

[bwilson4web]

This is some merit in this:

When inflated to the specified pressure, the tire acts as a major component of the suspension. When you significantly over inflate it, instead of absorbing (by flexing) on those impacts, the entire tire/wheel acts more as a solid body...given a big enough impact, that force can damage the tire and potentially, the wheel and maybe even the suspension.

The aluminum body of the BMW i3-REx appears to be susceptible to this. I run my tires at 51 psi and had a motor mount bolt failure six months later. But I was also hitting a split, speed bump with the driver side wheel in the gap. The suspension appeared to be working perfectly, smaller motion at higher speed, but it would put a torque on the motor mount. Still it took another three months before it was diagnosed.

I had started monitoring my tire temperature profiles and found the driver side rear had excessive negative camber. When I had the wheel alignment checked, the right side wheels were 'toe out' and the driver rear wheel had too much negative camber. Yet curiously, this same driving practice never affected our steel body and suspension, three Prius over a period of nine years.

FYI, I changed my driving style to be more respectful of the speed bump, including the split ones. Now I slow down and take them so both sides get the same, significantly lower impulse.

It also makes it harder for it to conform to irregularities in the road surface, limiting its surface contact, which will decrease rolling resistance, but also increase braking distance and affect handling. Raise the pressure high enough, the tire barely deflects, and the contact patch approaches just the area immediately at the road surface - a narrow strip. The bead is only so strong, as is the wheel.

I've not been able to confirm a problem with stopping distances but the literature reports the tires are less subject to hydroplane effects improving stopping distances and steering in rain. Regardless, I typically follow car racing articles that discuss the importance of tuning the tires to the track and conditions.

In our Prius, I did one inflation vs tire bead temperature test by fully inflating the tires, running 10 miles, and measuring the tire tread temperature. Then I reduced the pressure about 5 psi:

• higher pressure tended to equalize the tread temperature - so the tire with the camber problem had more equal temperature.
• higher pressure lead to lower temperatures - less rolling drag, by a factor of two.

So my approach is to correct the wheel alignment first. Then I can do a tire pressure vs tread temperature test.

Bob Wilson

 

[jadnashuanh]

The CFRP frame of the i3 creates a much stiffer chassis than most steel bodies, that literally become part of the suspension. The CFRP flexes very little, so the suspension, at least in theory, can work better with more control rather than trying to account for the spring effect of the chassis.

 

[CCJ]

Those of you putting in all that psi... Doesn't the ride get harder for you? I'm ok sacrificing some miles to be more comfortable. HOWEVER, I have never inflatted my tires to such amount of psi. So maybe my logic is not sound.

 

[bwilson4web]

Those of you putting in all that psi... Doesn't the ride get harder for you? I'm ok sacrificing some miles to be more comfortable. HOWEVER, I have never inflatted my tires to such amount of psi. So maybe my logic is not sound.

Take a tire pressure gauge and do the experiment:

• Fully inflate tires - 51 psi is embossed on the sidewall.
• Reset the trip meter.
• Drive a test route - look for well patched, bumpy road.
• Mark the "mi/kWh"; reset the trip meter, and; record your impressions.
• Reduce pressure 5 psi and repeat test drive ... DO NOT GO BELOW RECOMMENDED 34 PSI!

When done, share your results. Understand this is how we all learn. <GRINS>

Good luck!
Bob Wilson

 

[jadnashuanh]

If you were to take this to an absurd extreme, say you put 100psi in the tires...they would deflect very little to hold up the weight of the vehicle, and any imperfection in the road would be transmitted directly into the suspension by the tire/wheel assembly that is acting like a solid body, not a flexible one. That force could be enough to literally fracture your wheel or split the tire's carcass. Given the vehicle's weight, the suspension, and the tire size, the indicated tire pressure is a good compromise on efficiency, longevity, and comfort. If you regularly were running at maximum load, it might make sense to raise the tire pressure some. Most people run around with one or two people in the car, and the stock tire pressure should work. Too low of a tire pressure results in a lot of flex, higher temperature, and potentially damaging both the tire and/or wheel if you were to hit a sharp bump by pinching the tire and hitting the wheel.

 

[amcdonal86]

The thing that concerns me the most about your post is that the REx would not come on reliably. Obviously this is a huge concern for US spec cars, which from the factory, will only activate the REx when 5% battery remains. I can only imagine what a heapload of trouble I'd be in if I had run the battery down to 5% charge (4 miles?) and the REx wouldn't come on!

 

[EVBob]

The thing that concerns me the most about your post is that the REx would not come on reliably. Obviously this is a huge concern for US spec cars, which from the factory, will only activate the REx when 5% battery remains. I can only imagine what a heapload of trouble I'd be in if I had run the battery down to 5% charge (4 miles?) and the REx wouldn't come on!

It seems the only difference besides charging ports between the European and North American i3s is the coding.

On the ride back the REx was reliable - the issue with the initial trip and the REx not engaging (and having to do the manual fuel door release) appears to have been linked to the bad Fuel Pressure sensor that seems almost a common issue for the 2015s.

Would I recommend doing a long road trip in this car again...not really....not so much of reliability concerns...more so general seat comfort after several hours and having to stop every 80-90 minutes to refuel gets old...

 

[jadnashuanh]

The fuel tank size is different between the USA and many other countries (coding only, the tank is the same), as is the plug, but the actual charging interlock/protocols are the same. One additional potential difference is that in some areas, they have a 3-phase input for the acv.