Different Miles/Kwh on same year i3?

Greetings All,

We (better half and I) have noticed, on the less mileage (12.5K miles) i3 Rex we are getting about .2-.5 miles/kwh less than our higher mileage i3 (47K miles) Rex - both are 2015 models with 19" wheels, air pressure in the tires are within 1-2 lbs compared between the two and they have roughly the same wear on the rear tires...new one has 6.3 vs 5.7-ish on the 47k one. The one with Less Mileage has the Terra Package vs the 47k one has the Mega World Package.

We have switched i3s several times a month for several months on regular routes/commutes, and the difference in miles/kwh seems consistent. Any idea what could contribute to this? I wouldn't think the Mega World wheels could contribute this noticeable amount? The i3 gets it's miles/kwh by constant measuring of a kwh and odometer - it is not based on odometer reading compared to battery %?

Thanks in Advance!

It can be the extra weight on Terra and/or Tire pressure but I think just like the Aero wheels on Tesla are suppose to have about 10% higher efficiency...2015 i3 Mega has wheels similar to Aero could be the reason behind it.

I agree with i3Houston, I bet the Terra i3 weight is slightly higher than the Mega one. You could take both to the same scale and weigh each of them to compare. If they are different then load up the Mega and repeat the experiment. Then after that swap the wheels between the two!

-Tim

i3Houston said:

It can be the extra weight on Terra and/or Tire pressure but I think just like the Aero wheels on Tesla are suppose to have about 10% higher efficiency...2015 i3 Mega has wheels similar to Aero could be the reason behind it.

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Not only that, but the Mega wheels (style 427 for those outside North America) are the lightest i3 wheel. The angular momentum of a wheel affects efficiency but maybe not as much with EV's due to regenerative braking which would be greater with heavier wheels.

alohart said:

Not only that, but the Mega wheels (style 427 for those outside North America) are the lightest i3 wheel. The angular momentum of a wheel affects efficiency but maybe not as much with EV's due to regenerative braking which would be greater with heavier wheels.

Click to expand...

Now I am really tempted to swap the wheels on the two cars, to see if the mi/kwh follows them....just need to figure out how to have both cars need to have their tires changed at the same time....

Until then, would love to hear other drivers experience when switching to or from (more likely) from the Mega World/style 427 wheels?

I can't imagine the Terra World adding that much more weight from the Mega World trim...slightly heavier idrive unit with hard drive, leather vs wool/pleather, additional sensors for comfort access, more wiring...maybe adds another 20lbs at most to the car? Then again, this lower mileage car also has the HK audio and ACC...so those additional speakers & better amp would add probably another 5-10lbs? ACC - no idea how much weight that would add?

If the .5 mi/kwh is primarily just from the wheels, that is a pretty sizeable increase ...that is an additional 9 miles or roughly 12% increase in range for our RExs...wonder if BEVs would have the same % increases

Ok found out the Wheel weights

For the 427 (Mega World - LA Star Spoke/Pizza Pan Style): http://bmwfans.info/parts-catalog/I01/Europe/i3_Rex-IB1/L-A/jun2015/browse/wheels/bmw_i_la_wheel_star_spoke_427_19/

For the 428 (Terra World - Turbine Style): http://bmwfans.info/parts-catalog/I01/Europe/i3_Rex-IB1/L-A/jun2015/browse/wheels/bmw_i_la_wheel_turbine_styling_428_19/

Giga world - http://bmwfans.info/parts-catalog/I01/Europe/i3_Rex-IB1/L-A/jun2015/browse/wheels/bmw_i_la_wheel_turbine_styling_429_19/

20" Sport wheels : http://bmwfans.info/parts-catalog/I01/Europe/i3_Rex-IB1/L-A/jun2015/browse/wheels/bmw_i_la_wheel_double_spoke_430_20/


The Mega world wheels (427) are indeed lighter than the Terra World Wheels (428) at 16.2lbs vs 18.1lbs for the 5" fronts and 16.9lbs vs 18.5lbs for the 5.5" rears....roughly a 10.5% & 8.6% weight savings per wheel...

So I suppose between those weight savings and the more aerodynamic shape of the Pizza Pan wheels would net us a 12% increase in range?...that and maybe trimming 50-60 lbs (guesstimate) in accessory weight (Leather, ACC, HK & Comforfort package weight, etc)?

Interestingly enough, the Giga World has the heaviest wheels of the three trims at 19.6lbs for the 5" wheels and 20.1lbs for the 5.5" wheels.

20" sport wheels are 20.3lbs for the front and 20.7 for the rears....

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Figuring Weight difference between the 19" Mega World and 20" Sport wheels + tires:

The EP600 19" tires weight 16.32 for the fronts https://www.fleetfarm.com/detail/bridgestone-ecopia-ep600-tire-155-70r19-tlblps84q/0000000270288?Ntt=155%2070R19
18.3 for the rears: https://www.fleetfarm.com/detail/bridgestone-ecopia-ep600-tire-175-60r19-tlblps86q/0000000270289?Ntt=175%2060R19


The EP600 20" tires weigh 15.88 for the fronts: https://www.fleetfarm.com/detail/bridgestone-ecopia-ep500-tire-155-60r20-tlblps80q/0000000269844?Ntt=155%2060R20
17.64lbs for the rears: https://www.fleetfarm.com/detail/bridgestone-ecopia-ep500-tire-175-55r20-tlblps85q/0000000269852?Ntt=175%2055R20

Mega World:
Front - 32.52lbs per tire+wheel
Rear- 35.2lbs per tire+wheel

20" Sport:
Front: 36.18lbs per tire+wheel
Rear: 38.34lbs per tire+wheel

For fun:
Giga World
Front - 35.92lbs per tire+wheel
Rear - 38.4lbs per tire+wheel

On an ICE, the common thought on extra weight, all other things being equal, equates to about 0.1mpg/100#. I don't think the few pounds of additional wheel weight is likely your solution. Note, though, that the major component of MPGe differences between the BEV and the REx is because of the added weight on the REx verses the BEV. Not sure what the latest figures are, but seem to remember it being about 8-miles of range reduction for that increase (about 340#) of weight. The newer, higher capacity battery is also heavier, and that dropped it for all models verses the original ones regarding MPGe. It's one of those 'you don't get something for nothing' issues. It's the major reason BMW developed the CFRP body structure...to save weight and maximize range.

FWIW, does one vehicle constantly have more stuff in it? Differences in passenger weight, unless extreme, probably wouldn't account for it. It does take more to accelerate a heavier car, but steady state, not going up a hill, would be very similar. You'd also recoup a bit more going down a hill with the heavier car.