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2018 Chevy Bolt EV
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Without some details on methodology, I would hesitate to rely on this study or graph. There are a number of feature differences that can skew this kind of graph, seat and steering heaters, windshield heater, heat pump vs resistive heater. Additionally, there are practices that can offset some of the above. Finally, winter vs all season tires, and tire pressure.

I tracked my Bolt's efficiency to\from work for 2.5 years. The commute was 130 miles RT (65 each way), long enough to be statistically relevant and not based on a 5 mile commute that doesn't require HVAC use for example. Based on this data, seasonal differences were -20% in winter. My driving practices probably account for the performance being better than what the graph illustrates (-30%), I always precondition 20-30 minutes before leaving on cold mornings, rarely use cabin heat, always use seat and steering heat, wear warm clothes, and don't use winter tires. Yesterday was equal RT efficiency to my 2.5 year average despite AM temps 30F and afternoon temps 50-60F.

My son owned an eGolf (rated -20% above). His experience with all season tires was -30 to -40% and he traded the car after 2 weeks of winter driving due to inadequate range. Why were his results worse than the graph? I can't say for sure, but I know he is temperature intolerant, so likely a lot of HVAC use.

I find it flawed at best that Model Y (+1%) results are higher in cold weather. I know the car uses a heat pump for HVAC, but still it defies logic unless the stats come from a survey of owner experiences (the fanboy effect). The Tesla owners I know state 20% or more is a reasonable range loss figure for their experiences.

AAA did a study two years ago and claimed an average of 20-50% range loss in winter, with the higher figures coming from extensive HVAC use. That some EV may do a little better is understandable, but these AAA numbers are probably more realistic.

Some of the factors that reduce efficiency\range are chemical (battery composition), some are laws of physics (cold air is denser and thus more resistance), tire resistance also for similar reasons. Clearly, any HVAC use reduces efficiency\range as that is a fixed (or reduced) amount of energy used for something other than moving the vehicle (true to a lesser extent in summer too). Heat pumps are merely more efficient than resistive heaters, but they do not generate energy, saying so would be similar to declaring perpetual motion is real. Of course, climate goes beyond temperatures, wind speeds may be higher in winter months, leading to greater air resistance as well.

For all of the above complex reasons, it is dangerous to use specifics like this to advise new or prospective owners about what to expect, the chances of disappointment are great if you sell wrong info.

So, I tend to rely on the AAA study and suggest to be safe, prospective owners should consider a significant buffer when choosing a car based on range. Assuming a 50% range hit in winter means buying a car with 2X EPA rated range vs the owner's daily use. Drive 75 miles, make sure the EV has at least 150 miles of range. If the estimate is too pessimistic, they are pleasantly surprised.

Finally, for the fortunate few who can charge at home and work, the answer is completely different, basically buy whatever you want because it shouldn't be an issue unless you drive 300+ per day. And therein lies one of the best selling points to encourage workplace charging, that some employees may find cold weather makes EV ownership a hardship suggests employees will appreciate workplace charging even more and arrive in more comfort. That translates to an even more valuable employee benefit and perhaps a productivity gain for the employer.

I would appreciate Tesla owners weighing in, I find the above is not realistic and could sour new Tesla buyers when their cars fail to achieve the kinds of range\efficiency that the chart suggests. One theory I have is the Guess-o-Meter methodology. If the study is based on the GOM readings at full charge, I understand Tesla tends to use a set formula rather than consider recent driving efficiency the way many (most?) other EV do. Do Teslas actually deliver the GOM estimated range in the real world, or do they fall short in the winter?

My Bolt's GOM is heavily influenced by recent driving efficiency. Lately, my driving is mostly around town and averages around 4 mi/kWh. Daily charging brings the GOM up to about 180-190 miles at 90% SoC (I don't charge to 100%). Following my 5.2 mi/kWh commute yesterday, I was greeted with a GOM of 220 miles this morning. Same temperatures, but a long day at higher efficiency made a big difference in the range estimate.

As the Mark Twain quote goes...there are lies, damned lies, and statistics. My vote goes for keeping the discussion more general.
 
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