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Discussion Starter #1 (Edited)
A very effective winter efficiency boost!

Backstory - we put on my wife's winter tires yesterday in anticipation of winter finally arriving here, which are 195/65R15 Michelin Xice 3's on steelies from Tire Rack. I set the inflation pressure lower on these tires as well, to door sticker 38 PSI instead of the 44 PSI I was running in the stock tires for efficiency - I wanted better tire compliance for degraded road conditions and to optimize braking performance. It should be noted that the Xice winter tire has its max load rating at 50 PSI compared to 44 PSI for the OEM tire, keep that in mind when doing load calculations for your tires. Higher pressure could still be warranted in winter due to this important difference.

A correction factor was necessary to compensate for the tire diameter, the winter's are 1.92% smaller, and the odometer and the Wh/mile display will be off by this amount - the car will think it has traveled further than it actually has. One advantage of a tire that is slightly smaller and narrower is traction aids like low profile chains will fit much more confidently on the vehicle, perhaps offsetting Chevy's "no chains" recommendation in your risk-benefit evaluation. One downside is the loss of 1/4" of ground clearance - negligible in my opinion.

All that tire drivel is background information for my expectation that the wife's trip this morning would take a measurable hit to efficiency. Her last trip before the change was on the OEM tires at max sidewall pressure and outdoor air temps of 50F, returning a daily efficiency measure of 4.0Wh/Mile. Today was 10 degrees (F) colder, with lower tire pressure, on sticky new winter treads. The efficiency reading? 4.2Wh/mile! Accounting for the odometer discrepancy leads to a 4.12Wh/mile true result. Not bad!

There is one more energy hack I did in anticipation of the falling energy efficiency, and it has to do with my wife's weak constitution when it comes to cold weather - a heater hack. She can be a bit heavy with the heater use compared to the hard core here on the forums, and likes to keep it at 70F on fan speed low when it gets cold out, usually with max seat heat and steering wheel heat as well. I purchased a set of Venture brand heated 12V insoles for motorcyclists and put them in a pair of her slip on winter boots. I just put a Blue Sea cigarette lighter plug on the end of the harness, the insoles pull about 1-2 amps when connected directly; just plug into the dash. The cabin heater was completely unnecessary for her trip save for defog bursts, which is quite impressive given her aversion to being cold!

Conclusion, TL;DR: Michelin Xice 3's might be some kind of magically efficient winter tire, limiting heat use is the holy grail for winter driving efficiency, etc.
 

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Today was 10 degrees (F) colder, with lower tire pressure, on sticky new winter treads. The efficiency reading? 4.2Wh/mile! Accounting for the odometer discrepancy leads to a 4.12Wh/mile true result. Not bad! [/I]
I am not sure the differences in efficiency that you report are significant. its very easy to make small changes in a range of variables that would elicit such small efficiency differences. I am sorry to say that there are just too many variables for you to draw the conclusions that you have drawn here. I really can't think of a good experiment that would control all the variables so closely that you could detect such small efficiency differences between the two tires. Now, if the winter tires had made a 0.5 - 1.0 difference in efficiency, then I would be happier, but it appears the two tires are not really significantly different.
 

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I have always put snow tires on here at 10000 ft in Colo, but I got tired of the expense and hassle of changing them on the Prius so I just kept them on year-round for the last couple years. Not ideal, I know, but does not seem awful.

I anticipate the same protocol for the Bolt, but since it has brand-new all-weather Michelins, I figure I will keep those for at least one year. I did note BlackBolt's use of Michelin XIce tires. Are those highly recommended for winter use? In the past I used Blizzaks, which seemed very good, and change my view of the Prius in winter quite a bit.

I do note the heads up re. odometer error given tire size, but I guess you deliberately chose a different size than standard for the Bolt.
 

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Discussion Starter #4 (Edited)
I am not sure the differences in efficiency that you report are significant. its very easy to make small changes in a range of variables that would elicit such small efficiency differences. I am sorry to say that there are just too many variables for you to draw the conclusions that you have drawn here. I really can't think of a good experiment that would control all the variables so closely that you could detect such small efficiency differences between the two tires. Now, if the winter tires had made a 0.5 - 1.0 difference in efficiency, then I would be happier, but it appears the two tires are not really significantly different.
The primary finding was one of total surprise, more than anything. We previously were unable to get better than 3.4-3.8mi/kWh in equivalent weather conditions on the OEM tires at high pressure. The weather to efficiency correlation has been rock steady previously, and to see the efficiency go up with the tire changes was very, very unexpected. Since I changed both the tires and the heater use variables simultaneously, I am not interested in per-variable tracking, just the overall picture. And the overall difference was quite surprising, in the opposite direction vs. what I had anticipated. To be clear, this is looking like a +0.3-0.7mi/kWh differential in equivalent weather - but the sample size is small atm.

The Mchelin Xice is 2nd-best rated on the reviews from what I have found, after the Blizzak WS80. It has better dry handling characteristics, better mileage, and lower road noise, as well as a tread wear warranty. It is weak in heavy slush compared to other winter tires from what I have been reading, but the overall performance is highly rated. This will be our first season on them.

The 195/65R15 was the recommended tire size from Tire Rack for the Bolt (on that rim) and I concurred with their recommendation. I always like a tall sidewall and a narrow profile in winter driving. I'll keep track of how things progress with the weather.
 

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I did note BlackBolt's use of Michelin XIce tires. Are those highly recommended for winter use? In the past I used Blizzaks, which seemed very good, and change my view of the Prius in winter quite a bit.
I don't have any experience with other recent brands of winter tires, but I've used the XIce XI3 tires for a couple of years now and I've been very happy with them. I had them on my Prius C last winter and now on my Bolt this winter, and I've never been in a situation where the tires failed me. We don't normally get a lot of snow in Vancouver but we had three weeks of snow and ice last winter and going up and down hills with grades of around 6-8% was a complete non-issue.
 

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Discussion Starter #6
UPDATE:

Nothing short of amazing is all I can say. Afternoon commute to work, 34F outdoor temp, 25 Miles, left from a 50F garage and preconditioned on the plug. 4.6mi/kWh (4.51mi/kWh actual). Mostly rural highway 55mph roads.

Return trip, 24F outdoor, 25 miles, cold soaked, no plug at work. Dropped the total daily average down to 3.8mi/kWh (3.73mi/kWh actual).

The only other comparable trip we have on the stock setup was about 2-3 degrees colder, and the car returned 3.3 on the preconditioned first leg, and 3.1mi/kWh for the daily total.

I cannot believe that the addition of warm feet was all it took for her to be comfortable and make the cabin heater almost completely unnecessary. Interestingly, on a clear day, the defrost didn't seem to be necessary once the car is cold soaked, the windows stayed clear for the duration of the return trip - no precipitation. Note that she mentioned that with thin dress socks, the insoles are a bit too hot, and she cycles them off-on by unplugging them! I need to get one of the rheostat controllers to make them adjustable.
 

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I've seen a lot of mileage competition winners rolling on winter tires. I'm talking in the heat with zero chance of snow. I don't think you are imagining things. I've ran a set myself and I'm in Los Angeles.

Good tip on the motorcycle heated garments.
 

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I don’t think I’ll be in the market for shoes I have to plug in to help me keep warm. I’ll just set the cabin temperature to 72 and let the car take care of keeping me warm. I do like the heated steering wheel, and my back really likes the heated seats, but I don’t see any reason to stop using the cabin heater just because it costs a few more kilowatts.

The Bolt is already a very efficient car, if the miles per kilowatt drops 20%, that’s OK with me.
 

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Discussion Starter #9
I don’t think I’ll be in the market for shoes I have to plug in to help me keep warm. I’ll just set the cabin temperature to 72 and let the car take care of keeping me warm. I do like the heated steering wheel, and my back really likes the heated seats, but I don’t see any reason to stop using the cabin heater just because it costs a few more kilowatts.

The Bolt is already a very efficient car, if the miles per kilowatt drops 20%, that’s OK with me.
I sympathize with this, not everyone will chase efficiency, that is clear simply looking at the state of the US in particular.

It's an easier sell for someone like my wife. She wears slip on shoes, and already did the whole shoe switcharoo in winter, needed bulky boots to keep her feet warm but they are incompatible with a professional work environment. She is quite thin, and on top of that has something called renauds syndrome, which is a circulation thing with the hands, which makes cold (especially the steering wheel) painfully unpleasant. You should have seen her eyes light up when I told her the Bolt has an available heated steering wheel when we were shopping - I think Chevy sold her the car that very moment, before she even saw one!

In her Prius she would blast full temp heat from the time she left work until arriving home for 30+ minutes in the winter, and still come home with cold hands and feet on some days, she's just very sensitive and slow to recover. The faster warm-up of an electric car is an advantage here already but with the combo heated boots, seats, and steering wheel, this not only hasn't been a problem even in sub-freezing temps, but the "quality of life" component is substantially better - which makes me very happy indeed!

Now, compare that to me - I don't really get cold, and if I do, I don't really care. I wear lace up shoes and boots, I don't even own a slip on pair of shoes. Selling me on switching to heated footwear to drive in would be much harder, which is probably why I haven't bought a pair for myself yet. Different strokes!
 

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Discussion Starter #10
Another quick update, colder today.

Morning, preconditioned/garaged, 20F, clear, 4.1mi/kWh, 4.03 actual.

Return, 9 hour cold soak, 30F, clear, 3.8mi/kWh, 3.73 actual - daily average.

I'll do a few more over the next few weeks to round out the data, particularly looking for colder temps as they present themselves.
 

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Discussion Starter #11
I did a little experiment yesterday. It seemed that the battery temp. made a considerable difference in morning efficiency. I have a single car garage that is attached to my basement by means of a 32" man door, so I opened it up and let a 20" box fan set to low speed attempt to equalize the temperatures between the two areas. Both are "unconditioned" space, but the basement is always warmer as the garage is not weather sealed/insulated well, and only partially subterranean. This brought the temperature up to around 55F several hours before the commute - not as warm as the basement, but warmer than normal storage temperature by about 5 degrees.

11DEC2017

Morning, 32F, preconditioned/garaged, 32F, clear, 5.0mi/kWh, 4.9 actual.

Now before the trip home, about 1/4" of snow had fallen. The wife doesn't precondition at work, but she did put the defroster on yesterday while she was clearing the windows. This dropped the average efficiency down to 4.7, (4.61) in about 2 minutes before she left the parking lot. A good demonstration of the heater energy use impact I thought.

Return, cold soak, 32F, light snow, 4.1mi/kWh, 4.02 actual - daily average.
 

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Discussion Starter #12
Today was a doozy! I didn't blow any heat into the garage, and probably won't in the future - but I may add some weatherstripping and insulation to retain some more heat, good for both the car and working out there in the winter months.

Morning precondition/garaged, 30F, wind gusts, light snow covered roads in spots up to ~1", 3.9mi/kWh (3.83)... Many defrost uses required for fog forming on the inside of the windows.

Return, 17-18F, calm winds, more snow covered areas on the road, 3.5mi/kWh (3.43) daily average
 

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Discussion Starter #13
Today, standard commute:

Morning - preconditioned, [email protected] Outdoor 10F, clear & calm. 3.5mi/kWh (3.43)

Return - 17F, calm, 3.2mi/kWh (3.14) daily average.

Over the past few weeks I've noticed on the days I charge, the departure timed charging make a measurable impact on the first trip efficiency with the fresh extra heat in the battery.
 

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Thanks for that tip. I'll try it next time I charge. I think Butte is going to be about as good a place as any for testing out winter tips. We're at 5500 feet at the Continental Divide so there will not be many places that are consistently colder.
 

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Discussion Starter #15
Thanks for that tip. I'll try it next time I charge. I think Butte is going to be about as good a place as any for testing out winter tips. We're at 5500 feet at the Continental Divide so there will not be many places that are consistently colder.
I'll be interested to see if the departure charging time makes a difference for you, let me know.

Today I had her do data collection again since it was cold. Today was a charge day, so the battery was warmer - but the outdoor temps were cooler.

Morning - preconditioned, [email protected], outdoor 6F, calm, 3.8mi/kWh (3.73)

Return, outdoor 12F, calm, 3.2mi/kWh (3.14) daily average.

She had to use the heat on the way home a little bit due to the very cold temps to remain comfortable. The precondition + defroster use is more than adequate on the morning leg.

I will be doing some more efficiency mods soon. :nerd:
 

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Update

We're on target for a pineapple express winter storm event which initially will mean slightly warmer temps. Big difference! After a charge to 140 full this AM, drive to work and errands at 10-15 F and then warming up to near 30 in the PM. I run up to Homestake Lodge for XC skiing almost every afternoon. This features a 1000 foot climb up to Homestake Pass at the Continental Divide and 6 mile RT into the lodge. Today I was able to expend essentially 1 miles range driving in and out and then back to my house...a total of 16 miles. Range total now would be over 160 and mi/kWh is at 3.1, after starting at 2.2 this AM. I think the big difference was the improvement in regen as yesterday I gained essentially no miles on the descent.
I was able to do a bit more cycling of the heat on and off with the warmer temps.
 

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I too am very happy with the XIce3's! They seem to be as efficient as the Stock tires are in warmer weather. I'm running 205/60R16s which are almost the same diameter as stock 17s.
We had our first snow last week in Chicago (2-4 inches by me) and the tires worked very well on starts and stops.
In warmer weather ( 40s-50s) I've seen easily 4.5 mi/kWh, as the Temps dip into the 10-20s this dropped to the mid 3.5mi/kWh. Lately I've been running my heater( defrost and foot setting) at 71 and fan speed on 1 consistently without any preconditioning. The last few days we've seen -3F in the morning warming to about 8F. My garage is about 30-35F now.
No preconditioning, same heater settings, getting about 3-3.2Mi/kWh average and between 160-180miles on full charge. I turned off Hilltop Reserve for the winter months to get the most out of the car.
 

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Revelation

I suppose this isn't new to some....
I decided to try something a little different after I did a delayed charge to be ready at 9 AM. Actually charged up a bit before that, probably a bit after 8 AM...the lights flashed which I figured must mean it was charged as there was no other reason for it. Showed 154 miles as fully charged. So, I decided let's see how well it does just recycling cabin air without heat...I had the defrost indicator on but no heat, just re-circulation. Big difference! I'm sitting at about 3.7 mi/kWh compared with 2.1-2.5 when the heat was on, set to 67, blower on 2. So after 35+ miles driving today my indicated range is 150. The day was partly cloudy temps from 18 or so up to high 20s. Re-circulation seemed to do fine keeping windshield/side windows clear and I had the steering wheel heat on along with the seat.
 

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Discussion Starter #19
Could be worse!

Very nice! I have always been hesitant to use recirc in the winter to keep moisture from building up on the inside over time, in the carpets and other porous areas. If you can keep using recirc daily for a few weeks without any trouble, I'd be sold on this idea for sure. It'd be great if we could set a blend percentage instead of just binary options on this setting, too.

Now I've done some more efficiency mods, I don't know how well they'll work. The first is a heated blanket for the Mrs. - she's been using cabin heat more in the low teens and single digits and I'd like to see if this has any impact on her comfort level. We considered other heated gear, but it seemed too cumbersome to try and do a pants or a jacket. The blanket is rated at 5 amps, so this would be a total of 7 amps max of heated gear power.

I also went ahead and did this:


Who knows if that will have any impact. Since the commute sees a max of 55-60 mph, it may only be noticeable on the highway. Or not at all! The Mrs. insisted that these not be silver, so we plasti-dipped them black. She's ambivalent on it, it's at least par with the steel winter wheels she says. They are the pop on kind, I added some bungee cords and hooks to the back side for extra holding power. I have no idea if that will keep them fixed on there. It does keep them easy enough to remove to do air pressure, though.
 

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I also went ahead and did this:
Who knows if that will have any impact. Since the commute sees a max of 55-60 mph, it may only be noticeable on the highway. Or not at all! The Mrs. insisted that these not be silver, so we plasti-dipped them black. She's ambivalent on it, it's at least par with the steel winter wheels she says. They are the pop on kind, I added some bungee cords and hooks to the back side for extra holding power. I have no idea if that will keep them fixed on there. It does keep them easy enough to remove to do air pressure, though.

Oh man! I am dying to hear if these do anything. Keep us posted.
 
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