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Bridgestone Blizzak Efficiency Numbers

Discussion in 'Model X: Driving Dynamics' started by Solarman004, Apr 7, 2018.

  1. Solarman004

    Solarman004 Member

    Joined:
    Apr 27, 2016
    Messages:
    696
    Location:
    Colorado
    I just completed my first winter with 19" Bridgestone Blizzak DMV2 winter tires. I set a trip meter on the day I installed them, and below are the results from the day I changed them out this week. This is for my Aug 2016 MX 75D. Regular tires are the OEM 20" Conti-Silent.

    First, the efficiency numbers before the Blizzaks were installed:
    22,920 miles over 16 months which includes one full Colorado winter. Mild temperature average was 292 Wh/mile; cold weather average was 330 Wh/mi; and lifetime average at the time the Blizzaks were installed was 311 Wh/mi.

    For the Blizzaks: 3279 miles over 3.5 months. Average efficiency for this period was 374 Wh/mi. My lifetime average rose to 323 Wh/mi.

    There are caveats that make it difficult to determine how much of this efficiency loss is due to the tires. 62% of the miles driven in this period were on a road trip to the upper midwest during the deep freeze. For 2030 miles over 10 days, the car was exposed to a temperature range of -14 deg F to about +12 deg F. Most of the time we saw low single digit temps which made our 75 kWh battery beg for mercy.

    Additionally, the rest of this Blizzak period was during in an abnormally warm and dry Colorado winter. Diving temperatures in the 40s to 60s (deg F) leads to softer winter tires and increased friction.

    So I think I've concluded that the Blizzaks did have a negative impact on efficiency but I can't say precisely how much. I do know that trip planning with these tires on requires an efficiency estimate of 350 to 360 Wh/mi in the planner.

    With all this said, I don't second guess this decision. The performance of these tires in snow is superb.
     
  2. dhh12

    dhh12 Member

    Joined:
    Sep 11, 2016
    Messages:
    125
    Location:
    michigan
    Ok - you just made me realize I am not smart enough to own my car.....I feel like a peasant intellectually.

    Most lithium-ion batteries used in modern electric vehicles have a slightly negative or a very small entropy change, which means that the open cell voltage increases slightly as temperature decreases. This alone would actually improve performance at lower temperatures. However, the change in open cell voltage as a function of temperature is relatively small compared to other parameters, around 0-0.4 mV/K — that is less than 30 mV over a range of very cold temperatures (-35°C, -31°F) to room temperature. We can therefore rule out the net discharge reaction thermodynamics as a reason for poor performance at low temperatures -

    Good observations - do you think the average daily temperature was higher or lower when compared to the same period prior to the Blizzaks?

    Did you pre-heat the cabin while your car was charging?

    Do you think all other variables were constant or were there other factors - depth of snow, duration of heating, wife turned up heat excessively, higher average trip speed?

    Thanks.
     
  3. Solarman004

    Solarman004 Member

    Joined:
    Apr 27, 2016
    Messages:
    696
    Location:
    Colorado
    1. It's hard for me to make a comparison on average winter temperatures. Clearly, the average temps during the "big freeze" trip were well below the Colorado winter average of 20s and 30s (F). But for the other 38% of the mileage in this Blizzak period, our Colorado average temps this winter have been quite a bit higher than normal.
    2. During the "big freeze" trip: a) four seat warmers used at level 1 or 2; b) front windshield heat at 62 deg was the only cabin heat used to prevent interior window fogging and frosting; c) enroute, we preheated the car at every Supercharger; d) for the two overnight enroute stops, we stayed at hotels with Superchargers. Charged on arrival while battery was warm to 80% and then charged in the morning to 90 or 95% to preheat the battery (turns out that after cold soaking in single digit or negative temps, this added 10% did not bring back any regen); e) our 8 day stay was in a town with no SC. Plan was to trickle charge but that fell through when I discovered the old house we were staying at had an ungrounded electrical system and the UMC wouldn't work. So our short trips during the stay used a lot of battery warmer energy, and provided near zero regen. I used a supermarket Level 2 charger during the stay but couldn't preheat. Even turning on the front heater only to 65 deg, the heater was consuming more power than the Level 2 charger could provide (6 kW). If I turned on the heater, "Time to Charge" would jump to "24+ Hours."
    3. Drove in less snow this winter with the Blizzaks than last winter with the Conti all-season tires.
     
  4. Krash

    Krash Data Technician

    Joined:
    Apr 18, 2017
    Messages:
    1,631
    Location:
    Intermountain US
    If anyone still has their Blizzaks on and wants to test the rolling resistance, simply take iOS Powertools or Android Dashboard for Tesla and run vehicle tracking from some high speed down to 30 mph or so in neutral. Ideally do a few runs on both directions and send us the runlogs. We can crunch the numbers.

    Unfortunately I didn't know how soft a touch you needed to use to get into neutral. I took off my Hakka 8s for the OEM all seasons before I figured it out but will retest in October.
     

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