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New tires & Wh/mi?

Discussion in 'Model S: Battery & Charging' started by scaesare, Jul 1, 2014.

  1. scaesare

    scaesare Active Member

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    After having had my S for 13 months and 28K miles, I've gotten a pretty good feel for what my Wh/mi usage is under specific circumstances, particularly my commute to work which always follows the same route.

    Once spring came and the average temps were typically ranged from 60-80, my average energy consumption for my commute settled in to the 280ish range for Wh/mi.

    A week ago I had to get two new tires put on the car as I had a puncture in one rear, so I replaced the pair. I used the exact same model tire (thanks to a sale from Tire Rack who is participating here). I have them inflated to the same pressures. I also had the tires rotated at that time.

    For some reason my energy usage has jumped up to an average 320-330 for the same commute now. I can't figure out why. Temps have edged up a slight bit, but nothing major, and even through summer last year I was able to maintain a sub-300 average even with air conditioning typically.

    I did get 5.11 recently, but that was a couple of weeks ago, and I didn't notice any energy jump then. I also just found that my suspension auto-lowering was somehow reset to 100+ MPH (I don't know if this is a 5.11 artifact or something the tire shop did). I've since moved that back to the 50MPH setting I had previously, and that doesn't seem to have done it.

    Any other thoughts? Have other people experienced any energy usage jump with 5.11 and I just didn't notice it?
     
  2. rogbmw

    rogbmw Member

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    With the increased temperatures, is your A/C working more? I notice that my typical jump for A/C is roughly around 30 (example - 330 vs 300) when compared to the A/C off and just the fan running. I know it has been hot in northern VA recently (our son is visiting from Bethesda this week and just last night he was talking about them having some of the hottest days on record).
     
  3. scaesare

    scaesare Active Member

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    As I mentioned, temps have edged up slightly, but not enough that I would have expected it to make that much of a difference overnight. I also recall being able to average sub-300's for my energy usage during last summer... so I don't _THINK_ so...
     
  4. Electricfan

    Electricfan Member

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    Did the energy jump occur immediately after replacing the tires? If so, isn't it the tires? I'm not a tire expert, so I can't explain why, but if the jump came the day after the tire change how could it be anything else? There is going to be a difference in the way brand new tires vs tires with 28k miles on them work - you don't have to be an expert to know that.
     
  5. scaesare

    scaesare Active Member

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    Except replacing them with the same make/model and inflated to the same pressure... to make that much of a difference? 15%?

    Not to mention that when the car was new (and thus wear wasn't a factor) I didn't have energy usage like this.

    This is why I brought it up here... to see if there was anything else perhaps I hadn't accounted for...
     
  6. Electricfan

    Electricfan Member

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    But it sounds like you've eliminated everything else, so whatever's left must be the solution. I don't know if tire wear affects rolling resistance positively or negatively. Would be an interesting search on google.

    - - - Updated - - -

    Check this out -
    "Tread depth has a significant effect on tire fuel economy. Bridgestone tests show that as a tread wears, the fuel efficiency of a tire usually increases."

    Sounds like this might be your solution.

    Here is the article:
    http://www.bridgestonetrucktires.com/us_eng/real/magazines/ra_special-edit_4/ra_special4_fuel-tires.asp

    - - - Updated - - -

    And here's another - "This means that new tires are going to have more rolling resistance than otherwise identical, but worn out, tires. So when you buy a new set of tires, you should expect a loss in fuel economy."

    http://www.barrystiretech.com/rrandfe.html

    I think this mystery is solved!
     
  7. swegman

    swegman Member

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    I live in Montgomery County, MD, so probably not too far from you; thus similar temperature, traffic, etc. conditions. My energy usage has always been in the 340/345 range, and I don't drive the car hard. Only occasionally do I accelerate hard or brake hard.

    My P85 had the 21 inch Tesla wheels with Michelin Pilot tires. I recently replaced them with the 19 inch Tsportline wheels and Michelin Pilot A/S 3 tires. I was hoping to see a drop in energy usage (Tesla told me that the 21 inch wheels with the Michelin Pilot tires was costing me approximately 30 miles in range per full charge), but have not seen any difference. I guess the stickiness of the sets of tires are comparable.

    Eventhough you replaced the tires with the same tire, is it possible that the manufacturer changed the composition of the tires, and the new tires are stickier?
     
  8. paco3791

    paco3791 TMC OG

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    You might want to have your alignment checked since I've seen other threads where that has a significant impact on energy consumption. might have shifted something by accident when they rotated the tires?
     
  9. scaesare

    scaesare Active Member

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    Well, if it were a tread-depth issue I still don't understand why the car didn't behave this way when all FOUR tires were brand new a year ago, as opposed ot only two now...

    The alignment ideas is an interesting one... as well as the compound change...

    I'll see what happens after I have a longer sample size.

    Thanks for the ideas...
     
  10. scaesare

    scaesare Active Member

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    Well, for the second half of morning commute today, I turned off the A/C. Temps were about 80, which is where they've been the previous few days.

    I ended up arriving at work with an avg energy usage of about 290, rather than 320ish. I also tracked the averge ebergy usage using the 15-mile average on the energy app, and it was 250-260ish[1]. So.. it appears it may be A/C after all.

    I find this odd when compared to summer behavior last year. Once out of winter weather, sub-300's even with moderate A/C use was typical for my commute. I wonder if a FW update has made the A/C control algorithm a little more aggressive.

    I'm going to target a long stretch of highway where I typically can maintain constant speed on the way home and do some testing with the Instant mode of the energy app and see if I can see the change as well.


    [1] The energy usage on the app graph is always 20-30Wh/mi lower than my trip average for me, I assume this difference is due to non-locomotive load
     
  11. paco3791

    paco3791 TMC OG

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    Apologize if this is too obvious but, were you using Eco Mode for the HVAC system before? If it was on before and off now that might account for the discrepancy.
     
  12. scaesare

    scaesare Active Member

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    On the contrary it's a great thought... unfortunately that's not it. I only enable it for road trips, and there are enough indicators that I would have noticed...
     
  13. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Tire rolling resistance goes down as the tread depth reduces. Depending upon the tire, sometimes there is a noticeable difference between the new and old and sometimes less so.

    Check the tire pressures. They may be low. Always check the tire pressures the morning after the car is serviced.

    Generally, warmer temperatures mean better energy consumption values, not worse.
     
  14. Merrill

    Merrill Active Member

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    No, but just put 4 new oem conti's and notice the same. Was always below 300 and now slightly above. Could the new soft rubber cause more friction?
     
  15. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    The softer compound mates with the road surface more completely and so there is more friction. In addition the hysteresis value doesn't recover the energy as completely. But first check the tire pressures tomorrow morning.
     
  16. Rich J

    Rich J New Member

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    I would check tire pressure. I had a similar experience when I had 4 new tires put on by Tesla SC. I seemed to have 20 to 30 Wh/mi higher than before. About a week later a Tesla ranger checked tire pressure (after replacing 12 volt battery as part of Tesla preventative program) and noticed tires were under inflated by just 3 pounds on 3 of the tires. After he added air my Wh/mi went back to what it was before I replaced tires. I do not know why new tires were under inflated but may be common as new tires settle in. All I know is this made a big difference.
     
  17. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    The main reason is going to be temperature difference from when the tires were mounted to cold first thing in the morning pressures.
     
  18. scaesare

    scaesare Active Member

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    From my initial post:

    - - - Updated - - -

    Maybe. But these are the same make/model tires, and only two of them as compared to when I bought the car new and there were four of them, yet I didn't get this type of energy usage last year this time...
     
  19. drees

    drees Active Member

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    Tires will break in over the first couple thousand miles and rolling resistance will go down. Efficiency should go back up with a bit of time.
     
  20. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Tire manufacturers do change the specs without notice (similar to how Tesla does it), so just because it's the same tire make and model doesn't mean it's actually the same tire. That's why the recommendation is to always fit four tires together (assuming all four tires are the same size).
     

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