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Wheels, Tires, measurements (high odometer)

Discussion in 'Model S: Driving Dynamics' started by Drumheller, May 9, 2017.

  1. Drumheller

    Drumheller Member

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    I bought a 2013 P85+ CPO last year. It arrived with the staggered 21" wheels. I soon needed to purchase tires and decided to switch to 19" wheels. At that time, Tesla did not offer a wheel that looked similar to the dark gray cyclones I had on the 21"s so I went with TSportline for aftermarket 19"s that looked like the 21"s.

    I put Continental ExtremeContact DWS 06 on the TSportline 19s and I've been happy with the driving experience.

    During a long road trip, I noticed that my actual mileage was always more than the estimated. I then noticed that my displayed speed on the instrument panel was always higher than the radar speed when I passed one of the passive radar signs.

    When I took the car in for annual service, I mentioned it and wondered if the car was still set to 21" wheels instead of 19", which would account for the difference. The service dept said that it was still configured as 21", even though I had switched the settings in the controls, and they made the change.

    However, I noticed the same situation over the next 10,000 miles.

    Today I took it in for service and mentioned the same situation. The service adviser just called and informed me that my wheel and tire combination has a smaller diameter than any Tesla config. Based on my mileage and speed measurements, it's off by about 4%. TSportline has their specs on the website, and they match Tesla's specs, though slightly lighter. If that is the case, then the difference is either in the tires or I have a slightly out of spec set of wheels.

    I'm wondering if anyone else has encountered this and if they have any additional information to add. It's not a major issue, but it is a bit annoying to be adding extra phantom miles to the odometer and burning through warranty miles faster. I've put about 33,000 displayed miles on the car with this wheel + tire combination, so about 31,700 actual miles.

    I plan to try the Primacy tires next and see how that goes.
     
  2. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    The T-Sportline 19" wheels are a 19x8.5 (19" diameter, 8.5" width). However, that size doesn't really matter for speed errors, it's the tire size that would matter.

    What tire size are your ExtremeContact DWS06 tires?
     
  3. Drumheller

    Drumheller Member

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    245 / 45 R19
     
  4. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    245/45R19 is the correct size.

    I have the exact same wheels, T-Sportline 19x8.5 (although mine are silver, not dark gray), and I have a set of winter tires installed on them -- Nokian WRG3 245/45R19. I have not had any speed errors with those wheels/tires, the vehicle's indicated speed nearly exactly matches speed from GPS (use your phone's GPS/mapping application, or the Waze application to get your GPS speed).

    Are your tire pressures in spec? It should be 45 psi on all wheels.

    Now, the other item is that you have a P85+, which was originally shipped with and is designed to operate with the staggered 21" set. The difference in tire size between the 265/35R21 (which was the rear tires on the 21" staggered set) and the 245/45R19 is about 2%. So this could account for some of the difference you're seeing, but it sounds to me like there's something in addition to this that's causing even more error.
     
  5. Drumheller

    Drumheller Member

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    Thank you, I hadn't thought about that difference with the staggered setup. I'll check again with my phone. So far, it's been consistently 4 to 5% with every way I've measured, mileage and speed.
     
  6. St Charles

    St Charles Member

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    Look at Tire revs/mile for the OEM tires vs the Extreme contact. I have found that to be a bit more accurate vs size calculations.
     
    • Helpful x 1
  7. Drumheller

    Drumheller Member

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    Is there somewhere I can find that information? Thanks!
     
  8. Drumheller

    Drumheller Member

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    Found it on tirerack

    OEM: Michelin Primacy MXM4 have 751 revolutions per mile.
    Continental ExtremeContact DWS 06 have 750 revolutions per mile.

    Shouldn't make a difference or the DWS should report very slightly less mileage.

    When I get the next set of tires, I'm going to ask the shop to measure one of the wheels. This doesn't make sense.
     
    • Like x 1
  9. St Charles

    St Charles Member

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    Yeah, you got me. Those two numbers are near-as-makes-no-difference. that said, if one tire has a lot of tread initially and is now near it's end of life this can have an effect of making your car slower than indicated. if your initial tread was 16/32, and is now almost bald, the speed difference is about 4%.

    Proper inflation will have a similar effect if the tire is underinflated. This is harder to calculate but you might measure the height of your tire as it is sitting on the car now and compare that to the diameter listed on TireRack. If your tire is sitting an inch shorter then what you find online, it may account for the difference you are seeing.

    Assuming that Tesla measures speed through wheel rotation, you'll never stay accurate due to tire wear and inflation level.
     
    • Informative x 1
  10. Lasttoy

    Lasttoy Member

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    Tire rack told me if I change 19 to 21 the actual height is same, tire size changes from 245 to 225 lower sidewall
    That insures all readings are same.
    He also said smaller sidewall equals harder ride, almost like run flats,
     

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