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Range penalty for 21" wheels vs 19"

Discussion in 'Model S: Driving Dynamics' started by ReturnZero, Jul 7, 2016.

  1. ReturnZero

    ReturnZero Member

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    In the Model X world, the larger sized wheel had a pretty sizable hit on the efficiency and range of the vehicle. Is that the same deal on the Model S? Have any of you gone from OEM 19" to OEM 21" (or the other way around) and recorded what the change in energy usage was like?
     
  2. Boatguy

    Boatguy Member

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    Yes, the Design Studio shows the range hit for the 21" wheels.
     
  3. Garlan Garner

    Garlan Garner Active Member

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    Why is there a range hit?
     
  4. St Charles

    St Charles Member

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    The 21" wheels have more rotating mass and thus require more power to move.
     
  5. ReturnZero

    ReturnZero Member

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    I only see a difference of like 6 miles, or about 2%. Is that actually accurate? On the Model X it's much more drastic, like 10-15%.
     
  6. sorka

    sorka Active Member

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    I have both 19 and 21 inch sets with OEM tires on both. I've seen no difference in range at all. In fact, my lowest wh / mile ever on my 130 mile commute was with the 21" wheels.
     
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  7. FlatSix911

    FlatSix911 918 Hybrid

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    Tesla has stated a 3% difference in range on the Model S | Tesla Motors calculator ... YMMV :cool:

    upload_2016-7-8_0-33-9.png

    upload_2016-7-8_0-35-13.png

    upload_2016-7-8_0-36-23.png
     
  8. Garlan Garner

    Garlan Garner Active Member

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  9. jelloslug

    jelloslug Member

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    They are not the same weight, that's why.
     
  10. ReturnZero

    ReturnZero Member

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    Great info. Thanks everyone!
     
  11. Norfolk Enchants

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    The laden radius is about 2% bigger on the 245/35/21 versus the 245/45/19. Not sure how this translates into power usage but it must have an affect. Also, even without this laden radius difference, the higher concentration of mass at a further radius from the wheel center means increased centripedal force and moment of inertia at each wheel when driving. Hence the need for more power even though the unladen diameters of these two tire sizes are practically the same...

    ...then again, perhaps we are over thinking it and the simple answer is that the 19" tire spec has a much lower rolling resistance :)
     
  12. sorka

    sorka Active Member

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    21" tires = 27.752". 19" = 27.681".

    = 0.26% larger, not 2%.
     
  13. Norfolk Enchants

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    The laden (Static Rolling below not unladen) radius is 2% bigger on the 21". 334mm/327mm = 1.0214

    19 v 21 245.JPG
     
  14. sorka

    sorka Active Member

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    Static is with the wheel at rest. Even in your calculator, there is no difference in dynamic rolling radius (tire in motion).

    Further more, that calculator doesn't take into account side wall stiffness of the particular tire or tire pressure. The 21" tires run at 45 psi while the 19" tires run at 50 psi. Higher tire pressure will reduce the difference between static and dynamic radius on the same tire as the higher pressure will result in a smaller contact patch due to less compression but the higher pressure will also resist the tire wanting to fling or expand as it's rotational velocity increases.
     
  15. Norfolk Enchants

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    Yes, of course the pressure makes a difference, but unless there is an error state with the pressure, the sidewall [~50mm taller than the 21'] compression on the 19" will always be greater than that of the much shallower [much stiffer] sidewall on the 21" tire when under load. The effective radius of the at the static laden condition, of the 21" tire is 7mm more. I.e. the tire car will sit 7mm higher off the ground with the 21" tire even though the unladen diameter difference is minimal. Think about that. :)

    All that said, the larger SLR, increased rotational inertia, contact patch and compound differences together are likely what is driving a noticeable rolling resistance change between the two wheel/tire combos, which is in turn responsible for the range variance between trims.
     
  16. sorka

    sorka Active Member

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    Ground to center of hub is 1 mm higher with my 21" wheels mounted vs my 19" wheels on the rear yet the 21" tires are new and the 19" tires have about 1/2 their tread left. If even tread life was left on both, the 21" wheels would be a few mm shorter from ground to center of hub while loaded.
     
  17. Norfolk Enchants

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    Strange...
     
  18. sorka

    sorka Active Member

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    Tire pressures, sidewall thickness, not just height, and even tread pattern can make difference. The point being is that the calculator doesn't take into account specific tire characteristics and tire pressure.

    It could very well be that a different 21" tire or a different 19" tire could reverse that.
     
  19. FlatSix911

    FlatSix911 918 Hybrid

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    #19 FlatSix911, Jul 8, 2016
    Last edited: Jul 8, 2016
    The OEM 19" wheels weigh approximately 30.1 lbs. and the 21" wheels weight 35.2 lbs.
    Bottom line ... the increased weight of the larger wheels has a significant impact on range.
     
  20. Norfolk Enchants

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    Would like to see the full spec for each tire - maybe the used (max grown dimension) from your 19" is considerably larger than a new 21"? New to new (when the vehicle would be type approved and EPA range determined) I still think that the 21" should have a measurably larger laden radii than the 19", and that a swap top 21s should have your car sitting higher.
     

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