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245/35R21 front & 265/35R21 rear tires - Deeper meaning behind this and can it be changed?

Discussion in 'Model S: Driving Dynamics' started by [email protected] Bargain, May 19, 2018.

  1. Tesl@ Bargain

    Joined:
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    Central Europe
    The rims (in my case 21" Arachnids) obviously are the same, but the back wheels came with a wider tire. The Michelin Pilot Super Sport Acoustic is not a specific EV tire and my guess is that the wider rear tires are just supposed to provide a better wheel grip for RWD sports cars (clearly not an issue with a Model S 75 like ours).

    Since the tires can not be rotated that way, would it be possible to go all 245/35R21 or 265/35R21 once the according pair is used up and needs replacement, and is there any benefit (besides the ability of rotating tires) or downside doing so?

    Going all 265/35R21 would reduce the risk of making the front rims kaput but increase energy consumption. Going all 245/35R21 would reduce energy consumption but increase the risk of making the rear rims kaput. Those tires do not have a rim protection groove.

    As this specific setup is chosen by Tesla, why would they go this way now that the Model S is only available with AWD anyway? One would assume it makes most sense to have the same tire dimensions all around.

    P.S. Is it correct that the tire pressure for these 21" tires is supposed to be kept between 40 and 42 psi? They did not add a new sticker to the driver door frame.
     
  2. docherf

    docherf Member

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    Your 4 wheels are not the same size.

    Rear 9 inch wide. Front 8.5 inch.
     
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  3. Tesl@ Bargain

    Joined:
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    You mean that the rear rims are wider? If that's the case, I didn't know. The mentioned (European) tire dimensions show that the rear tires are 20 mm ~ 0.79 inch wider and from the looks of it one can clearly see the difference of the tires to the rims, which made me assume the rims are the same and just the tires with different width, which would have made using tires of same dimensions all around easily possible.
     
  4. docherf

    docherf Member

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    I think Tesla does this a lot. Even our Model X with the base 20 inch wheels are wider in the rear. It's usually stamped on the inward side of the wheel. Pics from model x. A little hard to get to. 9.0 in front, 9.5 in rear.
     

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  5. bishoppeak

    bishoppeak Member

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    Location:
    San Luis Obispo, CA
    An easier way to compare rim widths is to look at how far the lug nuts are recessed.
     
  6. animorph

    animorph Active Member

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    I assume the staggered tire sizes balance the car better having them all the same size would. If you increase the front tire width to match the back, or decrease the rear tire width to match the front, it is likely that the front would gain a little cornering grip, or the rear would lose a little cornering grip. That might make it more likely that the cars rear end would swing out during hard cornering (oversteer). All cars today are tuned for understeer (front wheels lose grip first), just to avoid that situation and make it easier for non-race drivers to control. That's part of what the larger rear tires are doing for you.
     

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