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any experts on tyre load index ?

Discussion in 'Model S: Driving Dynamics' started by Hans (Amsterdam), Jun 25, 2013.

  1. Hans (Amsterdam)

    Hans (Amsterdam) Model S res#3130

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    I wrote an email to Tesla, Goodyear and Dunlop on this matter, but after many weeks I still got no answer.

    Numbers:
    - acc. Edmund the actual curb weight of model S is 4.770 lbs at 47/53% weight distribution. this results in a load of 2.528 lbs on the rear tyres.
    - model S would take 5 adults, each 180 lbs, makes a total of 900 lbs. Looking at the position of people in the car I estimate 40/60% weight distribution. This makes 540 lbs on the rear tyres.
    - The trunk (directly above the rear tyres) I guess should be able to handle 250 lbs of luggage.

    Total static load on the rear tyres now is 2.528 + 540 + 250 = 3.318 lbs or 1.659 lbs per tyre.

    Now if my calculation is correct this means that the max. allowable load on the rear tyres is exceeded in this extreme case. Load index 96: max. 1.565 lbs. Load index 98: max 1.653 lbs.

    Furthermore it surprises me that similar ICE vehicles (i.e. Panamera) have lower curb weight but much higher load indexes for the rear tyres (101 - 107). Maybe because of their higher top speeds ?
    For my model S (hopefully to arrive in Oct) I will be considering tyres with a higher load index, just to be on the safe side.

    Any comments ?
     
  2. mnx

    mnx 2013 P85

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    #2 mnx, Jun 25, 2013
    Last edited: Jun 25, 2013
    The 19" goodyears have a lower load index than the 21" continental/michelins.

    FWIW: The sticker on the door says 5710 lbs // 2590 kg GVWR.

    GAWR (Gross axle weight rating) says 2813lbs front and 3131 rear. Your numbers are higher than these, I would say you have overloaded the car in this case. It looks like it was not designed to handle 5 adults and 250lbs of luggage.

    I'm not an expert though. :)
     
  3. Hans (Amsterdam)

    Hans (Amsterdam) Model S res#3130

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    I thought the car was designed to carry 5 adults, 2 children and some luggage.
     
    • Like x 1
  4. BriansTesla

    BriansTesla Old school meets new tech

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    One thing I can tell you about load index is that a higher index can really improve handling in a heavy car.
     
  5. mnx

    mnx 2013 P85

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    I'm not disagreeing with you, but AFAIK you're not supposed to exceed the GVWR.
     
  6. Hans (Amsterdam)

    Hans (Amsterdam) Model S res#3130

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    Correct, I agree, and if you do not exceed GVWR you will also not exceed max. allowable tyre load.
    GAWR rear is 3131 lbs, which is 1565 lbs per tyre and (how fortunate) exactly the max. load with load index 96 !

    Total max. allowable weight passengers plus luggage = GVWR minus CURB weight = 5710 - 4770 = 940 lbs ( ? ! ) .

    - - - Updated - - -

    Just had a thought. Does the GAWR include weight of the wheels and tyres ?

    I guess if GAWR stands for load on the axles you should not add weight of the wheel/tyres.

    Then the max. allowable weight of passengers and luggage would increase with the weight of all 4 wheels/tyres.

    So I can take all of my children on a holiday .
     
  7. clea

    clea Member

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  8. bluetinc

    bluetinc Member

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    Shifting the weight distribution of people to 55/45 (which I think may really be 50/50), and bringing your luggage down to 200 lbs, you should just make it. :)

    Peter

    In this case the luggage would go in front.
     
  9. William13

    William13 Member

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    These limits are over engineered to allow max to be exceeded.
     
  10. jerry33

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

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    Yes it does. GAWR is what the scale would show for that axle. You are not to exceed either the GVWR or GAWR. This should be possible if you put the luggage in the front. (Duffle bags work better than hard shell cases and are lighter.)
     
  11. Hans (Amsterdam)

    Hans (Amsterdam) Model S res#3130

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    There will be weight differences between 60 en 85, Panoroof and childrenseats in the back.
    Edmunds put the 85 on a scale and got 4.770 lbs with 21 inch and panoroof.
     
  12. Hans (Amsterdam)

    Hans (Amsterdam) Model S res#3130

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    20mm wider rear tyres from the Performance Plus Package are Michelin Pilot Sport PS2 265/35R21. These tyres have load index 101. Seems to prove your point.
     
  13. clea

    clea Member

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    Ah yes, I had forgotten that the specs represent the base model and so do not include the weight of the larger capacity battery nor the seats. Thanks for the clarification.
     
  14. widodh

    widodh Model S R231 EU

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    So why do we have these limits if we start crossing them?

    Limit == limit, otherwise, increase the limit. Simply going over the limit because it's over engineered wouldn't be a very wise decision imho.

    I'll follow this discussion closely since I have the same questions as Hans.
     
  15. wycolo

    wycolo Active Member

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    Index schmindex, if you load up this car simply put 4+ pounds more air pressure in the tires, especially the rear tires. My oem tires (Goodyears) have max pressure of '51 pounds' which is a bit more than the door placard lists.
    --
     
  16. BriansTesla

    BriansTesla Old school meets new tech

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    Does anyone have some thoughts on these tires for a stagger on the original 19" wheels. The ratings of this tire are very good, they are fairly cheap and the diameter is the same front to rear.

    Size UTQG Max Max. Tread Tire Rim Meas. Sect. Tread Overall Revs
    Service Description Load Inflation Depth Weight Width Rim Width Width Diam. Per
    Load Range Press. Range Width Mile


    Bridgestone Potenza S-04
    245/45R19 280 AA A 1653 lbs. 51 psi 10/32" 30lbs. 7.5-9" 8" 9.6" 9" 27.7" 753
    98Y SL
    Rear
    275/40R19 280 AA A 1819 lbs. 51 psi 10/32" 33lbs. 9-11" 9.5" 10.9" 10" 27.7" 753 JP *
    101Y SL
     
  17. wycolo

    wycolo Active Member

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    What's with the '51 pounds' ratings?

    51 Psi = 351632.62195 pascals

    So that's not it (not a round number).
    --
     
  18. mnx

    mnx 2013 P85

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    This is probably better suited to a new thread, but I'll reply here anyways... My next set of tires is probably the Potenza S-04. They look to be an excellent tire, and are fairly cheap (esp since they are on sale now @ tire rack). There are others with a 245/275 staggered setup. (Zextraterrestrial comes to mind).

    I'm not a handling expert, but AFAIK you'll introduce more understeer with wider rear tires.
     
  19. BriansTesla

    BriansTesla Old school meets new tech

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    I think a better explanation of the change would be that it will reduce oversteer. To me, the stock 19" rear tires look tiny from behind.

    Anyone have a link to info about a 245/275 staggered setup. Zextraterrestrial?
     
  20. mnx

    mnx 2013 P85

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    How different wheels/tires affect MS using the P+ package as a guideline

    That post and 3-4 posts down from there he talks about his setup. I'd suggest sending him an PM to discuss specifics if you don't get an answer to your q's from that thread.
     

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