2016 GT suspension recommendations

Discussion in 'Suspension, Brakes & Chassis' started by HourlyB, Sep 10, 2019.

  1. Norm Peterson

    Norm Peterson corner barstool sitter

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    Keep in mind that you do not have direct steering control over the rear tires, so a laterally stiff wheel/tire configuration out back does a better job of keeping the rear "in sync" than a softer setup. Makes for a more relaxing session when driving at 9/10ths+ on the track feels almost as laid-back as a brisk drive out in the country at half that.

    I doubt that 285s on 11s is something that can be adequately explained - you'll only understand it by driving. My understanding happened back in the 70's as the unexpected consequence of a significant tire change rather than by any direct intention. But any more, measuring width fitments feel a tad soft.

    You do have to get past any preconceived notions of appearance. Which I understand is a harder step for most people to take than it ever was for me.

    I'm with you on the idea of 11" all around.


    Norm
     
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    HourlyB

    HourlyB Well-Known Member

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    So for a F14 11 inch wheel with a 56mm offset at the front, I would want to run at least 16mm of offset at the front. That seems like a bit of a lot, doesn't it?

    I definitely would if I could, but I'd rather not put stress on the car in doing so.
     
  3. Norm Peterson

    Norm Peterson corner barstool sitter

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    What "stress" are you talking about that wouldn't be there with wheels that are 10" wide or narrower?


    Norm
     
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    HourlyB

    HourlyB Well-Known Member

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    Running a wheel that wide at the front will require about 10mm/.375 inches of spacers to bring the 26mm up to 36mm, which Bmac says is optimal. (The 19x11 F14's I bought are stated to have a 26mm offset and 179mm of backspacing, another version is 56mm offset/208mm backspace)
    More spacers generally means more force and wear on the suspension, right?
     
  5. BmacIL

    BmacIL Enginerd

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    The required offset is dependent on the wheel width, as the offset is from the center of the wheel. For an 11" wheel, you want an effective offset of +25 to +28, in that range, and depending on the suspension type. This usually means a 19x11 with +50 offset and a 25 mm slip-on spacer up front, and changing the studs to 1" extended versions.
     
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    HourlyB

    HourlyB Well-Known Member

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    So what would be the difference from the effective offset compared to the actual offset? Is the effective offset the distance between the inner "lip" of the wheel and the suspension components? And is there a formula? I'd feel better if I could do the calculations myself instead of badgering you guys constantly.
     
  7. Norm Peterson

    Norm Peterson corner barstool sitter

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    It's not that simple once you consider negative camber (which moves the resultant contact patch inward) and combine static weight with cornering force (those forces more or less act in opposition on the more heavily loaded outside corner with positive-offset wheels).


    "Effective offset" is actual offset (advertised offset) minus the thickness of any spacer that may be present, and the algebraic sign of the offset matters. It affects clearance between the tire & wheel and things like suspension components on the chassis side and sheetmetal clearance on the outboard side, but it is not the clearances themselves.

    I don't know how much wheel to strut clearance you get on an S550 with 11" wide wheels of +25 offset except that it's probably 10mm or so.


    Norm
     
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    HourlyB

    HourlyB Well-Known Member

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    Ahh yes, I see.
    *sparks and smoke pouring out of ears*
    What would the suggested amount of strut clearance be? 25mm or so?
     
  9. BmacIL

    BmacIL Enginerd

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    Good would be >= 5 mm. Acceptable would be in the 3 mm range. Effective offset of +25 gives approx. 5 mm of clearance.
     
  10. Norm Peterson

    Norm Peterson corner barstool sitter

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    That's way too much. The wheels themselves probably don't need any more than a couple of mm, but a more definite answer than that is going to at least involve tire size vs wheel width, with the more stretched tire fitments (narrower section widths) being tolerant of smaller clearances than measuring-width or min-recommended width fitments.

    Oh, hell, why not, a strut suspension is a strut suspension, right? No rubbing even out past 1.3g. About 1.1mm. 285/35's on 11" wide rims.

    full.jpg

    full.jpg


    Norm
     
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  11. Norm Peterson

    Norm Peterson corner barstool sitter

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    Thanks for the number, but is that wheel to strut or tire to strut?


    Norm.
     
  12. BmacIL

    BmacIL Enginerd

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    Obviously will depend on the tire, but that's wheel to strut. Tire could be a hair less depending on what size & brand/type.
     
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  13. Norm Peterson

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    Thanks. Gives me a little better idea about how the S550 and S197 compare.

    Obviously different people are comfortable with slightly differing static clearances.


    Norm
     
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    HourlyB

    HourlyB Well-Known Member

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    So if I buy another 2 of these 19x11 F14 wheels with 26mm offset/179 backspace, I would want to put a 5mm spacer up front like if I was running the 10 inch F14? The backspace is similar (10 inch has 181mm), but the offset is much different (10 inch has 40mm, but of course that's with a more narrow wheel)
    Sorry, this stuff is still confusing me.
     
  15. BmacIL

    BmacIL Enginerd

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    If you can buy 19x11 +26, they will fit well up front, no spacers needed. They'll stick out like crazy in the back. The +56 will fit well on the rear.
     
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