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275/40/17 same as 275/40/18?

This is a discussion on 275/40/17 same as 275/40/18? within the Wheels and Tires forums, part of the General Help category; Iam getting new wheels and I currently have 275/40/17" tires on all 4, the new wheels are 18x9. Is the ...

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    Go Vols! x10-wakerider's Avatar
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    275/40/17 same as 275/40/18?

    Iam getting new wheels and I currently have 275/40/17" tires on all 4, the new wheels are 18x9. Is the 275/40/18" tire the same size as the 17" the only difference being the size of the hole for the wheel?

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    Crazy Canuck ! Eugenio_SS's Avatar
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    you need 275/35-18.

    stock size = 275/40-17
    means 275mm width
    sidewall = 40% of 275mm = 110mm
    overall diameter = 2x sidewall + rim-size = 220mm (8.66") + 17" = 25.66"

    now, 275/35-18
    means 275mm width
    sidewall = 35% of 275mm = 96.25mm
    overall diameter = 2x sidewall + rim-size = 192.5mm (7.58") + 18" = 25.58" (very close)

    if you were to use 275/40-18
    means 275mm width
    sidewall = 40% of 275mm = 110mm
    overall diameter = 2x sidewall + rim-size = 220mm (8.66") + 18" = 26.66" (would be quite off)

    Hope this helps.
    Eugenio_SS
    almost stock triple-black 2000 SS convertible with 17x11s on all 4 w/ 315s at the track or on the street with 18x10.5s on all 4 w/ 315s: (1), (2)

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    230,55,147 91Z28's Avatar
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    Hey Eugenio, since you seem to be the wheel/tire man, I have a question. I have 275/40/18 on my rear tires and want to know if these are bad for traction. I know dedicated drag racers use small wheels with lots of sidewall, but if this setup works for corvettes it can' be that bad?

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    Crazy Canuck ! Eugenio_SS's Avatar
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    Quote Originally Posted by 91Z28
    Hey Eugenio, since you seem to be the wheel/tire man, I have a question. I have 275/40/18 on my rear tires and want to know if these are bad for traction. I know dedicated drag racers use small wheels with lots of sidewall, but if this setup works for corvettes it can' be that bad?
    1st, i'm not "the man"... just a guy that knows some ...
    as for traction, it's not really a matter of a given size.
    it depends a lot more on the compound and suspension setup than size itself.
    another thing is sidewall helps for deflection, so having a 275/40 either on 17 or 18s would allow for roughly the same lee-way.
    18s do offer more rotational mass, and on top of that further away from the center of rotation, increasing rotational inertia... which won't help... but you'll be fine.
    i use BIG skinnies 315/35-17 even when @ drag... and they are over 55lbs on each corner.

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    Go Vols! x10-wakerider's Avatar
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    Thanks EUGENIO!!!!!!!!

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