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ok...but whats this "offset", and what about width?

This is a discussion on ok...but whats this "offset", and what about width? within the Wheels and Tires forums, part of the General Help category; I've browsed through other threads explaining how to maintain the overall diameter of a tire when going with a different ...

  1. #1
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    Question ok...but whats this "offset", and what about width?

    I've browsed through other threads explaining how to maintain the overall diameter of a tire when going with a different rim size. When going from factory 16" rims to 17" rims, you need one of these 3 sizes

    245/45-17 = 25.7"
    275/40-17 = 25.7"
    315/35-17 = 25.7"


    That I'm understanding, but what about rim width? I'm going to be buying a set of the Z06 17x9.5's (all four are 17"), so how do you know which size tire to buy to accommodate to new rim width?

    Also, I read about offset..what exactly is that? How do you choose the right offset for new rims - such as the Z06 17x9.5?

    Thanks

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    ehh, anyone have a clue here?

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    Member Fastcar's Avatar
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    Quote Originally Posted by sketterman
    ehh, anyone have a clue here?
    Technically, if you consider where the wheel bolts to your hub on the car as a zero point or center plane, a wheel with zero offset would have equal amounts of the wheel on each side of the center plane. In other words, if you were to measure from the center plane outwards on either side to the wheel rim on either the front or back of the wheel it would be an equal distance. When you change the wheel offset the wheel won't be exactly centered; either the wheel will be shifted more towards the inside or outside of the car. I don't know the proper offset for F-body wheels. When you see someone with the wrong offset wheels which cause the wheels and tires to stick outside of the body, that's bad for the car because it puts a heavy load on the front wheel bearings and rear axle bearings.

    http://www.yokohamatire.com/utcustom.asp
    Last edited by Fastcar; 02-09-2006 at 07:12 PM. Reason: added link

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    well the rims Im going to buy like I said are Z06 rims, and they claim they will fit any 93-newer camaro or TA, and of course vettes. So I guess the offset isnt my concern here, I just wanted to know what it was so thanks for that but with width, I wasnt sure what size tires to buy since they are 9.5 width. I've heard that 245/45/17 will keep the same overall diameter, but will it fit a rim that is 9.5 width? Or do I need the 275/40/17 to still maintain the same overall diameter, AND be wide enough to fit the rim?

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    Member Fastcar's Avatar
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    Quote Originally Posted by sketterman
    well the rims Im going to buy like I said are Z06 rims, and they claim they will fit any 93-newer camaro or TA, and of course vettes. So I guess the offset isnt my concern here, I just wanted to know what it was so thanks for that but with width, I wasnt sure what size tires to buy since they are 9.5 width. I've heard that 245/45/17 will keep the same overall diameter, but will it fit a rim that is 9.5 width? Or do I need the 275/40/17 to still maintain the same overall diameter, AND be wide enough to fit the rim?
    Tire Rack recommends a wheel width of 7.5 - 9 inches for the 245's and a wheel width of 9 - 11 inches for the 275's. If you go with the 9.5 inch wide rims, offset is critical because the tire may rub on the inside of the wheel well. Some of the other members I believe have had problems with that happening, especially if the car's been lowered.

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    I see, well I also plan on slapping on some Sportlines too, which is why this thread was started, I was a bit concerned about that. I think the offset of the rims was 56mm, or something very close to that. Is that the right area for this kind of app?

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    Here ya go... pulled this from LS1Tech.com so credit to them.

    TIRE CALCULATOR !

    http://www.discounttiredirect.com/d...nfoTireMath.jsp

    http://www.discountpartcenter.com/tirecalc.html

    Camaro & Firebird Fitments
    --------------------------------------------------------------------------

    Bolt Pattern

    5 x 4.75" or 5 x 120.65 mm

    The numbers in the columns are as follows:

    WIDTH ..... OFFSET ......... WIDTH OF TIRE

    Front and Rear

    7.0" ..... +35 to +40 mm .... 215, 225, 235
    7.5" ..... +35 to +45 mm .... 215, 225, 235
    8.0" ..... +38 to +55 mm .... 225, 235, 245
    8.5" ..... +38 to +45 mm .... 235, 245, 255
    9.0" ..... +38 to +56 mm .... 255, 265, 275
    9.5" ..... +38 to +56 mm .... 255, 265, 275
    10.0" ... +38 to +48 mm .... 265, 275

    REAR Only

    10.0" ... +38 to +54 mm .... 275, 285
    10.5" ... +38 to +50 mm .... 285, 295
    11.0" ... +45 to +56 mm .... 315

    Z06 Corvette Replicas:

    17"x9.5" +50 to +56 mm no problems. 275/40R17.

    18"x9.5" +50 to +56 mm 275/35R18 or 285/35R18.

    18"x10.5" +50 to +53 mm. Higher than 53 mm will require the BFH mod. 285/35R18s thru 315/30R18. Over 295 may require rolling the fenderlip and will need the BFH.

    Y2k Corvette Replicas:

    17"x8.5" +56 mm

    17"x9.5" +50 to +56 mm

    18"x9.5" +50 to +56 mm

    17"x11" Wheels

    ZR-1 Style for Camaro +50 mm (Known as Grand Sport offset)
    ZR-1 Style fo Firebird +36 or +50 mm The wheel well on the "bird" is a little wider.

    American Racing TT-2's +45 mm

    With 17"x11"s there is always a possibility of needing the BFH and/or fender rolling mods with 315s. If lowered, an Adjustable Panhard Bar becomes a virtual necessity. Some have used the +38 offsets with an 11" wheel but it does stick outside the fender and is definitly not recommended on lowered vehicles. +50 and +56 are the two most common. +50 is the better fit (for the ZR-1 replica).

    For road race only applications a 17"x11" at all four corners can be made to fit.

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    by the way BFH is Big Freakin Hammer mod... It means u gotta hammer the hub inside of the wheel well to make the wheel fit without rubbing

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    Hey man thats some awesome fxckin' research..I really appreciate that you have no idea damn..that solves half my problem, now I just gotta find out if lowering the car on sportlines will affect it at all, it seems only issue comes with 11" rims, so with mine only 9.5 I should be good to go. Again, thank you big time bro

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    Member Bowtie Guy's Avatar
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    I have 17x9.5 ZR1 with 56 mm offset on a 2002 Z28 with 285/40/17 BFG. They fit just fine with no issues. Well see what happens when I go to the Eibach springs and Koni shocks.
    Bowtie good! Blue oval not so good! Bob in the PRK

  11. #11
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    well remember, as long as you follow the guidelines of what i posted and keep the overall diameter the same, and you keep a 9.5" wide tire, then lowering shouldnt be a problem because WS6 cars are 9.5" wheels and plenty of them are lowered.

    Good luck
    -Scott

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