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  1. #1
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    Default "0" offset....Will this fit.

    I'm looking at a set of 16x7 wheels with a "0" offset. Meaning from the mounting flange to the front lip and to the rear lip the measurement is the same. Backspace using the .5 inch method, should be 3.5 inches.

    Will these fit an 85 GT? Eyeballing it, it should fit. Anyone know for sure?

    If they'll fit, I'll be running a 225 series tire.
    85 Saleen Mustang(s)

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    FEP Super Member erratic50's Avatar
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  3. #3
    FEP Super Member xctasy's Avatar
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    Nope, won't fit. Ford is designed around E22 or E36 offset for 6 to 7" rims.


    I'm an ex GM guy. Based on what I know about GM Independent Fornt Suspension Syems, Its okay for GM suspension systems, but not Ford IFS systems. Some Holden Toranas were E22 or E28, but they had massive guard flares. Same with H body Vegas, Monzas and Skylarks

    Most of the F car 1978 to 1981 SnowFlake WS6 and Z28 Handling package alloy wheels were 0.0 mm E0 offset.

    My mate has a set of 295/50 15's on the back of his factory 15 x 8 inch rims on his 301 FireTurd Turbo.

    See http://www.78ta.com/Pages/rims.htm




    The offset whether it be positive or negative does make a difference on how the car handles. To determine the offset of the rims, you first need to measure the width of the rim from edge to edge. Divide that in half to get the centerline of the rim. Now take your backspacing and subtract the measurement of the centerline of the rim from it to get your offset. So, in the example shown below of a 15x8 snowflake rim, you see that the rim is 9" from edge to edge which means the centerline is 4 1/2". Take the backspacing of 4 1/2" and subtract the centerline measurement of 4 1/2" and it gives you an offset of + 0". So, the simple math is: offset = backspacing - (width of rim /2).


    Once you know the lug pattern, the backspacing, and the offset of the rims, then you can determine what rim you would be able to fit on your car. The measurements of the stock rims on the Firebirds and Trans Ams are as follows:
    Rim Type Offset Backspacing
    Rally II +1/4" E6.35 4 1/4"
    Honeycomb +1/2" E12.7 4 1/2"
    15x7 Snowflake +1/4" E6.35 4 1/4"
    15x8 Snowflake 0" E0.0 1/2"

  4. #4
    Moderator wraithracing's Avatar
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    Most 7" wheels for the Fox Mustang use somewhere from an 18mm to 22mm offset.

    So your Zero Offset wheel will stick out @ 0.9" further than say the new Reproduction TRX wheels will. You will have plenty of clearance at the strut, but doubtful you will clear the wheel lips front and rear.
    Last edited by wraithracing; 12-28-2017 at 01:32 PM. Reason: Spelling
    ​Trey

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  5. #5
    FEP Senior Member Patrick Olsen's Avatar
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    Quote Originally Posted by BaconB8 View Post
    I'm looking at a set of 16x7 wheels with a "0" offset. Meaning from the mounting flange to the front lip and to the rear lip the measurement is the same. Backspace using the .5 inch method, should be 3.5 inches.
    I'm not sure what the ".5 inch method" is, but it's not right. A 16x7" wheel is ~8" wide from lip to lip, so with a 0 offset the wheel has 4" of backspacing (and 4" of frontspacing). The stock 15x7" turbine & 10-hole wheels, and the stock 16x7" Pony wheels, all are +23mm offset, or about 4.9" BS.

    Quote Originally Posted by BaconB8 View Post
    Will these fit an 85 GT? Eyeballing it, it should fit. Anyone know for sure? If they'll fit, I'll be running a 225 series tire.
    Stock suspension? Do you have caster/camber plates?

    As Trey said, your new wheels would be sticking out ~0.9" farther than those OEM wheels. In the rear, I think you should be fine, as the stock wheel fitment is sucked pretty far into the wheel well. Up front it'll be a tighter fit. If you have c/c plates and run reasonable negative camber that'll help. 225/50-16s (rather than the 225/55s that were used on the 16x7" Pony wheels) would also help.


    Quote Originally Posted by xctasy View Post
    Nope, won't fit. Ford is designed around E22 or E36 offset for 6 to 7" rims.
    Which doesn't mean that going beyond those numbers won't fit.

    Quote Originally Posted by xctasy View Post
    I'm an ex GM guy. Based on what I know about GM Independent Fornt Suspension Syems, Its okay for GM suspension systems, but not Ford IFS systems. Some Holden Toranas were E22 or E28, but they had massive guard flares. Same with H body Vegas, Monzas and Skylarks
    ...blah blah blah...
    Once you know the lug pattern, the backspacing, and the offset of the rims, then you can determine what rim you would be able to fit on your car. The measurements of the stock rims on the Firebirds and Trans Ams are as follows:
    Rim Type Offset Backspacing
    Rally II +1/4" E6.35 4 1/4"
    Honeycomb +1/2" E12.7 4 1/2"
    15x7 Snowflake +1/4" E6.35 4 1/4"
    15x8 Snowflake 0" E0.0 1/2"
    I'm sure all of the Firebird and TA owners will be thrilled this information is finally available here on this Mustang/Capri forum!

  6. #6
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    Here is a great site for comparing a known set of wheels to the new ones you want to try:

    http://www.willtheyfit.com/

  7. #7
    FEP Super Member xctasy's Avatar
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    Quote Originally Posted by Patrick Olsen View Post
    .......
    I'm sure all of the Firebird and TA owners will be thrilled this information is finally available here on this Mustang/Capri forum!
    Just for your info. Last time I mentioned GM,

    Quote Originally Posted by xctasy View Post
    Thanks Trey, I needed that.




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    I won't even talk about the Ford Borg Waner 78 Diff the F car ran for seven years either...

    Quote Originally Posted by xctasy View Post
    .......
    Due to the problem with finding good Fox 7.5 and 8.8 diff housings at a competitive price down here, I was going to use the Borg Warner 9 Bolt GM F-car M78 Rearend or "78 series". 7.625/7.875" BTR diff found in Falcons, Valiants, Commodores, Camaros and Firebirds, Centuras and Aussie Cortinas, Pintaras and Skylines. They are basically a Salisbury diff, used internationally since GM's Holden subsidary was able to organise it for the F cars when the PBR braking system was also outsourced for F cars and 84 onwards Vettes. That Australian brake and axle content allows a Fox body owner to pick up Commodore VK to VP Panhard rod four link diffs and SVO style brake kits to be made using the US M78 F-body axle.

    So I looked into it a bit more

    .......
    woops, I did it again...

  8. #8
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    The .5 comes from measuring at the bead, and not lip measurement. Widths are measured from the bead, where backspace and offset is overall.
    85 Saleen Mustang(s)

  9. #9
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    Bummed the wheel offset is wrong. Thanks for the guidance.
    85 Saleen Mustang(s)

  10. #10
    FEP Senior Member Patrick Olsen's Avatar
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    Quote Originally Posted by BaconB8 View Post
    The .5 comes from measuring at the bead, and not lip measurement. Widths are measured from the bead, where backspace and offset is overall.
    Ah, gotcha. So it's really the 1" method, because that 0.5" needs to be accounted for on both faces of the wheel. Although I suppose it depends on how you do the math to use the 0.5" or 1" method.

    [And it's just a rough guide. Years ago I happened to have 3 bare wheels handy - a 16" Pony wheel, an OEM Subaru wheel, and an aftermarket Subie wheel. All 3 were advertised as 7" wide, but they measured 7-7/8", 8", and 8-1/8" wide overall. I've got a few bare wheels at the house now, I should measure those and see how they stack up.]

  11. #11
    FEP Senior Member cb650's Avatar
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    I had some 8" draglites that only measured 7 3/4. And the extra "inch" was on the outside compared to a 10 hole. I wanted all the extra to the inside thats why I went with the goofy aftermarkets I did. LOL

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