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  1. #1

    Default Rear fitment 17x12 with 2 inch flare backspacing ??

    I've searched and searched and can't seem to figure out what backspace I should run with 17x12 wheels and tiger racing 2 inch flares. I'm focusing on the rear of the car only right now. Also some people may have read a thread I posted awhile ago on fitment for 15s. It turns out the setup I wanted to have wouldn't look too hot so now I'm back to my original wheel/tire setup. Please help me figure my backspacing with flaring! Thanks!

  2. #2
    FEP Super Member erratic50's Avatar
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    I remembered reading a decent guide a while ago in my dads stash of car magazines. I found the article posted here:

    http://www.superchevy.com/how-to/whe...-size-matters/

    Good luck! Be sure to allow plenty of room for side to side movement of the rearend unless you've welded in a panhard or watts setup that works really well.

  3. #3
    FEP Senior Member Patrick Olsen's Avatar
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    What rear end is in the car?

    I'm sure if you search around here or on other Mustang forums, you'll find folks running 17x10s under stock fenders. Figure out what offset / backspacing they're running, then run the same backspacing. All of your added 2" will be to the outside, where your flares are.

  4. #4
    Moderator wraithracing's Avatar
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    The standard offset for a 10" wheel with Fox body track width is 25mm or @ 6.25" of backspacing.

    If you are running the 94-98 rear track width, the SVO track width, or the 99-04 rear track width then you can run additional offset.

    As stated if you have 2" flares then you can and will want to push the extra 2" of wheel width to the outside to fill the flares. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  5. #5

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    Thanks for the replies guys. I'm using sn95 axles. Will using 17x10 backspacing on a 17x12 wheel really fill the flare? Seems too good to be true haha

  6. #6
    Moderator wraithracing's Avatar
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    Just remember that backspacing and offset are not measured the same way. So when you have 2 different width wheels with the same backspacing the offset will be different for each wheel. Offset is measured from the centerline of the wheel.

    Which SN95 axles as the 94-98 is one width and the 99-04 is a different width.

    Track width for a Fox is @ 57"

    Track width for a 94-98 Mustang is @ 58.7"

    Track width for a 99-04 Mustang is @ 60.3"

    When using an SVO or 94-98 rear axle width on my Foxes I can generally run a 17X9 with a 24mm offset.

    When using a 2003/04 Cobra IRS in my 79 PC, I have to run a 17X9 with a 36mm offset to clear the fender lip in the rear.

    Just using the rough numbers of the 94-98 rear track width. Your track width should be @ 3/4" wider per side than the Fox so that is @ 19mm. That would require a 10" wheel to have @ 44mm of offset to fit inside the stock wheel well. Then you would still have the 2" of the flare left to cover the extra 2" of the 12" wide wheel.

    If my math is right tonight. The backspacing for each wheel would be @ 7.2".

    The offset for the 10" wide wheel would be @ 44mm (1.7")

    The offset for the 12" wide wheel would be @ 18mm (0.7")

    I have no idea what size tire you are running, your actual suspension setup, wheels, brakes, ride height, etc. So those numbers above may work just fine and then again they may not fit at all! The only way to know for sure is to Measure . . . Measure . . . Measure . . . and finally Measure Again!

    This tool can help you play with different offsets, sizes, tires. etc. to give you some rough numbers and ideas of what might work!

    http://www.rimsntires.com/specspro.jsp
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  7. #7
    FEP Senior Member Patrick Olsen's Avatar
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    Quote Originally Posted by PredatorGT View Post
    Thanks for the replies guys. I'm using sn95 axles. Will using 17x10 backspacing on a 17x12 wheel really fill the flare? Seems too good to be true haha
    If X" of backspacing on a 17x10" wheel doesn't rub the inside of the wheel well, then X" of backspacing on a 17x12" wheel will also not rub. Not sure what's too good to be true about that, or what's funny about it.

    Of course, as wraith said, you have to factor in suspension setup and tire sizing and ride height and everything else. If you want to do something not many folks are doing, then you have to do the homework to make sure it'll work.

  8. #8

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    I didn't want to sound like I doubted you so I tried to be lighthearted about it. I didn't know all of the extra width of the wheel would be moved to outside like you said. Any ways, I've selected 335/35 tires and plan to run a coil over conversion for the suspension!

  9. #9
    Moderator wraithracing's Avatar
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    Quote Originally Posted by PredatorGT View Post
    I didn't want to sound like I doubted you so I tried to be lighthearted about it. I didn't know all of the extra width of the wheel would be moved to outside like you said. Any ways, I've selected 335/35 tires and plan to run a coil over conversion for the suspension!
    The tires and coil overs are fine. The question is are you still running the stock quadra bind or are you upgrading to a Torque Arm, or something else. Are you running a panhard rod? All of that will affect how the suspension behaves and how much it moves in the chassis during high speed corners and transitions.

    That large a tire will not give you a lot of "wiggle" room so if your suspension moves around due to no panhard rod or watts link then you are more likely to have a rub on the inner wheel wells depending on your offset/back spacing. You could also have rubbing on the outside too again depending on where the wheel/tire combo sits in the opening. I would assume you are ditching the OEM quad shocks and would most likely for tire clearance, so the question is what are you doing to address wheel hop? Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  10. #10

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    I planned to run at least a panhard bar. A buddy of mine says to go ahead and do a torque arm too but that's still up in the air. Still spooked about what BS I should run. Trey, with my setup (sn95 axles, 2" flares, coils, panhard, 335s, 12s) in your honest opinion what would be an ideal BS to run? I could always use small spacers to fine tune if need be

  11. #11
    Moderator wraithracing's Avatar
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    Quote Originally Posted by PredatorGT View Post
    I planned to run at least a panhard bar. A buddy of mine says to go ahead and do a torque arm too but that's still up in the air. Still spooked about what BS I should run. Trey, with my setup (sn95 axles, 2" flares, coils, panhard, 335s, 12s) in your honest opinion what would be an ideal BS to run? I could always use small spacers to fine tune if need be

    Are you looking at a specific wheel as that may limit you on your BS/Offset choices. If you are looking at truly custom wheels, then you more options but obviously the prices go up. Wheel brands such as Forgestar allow you tons of offsets and sizes while still keeping the price reasonable.

    http://www.forgestar.com/wheels/finishes/

    As for offset/BS I hate to guess since there are so many variables and things to consider. Most likely the BS I mentioned above will get you in the ball park and allow tweaking from there with spacers. Obviously you are better off to run a bit more BS/offset and then space the wheel out as needed. If you don't have enough BS/offset then you won't fit under the flares to begin with.

    I have a set of ole' Cobra R replicas in the 10.5" wide with a set of 335's on them. Give me a couple of days and I will throw them on my Road Racer with the SVO rear axles and brakes. That will allow me to check some clearance issues and give you a better idea if that BS/offset is in the ball park.
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  12. #12

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    Good 'ol steelies! Can be custom made and super cheap! I know they're heavy but it's hard to beat the pricing. Thanks for your effort trey

  13. #13

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    Quote Originally Posted by wraithracing View Post

    I have a set of ole' Cobra R replicas in the 10.5" wide with a set of 335's on them. Give me a couple of days and I will throw them on my Road Racer with the SVO rear axles and brakes. That will allow me to check some clearance issues and give you a better idea if that BS/offset is in the ball park.
    I'd like to see this too.

    Jess
    Previously owned;
    1979 Mustang, v6 swapped to EFI 393, custom installed m122 blower, 4r70w trans, Megasquirt II, T-top swaped in.
    1990 Mustang, 545 BBF, C-4 with brake, ladder bars.
    1983 Mustang, 1984 SVO Mustang
    1984 Mustang convertible, v6 swapped to 351
    1986 Mustang GT, 1989 Mustang GT convertible
    1992 Mustang coupe, 4 swapped to 302

  14. #14
    Moderator wraithracing's Avatar
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    Alright I had a short amount of time before the rain started here again to throw the wheels on my Road Racer.

    I actually have two different brands of the Cobra R replica wheels I am not sure what they are anymore, but both are China Made copies. The first one is a 17X10.5 with a 28mm offset (@ 6.9" BS) wearing a set of 335 tires.

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    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  15. #15
    Moderator wraithracing's Avatar
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    The second set I have are the same 17X10.5" wheels with a 27mm offset (@6.8" BS). So not really any difference just different manufacturers. The tires are a set of Hoosier DOT road race tires 315 size.

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    The last picture above shows that the tire/wheel clears the OEM quad shocks . . . Well at least at a static ride height and no lateral force on the vehicle!

    I have no idea if there would be any rubbing while driving or cornering as I did not have time to test today and I have not had these wheels installed on this Mustang before. Once I get the last few items sorted out on the Road Racer, I should have time to throw on the wheels and give a spin or two around the block.
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  16. #16

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    Thank you.

    I plan to add a set of 31 spline Mark 7 length axles and SN-95 front control arms to my '79(already has 13" cobra disks up front). I'm currently using the Mark 7 brakes flipped end for end with stock fox length axles, obviously I'd swap the caliper brackets back the way they belong. My current rear rims are 18 x 10" with a 295 tire on them. Your pics shows about how much flare I'd need. Sometime down the road I'll get wheels with more backspace to add a bigger tire.

    Jess
    Previously owned;
    1979 Mustang, v6 swapped to EFI 393, custom installed m122 blower, 4r70w trans, Megasquirt II, T-top swaped in.
    1990 Mustang, 545 BBF, C-4 with brake, ladder bars.
    1983 Mustang, 1984 SVO Mustang
    1984 Mustang convertible, v6 swapped to 351
    1986 Mustang GT, 1989 Mustang GT convertible
    1992 Mustang coupe, 4 swapped to 302

  17. #17
    FEP Super Member erratic50's Avatar
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    Tons of room there by the time you add a panhard and flares.

    more room can be had by flipping or eliminating the quad shocks too

  18. #18

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    Great info.

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