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  1. #1
    Join Date
    Apr 2007
    Location
    Colorado Springs, CO
    Age
    32
    Posts
    291

    backspace question

    What is the minimum backspace that will fit a 68 Cougar 15 inch rims.

    Thanks
    Evil Prevails when good men fail to act....
    Kick the tires and light the fires big daddy...

    CHUCK

    1968 MERCURY COUGAR (STD) Building
    2002 FORD CONVERSION VAN
    1972 FORD RANCHERO

  2. #2
    Join Date
    Mar 2011
    Location
    White Salmon, WA
    Posts
    10

    Re: backspace question

    If I remember correctly about 3.5" it all depends on tire size and rim width though. On a 15x8 you will likely want around 4.25. The best way I know and what I used to do when doing custom wheels even in 17" is to measure the fit of the tire/wheel package. To do this know the width of the tire you want to run. Let say 235 for arguments sake. 235/25.4 is 9.25" tread width. So take a tire off, put a straight edge against the axle hub/drum extending it up into the wheel well and start your measurement from the back of that edge. get that 9.25 where you have lip clearance at the quarter panel. Factor in the width of tread you want and leave enough wheel well and lip clearance (at least 1"). Measure twice as always, write it down and check again.

    I used to do this on all sorts of hot rods etc and always had great fit. You can easily get a 255 in there and likely 265/50/15. If you need more info I can pull my 68 apart and measure it. I have 18x9.5 on the rear (not by choice, leftovers from wifes 04 stang).

  3. #3
    Join Date
    Apr 2007
    Location
    Colorado Springs, CO
    Age
    32
    Posts
    291

    Re: backspace question

    Quote Originally Posted by Talon258 View Post
    If I remember correctly about 3.5" it all depends on tire size and rim width though. On a 15x8 you will likely want around 4.25. The best way I know and what I used to do when doing custom wheels even in 17" is to measure the fit of the tire/wheel package. To do this know the width of the tire you want to run. Let say 235 for arguments sake. 235/25.4 is 9.25" tread width. So take a tire off, put a straight edge against the axle hub/drum extending it up into the wheel well and start your measurement from the back of that edge. get that 9.25 where you have lip clearance at the quarter panel. Factor in the width of tread you want and leave enough wheel well and lip clearance (at least 1"). Measure twice as always, write it down and check again.

    I used to do this on all sorts of hot rods etc and always had great fit. You can easily get a 255 in there and likely 265/50/15. If you need more info I can pull my 68 apart and measure it. I have 18x9.5 on the rear (not by choice, leftovers from wifes 04 stang).
    Thank you this truly helps. I will keep ya posted
    Evil Prevails when good men fail to act....
    Kick the tires and light the fires big daddy...

    CHUCK

    1968 MERCURY COUGAR (STD) Building
    2002 FORD CONVERSION VAN
    1972 FORD RANCHERO

  4. #4
    Join Date
    Dec 2002
    Location
    Chesterland, Ohio
    Age
    48
    Posts
    6,022

    Re: backspace question

    Backspace ultimately depends on how wide the wheel and tire is. The narrower the rim, the less backspace you can get away with.

    You would ideally want the mounting flange of the wheel to be centered in the wheel with respect to dish and backspace. More backspace = less dish which also affects "looks" just as much as overall fitment.

    So basically you need to decide how wide the 15" rim is going to be. Then backspace can be calculated to get it to fit centered in the wheelwell.

    Mark
    '68 XR-7 351W C6 3:50 1 of 1

    Anyone can restore a Classic, but it takes a Real Man to cut one up!

    Buckeye Boys Rod & Custom - East

    Reserved parking at the Classic Cougar Garage.
    First Official "Ride Of The Month" at ClassicCougarCommunity.Com
    Illegally parked on the Curb

  5. #5
    Join Date
    Apr 2007
    Location
    Colorado Springs, CO
    Age
    32
    Posts
    291

    Re: backspace question

    Thinking of 15x10 will it fit the 68 Cougar without modifying anything?
    Evil Prevails when good men fail to act....
    Kick the tires and light the fires big daddy...

    CHUCK

    1968 MERCURY COUGAR (STD) Building
    2002 FORD CONVERSION VAN
    1972 FORD RANCHERO

  6. #6
    Join Date
    May 2008
    Location
    Cedar Rapids, Iowa
    Age
    49
    Posts
    9,319

    Re: backspace question

    I wish somebody would buy that Percy wheel fitment tool from summit/jegs and loan it to everyone who needs this info.... Wink., wink, nudge, nudge... I may need it soon
    1969 E-cat warmed-over 351W AOD

    1969 XR7 S Code vert in progress

    1968 F code XR7 - waiting for re-imbursment from bro-in law :>\

    1998 F150 4x4 D.D - 300k on the clock!

    2001 F150 4x4 backup for 98 ;>P

    2 x 1985 Suzuki Madura 1200's. One done - one in progress

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