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Backspacing/offset for new rims on 91 merc?

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    #1

    Backspacing/offset for new rims on 91 merc?

    i've pretty much decided to go with american racing Baja rims, same style rim as the Magna 302's beautys. I love deep looking rims with a fat tire around it. Get my friends drulin over this thing, haha. Spokes aren't quite cuttin it for a 17 year old, lol. Heres what i'll be getting around spring when i can save up the $:

    -15"x7 for the front with 225-235/70/15 tire.

    -15"x8 for the back with 275/60/15 tire.

    now for the tricky part (for me anyways), what backspacing and offset should I go with for no rubbing but still have the tires out fairly close to the fenders? I will be adding adjustable air shocks to the back to stiffin things up a little bit to.

    thanks allot guys, andy
    Finally have an on the books porting/custom fab business!
    HO bottom end,GT40Ps,cut/welded/ported upper+lower GT40 intakes,Comp XE258 cam,MS3X megasquirt computer,8 LS2 coils,2 dry systems + a 3rd wet,3 core rad w fans..1100hp Lentech WR AOD,custom 4" aluminum/moly Dshaft,custom rear/back half chassis adjustable 4link,wilwood 4 piston,moser 9" axles,locker, M/T 30x12's,4 staged fuel pumps,100lbs sound insulation,power/remote everything,2000W sound.4480lbs. 4.5s 0-60,12.8 1/4

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    #2
    couldn't edit past 30 min so just adding 1 thing:

    4" stock backspacing

    +20mm offset (from my calculationg)
    Finally have an on the books porting/custom fab business!
    HO bottom end,GT40Ps,cut/welded/ported upper+lower GT40 intakes,Comp XE258 cam,MS3X megasquirt computer,8 LS2 coils,2 dry systems + a 3rd wet,3 core rad w fans..1100hp Lentech WR AOD,custom 4" aluminum/moly Dshaft,custom rear/back half chassis adjustable 4link,wilwood 4 piston,moser 9" axles,locker, M/T 30x12's,4 staged fuel pumps,100lbs sound insulation,power/remote everything,2000W sound.4480lbs. 4.5s 0-60,12.8 1/4

    Comment

      #3
      Read the FAQ's. Still have any questions, ask.
      Builder/Owner of Badass Panther Wagons

      Busy maintaining a fleet of Fords

      Comment

        #4
        I had the same exact thing on my car; 225 70 15s in the front on 15x7/ 15x8 AR Ansen Sprints. My wheels were 0 offset, and they rubbed the outside fender lip with the factory rear springs, and folk sitting in the back (on my '90). But, they are on my brother's '88 now, and they do not rub. What gives, right?

        Those are some beefy meats for the back, and they should look awesome.
        **2012 Ford Mustang Boss 302: 5.0/ 6 spd/ 3.73s, 20K Cruiser
        **2006 MGM,"Ultimate": 4.6/ 2.73/ Dark Tint, Magnaflows, 19s, 115K Daily Driver
        **2012 Harley Davidson Wide Glide (FXDWG):103/ Cobra Speedsters/ Cosmetics, 9K Poseur HD Rider
        **1976 Ford F-150 4WD: 360, 4 spd, 3.50s, factory A/C, 4" lift, Bilsteins, US Indy Mags, 35s Truck Duties

        Comment

          #5
          thanks, the 15" rim i'm looking at with my bolt pattern and width come in 1 offset choice thats resonably close:

          7" wide rim= -6mm (will be sticking out 1.25" more towards the fender)
          8" wide rim= 20mm(perfect match to stock offset)

          so my only concern is fitting in the front rims with -6mm offset with 3.75" backspacing compared to the stock 19mm and 4" backspacing. Has anyone tried a switch like this, and does she fit?

          -P72Ford, with the 0 offset, do you think that -6 would have been to close, and do you think i will have to stiffin my front suspention to, or will it be fine? Oh, and thats a nice lookin car you got by the way.

          thanks guys, andy
          Finally have an on the books porting/custom fab business!
          HO bottom end,GT40Ps,cut/welded/ported upper+lower GT40 intakes,Comp XE258 cam,MS3X megasquirt computer,8 LS2 coils,2 dry systems + a 3rd wet,3 core rad w fans..1100hp Lentech WR AOD,custom 4" aluminum/moly Dshaft,custom rear/back half chassis adjustable 4link,wilwood 4 piston,moser 9" axles,locker, M/T 30x12's,4 staged fuel pumps,100lbs sound insulation,power/remote everything,2000W sound.4480lbs. 4.5s 0-60,12.8 1/4

          Comment

            #6
            I think I ran a 15x7 in a 3.75 offset and they were fine. They may have been 3.25 though. Either way I had a 10.50 wide tire on em and no rubbing so you should be fine.
            1989 Grand Marquis LS
            flat black, 650 double pumper, random cam, hei, stealth intake, Police front springs, Wagon rear, Police rear bar, wagon front ,exploder wheels, 205/60-15 fronts 275/60-15 rears, 1 5/8" headers, 2.5" offroad x pipe, Eclipse front bucket seats, Custom floor shifter, 4.10 gears, aluminum driveshaft and daily driven. 16.77@83mph

            Comment

              #7
              Originally posted by merc91 View Post
              -P72Ford, with the 0 offset, do you think that -6 would have been to close, and do you think i will have to stiffin my front suspention to, or will it be fine? Oh, and thats a nice lookin car you got by the way.

              thanks guys, andy
              The front wheels never rubbed the outer fender lips. IIRC a negative offset moves the outer rim more towards the outside of the car. 6 mm is only about a quarter inch, so I can't imagine that being an issue. The 7" wheels aren't available with 0 offset, because that'll be fine?

              For the rear wheels, a 20 mm offset is about .75" (moving the rim towards the inside of the car). I had plenty of clearance on the inside of the wheelhouse, but my fatties used to rub on the oustide with weight in the back. Moving the wheel in with the 20 mm offset should be advantageous, and may alleviate this potential problem.

              Thanks for the comments on 'The Red Box'...
              **2012 Ford Mustang Boss 302: 5.0/ 6 spd/ 3.73s, 20K Cruiser
              **2006 MGM,"Ultimate": 4.6/ 2.73/ Dark Tint, Magnaflows, 19s, 115K Daily Driver
              **2012 Harley Davidson Wide Glide (FXDWG):103/ Cobra Speedsters/ Cosmetics, 9K Poseur HD Rider
              **1976 Ford F-150 4WD: 360, 4 spd, 3.50s, factory A/C, 4" lift, Bilsteins, US Indy Mags, 35s Truck Duties

              Comment

                #8
                Originally posted by P72Ford View Post
                I had the same exact thing on my car; 225 70 15s in the front on 15x7/ 15x8 AR Ansen Sprints. My wheels were 0 offset, and they rubbed the outside fender lip with the factory rear springs, and folk sitting in the back (on my '90). But, they are on my brother's '88 now, and they do not rub. What gives, right?

                Those are some beefy meats for the back, and they should look awesome.

                A 1990 has a wider rear axle.
                Builder/Owner of Badass Panther Wagons

                Busy maintaining a fleet of Fords

                Comment

                  #9
                  Originally posted by mrltd View Post
                  A 1990 has a wider rear axle.
                  Ah yes, we learned that on Saturday evening. So, I guess we know what gives then, eh?
                  **2012 Ford Mustang Boss 302: 5.0/ 6 spd/ 3.73s, 20K Cruiser
                  **2006 MGM,"Ultimate": 4.6/ 2.73/ Dark Tint, Magnaflows, 19s, 115K Daily Driver
                  **2012 Harley Davidson Wide Glide (FXDWG):103/ Cobra Speedsters/ Cosmetics, 9K Poseur HD Rider
                  **1976 Ford F-150 4WD: 360, 4 spd, 3.50s, factory A/C, 4" lift, Bilsteins, US Indy Mags, 35s Truck Duties

                  Comment

                    #10
                    thanks a ton! Nice to hear that things should fit, and i'll take a couple measurements with clearences now to get an idea also. And the 20mm for the back is perfect match to the 19 that is stock, so i'll just be adding .75"of rim and 1.2" of tire to each the outer and inner profile.

                    Should I be stiffining up my front suspention also or could I get away without it for a while?...
                    till i go all out with handling and other things when i get a co-op here in the plants, hehe.


                    thanks again, andy
                    Finally have an on the books porting/custom fab business!
                    HO bottom end,GT40Ps,cut/welded/ported upper+lower GT40 intakes,Comp XE258 cam,MS3X megasquirt computer,8 LS2 coils,2 dry systems + a 3rd wet,3 core rad w fans..1100hp Lentech WR AOD,custom 4" aluminum/moly Dshaft,custom rear/back half chassis adjustable 4link,wilwood 4 piston,moser 9" axles,locker, M/T 30x12's,4 staged fuel pumps,100lbs sound insulation,power/remote everything,2000W sound.4480lbs. 4.5s 0-60,12.8 1/4

                    Comment

                      #11
                      It'll be fine without doing the front
                      Builder/Owner of Badass Panther Wagons

                      Busy maintaining a fleet of Fords

                      Comment

                        #12
                        Originally posted by merc91 View Post
                        And the 20mm for the back is perfect match to the 19 that is stock
                        What is meant here? Because stock wheels use a zero offset, and you certainly can't be talking about backspacing.

                        My best lack-of-advice to chime in with, having lived with a couple sets of high-scrub-radius wheels (15x8 all around, 3.75" BS and 15x8.5/15x10, unknown BS because I've never measured it), is to get zero offset in most cases for best tire clearance and to maintain primarily stock handling characteristics, and possibly keep the front tires on the shy side of 27" if going wide, such as a 245/60/15 or 265/50/15.

                        Other than that, the ARE Baja is a great-looking wheel and I'm eager to see pics of it on your car!
                        Last edited by 1987cp; 11-26-2008, 01:18 AM.
                        2012 Mazda5 Touring | Finally working on the LTD again!

                        Comment

                          #13
                          isn't offset the distance in mm from the center plane of the rim to the mounting surface?
                          backspacing is 4" on a 6.5" wide rim which gives me an offset of +19mm. This is on a 91 marquis to which could be a little different.

                          ...Just from what i have read on measuring offset, if i'm wrong that changes things allot. I would like the deepest rim i can get on there and 0 offset is much better starting than +19 for that.

                          Yeah they look perdy, and for tires i'm wrapping around some BF Goodrich Radial T/A's with the super black, smooth sidewall with raised white letters for an over all muscle car look. It's gunna have to wait till march though. I can't wait!

                          Thanks for the help guys, andy
                          Last edited by merc91; 11-26-2008, 11:28 PM.
                          Finally have an on the books porting/custom fab business!
                          HO bottom end,GT40Ps,cut/welded/ported upper+lower GT40 intakes,Comp XE258 cam,MS3X megasquirt computer,8 LS2 coils,2 dry systems + a 3rd wet,3 core rad w fans..1100hp Lentech WR AOD,custom 4" aluminum/moly Dshaft,custom rear/back half chassis adjustable 4link,wilwood 4 piston,moser 9" axles,locker, M/T 30x12's,4 staged fuel pumps,100lbs sound insulation,power/remote everything,2000W sound.4480lbs. 4.5s 0-60,12.8 1/4

                          Comment

                            #14
                            sorry, actually a +6mm offset stock with the 4" backspacing. looked at some charts and more accurate formulas and the +6mm is much better than the +19mm i got with the simple equation. So my front will only stick out .5" more + the extra 1/4" of rim width so total of 3/4", and the back will be .5" inward more+3/4" extra rim so total of 1 1/4" more. Thanks, +19 seemed a little high for a older RWD car haha. Well that's great.

                            Thanks again, andy
                            Finally have an on the books porting/custom fab business!
                            HO bottom end,GT40Ps,cut/welded/ported upper+lower GT40 intakes,Comp XE258 cam,MS3X megasquirt computer,8 LS2 coils,2 dry systems + a 3rd wet,3 core rad w fans..1100hp Lentech WR AOD,custom 4" aluminum/moly Dshaft,custom rear/back half chassis adjustable 4link,wilwood 4 piston,moser 9" axles,locker, M/T 30x12's,4 staged fuel pumps,100lbs sound insulation,power/remote everything,2000W sound.4480lbs. 4.5s 0-60,12.8 1/4

                            Comment

                              #15
                              Maybe this'll help clear up the guesswork: http://www.mickeythompsontires.com/t...p?bulletin=s10


                              TO CONVERT OFFSET TO BACKSPACING:

                              For positive offset wheels: (Wheel Width +1)/2 + (offset * .03937)

                              For negative offset wheels: (Wheel Width +1)/2 - (offset * .03937)

                              TO CONVERT BACKSPACING TO OFFSET:

                              Backspacing – (Wheel Width + 1)/2 * 25.4 = offset
                              2012 Mazda5 Touring | Finally working on the LTD again!

                              Comment

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