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  1. #1
    FEP Member 86MustangGtRob's Avatar
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    Default Anyone running a 245 40 R17 or a 255 40 R17 front tires?

    Hi guys,

    I have a 1985 Gt with pony r rims. I currently have 245 45 17 front tires and 275 40 17 rears. My fronts are old and was wanting to change them to a lower profile.

  2. #2
    Moderator wraithracing's Avatar
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    I run 255/40/17 tires on the front of my Pace Car with 17X9 Cobra R wheels. I don't have any issues with the size on the front, but I probably wouldn't recommend a 255 on an 8" wheel. Not sure if yours are 8" or 9" just thought I would mention that. Yes it will fit, but in my experience the 255 gets squeezed down on the 8" wheel compared to the 9". You are looking about 0.5" - 0.7" difference in overall height when comparing the 245/45 to the 255/40 depending on tire brand, wheel size, etc.
    ​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

  3. #3
    FEP Member 86MustangGtRob's Avatar
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    Thanks for the input Trey I have a 8" rim in the front. I was looking for a smaller front tire.

  4. #4
    Moderator wraithracing's Avatar
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    Quote Originally Posted by 86MustangGtRob View Post
    Thanks for the input Trey I have a 8" rim in the front. I was looking for a smaller front tire.
    The 255/40 will be shorter but I wouldn't call it smaller.

    A 245/40 will be @ 1" smaller overall diameter compared to the 245/45. 24.7" compared to 25.7" again approximately as ever manufacturer and brand can vary in overall height and width. The 255/40 is @ 25" overall diameter for comparison. 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
    FEP Super Member escogt's Avatar
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    245/40 fronts on a 17x8 wheel
    '85GT Bright Atlantic Blue
    '92LX Bimini Blue-sold
    '93 COBRA Teal Metallic-sold
    '86SVO Oxford White-sold
    '86GT 'Vert True Blue-sold
    '81'GT' Medium Red-sold

  6. #6
    FEP Member 86MustangGtRob's Avatar
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    I always liked the look of your car. The 40 series looks good in the front. The rims I have in the front are the ones you sold me 7 years ago.

  7. #7
    FEP Super Member escogt's Avatar
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    Quote Originally Posted by 86MustangGtRob View Post
    I always liked the look of your car. The 40 series looks good in the front. The rims I have in the front are the ones you sold me 7 years ago.
    Thanks, Rob. I remember!
    '85GT Bright Atlantic Blue
    '92LX Bimini Blue-sold
    '93 COBRA Teal Metallic-sold
    '86SVO Oxford White-sold
    '86GT 'Vert True Blue-sold
    '81'GT' Medium Red-sold

  8. #8

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    I’m running the same front combo as mike. Rear is a 275 tire. The rear wheel was 10” I cut them down to 9 1/2” looks much better with 275 tireName:  42661A0A-12C5-4C98-B716-CF367CCBBDFE.png
Views: 229
Size:  1.43 MB

  9. #9
    FEP Member 86MustangGtRob's Avatar
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    Your t-top coupe looks amazing. I love the stance. If you don't mind me asking. How much did it cost to do?

    Merry Christmas

  10. #10

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    I did almost everything myself except for the body work. So I saved a lot of labor $$
    Even with that it’s still to much to mention. But I built the car I wanted my way. You can’t cut corners and build your for ever car.

    Merry Christmas

  11. #11
    FEP Member 86MustangGtRob's Avatar
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    That is true. I poured a lot of money on my 85.

  12. #12

  13. #13
    FEP Member 86MustangGtRob's Avatar
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    The engine bay looks incredible. I love the ford racing valve covers.

  14. #14

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    Geezz man you are making us seriously jealous of that ride. Wow what a beauty.

  15. #15

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    Thanks. It’s a 408. Scott rod weld in panels. Tucked wiring. And more

  16. #16
    FEP Senior Member Quicksilver's Avatar
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    I'm running 245/40/17 on 8" rims in the front and 275/40/17 on 9.5" in the rear. Because of the back spacing/offset on the front rims, I have to run 245/40/17s. I originally had 245/45/17s, but they would rub on the front fender lips as I turned. I discovered this after paint and bodywork. One suggestion was to swap in the 91-93 front fenders to get the clearance. My solution was to get 245/40/17s. They work great as I also have 5 way adjustable struts up front. Having said that, one time coming home from Carlisle on I 81, I hit a pothole at 70 mph. Besides being annoying, the hit broke the bead and caused a slow leak. So when I stopped for gas, the tire went flat. I had to get flatbedded home. The next day, I had the tire resealed and everything was fine. Likely caused in part by the low profile sidewall. But, the car rides and drives great. I wouldn't change a thing.
    Rob

  17. #17
    FEP Super Member erratic50's Avatar
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    245/45/17 rubbing on the fender extensions is a suspension adjustment thing

    I run caster camber plates centered in the opening and shoved all the way towards the windshield

    I had to use camber bolts and some pry bar persuasion to get the negative camber I want but there is actually capacity for up to -6 on each side even with the X2 ball joints making negative camber harder to come by

    Anyway ..... 17” tribar rims with stock spindles and ranger rotors or with SN95 spindles the 245/45/17 clear on mine

    the stock spindle setup rubbed badly on the frame rails and needed a spacer there. Just barely cleared the struts

    With the SN spindles they just barely rub the frame rail in the last 1/8 turn. A wider K member from a newer car or a rack limited to 2.25 turns would help with this ....

    a good friend runs 255/40/17 on a 17x9 with 27mm. Have to use a rack limiter but they clear and it handles great

  18. #18
    FEP Member 86MustangGtRob's Avatar
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    Default

    Thanks for sharing your experience. I'm on the fence with going with 245 40 or a 245 45 on the front. The lower profile on the front would look good.

  19. #19

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    Looks best with the same sidewall height front and rear.

  20. #20
    Moderator wraithracing's Avatar
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    Quote Originally Posted by 86MustangGtRob View Post
    Thanks for sharing your experience. I'm on the fence with going with 245 40 or a 245 45 on the front. The lower profile on the front would look good.
    Just keep in mind the lower the profile, generally the harsher the ride quality. If you are going from the Pony wheels with 16" tires you will notice a significant difference in ride quality just going to the 17's wheels/tires because of the lower profile alone.

    Also 245/45 is a more common tire size and often is a cheaper option than the 245/40. Probably not a deal breaker, but something to consider.
    ​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

  21. #21

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    Quote Originally Posted by badnightrain View Post
    Name:  152E4AA9-88DF-4E33-8097-A8B3693A884F.jpg
Views: 222
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    Everything has been done
    WOW! That is awesome!

  22. #22

    Default

    Quote Originally Posted by 86MustangGtRob View Post
    Thanks for sharing your experience. I'm on the fence with going with 245 40 or a 245 45 on the front. The lower profile on the front would look good.
    Fwiw, you're well into the so-so Ford factory and assembly tolerances.
    Therefore, no-one can "guarantee" that a specific tire or rim will work fine. The same goes for the amount of caster adjustment you can get from your car and CC Plates.


    Tire sizes are like dress sizes.
    In reality, they don't mean a damn thing.
    If I sell you a 245/45/17 tire that is 12" high and 2" wide, then BFD! And, sorry - no refunds!!
    There's no law, no 100% defined standard, etc.

    Even from year to year, a specific tire model and size can (and often do) change.
    Add in the cheap ricer tires (like the the one I sold you above ), the full out performance tires, and snow tires, and you get a very appreciable difference in what exactly a 245/45/17 tire "is".
    That's why Tirerack, and reading the specs for a specific tire model and size is important.

    If people are willing to push out/adjust the front of the fender a little (it's held in position by a metal rod), then they can get more needed "breathing room".

    For me, and my car, I'm keeping the body very close to stock - because I want to.
    For you and your car, it's your choice, not mine or anyone else's.


    I've run the M2300K kit, and 245/45/17 tires, on my car since the mid-90s.
    I have steering rack limiters, a small spacer, MM CC-plates, a bump-steer kit, and ABS.
    For a while, I would run 4-Blizzaks on my 'stang so that I could drive it ~once a month in the winter.

    In the summer, I like the Bridgestone RE-7xx series (iirc, with a joke of a 200 wear rating).
    I've gone through a few tires. I'm even on my second set of Blizzaks.

    I got a flat tire once. I got the same exact tire/model as a replacement, and Bridgestone had very slightly changed the tire so it was a touch wider. So, off to the back that tire went.

    Tire pressure also makes a difference. I like my tires a little stiffer.
    And, don't forget there is the geometry of the tire between full extension and full compression - and the tire at full turn right/left. In some cases, some rubbing may occur.

    Don't forget about wider tires and your caliper brake hose. The mounting point for the hard-line and brake hose should be moved (?back, up?). I also use rubber coated clamps to keep my caliper hose from rubbing on my tires.


    I posted links to my car pictures and specs before:
    http://www.veryuseful.com/mustang/te...Mach1_springs/

    Btw, that hood gap was 100% as it came from the factory.
    Since those pictures, I've had the engine professional rebuilt. Hence, a more correct hood gap.


    Good Luck!
    Last edited by stangPlus2Birds; 01-05-2020 at 02:12 PM.

  23. #23

  24. #24

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    Badnighttrain,

    Post a photo of one of your strut towers from directly above the strut tip. I think that the c/c plates are installed incorrectly.
    Jack Hidley
    Maximum Motorsports Tech Support

  25. #25
    FEP Member 86MustangGtRob's Avatar
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    Default

    Thanks for your input Trey. I am going with a 245 45r17 in the end. Like you said it's the most common and has the price up here in Canada. The ride quality is great with my current 17" set up.

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