Front + Rear 18x12 trials and tribulations

Discussion in 'Boss 302 and S197 Technical Forum' started by neema, Apr 25, 2019.

  1. neema

    neema TMO Race

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    Figured I'd share in case anyone else wants to go down this avenue. I think most people know the "why" you go down this avenue. Anyways, I'll cut the crap and get to details.

    I currently use 305/35/18 NT01s, which is a ~26.3" OD. Haven't tried taller OD tires yet.

    Wheels are Forgestar CF5s, et38 up front and et58 in the rear, or notably, 8" backspace in the front and 8.78" in the rear. My MO was to mount wheels as tightly as possible to inboard obstructions and use spacers for wider tires as needed. These wheel dimensions fit with very, very little clearance between inboard hardware, which is great! Use 3, 5, 7mm spacers as needed for tires. Note: I'd probably do 1mm less offset (et37) up front. I didn't have any issues driving around town, but on track, I took a little paint off the strut. I now have a 3mm spacer up there.


    If you wanted identical wheel sizes on all four corners, 18x12 et58 wheels with a 20-25mm spacer should do the trick


    Wheel clearance steps by axle:

    Front:
    • Cortex offset struts
    • you may need to trim or use spacers on the swaybar endlink
    • camber plates (presumably you have these if you have Cortex struts). I have 2.6°, limited by the camber plate, not by the hole in the strut tower. More camber would probably allow for a 335?


    Inboard clearance with no spacer

    IMG_7012.jpg
    What it looks like outside
    IMG_7026.jpg

    Rear
    • bump stop bracket trim/removal and either bump stops relocated or bump stops on rear shocks
    • Stock, or as close to OEM rear shock style mount. If using Cortex rear coilovers: 1. divorce the spring and put on a weight jacker in the OEM location, 2. invert/flip the shock upside down, and 3. ideally remove spring perches. You can avoid spring perch removal (like me) and run a 10mm spacer, but now you're dealing with some rear tire protrusion. I don't rub but have since ordered rear JRis with OEM style mounts, rather than eyelets, to make adjustments easier (in the trunk rather than under the car) and open up more room
    • properly centered watts link
    • with a shorter 315/30 or 335/30, you may be able use a small spacer and OD

    With an OEM style shock, I may have been able to pull in the rear wheel a few more mm, but on 18s it gets tough since the rim gets close to the top of the shock mount. 20" wheels can usually go to et61 because the wheel is hanging out in slightly different parts of the wheel well.


    Some photos of the inverted rear shock that I have. You can see the spring perch still in place that takes up a little space. Disregard the bump stop on the axle. I run mine on the shock
    IMG_2684.JPG

    Still affords a little more space than how Cortex runs the coilover out of the box, like the image below.
    IMG_2145.JPG

    What I'm changing to:
    IMG_7028.PNG

    How the car sits now:

    IMG_7021.jpg IMG_7024.jpg
     
    Last edited: Apr 27, 2019
    smallblock and Grant 302 like this.
  2. VoodooBoss

    VoodooBoss Rick Moderator

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    Thanks for posting. I’m on my phone and your images aren’t showing. Did you upload them directly on the forum using the “Upload a File”?
     
  3. ArizonaBOSS

    ArizonaBOSS Because racecar. Moderator

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    I also cannot see the images on a desktop connection. But yes, great for sharing!
     
  4. neema

    neema TMO Race

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    How I manage to still mess up image hosting blows my mind. Fixed links. hopefully it works
     
    Last edited: Apr 26, 2019
  5. VoodooBoss

    VoodooBoss Rick Moderator

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    Working. We added photo hosting a couple of years ago and that’s your best bet.
     
    neema likes this.
  6. ChrisM

    ChrisM No bad days.

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    Wow, that's amazing! The grip must be otherwordly.
     

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