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  • Tilting S13 subframe

    I run autocross and I'm about to install an s13 subframe with ISR solid bushing. I did a bit of reseach and was wondering, is adding 1/4 inch shims to the front of the subframe an effective way to reduce anti-squat an appreciable ammount? Does it pose a risk to the studs?

  • #2
    Yes - extreme risk. Do not tilt with solid bushings. Hell, don't tilt it at all!
    '18 Chevrolet Volt - Electric fun hatch for DD duty!


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    • #3
      Originally posted by Def View Post
      Yes - extreme risk. Do not tilt with solid bushings. Hell, don't tilt it at all!
      Thanks. On the SPL site it says:

      "Our slide-in shim system allows you to quickly raise or lower the subframe to fine-tune the roll center/anti-squat behavior to your preference. Raising the subframe will compensate roll center for a lowered car at the expense of increasing anti-squat. Lowering the subframe will decrease anti-squat at the expense of roll center."

      So shimming the top of the subframe to lower it (equally, no tilt) also reduces anti-squat? I read somewhere that Solid bushings like ISR technically lowers the subframe as the top part is thicker then stock, is that true?

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      • #4
        Yes, it is slightly changing the rear subframe's instant center location, which will affect anti-squat. It's a small small change though, and your roll center is going to start dropping if you're really low.

        Honestly, if you have an S13 and want to get a better performing rear suspension setup, just get an S14 rear subframe. It's a pretty easy swap all things considered, and it has good geometry. I'd recommend raising it UP as high as you can to raise the rear roll center very slightly.
        '18 Chevrolet Volt - Electric fun hatch for DD duty!


        DefSport Koni Sleeve and Spring Perch Buy!!!
        http://www.nissanroadracing.com/showthread.php?t=5902

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        • #5
          Originally posted by Def View Post
          Yes, it is slightly changing the rear subframe's instant center location, which will affect anti-squat. It's a small small change though, and your roll center is going to start dropping if you're really low.

          Honestly, if you have an S13 and want to get a better performing rear suspension setup, just get an S14 rear subframe. It's a pretty easy swap all things considered, and it has good geometry. I'd recommend raising it UP as high as you can to raise the rear roll center very slightly.
          Thanks, this is my 1st year autocrossing so I'll just run this subframe for now and see how it goes. How much lower then stock can you go before starting to negatively affect roll center? I don't care about looks, just grip.

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          • #6
            Stock varies wildly due to chassis weight due to stock springs. I would say roughly a 1-2 finger gap (~3/4-1.5") from top of a 255/40-17 to the fender is about right for a general range.
            '18 Chevrolet Volt - Electric fun hatch for DD duty!


            DefSport Koni Sleeve and Spring Perch Buy!!!
            http://www.nissanroadracing.com/showthread.php?t=5902

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            • #7
              Incidentally, tilting your subframe would bump you to Prepared in AutoX. That's the first level where you can move the suspension pickups on the frame side. I suggest sticking with the S14 subframe, which keeps you in Street Prepared or Street Modified.

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              • #8
                Originally posted by cdlong View Post
                Incidentally, tilting your subframe would bump you to Prepared in AutoX. That's the first level where you can move the suspension pickups on the frame side. I suggest sticking with the S14 subframe, which keeps you in Street Prepared or Street Modified.
                Speaking of which. In my local events the rules are slightly different, but there is a regional even coming up this is under SCCA rules so I was looking up the classing. My car is bone stock except for a 6 puck clutch, LSD and godspeed tension arms.

                Am I crazy or do those hemi joins arms bump me directly to Prepared?

                If so that's nuts!

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                • #9
                  Heims bump you to Street Modified.

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                  • #10
                    SCCA rules do not like many commonly available mods like solid bushings or even bolt-on chassis braces. They would rather everything be expensive and esoteric to fit their narrow-minded ruleset.
                    This is the same in club racing as well... 40 year old cars with >2x the stock horsepower and slicks, yet they're required to run the stock calipers and stock size rotors.. but they're allowed to modify fenders and bumpers to add brake ducting in a class called "Production" wheres in a class called "Super touring" designed to accept tuner cars will allow engine swaps, 13" 2-pc rotors and 4piston calipers, but you must run 100% OEM fenders, bumper, etc. you're allowed composite hood, but must be OEM shape-- no hood vents or strange contours allowed..

                    yeah, makes sense to me!
                    Originally posted by SoSideways
                    I don't care what color they are as long as they are LONG AND HARD.
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                    • #11
                      Originally posted by e1_griego View Post
                      Heims bump you to Street Modified.
                      Mmm, you might be right. Street Modified says:
                      E. Suspension components are unrestricted as long as they use the original attachment points. Cars equipped with MacPherson strut suspension may add or remove material from the top of the strut tower to facilitate installation of adjuster plate. The sides of the strut tower may not be modified.
                      But does that mean that S14 subframe is not legal in SM because it changes the original attachment points?

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                      • #12
                        It was clarified that it is allowed because the SP ruleset which allows update/backdate.

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                        • #13
                          If this is your first year, I wouldn’t focus on classes but rather have fun in your car and work on technique. Run what you brung, and remember that Tires are the most important thing you can do to improve times.

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                          • #14
                            Originally posted by jfryjfry View Post
                            If this is your first year, I wouldn’t focus on classes but rather have fun in your car and work on technique. Run what you brung, and remember that Tires are the most important thing you can do to improve times.
                            Burning through pricey tires, sometimes with a setup that doesn't emphasize tire life, will make you go faster. But it's generally one of the most expensive ways to go faster as it's a recurring consumable cost.

                            If you're still learning, run on some "reasonable" tires that are consistent with temp and just go out there and drive. I would get something that wears like iron like a Nitto NT05 or I think Federal RSR/RSRR's, and maybe the new Nexen SUR4 are pretty long lasting tires with pretty decent grip and not really pricey.
                            '18 Chevrolet Volt - Electric fun hatch for DD duty!


                            DefSport Koni Sleeve and Spring Perch Buy!!!
                            http://www.nissanroadracing.com/showthread.php?t=5902

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                            • #15
                              Originally posted by Def View Post
                              Yes - extreme risk. Do not tilt with solid bushings. Hell, don't tilt it at all!

                              Could you please educate me on this? Not just the potential stress in the studs but the pros and cons of adjusting instant center, roll center etc...? I'll be honest I'm pretty noob when it comes to stuff like that, I'm starting to understand roll center but I know I need to learn more. I have a spare S13 sub-frame which I've reinforced and need to pick up bushings for, I can't decide if I should get the SPL bushings (so I would have the ability to adjust as necessary in the future) or just get the cheaper ones like GK Tech.

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