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  • Tire size for S15 / setup questions

    I'm new here and want to say you guys have an amazing forum here. Hopefully you can excuse some questions from a newbie - for some background, my car is fairly low powered (~200hp at wheels) and mostly for the street, but am looking to get more outright grip all round and a racier setup as the car is only used on weekends for mountain runs etc.

    Currently running 18x8.5" rims (+30) all round with 235/255 rubber, but they're old and hard so I'm about to invest in some new treads.

    Fairly set on Federal 595-RSR's (140 treadwear and not as good as R888's, but not far off from what I can gather), however I'm unsure on width. My plan was to run 245x35 all round, as the car has some small understeer tendencies at lower speeds / turn-in, possibly due to tyres, and I feel running the same all round would suit it quite well.

    The other options are 235x40 F / 245x35 R, or 235's all round. Are there any benefits to going narrower, like better contact patch through the stroke, or is that outweighed by the increased ultimate grip of a wider tread?

    Thanks in advance, I'm sure I'll have more questions later!
    Udi

  • #2
    While I'm at it - another one, about swaybars.
    I've got a whiteline front swaybar (27mm adjustable) that I haven't bothered putting in because I don't have a rear one to match. I've heard that these can make a big difference and kill off some turn-in understeer, but is it best to get the rear one as well before mounting? I'd like the car as neutral as possible.

    The car is running stock shocks (22,000 miles on clock so everything is fairly tight still) and ~1" lower/stiffer springs - if it matters.

    Comment


    • #3
      I'd go with a square setup so you can rotate tires.. I haven't had an issue with understeer from square setup that I haven't been able to tune out with setup changes.

      I run 235/45/17 on 17x8 myself, but only have about 150whp. Pretty much anything you mention will work okay for your setup. most people wouldn't even notice the difference.

      Sway bars-- depending on what rear diff you have, you may or may not want more sway bar. If you're running stock shocks though, both front and rear bar will probably help overall grip, but I've found the bigger the bar you put on the front, the happier the car is.
      Originally posted by SoSideways
      I don't care what color they are as long as they are LONG AND HARD.
      '04 G35 Sedan 6MT- The DD
      '96 240SX- The Track Toy

      Comment


      • #4
        ...what he said. ^^^

        Comment


        • #5
          Thanks for that.
          The diff is the stock HLSD (S15-R), and to be honest I can't feel a lot of body roll with the stock shocks. I do know they increased the damper rates over the 14 and they probably haven't had a chance to wear out yet either. I guess I will just try the new rubber first, and only mount the swaybars if more grip results in excessive roll.

          The other thing I noticed is that guys here are running a lot of -ve camber, personally I've only got about -1.75 front and -1.25 rear. Is this something that basically increases with stickier rubber and higher overall speeds (faster tracks perhaps)?

          Also, I notice everyone is on zero toe up front (I am too), would it be okay to run a tiny bit of front toe out to get a little more turn-in liveliness, or should good tyres give me all I need?

          Edit -
          This is what I had planned for my next alignment anyway, pretty close to current:
          Caster: 7.5°
          Camber: -1.75° F, -1.35° R
          Toe: 0.5mm toe-out F, 1.0mm toe-in R (per side)

          Comments/criticisms would be great.
          Last edited by udi; 10-09-2011, 10:13 PM.

          Comment


          • #6
            A lot of that depends on your driving style and requirements.

            My car is road race-only with full cage, R-Comps (BFG R1), coilovers, etc. For this, you want quite a bit of camber since the tires are designed to require it under race conditions.

            For a street car, -1.75/-1.25 is about all you want to keep from trashing the inside edges of the tires during street driving.

            With the HLSD, I've found that no rear bar and lots of suspension droop in the rear does best to keep from frying the inside tire. (I run the HLSD with a 4.6 ring & pinion at some tracks). More front roll stiffness helps here so the rear doesn't hike the inside leg like a FWD car. The issue is that you can make the front too stiff and then the car understeers- it's a compromise. Your stock shocks should provide enough droop in the rear that this shouldn't be a problem though.

            As for toe, that depends on your driving conditions. For AutoX, people run quite a bit of toe out to make the car turn in better. for road course use, that makes the car twitchy and unpredictable under braking, as well as eats inside shoulders during steady-state cornering. For street use, you want zero toe or just a touch of toe in to keep the car nice and stable.
            Originally posted by SoSideways
            I don't care what color they are as long as they are LONG AND HARD.
            '04 G35 Sedan 6MT- The DD
            '96 240SX- The Track Toy

            Comment


            • #7
              Keep the front at zero toe, any toe you run will really start decreasing tire life.

              If you want more lively front turn in, make sure you run spherical front tension rods. I'd also say a little more front camber is fine for a street car as long as you drive it hard here and there. If it's a daily driver -1.5 is about the most I'd go with up front, but if you drive hard I'd say around -2 to -2.5 is the max. You will notice MUCH more steady state grip and turn in quickness with more front negative camber.
              '18 Chevrolet Volt - Electric fun hatch for DD duty!


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

              Comment


              • #8
                I will stick with zero toe like you guys suggest, and for camber I think my front maxes out at about -1.8 anyway (no camber tops).

                I have another question. I took the spare and jack out of the back, and after a hard drive today I noticed the back had a greater tendency to come out (moreso off power, but on power too). I did expect something like that, however I'm wondering how you guys get around this?

                My lame solution is to be gentler on the throttle and keep the car on the edge of understeer if I'm getting scared, but would there be any benefit in going for a little wider rubber at the back to deal with this?

                Or should I just put my spare back in... I'm a bit picky with what I can strip out since it's a street car too (like the AC needs to stay), and am wondering - is it better to have less weight in total, or worry more about F/R weight balance?

                Comment


                • #9
                  Removing that much weight off the car is still tunable with tire pressure and alignment changes that won't affect tire life much. i.e. I'd run just a touch more camber in the back to help keep it planted in corners, but that will make inside rear wheelspin even worse if you have an HLSD.

                  for street driving, you shouldn't be driving the car that hard anyway.
                  I also wouldn't be going too far without a spare tire available. never know when you're going to run over a screw or something.
                  for track events and such, I always pull all the weight out like spares and whatnot, then tune the difference in handling with tire pressures and alignment settings.
                  Originally posted by SoSideways
                  I don't care what color they are as long as they are LONG AND HARD.
                  '04 G35 Sedan 6MT- The DD
                  '96 240SX- The Track Toy

                  Comment


                  • #10
                    Hit up a track day or twenty with instruction, you'll get all the answers to your questions then, and know more about what you want to modify on the car.
                    '18 Chevrolet Volt - Electric fun hatch for DD duty!


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

                    Comment


                    • #11
                      Appreciate the advice. I plan to hit the track with it eventually, but in the meantime there are a few good mountain runs here with virtually no one else on the road, so that makes up the majority of my driving.

                      Just got the new rubber mounted today, went with what I asked about in my original post (245 all round on 8.5") and it feels pretty good. Turn in seems to have improved and the car rotates well / feels more balanced.

                      Which brings me to my next question - what's the best way to lower the car a little more? It's quite high - I can easily put three fingers between tyre and guard on the rear, and while it drives fine, it looks a bit silly. I'm sure getting the COG down wouldn't hurt either. The rear is noticeably higher than the front (the front I'm happy with).

                      I've read a little about the koni 8611s on here, but would it be silly to only buy a pair for the rear? Or should it be done as a set?

                      How much shorter are they than the factory struts / are they adjustable (if so, how?). I'm presuming my current lowered springs that fit the factory struts will fit the konis too?

                      Comment


                      • #12
                        The Koni 8611 is an insert for a strut housing, not a replacement strut. http://www.koniracing.com/8611.html
                        You will need to find or make a housing to hold the insert to make them fit on the rear.. Usually the way that's done is to buy housings from Veilside or someone else that they drop into.

                        As for the practicality of using the 8611s in the back, that's probably overkill, depending on what you have up front. The 8611 is a pretty nice shock and you would be best served to run them on the front with either 8610 or 8611 in the rear. (8610 are a single adjustable version and are about $100 less per shock.)

                        If you already had something nice up front, I'd say to match them. But if you're only doing one end of the car, you *can* use these, but I would not necessarily recommend it- there's much better ways to spend your money than buying a single pair of shocks.
                        Originally posted by SoSideways
                        I don't care what color they are as long as they are LONG AND HARD.
                        '04 G35 Sedan 6MT- The DD
                        '96 240SX- The Track Toy

                        Comment


                        • #13
                          Sorry, I should have specified I just meant Konis in general. Open to suggestion on what to get exactly.

                          It sounds like I should wait until I can afford to do all corners before I bother though. Is there anything I can do in the meantime to lower the rear a little (half an inch would be perfect). The springs are currently *just* captive at full droop so I can't really cut them, but is there anything else I can do - like shorten the strut?

                          For later though - is there another shock you would recommend for the rear? With the rear being a normal shock I figure it doesn't use the inserts - so what do you mean by 8610/8611 on the rear? What do people normally run in the rear if they get an 8610/8611 insert up front?

                          And would you be able to explain how they are lower than the factory struts - front and rear? And by how much roughly?

                          Comment


                          • #14
                            There are lots of ways to lower the car, through shorter strut housings, shorter (and stiffer) springs, or adjustable spring perches. Without buying adjustable parts or welding, there's nothing you can do with a regular strut and spring to change the ride height.

                            In order to make an 8610 or 8611 fit on the rear, you have to fabricate a housing for it, just like you would on the front.

                            As for a mixed 8611/8610 setup, lots of people install 8611s up front and 8610 in the rear to save a few bucks. the front suspension is more important to control because it does the majority of the braking and steering. the rear shocks don't have quite as much work to do (in a general sense) and don't care as much about compression damping as the front, so you can get away with no compression adjustment in the rear.
                            Originally posted by SoSideways
                            I don't care what color they are as long as they are LONG AND HARD.
                            '04 G35 Sedan 6MT- The DD
                            '96 240SX- The Track Toy

                            Comment


                            • #15
                              Appreciate that. I have a heap more questions after digging around here and online if you don't mind.

                              I'm still having trouble getting around the whole ground control and cartridge deal, do ground control make the housings for the koni cartridges - so you can basically just buy a complete kit that you can simply bolt on?

                              And what's the process if you don't do that, do you use your stock front struts as housings for them? And then presumably fabricate something for the rear? Any links to details / a guide would be handy.

                              Which leads me to this - is there not an off-the-shelf koni shock that will work to replace the stock rear shocks? If so, is there some reason people buy the 8610/8611 cartridge for the rear instead of those?

                              I've skimmed through the thread about it on here but it gave me more questions than answers.

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