- Kyosho ZX5FS2SP - Wayne Schroeder - Fastlane Raceway - Blue Spring - 01.01.2014 -

Fastlane Raceway

At fastlane, the track can get quite bumpy in some places, while being very smooth in others. This means the car must be able to handle the bumps well, while being able to rotate freely and get on power quickly. Lately I have been on a mission to dramatically reduce rear traction, of which I seem to have previously had an endless supply, to add rotation and steering ability. The reason for this is my dislike of the -2mm front/rear arm modification, which affects stability on our bumpy track significantly. The "long car" can be pushed so much harder without the track punishing you. The direction I have taken was to continue raising the rear roll center with washers and RF and RR shims (increase notches), moving the hubs back, and trying stiffer sway bars. After going all the way back on hubs, 3mm under the hub ball stud, a low mount with no washers on the inside, a 1.3 sway, RF 3 notch shim, RR 2 notch shim, I got the car to finally become too loose in the rear. I then worked backwards on changes until I determined that a simple tightening of the front diff a bit paired with a return to the 1.2 sway bar felt best. The front diff tightening tamed rotation, but the car was still loose when unloading from a high speed corner. The return to the 1.2 sway resolved this. I am very happy with this setup and will be leaving it alone to expose it to various levels of traction and track conditions to see how it fares.

Platform Notes
  • Front droop greatly affects low speed steering, forgiveness, and rear traction.
    • Be very careful when removing droop from the front. What it may provide in stability in high speed situations, it returns in the form of less steering in slow off power situations.
    • The car is noticeably more forgiving with more front droop and tends to get upset far easier with less front droop when landing "whipped" or when over driven in general.
    • Removing front droop makes the car have noticeably less on power traction—more so than I was expecting for even a 1mm change.
  • Rear droop greatly affects on power steering and rear traction in general.
    • With the original "two low" rear roll centers
      • A change from 26mm back to 25.5mm rear shock length provided a noticeable increase in on-power steering
      • Basically, the more droop the rear end has, the more hooked up it is on power and the less the car wants to turn.
    • With my newer "much higher" rear roll centers, I doubt the reaction will be the same any longer.
  • The rear of this car car lacks camber gain in general and the rear roll center is very low in "standard configurations".
    • When I went from a 1.2 to a 1.3 sway bar, the rear became MORE stuck, which is a definite indication that it was rolling too much and steering came from the rear end washing out (rolling over).
    • I have since went to higher roll centers via the use of FR and RR shimming, as well as additional washers on alu hubs, and low mount ball at the inside link.
    • The rear of the car should be redesigned IMHO to place the rear further in the camber gain curve at ride height and in a better rear roll center starting point. This is a platform weakness in my opinion.
  • Diff settings.
    • With traditional setups, run the diffs loose in general. Jared told me this. He couldn't be more right. My track testing agrees 100%
      • Both diffs should be tight enough that they "do something", but not much more than that. Traditionally, the front should be looser than the rear. The best way I can describe this is having the rear as loose as you would ever run a 2wd if you ran stock buggy, and the front even looser. Serious.
    • With the higher rear roll center, and hubs moved back, tighten the front a bit to help tame rotation and steering feel.
      • In general, with my latest setups where I have been seriously loosening the rear end up with a higher RC and hubs moved back, I run the rear diff a little tighter, and the front tighter than the rear. I would describe the rear as "loose to medium" and the front as "medium".
    • Tighten the rear diff as a function of the required slipper setting if a tight slipper is required.
      • Test roll the car backwards on the rear tires only down your legs towards your knees while holding the spur. Do this in quick bursts as to test whether the slipper slips or the diff. Verify the diff is not slipping by ensuring that the center drive shaft moves—you will also generally feel the diff slip. Leave some tolerance in the setting between the rear diff and slipper--once the rear diff slips, then locks up, the game is over, and the car is a pile of poop for at least 10 minutes of cool down on the bench.
    • If the rear diff slips, you will not hear it, but the car will start driving like poop and the rear diff will be grindy and tight when you come in. After it cools down, it will be loose again.
    • Check the rear diff setting often. Be ready to replace that ball cup :)
    • When it is time to rebuild the rear diff, it will start to slip and go to poop during runs even when you have it way tighter than normal. If the rear diff is anything other than new, and you have a few moments, rebuild it with freshly sanded rings!
    • Front diff greatly affects low speed steering and rotation, where as rear diff greatly affects on power steering.
      • Tighter == less steering.
  • The center drive shaft plastic outdrives that go into the tranny cases will work the o-ring off and throw their shaft pins. Super glue that stuff together as you should always replace the o-ring and plastic piece together. Snip the o-ring and tap out the pin with a 1.5 when replacing that part.
  • The -2mm front and rear mods (shaving arms, shimming wheelbase shorter) add responsiveness at the expense of corner stability, stability through bumps, and tendency to traction roll.
    • Front mod is worth more than rear and adds steering. Rear only adds responsiveness.
      • A good balance is to do just the front mod.
    • When running the front mod, run 0 ackerman washers. When not, run 1mm ackerman washer. Running 2mm will hit the transmission case.
    • The front/rear mod is most needed when running gold springs in the rear. Since I run reds, my car is far more willing to turn and rotate without this mod or its caveats.


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