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Comparo: Kyosho vs. PN Top Damper

Posted 09-07-2011 at 05:41 PM by color0
Updated 09-07-2011 at 05:44 PM by color0
...And welcome to the second edition of our series of parts comparisons. This time, it's about top dampers, specifically the Kyosho Oil Damper vs. the PN Racing Dual Spring Center Shock as adapted to my personal car setup. So yes, once again this is going to be strictly my opinion, and I don't think there is a totally superior product between the two of these. So think of today's article as a pros-and-cons list between these two great top shocks.

A little foreword to the rest of this article: I realize that I have left out three other brands of popularly used top shocks, namely Atomic, 3racing and Route 246 (which is basically 3racing-made). With all apologies to Atomic, I simply can't fit your oil damper into my car and leave space for a transponder... As for 3racing and R246 oil shocks, I've never purchased one because all the ones I've bench-tested feel inferior to the "original" Kyosho oil shock. So on that note...

If you'll excuse my picture quality, here is the Kyosho Oil Damper doing its thing on my current chassis setup:

The Kyosho Oil Damper is a "true" oil shock absorber in that you have a chamber of oil, and there's a piston inside moving back and forth which churns the oil to provide damping. So because of that large volume of oil, it does feel very smooth in your hands. Well, at least until all of that leaks out, which is another issue...

Yes -- it leaks like a shattered bathtub. If you build this shock according to Kyosho's instructions, you'll lose some 20% of the internal oil within a few runs, and when you bring the car back and test out the shock, it'll feel grainy. Not exactly "good" damping characteristics. The solution to this is inherited from 1/10 touring car shocks: before you add any oil to the Kyosho shock, take it all apart -- unscrew the cap, unscrew the black ball end from the shock shaft, and pop the shaft out of the shock body -- and add a little bit of specialized O-ring grease to the bottom of the shock body where the single O-ring resides. I was taught to use Associated Green Slime, however there are definitely equivalent products that work just as well. Don't put too much in! This stuff is only for sealing the O-ring, it's not for damping purposes. After you pop the shaft back in, the seal should be well-formed; clean the threads on the shock shaft and screw the black ball end back on.

Another quirk of the Kyosho shock is its lack of downstop adjustability. Fully extended, it's about 2mm longer than it needs to be -- while this makes it perfect for certain 96mm wheelbase applications, it leads to comical amounts of rear suspension downtravel on "standard" wheelbase settings (86/90/94/98/102mm). Once again, clever solution from the 1/10 gang:

The yellow part is the shock body in this diagram, and the T-shaped thing the shaft and piston. The orange part is what we add to get some downstop adjustability from this oil shock. It turns out that small plastic straws (think: WD-40, compressed air cans) are the perfect size to fit in this space, so find yourself a straw, snip off a 2mm chunk and rebuild your Kyosho oil shock. Typically, a 2mm piece of straw will make the shock the perfect length for standard wheelbases -- the rear pod will sit level with the main chassis when the shock is fully extended. A lot of people like this, but sometimes you do need a little bit of extra downtravel, and to do that, you can partially unscrew the black ball end. Don't go overboard! I wouldn't recommend unscrewing more than about 0.75mm worth, the black ball end is easy to strip so you want as much thread contact as you can afford.

With these two tweaks to the shock, it performs very well -- the oil volume produces fluid damping and you can even adjust "rebound" damping by closing the shock body at different stages of shaft extension. As a final note, I am using the optional spring set also offered by Kyosho (Red-Green-Yellow, soft-medium-hard respectively). On very soft T-plates such as the PN G10 T-plates, the Red spring is a tad too soft, so only the Green and Yellow are really that useful. Save the Red spring for those times that you're using a stiff T-plate, and using the top shock only for damping and maintaining level ride height.

Now for our other contender: PN Racing's Dual Spring Center Shock.

The PN shock is NOT a "true" shock absorber, but it's a tube damper, using the thickness of the grease you apply to provide damping. Ironically, because you have to use thick grease on this shock, it rarely ever leaks out, and so it lasts a lot longer than the Kyosho shock between rebuilds. I've cleaned mine twice -- once because I got fed up with a rough spot on one part of the shaft, and the second time because I was giving it to fellow Greyscale driver EMU for an experiment. Despite the exposed greasy surfaces the PN shock is incredibly grime-resistant. An occasional re-greasing is all that's needed to keep up performance, very user-friendly experience for me. Preload adjustments on the PN shock are a breeze, turn the collars and nuts however much you need, definitely more useful than the Kyosho shock's preload spacers.

The "bottom" spring on the PN shock is the main spring, and the "top" spring is the rebound spring, which essentially is a downtravel adjustment like we implemented on the Kyosho shock. However, since it's a spring, you get to not only control your resting ride height, but also how strictly your chassis will enforce said ride height. In my experience this is a great tuning tool for drivers who rely on weight-shifting techniques: a softer rebound spring creates a milder turn-in response, and harder begets sharper turn-in response. On high-grip tracks I sometimes forgo the top spring and insert a block instead for the quickest turn-in, but on low-grip tracks sometimes you need a little forgiveness, and I'll use an MR02 front spring, medium to medium-hard.

The PN shock isn't without its faults, however. It excels where the Kyosho shock is the biggest pain in the butt (longevity, ease of use) and the weight is not so bad (a tick heavier than the Kyosho), but the length! Because the PN shock is a through-shaft design, it doesn't ever get shorter when you compress it. So, when you're racing your Mini-Z and need a space to mount the transponder, you need to clear a little space ahead of the shock (1-2mm) if you want to have some upward suspension travel. Of course, this makes things difficult when you're trying to fit the chassis under certain bodies that require pushing the transponder back -- I'm talking about the 599XX and HSV-010. Due to this conundrum I have been forced to use the Kyosho shock with these bodies, and use a short motor mount moved backwards in order to allow a normal transponder placement.

As a final note for the PN shock, PN also has an optional spring set for the main spring of this dual-spring shock, and I really like the fine-tuning possibilities it provides. Instead of Kyosho's set of three, you get seven springs of usable spring rates -- the softest Orange spring is really only useful for setting ride height, but the Blue through White springs (2nd softest to 2nd hardest) are all fully useful. I myself have never used the hardest Yellow spring, it just seems like a bit much. I imagine it will be useful on a high-grip track if you have no T-plate (i.e. running the PN Gimbal or Qteq Pivot Ball T Bar system) and need the spring to compensate as such.

So there it is, my thoughts on the two most popular top shocks for Mini-Z's as of current. Can I pick a favorite? No, not really -- I tend to use the PN shock more (I am l-a-z-y! Hate rebuilding shocks), but for certain bodies like the 599XX and HSV-010 I've been using the Kyosho shock and not really minding much at all. I do think the PN shock has an advantage with the rebound spring tuning, but at the same time the Kyosho shock is a bit smoother and lighter, and theoretically at least produces more effective damping. I hope this article was helpful in some way, shape or form, and please stay tuned for more bodywork this month!
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