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  1. #1
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    Question Shock oil viscosity value questions

    So, I've been messing with the tuning of my Slash for about a month now. I've tuned the suspension geometry to the point where it sticks like glue to the track I race/bash on, but is still a rocket in the straights.

    The problem I keep running into is suspension give. I'm more or less shooting in the dark in this area, since I know nothing about oil viscosities/flow rate. The whoops and jumps on this track are still causing me problems in that I either don't have enough dampening, or it's rebounding too quickly, throwing the tires out of the dirt.

    Shocks set up like so:

    Front
    50wt/650cSt fluid w/ 2-hole piston head
    Pink-dot springs (+10%)
    4mm preload

    Rear
    40wt/500cSt fluid w/ 2-hole piston head
    Blue-dot springs (+20%)
    6mm pre-load

    I know the springs are part of what's causing the bounce-out, but without them the truck bottoms out and transfers a lot of it's forward momentum right into the dirt. If I go to a softer spring, the dampening force of the shocks isn't cutting it.

    I'd like to experiment with different shock fluids, but I'm frankly a little confused about cSt and such. Does the cSt number follow a linear progression? That is to say, does a 400cSt fluid flow twice as fast as an 800cSt, and half as fast as a 200cSt?

    I don't need exact flow rates, just a general idea of how the cSt numbers break down. Given that the piston heads on the shocks are 1, 2, or 3 hole, I can calculate the differing flow rates based on a comparison of cSt values, but only if the numbers are linear. If they bell curve, or worse yet run exponentially, this is all moot.

    Thanks in advance, and sorry if this is a little heavier-duty type tuning question that usual.
    Slash 4x4 Ultimate TQi, fully loaded

  2. #2
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    Try heavier oil with one hole and a softer spring. I run 80 wt and have good dampening without bottoming out or rebounding up too fast


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    Last edited by robdog; 06-21-2012 at 07:57 PM.

  3. #3
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    Quote Originally Posted by robdog View Post
    Try heavier oil with one hole and a softer spring. I run 80 wt and have good dampening without bottoming out or rebounding up too fast
    Yeah, I kinda gathered that. My original question wasn't "what do I do?", but rather more "What does this mean?"

    I appreciate the help, nonetheless.

    Quote Originally Posted by DirtRocket View Post
    • Does the cSt number follow a linear progression?
    • Does a 400cSt fluid flow twice as fast as an 800cSt, and half as fast as a 200cSt?
    Oh, while I'm here, does anyone, Traxxas or 3rd party, make single-hole piston heads for Big Bore shocks? I can't seem to find any on Traxxas' site, and I'm about ready to have a set machined at work.
    Slash 4x4 Ultimate TQi, fully loaded

  4. #4
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    Thought this was interesting so I did some research. Silicon oil unlike motor oil, exhibits a Newtonian behavior meaning it is linear like water. Temperature and stress don't affect silicon near as much as motor oil which is non-linear. So if I understand what I read, 40wt 1 hole piston should be close to the effective use of 80wt 2 hole piston. You could also try RPM two stage pistons which react differently to small impacts and large impacts. I have read a lot of good things about them.

  5. #5
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    Quote Originally Posted by Slaughter33 View Post
    Silicon oil unlike motor oil, exhibits a Newtonian behavior meaning it is linear like water. Temperature and stress don't affect silicon near as much as motor oil which is non-linear. So if I understand what I read, 40wt 1 hole piston should be close to the effective use of 80wt 2 hole piston.
    This is exactly what I was wondering. Thanks for the help! I'm off to experiment!
    Slash 4x4 Ultimate TQi, fully loaded

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