Originally Posted by
metalnut
You focused on the wrong part of my post. To clarify, I did take my shocks fully apart to verify and rebuild everything. I have two-hole pistons, the only thing I was unable to do is measure those holes accurately. Maybe they're 1.5, maybe 1.6, I don't know. I decided to use them as is for now, as I'm not good enough to be able to tell the tiny difference.
My question still stands: what feels different between "pack vs low speed dampening vs plushness"? I'd be happy to read about it if anyone has a valuable link
Hideeho
1st lets make sure everyone is on the same page for terms:
Plush - how the car feels going over bumps & into corners, how smoothly the wheels & shocks absorb bumps & leaning
damping - how much the piston is slowed by moving trough the oil
pack - when the piston tries to move through the oil faster than the holes in the piston will allow, i.e. when landing a jump as opposed to cornering (similar to high speed damping from 1:1 cars)
hydrolock - when the piston can not move because the forces being applied to piston are insuficient to overcome the resistance of the oil
pre-load - setting the shock so there is not enough room in the shock body for the oil to displace enough to compensate for the shock shaft entering the shock body. This will also cause hydrolock.
Now, on to the explanation.The number of holes will change how the shocks feel. For example lets look at a few theoretical pistons. We will assume all shock bodies are the same diameter, with the same cst (or wt) oil, at the same temperature.
1. 1 hole of 4mm diameter, 1mm thick (1x4x1)
2. 2 holes of 2mm diameter, 1mm thick (2x2x1)
3. 4 holes of 1mm diameter, 1mm thick (4x1x1)
4. 2 holes of 2mm diameter, 2mm thick (2x2x2)
5. 2 holes of 2mm diameter, 2mm thick tapered botom (2x2x2t)
6. 2 holes of 1.5mm diameter & 2 holes of .5mm diameter, 2mm thick (4x1.5/.5x1)
The 1x4x1 will have the least damping & the least pack.
More holes of the same total diameter will give slightly more damping & much more pack, so the 4x1x1 will have the most pack but only slightly more damping. The 2x2x1 is a balance between the 2.
A thicker piston will cause more damping & more pack. The 2x2x2 will have more pack & damping than the 2x2x1.
Adding a taper to the bottom of the piston will allow the oil to pass more rapidly in 1 direction than the other. The 2x2x2t will have virtually identical pack & damping to the 2x2x2, but will return from compression faster. The taper is generaly of the whole piston but at least 1 company (CSI 1/8 cars only) is now offering pistons with the individual holes tapered.
Having holes of different diameter will allow tuning of the difference between the damping rate & the pack rate. The damping of the 4x1.5/.5x1 will be very similar to the damping of the 4x1x1 but will start to pack sooner but not as much & will give another level of pack at a higher speed of piston travel (the .5mm holes hydrolock before the 1.5mm holes do). The net result is lower damping to allow the car to roll in a corner while giving more pack on large bumps & even more pack for landing big jumps. This style piston is offered by CSI (1/8 only) & avid (for the b4.2!)
One other type of piston that is offered by RPM & RCShox is a variable hole piston. These 2 pistons opperate in different ways to accomplish the same thing. The concept is, as the piston moves up in the shock 1 or more holes are closed causing more damping & pack, but as the piston moves down those holes are opened to allow the piston to move faster. It is the same concept as the tapered piston, only more so.
All these numbers are made up & don't have any real value in relation to a b4.2 buggy other than to give the idea of how a shock works.