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Not sure what pistons your car uses? Search for your car and check the manual.
Estimated damping
5×1.3 @ 500 cSt → 6×1.3 @ 500 cSt
Cornering, braking, weight transfer
Chatter and rough track, wheels still down
Jumping & landing
Newtons at 0.1 / 0.5 / 1.5 m/s. current 17.4 / 121.4 / 620.5, new 14.3 / 95.2 / 463.7
Roll damping is how the damping works during normal chassis roll; pack is a much stronger damping effect that kicks in when the shocks compress quickly: over bumps with the wheels still down, or taking off and landing from jumps.
Which change does what
Oil and pistons do not do the same job. Each change below moves the three numbers by a different amount, and the pattern is the point: some levers fade as the shaft speeds up, some grow, one lifts everything at once. Figures are for a typical 1/8 shock (5×1.3 mm, 2.5 mm thick, 500 cSt); the sizes shift with your own shock, the shapes hold.
One caveat worth more than the numbers themselves: a step is not a fixed amount. Going from 8 holes to 7 is worth +15%; going from 3 to 2 is worth +62%. Same change, 4× the effect. Where you are starting from matters more than the size of the step, so read each row as what that particular step is worth, not what a hole or a bottle is worth in general.
Shock oil
one step thicker (500 → 600 cSt)
+18% roll · +13% bump · +8% jump
Oil owns the slow end and lets go as the shaft speeds up. It is the fine adjustment. Reach for it when the car is close and you want to nudge how it leans, not how it takes a landing.
And it gives less the thicker you already are: a step at 800 cSt = +12%, the same step at 500 = +18%.
Piston thickness
one step thicker (2.5 → 3.0 mm)
+14% roll · +10% bump · +6% jump
Almost the same lever as oil, in both shape and size: a half-millimetre of piston is worth roughly one oil step. Useful when you are already at the top or bottom of the oils you own.
Diminishing the same way: a step at 3.5 mm = +11%, the same step at 1.5 mm = +19%.
Hole count
one fewer hole (5 → 4)
+28% roll · +36% bump · +44% jump
The opposite of oil: it bites hardest where the hits are hardest, and this is not a fine adjustment. The number above is what the FIFTH hole is worth, because a hole is not a fixed amount. On that 1/10 piston it reads +57% / +74% / +94%.
It accelerates as holes run out: going 8 → 7 = +15%, going 3 → 2 = +62%.
Hole size
0.1 mm smaller (1.3 → 1.2 mm)
+35% roll · +36% bump · +37% jump
The blunt one. It lifts all three roughly equally, because diameter drives the oil resistance and the orifice restriction at nearly the same rate, so it scales the whole curve instead of tilting it. A tenth of a millimetre moves the slow end more than dropping a whole hole does, which surprises people.
And it bites harder on smaller holes: 0.1 mm off a 1.6 mm hole = +27%, 0.1 mm off a 1.1 mm hole = +44%.
Straight vs tapered
straight → tapered, 12°
compression -18% roll · -7% jump · rebound -22% roll · -33% jump
The only change here that treats the two strokes differently. A taper frees rebound more than it frees compression, so the shock extends more easily than it packs, which is why it suits bumpy tracks and big landings.
That is why swapping a piston and “correcting it with oil” never quite lands. The two levers have different shapes, so you can match the roll feel or the pack, not both. Which one you protect is the actual decision.
How to read this
The three numbers are the same change measured at three shaft speeds, because a shock does not behave the same way at all of them. Roll damping is what you feel leaning on the car through a corner or under brakes. Bump pack is the fast stuff with the wheels still on the ground: chatter, ruts, a rough section. Jump pack is a landing. If you race on carpet or a smooth touring track, read the first two and ignore the third.
Pistons and oil together control your car's damping feel (if shock mounting is fixed), but they do it in different ways. Oil moves roll damping almost on its own and fades as the shaft speeds up; holes and thickness move all three, and they bite hardest at the fast end. That is why swapping a piston and “correcting it with oil” never quite lands. You can match the roll feel or the pack, not both. Watch the three numbers move apart as you change one side and you can see it happen.
A tapered piston here means the piston body, not the holes. Enter the thickness the manufacturer quotes, measured at the inner edge against the centre hole, plus the angle the face falls away at, looking at the piston from the side. Most are somewhere around 15°, and every brand grinds them a little differently, so put your own number in if you know it. Taper facing down is the usual way in RC; run it upside down and the compression and rebound rows swap.
Not sure which one you have? 1/8 buggies and truggies are 16 mm almost across the board, though the shaft is not uniform: Tekno run 4 mm, the Associated RC8 B4 series 3.5 mm. On 1/10 off-road it is 13 mm on most cars released since 2022, and 12 mm on older platforms and the whole Associated B6 family. Touring, pan, oval and anything else: measure the shock body and use Custom.
Assumes emulsion or bladder shocks in good condition and round holes; valved or pocketed pistons (VRP-style) are a different device. wt → cSt uses the shock oil viscosity chart.
Treat the numbers as a direction and a size, not a measurement. They come from a model of how oil flows through your piston (the standard maths any damper is designed with), not from a dyno. Nobody has put these pistons on a rig, so trust the direction of a change more than its exact size. Nothing in the model is specific to a class or a surface, so it works for touring, pan and oval shocks as well as off-road; pick Custom for any bore and shaft it does not list.
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