Baseline is always plotted. Settings 1 and 2 start empty — switch to one, tick Show on chart, and edit. On Panel A compression sits right of zero, rebound left; on Panel B the faded line is spring alone.
Click-drag a cap clockwise to add clicks or tune steps.
The internals the clickers can't reach. These change the shape of the curve, not just its height.
Sets the damping floor below the clicker's reach. More bleed = softer off-the-top.
Compression knee — shaft speed where the shim stack takes over from the bleed.
Rebound has its own crossover gap and shim stack, so in a real damper this is set independently — there is no fixed ratio to compression.
Lower-leg lubricant. It sets stiction and breakaway force, not the damping curve — a separate thing from damper fluid.
Separate from damping — shapes the bottom-out curve, not the velocity curve.
Editing BASELINE only. These changes apply to this one scenario — switch setups above to compare.
Rebound plotted left of zero as positive force, the same convention as a dyno printout. Line style tells you which setup.
Last 25 mm shaded — hydraulic bottom out adds force as the fork goes deeper and faster.
Same fork, same clicks, same everything — only heat soak changes, one lap at a time. Watch how far the curve drops by the last run without anybody touching a dial.
1 · The damping curve
Both compression and rebound use the same piecewise shape: a straight line below the crossover, a power curve above it.
n sets the character above the knee. n < 1 is digressive (force flattens off), n = 1 is linear, n > 1 is progressive. This build runs n = 0.82 compression and 0.85 rebound — both digressive, which is how most modern MTB stacks behave. It is not currently exposed as a control.
2 · Where k_low and k_high come from
The two viscosity exponents are the load-bearing assumption in this whole tool. Low-speed flow is bleed-orifice dominated and close to laminar, so force tracks viscosity almost linearly (0.90). High-speed flow through shim ports is closer to turbulent and much less viscosity-sensitive (0.28). That gap is why heat guts low-speed support while barely touching big-hit control.
3 · Oil viscosity vs. temperature
ASTM D341, the Walther relation, solved from each oil’s published 40 °C (104 ℉) and 100 °C (212 ℉) points:
4 · Oil temperature
Each run adds less heat than the one before, approaching an equilibrium the damper can shed.
5 · Spring, bottom-out and friction
Negative tokens (Noken-style high-volume cap) push prog down toward linear. The floor at 0.95 keeps the curve physical.
6 · Cavitation
A flat ceiling at 1950 N. Above it the model is not describing anything real — it marks where a fork-sized damper tends to run out of oil supply and go harsh, not a calculated limit.
7 · What is sourced and what is not
Read the shapes and the percentages, not the newtons. The relationships this tool draws — how a curve bends, how far two oils diverge when cold, how much low speed fades relative to high speed — are the part worth trusting. The absolute forces are illustrative. No dyno data from any manufacturer was used, and nothing here has been validated against a real damper.
8 · Known gaps
Seal and bushing friction is folded into a single bath-oil term rather than modelled. There is no negative spring or top-out behaviour. Rebound and compression share one bleed value. Shaft-speed distribution across real terrain is not represented, so the chart shows the whole velocity range equally even though a rider spends most of their time in a narrow band of it. The "bushing oil" list drives the damping curve as an educational stand-in — on many forks (semi-bath, open-bath, DVO/EXT-style serviceable dampers) that's genuinely the same fluid, but fully sealed cartridge dampers (Fox FIT, RockShox Charger) run their own largely fixed internal fluid instead, closer to 15 cSt @ 40°C / 104℉ regardless of what bushing oil is in the lower legs. One entry, marked with an asterisk, is an estimate rather than a published figure — see tier 9.
9 · Oil data provenance
The bath-oil list comes straight off the Motorex SUPERGLISS K technical datasheet (viscosity per DIN 51562-1, VI per DIN ISO 2909, pour point per ASTM D5950): 32K is 33 / 5.8 cSt, VI 118, pour −18 °C (0 ℉); 68K is 67 / 8.7, VI 102, pour −21 °C (−6 ℉); 100K is 103 / 11.3, VI 102. Shockcraft publishes matching temperature windows — 32K for −10 to 10 °C (14 to 50 ℉), 68K for 0 to 30 °C (32 to 86 ℉), 100K for 10 to 40 °C (50 to 104 ℉) — which is why those ranges appear in the dropdown.
Worth knowing: Supergliss is a slideway oil, and Motorex explicitly says do not use it in fork dampers. It lubricates bushings. That is exactly why this tool keeps the two lists separate — the damper list drives the curve, the bath list drives stiction only.
The cold damper entry, Motorex Racing Fork 2.5wt, uses the post-2016 reformulation figures (14.5 / 4.5 cSt, VI >250) that Motorex confirmed directly to Shockcraft after an earlier published table was found to be wrong. Its VI of 260 is among the highest in the list, which is what lets it stay workable when thicker oils stiffen up.