What is Anti-Squat?
When you pedal hard, the rear suspension wants to compress (squat) under the load transfer. Anti-Squat is the percentage of that compression the linkage counteracts.
Anti-Squat measures how effectively the rear suspension linkage resists the tendency to squat (compress) when the rider accelerates. Under hard pedalling, the chain tension and acceleration-induced weight transfer both push the rear suspension down. Without Anti-Squat, the bike would bog down into its travel with every pedal stroke, wasting energy and reducing traction.
A well-designed Anti-Squat curve keeps the bike高效 pedalling without making the suspension feel locked or harsh over bumps. It's one of the most important kinematic parameters for any bike that needs to climb or sprint.
The Physics of Acceleration
Anti-Squat exists because the chain line and acceleration torque create opposing forces on the swingarm.
When you pedal, two things happen simultaneously. First, the chain pulls on the rear cassette, creating a torque around the rear axle that can either compress or extend the suspension depending on the chain line relative to the pivots. Second, acceleration shifts weight rearward, compressing the shock. Anti-Squat is the combined effect of these two forces.
The critical relationship is between the chain line (an imaginary line from the chainring to the cassette cog) and the instant centre (IC) of the rear linkage. If the chain line passes above the IC, pedalling forces extend the suspension (high Anti-Squat). If it passes below, pedalling forces compress it (low Anti-Squat).
- 1Chain on larger cassette cog → different chain line angle → different Anti-Squat
- 2Main pivot above the chain line → higher Anti-Squat
- 3Main pivot below the chain line → lower Anti-Squat
- 4Horst-link / split-pivot designs → Anti-Squat varies with gear selection
How Anti-Squat is Calculated
Anti-Squat is the ratio of the anti-compression force (from chain tension and linkage geometry) to the squat force (from acceleration weight transfer).
Anti-Squat (%) = (F_anti / F_squat) × 100F_anti = chain-tension-induced extension force · F_squat = acceleration-induced compression force
To find F_anti, draw a line from the rear axle through the IC. Then draw the chain line from chainring to cassette. The intersection and its perpendicular distance to the rear axle determine the mechanical advantage of the chain tension in resisting squat.
F_squat depends on D_COG height, wheelbase, and acceleration rate. A higher D_COG or shorter wheelbase increases the squat force, requiring higher Anti-Squat to counteract it.
Interpreting Anti-Squat Values
The right Anti-Squat depends on the bike's purpose and the rider's expectations.
- 1Low (50–70%): Suspension stays active under power. Great for technical climbing traction, but the bike may bob when sprinting on smooth terrain.
- 2Moderate (70–90%): Balanced pedalling efficiency and suspension activity. Common on trail and all-mountain bikes.
- 3High (90–110%): Very efficient pedalling, minimal bob. The suspension extends slightly under power. Good for cross-country and enduro racing.
- 4Very high (>110%): Suspension actively extends under pedalling. Can feel harsh and cause the rear wheel to skip over rough terrain. Used on some downhill bikes for sprint acceleration.
Most designs target peak Anti-Squat in the 80–100% range at the sag position (where the bike spends most of its time pedalling), dropping off as the suspension compresses deeper. This ensures efficient pedalling at sag while allowing the suspension to remain active for absorbing hits.
Design Trade-offs
Anti-Squat is inseparable from Anti-Rise, leverage ratio, and pedal kickback — changing one changes the others.
Raising the main pivot increases Anti-Squat but also increases pedal kickback (the rear wheel's tendency to push the cranks backward over rough terrain). Lowering the pivot reduces pedal kickback but decreases Anti-Squat. Designers must find the sweet spot for the intended riding style.
- 1Single-pivot designs: Anti-Squat is determined entirely by main pivot height and chain line — simple but limited tuning.
- 2Horst-link / four-bar: Anti-Squat can be tuned somewhat independently of Anti-Rise via the horst pivot position.
- 3VPP / DW-Link: Counter-rotating links allow complex Anti-Squat curves that vary through travel in ways single-pivots cannot.
- 4Chain growth (related to Anti-Squat) directly causes pedal kickback — higher Anti-Squat generally means more kickback.
Anti-Squat in BikeSPEZL
The R&D module calculates Anti-Squat for every gear, at every point in the travel, using your actual D_COG.
In BikeSPEZL's Ride Dynamics simulation, Anti-Squat is computed from your KinematicDesign pivots, the drivetrain configuration (chainring teeth, cassette cog, crank length), and the D_COG from your rider scan and bike build. You can see how Anti-Squat changes when you shift gears, adjust sag, or move a pivot — all in real time.