Geometry tells you how a bike fits and steers. Kinematics tells you how its rear suspension actually behaves: how it pedals, how it ramps up on big hits, how it reacts under braking, and how to set it up. This guide explains every term on a leverage chart in plain language, and, crucially, how to use the numbers instead of trusting the badge on the frame.
First principle: analyse the bike, not the system
It is tempting to ask “is VPP better than a single pivot or a Horst-link?” The honest answer is that the question doesn’t make sense. Move a single pivot location on a Horst-link frame and you can take it from supremely progressive and aggressive to regressive and prone to bottoming, and it is still a Horst-link. The suspension layout sets what is possible; the pivot positions set how the bike actually rides. So judge each model by its own leverage, anti-squat and anti-rise curves, never by the name of the linkage.
Leverage ratio and the leverage curve
Leverage ratio (LR) is how far the rear wheel moves for each millimetre the shock shaft moves: LR = wheel travel divided by shock stroke at any point. A 160 mm bike on a 65 mm stroke shock averages about 2.46.
The curve matters more than the average. The starting leverage ratio (top of the stroke, around sag) sets small-bump feel; the ending ratio (near bottom-out) sets resistance to harsh bottoming. A very progressive bike like the Black Market Roam, for example, starts around 4.2:1 and ends near 1.6:1, roughly three times less leverage at the bottom, which is why the shock barely moves early in the travel and then races through the last part of the stroke.
Progressivity
Progressivity is how much the leverage ratio falls from start to end:
Progression % = (start LR − end LR) divided by start LR, times 100.
- Linear (roughly 0–10%): consistent, easy to use full travel, can blow through on big hits. Pairs with air shocks, which add their own ramp.
- Progressive (roughly 15–30%): ramps toward bottom-out, resists harsh bottoming, supports jumps and drops. This is what lets you run a coil shock well.
- Regressive: gets easier to move deeper, rare and undesirable.
As a benchmark, enduro bikes average around 20% progression and downhill bikes more, because more aggressive use needs more bottom-out support. A progressive frame is soft and supple in the first part of the travel and then gets much stiffer near the end, so it resists bottoming, but past a point you have to run it soft to use full travel. It is a compromise between initial softness and final stiffness.
The sag trap on progressive bikes
Here is something most riders never hear: on a very progressive bike, the sag you measure at the shock is not the same as the sag at the wheel. Because the leverage is so high early in the travel, a given shock sag translates to more sag at the wheel. On a steep curve, 23% at the shock can be 30% at the wheel, and 30% at the shock can be 40% at the wheel. Wheel sag is what actually matters, so on progressive bikes set sag at the wheel, and expect to need a heavier spring or more pressure than a linear bike to get the same number.
Instant centre, virtual pivot and axle path
The instant centre is the point the rear wheel and brakes rotate around at a given moment, also called the virtual pivot point. It governs both pedalling (anti-squat) and braking (anti-rise) behaviour. On a true single pivot it is simply the main pivot and it does not move, even on bikes that look complex (a downhill bike with a rocker and links can still be a single pivot, with the extra links only fine-tuning the leverage curve). On a linkage bike the instant centre is found by extending lines through the two link pairs to their intersection, and it moves through the travel, which is exactly why it is called “instant”.
The axle path is the line the axle traces. A more rearward early path swallows square edges and high-speed hits better, at the cost of more chain growth (and the pedal kickback that comes with it).
Anti-squat: pedalling support
The simplest definition: anti-squat is what the chain tension does to the suspension. When you pedal, two things try to compress the rear suspension, weight transferring rearward under acceleration, plus a vertical force from the up-and-down of pedalling itself (worse when sprinting out of the saddle or with rough technique). Anti-squat is the design’s chain-driven resistance to that squat.
It is measured as a percentage at sag: about 100% is neutral; above 100% the bike tends to extend under power, below 100% it squats. To find it graphically you locate the instant centre, draw the swing-arm line from the rear axle to the instant centre, draw the chain line, and the intersection of those two lines falls into a low, good, or high zone. Because the chain line depends on chainring and cog, anti-squat changes with gear and through the travel. Some riders deliberately want a bit over 100% to kill pedal bob, since bob is energy wasted compressing the shock, though the trade-off is more pedal kickback and a firmer feel over bumps under power. A note on modern high-pivot idler bikes: a chain line below the chainring can in theory make the chain compress the suspension (negative anti-squat), but you must always check the swing-arm-line intersection rather than assume from the chain line alone.
Anti-rise and braking: watch the caliper
Anti-rise describes how the rear reacts under braking, set by the line from the rear contact patch to the instant centre. High anti-rise keeps geometry steadier but stiffens the suspension under braking; low anti-rise keeps the rear active and plush into braking bumps but lets the bike pitch more. A practical way to read it without any software: watch how much the brake caliper rotates around the disc as the suspension compresses. A caliper on the seat stay moves about half as much as one on the chain stay, which is why seat-stay-mounted brakes give roughly half the anti-rise and keep the suspension more independent under braking.
Pedal kickback
As the suspension compresses and the axle moves rearward, the chain effectively lengthens and tugs the cranks backward slightly. That is pedal kickback, the price of rearward axle paths and high anti-squat.
Sag, spring and preload
Set sag first; every other figure is referenced to it. Rough targets: trail and enduro ~28–32% rear, cross-country ~20–25%, downhill ~30% and up (measured at the wheel, per the sag trap above). Air springs are naturally progressive and tunable with volume spacers and chamber changes; coil springs are linear and beautifully supple but rely on a progressive frame to resist bottoming. On a coil, the preload collar does not change spring rate; it raises the force needed to start the shock moving at all. Add more than a few millimetres of preload and the shock will not budge until you exceed a threshold force, so it skates over small bumps and loses traction. You can prove this with a simple drop test: a correctly sprung shock compresses when you drop the bike lightly, while a heavily preloaded one barely moves and will not stay planted. The fix is always to reach correct sag with the right spring rate, not preload, a stiffer spring and a softer, preloaded spring can need the same force to bottom out, but only the stiffer spring stays sensitive off the top.
Damping, and the rebound “curb test”
The spring controls force; the damper controls how fast the bike moves. Compression damping resists compressing (low-speed for body movement and pedalling, high-speed for square edges); rebound controls how fast the shock extends back. Rebound is the most-felt and most-misset adjustment, and a shock’s 10–20 clicks contain only about three that are actually usable for a given rider.
To find your baseline, use the curb test: roll off a curb at walking pace, seated, no brakes, and set rebound as fast as it can return to sag without oscillating past it. That point is “critical damping”, the slowest of your three usable clicks, there is no benefit going slower. From there you can go at most one or two clicks faster, never more. Faster rebound gains traction (the tyre stays planted) but amplifies oscillations, even pedal bob, and costs chassis stability on takeoffs and landings. The guiding principle: stability matters more than outright traction, so run XC and trail near critical, and add a click or two only for rocky, high-speed or downhill terrain.
How to use all this when choosing a bike
Read the numbers, not the badge. Want easy, confident pedalling? Look for anti-squat near 100% at sag in your common gears. Ride rough, fast terrain? A rearward axle path and a coil-friendly progressive curve (15%+) will reward you. Brake hard into chop a lot? Lower anti-rise (often seat-stay brakes) keeps the rear working. None of these is universally “better”, they are trade-offs. Pick the trade-offs that match how and where you ride, set sag at the wheel, then dial damping with the curb test.