Suspension basics: setting sag and preload

Rider sag — how far the suspension settles under you, in full kit, off the stand — should be roughly 30–40 mm (1.2–1.6 in) at each end on a street bike, about a third of the available travel. You set it with the preload adjusters, you measure it with a helper, and it is the highest-value suspension adjustment on any motorcycle. Most bikes leave the factory sprung for a rider of about 75 kg (165 lb); if that is not you, the factory setting is not for you either.

Static sag and rider sag

Static sag is how much the bike settles under its own weight; rider sag is how much it settles with you aboard. Rider sag is the number you set. Static sag is the cross-check that reveals whether the spring itself is right: with rider sag correct, almost no static sag means the spring is too soft and has been over-preloaded to compensate, while a lot of static sag means the spring is too stiff. Keep both numbers — together they tell you more than either alone.

The three-measurement method

You need a tape measure, a helper (two is better), and ten minutes. Measure between the same two points every time: at the rear, vertically from the axle to a fixed mark on the tail; at the front, along the fork leg from the dust seal to the lower triple clamp — a zip tie around the stanchion makes the front easy to read.

• L1 — suspension fully extended: rear wheel off the ground on a stand, front unloaded the same way.
• L2 — bike off the stand, upright under its own weight.
• L3 — you aboard in full riding kit, feet on the pegs, helper steadying the bike.

Rider sag is L1 minus L3; static sag is L1 minus L2. Suspension friction makes single readings lie, so take L3 twice — once after pushing down and letting it rise, once after lifting and letting it settle — and use the average. Set your tyre pressures before you start; a soft tyre adds its own squish to every number.

The numbers to aim for

Bike type	Rider sag, front	Rider sag, rear
Sport or supersport	30–35 mm	25–30 mm
Naked or standard	30–40 mm	30–35 mm
Sport-touring or touring	35–40 mm	30–40 mm
Adventure, long travel	40–60 mm	40–60 mm

The principle behind every row is the same: roughly a third of total travel, so the wheel can extend into dips as well as compress over bumps. Where your manual or suspension manufacturer states figures, those win.

Setting it with preload

More preload means less sag; less preload means more. At the rear it is a threaded collar or stepped cam on the shock — C-spanner or the toolkit hook wrench — or a remote knob on better-equipped bikes. At the front, hex adjusters on the fork caps; basic forks without adjusters need spacers changed internally, which is a bench job.

Work in small steps and re-measure after each change. Do the rear first: rear preload changes the bike's attitude enough to shift the front reading. When both ends land in range, write down the final settings — collar position, lines showing on the fork adjusters, and the sag numbers themselves — in your maintenance log. Suspension settings are exactly the kind of baseline you want back after a tyre change or a curious borrower.

Load changes the numbers too. A passenger or full luggage adds sag at the rear, which is why the manual says to wind on preload for two-up riding — and why trip preparation includes the suspension, not just the tyres.

What wrong sag feels like

Too little sag — too much preload — rides harsh. The wheel sits near the top of its stroke, small bumps hammer through instead of being absorbed, and the bike deflects off mid-corner ripples rather than tracking them. Too much sag — too little preload — feels wallowy and vague: the bike uses up its travel early, bottoms on dips and under hard braking, and steers slow because the rear sits low. If a new looseness or wander appears without any settings having changed, check the obvious wear items first — a weave has more likely causes than suspension settings that were fine last month.

Preload is not stiffness

A spring's rate is fixed by its construction — so many newtons per millimetre, preloaded or not. Winding on preload does not stiffen the spring; it compresses it against its seat, which changes where in the travel the bike sits and how much force is needed before the suspension begins to move. That is all. The harshness people feel after maxing out preload is the suspension riding at the very top of its stroke, not a stiffer spring. Preload positions the bike; the spring rate suits it to your weight. When the first cannot fix the second, stop turning.

When sag will not come into range

If the adjuster is at maximum and rider sag still exceeds the target, the spring is too soft for you; if everything is backed off and sag is still too small, it is too stiff. The honest fix is correct-rate springs — $100–300 (€90–280) an end, fitted — and it transforms a bike more than most bolt-on parts riders spend that money on. And if sag measures perfectly yet the front still dives hard and clunks over sharp bumps, the springs may be fine and the damping gone: fork oil degrades like engine oil, and almost nobody changes it.