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The short answer: Set your suspension sag first (usually 25-30% of travel for the fork, 30-35% for the rear), then adjust rebound and compression based on feel and terrain. Your weight is the starting point, but your riding style and bike geometry matter too. This guide walks you through the process step by step, without fancy equipment or lab claims, just practical adjustments you can do at home.
Sag is the amount your suspension compresses under your static body weight when you’re sitting on the bike in your riding position. It ensures your suspension uses its full travel effectively and keeps your bike balanced. If your sag is too low (too little compression), you’ll feel every bump and lose traction. If it’s too high (too much compression), you’ll bottom out and feel mushy.
To set sag, you need a shock pump (for air shocks) and a tape measure or ruler. For the fork, find the O-ring or zip tie on the stanchion. Push it up against the wiper seal, then sit on the bike in your normal attack position (slightly standing, elbows bent). Gently bounce a few times, then step off. Measure the distance between the O-ring and the seal. Divide that by the fork’s total travel (found on the fork or in the manual). That’s your sag percentage.
For the rear shock, use the same method on the shock shaft (if visible) or the rear axle travel. If you have a coil shock, you’ll need to swap springs for different rates, but most modern bikes have air shocks where you add/remove air with a pump.
Start with the recommended air pressure from the manufacturer based on your weight. Then adjust in 5 psi increments until you hit the target sag. Remember: sag is personal. Heavier riders need more air, lighter riders less. But your weight is only the starting point. Your gear (backpack, water bottles) and riding style (aggressive vs. casual) will shift it by 5-10%.
Rebound controls how fast your suspension extends after compressing. If it’s too fast, the bike feels springy and kicks you off-line. If it’s too slow, the suspension packs down and feels harsh over consecutive bumps.
Start with the rebound set to the manufacturer’s baseline (usually a number of clicks from fully closed). Then ride a rough section at speed. Observe: if the fork or shock extends too quickly (you get bounced up), slow the rebound (turn the knob toward the slow/hard symbol). If it feels like it’s still compressed when the next bump arrives, speed it up (turn toward fast/soft).
A simple test: push down on the front of the bike (grab the bars, apply brake, push down). Release. The front should return to full extension without bouncing past it. If it bounces, slow rebound. If it takes more than a second to return, speed it up.
For the rear, do the same with your heels on the pedals, but it’s easier to have someone push down on the saddle. The shock should return smoothly without a pogo effect.
Remember: rebound is temperature-sensitive. In cold weather, oil thickens, so you might need to open it a click or two. In hot, close it a bit.
Compression damping controls how fast your suspension compresses. There are two types: low-speed (for pedaling, braking, and body weight shifts) and high-speed (for big impacts like drops and roots).
Low-speed compression (LSC) affects how the bike sits under braking and pedaling. If it’s too open, the bike dives too much under braking and sags when you stand up to pedal. If it’s too firm, you lose small-bump compliance and traction. Start with LSC fully open or at the manufacturer’s baseline. Then, on a smooth climb, see if the bike bobs excessively. If yes, close LSC a few clicks until it stabilizes while still absorbing bumps. On the fork, LSC also affects how it dives when you brake hard.
High-speed compression (HSC) only matters for big hits. It prevents bottom-outs. If you’re using full travel often and hearing a hard clank, increase HSC. If the bike feels harsh on trail junk, open it. Many trail bikes have a single compression dial that blends both. In that case, focus on LSC for pedaling and HSC only if you’re bottoming out hard.
Pro tip: Air pressure also acts as a compression adjustment. Adding air increases bottom-out resistance. So if you’re close to sag target but bottoming out, add a few psi instead of closing HSC. Keep notes on settings for different trails.
Your weight tells you where to start, but your style tells you where to finish. If you’re a smooth, cross-country rider, you’ll want a bit more sag and faster rebound for traction. If you’re a downhill freerider, run less sag (more air) and slower rebound for stability. If you’re in between, use the 50/50 rule: start at the middle of the recommended pressure, then adjust based on how the bike feels.
Terrain matters too. On rocky trails, you want more small-bump compliance (open LSC, maybe softer air). On smooth trails with jumps, you want better pedaling efficiency (close LSC, a bit more air). Always test on the type of trail you ride most.
Also, check your tire pressure. It interacts with suspension. Lower tire pressure (around 20-25 psi for tubeless) can make up for a suspension that’s slightly too firm. But don’t go too low or you’ll get pinch flats.
Finally, remember that suspension settings are a personal preference. Some riders like a plush, squishy feel; others prefer a firm, responsive one. Use your weight as a guide, but trust your butt. If the bike feels good, it is good.
Your weight can change over time, and so can your bike’s suspension. Re-check sag every few months or after major changes (new shock, different shock pump, significant weight gain/loss). Also, if you notice the suspension feeling different after a ride, it might be due to air pressure loss (air shocks lose a few psi over time). Pump it back up to your recorded baseline.
If you have a coil shock, you might need to change the spring rate if your weight changes by more than 10 lbs. Consult the shock manufacturer’s chart. For air shocks, just add/remove air.
Also, if you’re riding a new bike, give it a few rides to break in. Seals and bushings need time to loosen up. Then do a fresh setup.
You really need a shock pump. They’re budget-friendly and available at any bike shop or online. Without one, you can’t adjust air pressure, which is the core of setting sag. For coil shocks, you might not need a pump, but you’ll need a spring rate tool to swap springs.
You can use the O-ring method and estimate the percentage by eye, but it’s not precise. Better: use a zip tie on the fork and a marker on the shock. But digital calipers or a ruler are best. If you don’t have one, use a piece of string and measure later.
Lockout is for smooth climbs. But if you set your LSC correctly, you might not need it. Use lockout for long pavement sections or steep fire roads, but remember to open it for descents. It doesn’t affect sag.
Setting up suspension is a skill that improves with practice. Start with the numbers, but end with feel. And if you’re in the market for a new mountain bike, check out our mountain bike buying guide for honest comparisons to help you choose a bike with good suspension adjustability. Happy riding!
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