Suspension Sag on an E-Moto: Why Setup Comes Before Upgrades

Before spending money on a shiny new fork, grab a tape measure. Your e-moto might need a better setup before it needs better parts.

At Radmoto, we don't pretend to be suspension experts. Spring rates, air chambers, damping, geometry and riding style all interact, and a good suspension specialist earns their keep. But we do see bikes arrive with overlooked basics, including air-assisted suspension running with far too little pressure. A few checks can help you figure out whether you need an adjustment, a service or an upgrade.

First, make sure your suspension is healthy

Clean the fork legs and look around the seals. A thin trace of lubricant can be normal on some designs, especially after service. That is different from fresh oil repeatedly running down a leg. Dripping oil, puddles, or oil near the brake rotor, pads or tire means stop riding and have it inspected. Don't wait for a puddle if the leak keeps returning.

With the bike switched off and securely supported, gently cycle the suspension. It should move and return without hanging up. If it sticks near the top or bottom, stays compressed, makes unusual noises or binds, get it checked before riding. A closed lockout or incorrect setting can affect movement, but don't force it or assume a knob will fix a mechanical fault.

“Blown” doesn't automatically mean the whole fork belongs in the trash. Seals, oil, worn parts, alignment or internal problems may be serviceable. Diagnose it before buying its replacement.

What is suspension sag?

Sag is how far the suspension settles from full extension under weight. Free sag measures the bike alone; rider sag measures the bike with you aboard in riding gear. It places the suspension partway into its travel so the wheels have room to move both up over bumps and down into dips.

Too much or too little sag changes the bike's balance and available travel. Use the target for your exact bike, fork and shock. A full-size motocross bike's millimeter setting is not a shortcut for a lightweight e-moto.

How to measure sag at home

You need a tape measure marked in millimeters, your normal riding gear, a suitable stable stand and a helper or two. Have the manufacturer's setup instructions handy. Turn the bike off and keep clear of the throttle.

1. Measure at full extension. Safely support the bike using its approved lifting points so the suspension being measured is unloaded. At the rear, measure from the axle center to a repeatable marked point on the chassis above it. Record this as A. Don't lift by an unsupported plastic fender.
2. Measure the bike alone. Put it on level ground, upright and supported by a helper. Gently settle the suspension and measure the same points. Record B.
3. Measure with you aboard. Wear your helmet, boots and usual riding load. Take the riding position specified by the manufacturer, with feet supported on the pegs or pedals and helpers balancing the bike. Settle gently and record C.
4. Subtract. Free sag = A minus B. Rider sag = A minus C. Repeat to check consistency.

For example, A = 600 mm and C = 540 mm gives 60 mm of rider sag. Those numbers demonstrate the math, not a recommended setting for your bike.

For the front, use the maker's measurement method, commonly along the fork's travel direction or with its supplied travel O-ring. If you measure directly at a rear shock shaft, calculate percentage using shock stroke, not rear-wheel travel. Linkage makes those different measurements. If readings vary substantially depending on whether you push down or lift and release, friction or binding may need attention.

Adjust the spring support before chasing the clickers

On a coil system, the permitted preload adjustment changes the starting compression of the spring and the sag. It does not turn a soft linear spring into a higher-rate spring. Stay within the manufacturer's preload limits. If you cannot achieve both its rider-sag and free-sag targets, ask about the correct spring rather than winding the collar endlessly.

On a user-adjustable air spring, use a proper suspension shock pump and the maker's pressure chart as your starting point. Add or release pressure in small increments, follow any chamber-equalization procedure, then remeasure. Never exceed the stated pressure limit.

We regularly see riders overlook this check. If your suspension requires air, checking it can be a straightforward home job. But not every fork needs air added, and not every valve is a rider-adjustable air spring. A damper reservoir's gas charge is a service operation. Identify the exact component and valve first. If pressure will not hold, repeated pumping is not a repair.

Rebound and compression, without the rabbit hole

Rebound damping controls how quickly suspension extends after a bump. Too little can feel springy or kicky. Too much can prevent recovery between repeated bumps, leaving less travel for the next hit.

Compression damping controls resistance while suspension compresses. More is not automatically better: excessive damping can feel harsh and reduce the wheel's ability to follow uneven ground. “Low-speed” and “high-speed” describe suspension movement, not your speedometer reading.

Start with the manufacturer's baseline after setting spring support. Write down pressure, preload and clicker positions, including whether clicks are counted from open or closed. Never force an adjuster against its stop. Make one small change at a time and compare on a familiar, low-risk section at a controlled pace. Keep tire pressure and riding load consistent. If the change feels worse, return to your recorded baseline.

Where to find settings for your e-moto

• KKE and FastAce: These are two of the most common fork brands we see at Radmoto. Visit KKE Racing or FastAce with your model number, bike year and geared-up rider weight. OEM versions and aftermarket versions can differ.
• Surron Light Bee X: The UK distributor's owner's manual describes preload and rebound controls, including that increasing rebound damping slows extension. It also gives a pressure recommendation for the fork shown. Match your actual fork to the manual before using that number; Surron specifications and suppliers vary.
• Bonnell 775 MX: Bonnell specifies an SR Suntour RUX 38 RC+ fork and Voro coil shock. Its owner's manual library includes suspension setup guidance. The linked 775 MX manual shows a 25-30% rear-shock sag range and explains fork compression and rebound. Apply it only to the matching bike and component version, and confirm the latest guidance with Bonnell if yours differs.

We haven't found a single trustworthy click-count chart that covers every KKE or FastAce-equipped e-moto, because there isn't one setup that fits all those combinations. Manufacturer settings are a starting point, not a competition to see who can close the most knobs.

When better suspension makes sense

Some inexpensive suspension has fixed damping, preload-only adjustment or a limited useful adjustment range. A dial on top does not prove you have a sophisticated damper. Check what the manual says it actually controls. If an advertised adjuster makes no meaningful difference, have it checked rather than assuming all cheap forks have “fake knobs.”

We also see mountain-bike suspension pushed beyond its intended job on e-motos. Bike weight is part of the problem, along with speed, braking loads, impacts and the rider. A fork fitting the headset doesn't establish that it is approved for the bike. Equally, MTB-derived suspension is not automatically unsuitable: a manufacturer-specified system on a bike such as the 775 MX is a different case from an unapproved swap.

For a serious upgrade, Sirris and EXT are two premium e-moto suspension names we point riders toward. They are not the only good options, and price alone cannot tell you what suits your bike. Correct fitment, spring choice, tuning support and serviceability matter.

Upgrade when healthy, correctly set-up suspension cannot meet your riding needs, or when the spring and damping options are genuinely limiting you. A service or spring change may be the better first purchase.

Bring us the bike, the numbers and the question

Tell Radmoto your bike model and year, fork and shock model, geared-up weight, current settings and what feels wrong. “It kicks after a bump” gives us more to work with than “the suspension is bad.” Photos of the components and adjusters help too.

We can help you work out a sensible next step and recognize when specialist suspension advice is the right move. Start with the setup. Your wallet might enjoy the ride too.

Photos: existing Radmoto product catalog. Technical references checked November 9, 2026: manufacturer resources linked above, Öhlins suspension setup guidance, and FOX seal-lubrication guidance. Follow the instructions for your actual equipment; this overview does not replace its service manual.