What the Engwe M20 rear shock upgrade involves
The Engwe M20 comes with a basic coil spring rear shock that works adequately for casual riding but can feel harsh on rough terrain and offers little adjustment for different rider weights or riding styles. Upgrading to an air shock or a higher-quality coil shock replaces this component with one that compresses and rebounds more smoothly, absorbs bigger bumps without bottoming out, and often includes damping controls to tune how quickly the shock responds.
The upgrade is a bolt-on replacement — you remove the old shock, bolt the new one into the same mounting points, and reconnect the brake line if your model has hydraulic disc brakes routed near the shock. Most riders can complete the work in 30 to 45 minutes with basic tools. The cost of the shock itself ranges widely depending on the model you choose, from budget coil options around $80 to $150 to mid-range air shocks in the $200 to $400 range.
Key Takeaways
- The stock Engwe M20 shock can be replaced with an air shock or upgraded coil shock using the same frame mounting points and basic hand tools.
- Air shocks offer adjustability and lighter weight but require occasional pressure checks; coil shocks are simpler and more durable but heavier and less tunable.
- You need to know your body weight and riding style before choosing a shock, because spring rate and damping are matched to specific rider profiles.
- The brake line must be carefully routed or disconnected during removal to avoid damage, and some shocks require spacers or adapters to fit the M20 frame geometry.
- After installation, the shock should be bled of air (if air) or tested for proper compression and rebound before riding at full speed.
Choosing between air and coil rear shocks
An air shock uses compressed air inside the shock body to provide spring force. You adjust the air pressure using a hand pump to match your weight and riding preference, and many air shocks include a separate damping adjustment knob to control how fast the shock compresses and rebounds. Air shocks are lighter than coil shocks and take up less space, which matters on compact frames like the M20. The trade-off is that air pressure can drift over time, so you need to check and top up pressure every few weeks or after heavy riding.
A coil shock uses a metal spring wrapped around the shock body. The spring rate is fixed at the factory based on the weight range it is designed for — typically light, medium, or heavy rider. Coil shocks are simpler, more durable, and require no maintenance beyond occasional cleaning. They do not adjust as easily as air shocks, and they are heavier, which affects the M20's handling slightly. If your weight falls clearly into one category and you do not plan to change your riding style often, a coil shock is reliable and cheaper.
For the M20 specifically, air shocks are more popular because the bike is used for mixed terrain and commuting, where adjustability and light weight matter. However, if you ride mostly on smooth paths or want a set-it-and-forget-it component, a quality coil shock works well.
Shock specifications and compatibility with the M20 frame
The Engwe M20 frame accepts a rear shock with a stroke length of 50 to 60 mm and a mounting distance (eye-to-eye) of approximately 190 to 210 mm, depending on the exact frame revision. Before ordering a shock, measure the distance between the two bolt holes on your current shock or check the Engwe M20 manual for the exact spec. Shocks that are too long will not fit; shocks that are too short will not provide enough travel or will sit loose in the frame.
The shock must also match the spring rate to your body weight. Most manufacturers list spring rates in pounds per inch (psi for air shocks, lbs/in for coil). If you weigh 150 to 180 pounds, a medium-rate shock is standard. If you weigh less than 150 pounds or more than 200 pounds, you need a shock tuned for that range, or an air shock where you can adjust pressure to compensate. Installing a shock with the wrong spring rate will make the bike feel either too soft (bottoming out on bumps) or too stiff (bouncing and losing traction).
Check whether the shock uses a standard eyelet mount (a hole at each end for bolts) or a special adapter. Most aftermarket shocks for the M20 use standard eyelets, but some budget models may require a spacer or adapter ring to center the shock properly in the frame.
Tools and parts you will need
To remove and install a rear shock, gather a 5 mm or 6 mm Allen wrench (hex key), a 15 mm wrench or socket for the mounting bolts, a hand pump if you are installing an air shock, and a clean rag. If your M20 has hydraulic disc brakes, you will also need a small flathead screwdriver to carefully pry the brake line away from the shock during removal, and possibly some electrical tape or zip ties to find it out of the way.
Before you start, lay out a clean work surface and have a small container ready to hold the bolts and any small parts. Take a photo of the shock orientation and brake line routing before you remove anything, so you can reinstall correctly. If the shock is stuck or corroded, spray the bolt holes with penetrating oil and let it sit for 10 to 15 minutes.
Step-by-step removal and installation
Removal: Flip the M20 upside down or use a bike stand to lift the rear wheel off the ground. Locate the two bolts that attach the shock to the frame — one at the top near the seat tube, one at the bottom near the swingarm. Unscrew both bolts and carefully slide the shock out. If the brake line is routed near the shock, gently pry it away with a screwdriver and find it with tape so it does not get pinched or bent. Set the old shock aside.
Installation: Slide the new shock into the frame, aligning the bolt holes. Insert the bolts by hand first to make sure they thread smoothly, then tighten them firmly with your wrench — do not over-tighten, as this can strip the threads or crack the frame. Reconnect the brake line if you moved it, making sure it has at least 1 inch of slack so it does not pull when the shock compresses. If the new shock is an air shock, use the hand pump to inflate it to the pressure recommended for your weight (usually printed on the shock body or in the manual).
After installation, compress the shock by hand several times to make sure it moves smoothly and rebounds fully. Spin the wheel to confirm the brake line does not rub or get caught. Take a short test ride on flat ground before riding on rough terrain.
Common problems during upgrade and how to avoid them
Brake line damage: The most frequent issue is pinching or kinking the hydraulic brake line when removing or installing the shock. Before you touch the shock, photograph how the line is routed. During removal, tape the line to the frame or seat tube so it stays out of the way. During installation, feed the shock in slowly and check clearance before tightening the bolts fully.
Shock bottoming out: If the new shock compresses all the way to the frame on bumps, the spring rate is too soft for your weight or the air pressure is too low. For air shocks, add 5 to 10 psi and test again. For coil shocks, you may need to swap to a stiffer rate. This usually means ordering a different shock, so get the spring rate right before you buy.
Shock not rebounding: If the shock stays compressed and does not push back up, the damping is set too slow or the shock is damaged. On air shocks with damping adjustment, turn the knob counterclockwise to speed up rebound. If that does not help, the shock may have an internal leak and will need to be replaced.
Bolts coming loose: After your first few rides, stop and check that the shock bolts are still tight. Vibration can loosen them over time. Tighten as needed, then check again after 10 more miles of riding.
Frequently Asked Questions
Can I use a shock from a different e-bike brand on my M20?
Only if the eye-to-eye distance and stroke length match exactly. Many e-bikes use different frame geometries, so a shock from another brand may be too long, too short, or sit at the wrong angle. Always verify the measurements before ordering. When in doubt, contact Engwe support with the shock model number to confirm fit.
Do I need to bleed air from an air shock after installation?
Most air shocks come with a small amount of air already inside. After you bolt it in, use the hand pump to inflate to the recommended pressure for your weight. You do not need to bleed it unless you are replacing an old air shock and want to start fresh — in that case, press the valve to release all air, then pump to the correct pressure.
How often should I check the air pressure in a new shock?
Check it every two to three weeks during regular use, or after a long ride on rough terrain. Air can slowly leak past the valve seal over time. If you notice the bike feeling softer or bottoming out more often, the pressure has probably dropped and needs a top-up.
What if the new shock does not fit because the bolts do not line up?
The frame mounting holes may be slightly misaligned or the shock may need a spacer. Try gently tapping the shock with a rubber mallet to shift it into position before tightening the bolts. If the holes are still off by more than 1/8 inch, contact Engwe or the shock manufacturer — you may need an adapter plate or a different shock model.
Can I upgrade the rear shock without removing the wheel?
Yes. You do not need to remove the wheel to access the shock bolts. Lifting the rear of the frame with a stand is enough. However, removing the wheel gives you more space to work and makes it easier to route the brake line safely.