How to Properly Tighten e-bike Hub Motor Axle Nuts

Keeping your e-bike’s hub motor axle nuts tight is one of those small details that makes a big difference for safety and performance. The key is to be sure the wheel sits all the way in the frame before you tighten things down.

Use a torque wrench if you have one, and aim for around 35–40 Nm so the wheel stays locked in place without slipping. You don’t want to crank so hard that you strip the threads, but the nuts should feel solid and secure. A loose axle can be dangerous, so taking a few extra minutes to get this right is well worth it.

This guide will walk you through the tools, the steps, and a few handy tips so you can tighten your axle nuts with confidence and ride worry-free.

What Are E-bike Hub Motor Axle Nuts?

E-bike hub motor axle nuts are the sturdy bolts that lock your wheel, and the motor inside it, to the frame. Instead of the quick-release skewers you see on many regular bikes, most e-bikes with hub motors use solid axles with flat sides and threaded ends.

The nuts tighten onto those threads to clamp the axle into the dropouts, which are the slots in your frame or fork where the axle sits. This keeps the wheel steady against motor power and road bumps.

They’re usually steel and often paired with washers. Some of those washers are special torque washers with little tabs that slot into the dropout to stop the axle from turning.

On rear hub motors, one side of the axle also has the motor cable coming out, so that nut might have a cable guard or need a crowfoot wrench to reach.

If you ride a long-tail cargo e-bike or run a high-powered motor, you might also see torque arms. These are extra brackets that bolt to the frame and grab the axle to help spread out the force.

Whatever the setup, the axle nuts are the main hardware keeping your wheel secure, so it’s worth knowing how they work.

Why Properly Tightening E-bike Hub Motor Axle Nuts Matters

If your hub motor axle nuts aren’t tight enough, you’re asking for problems. Loose nuts let the wheel shift or wobble, and in the worst case the wheel can even pop out of the dropouts – a seriously dangerous failure.

Even a little looseness lets the axle creep under the motor’s torque, and that tiny movement can do big damage. It’s how “spin-outs” happen, where the axle chews up the dropouts or even slices through the motor cable.

Properly tightened nuts lock the axle in place so all that motor power pushes you forward instead of tearing into your frame.

Cranking them down too hard isn’t great either. Axle threads and nuts have their limits, and if you go way past spec you risk stripping threads or squeezing things so tight the wheel bearings start binding.

Some riders have measured M12 axle nuts holding up to around 80–130 Nm, but anything beyond about 60 Nm feels sketchy for long-term durability. Most e-bikes recommend something in the ballpark of 35–40 Nm (about 25–30 ft-lbs), which is snug, safe, and easy to reach with a normal wrench or torque wrench.

The payoff for getting it right is huge. Properly tightened axle nuts keep your wheel straight, your brakes aligned, and your motor and frame out of harm’s way. It’s one of those small, simple checks that makes a big difference in both safety and how smooth your ride feels.

Tools and Preparation for Tightening E-bike Hub Motor Axle Nuts

Before you tighten your hub motor axle nuts, it helps to have the right tools and a safe setup. Here’s what you’ll want on hand:

Wrench

Most e-bikes use axle nuts in the 15, 17, 18, or 19 mm range. Standard commuters often fall in the 15–17 mm range, while beefier fat-tire or cargo models sometimes need 18–19 mm.

An adjustable wrench can work, but a fixed-size wrench or socket gives you a better grip and is less likely to slip. These nuts can be on tight, so make sure the tool feels solid.

Torque wrench (recommended)

If you want to hit the exact spec, a torque wrench is the way to go. Many hub motors call for about 35–40 Nm, but check your bike’s manual if you can.

Because one side of the axle usually has the motor cable, you may need a crowfoot adapter to fit the torque wrench in place. If you don’t have a torque wrench, no stress. You can tighten by feel, and I’ll walk through that later.

Hex/Allen keys

If your bike has a torque arm or accessories clamped to the axle, you may need Allen keys to loosen or snug those bolts back down after adjusting the wheel.

Gloves and safety prep

Throw on some gloves to save your knuckles, and power the bike down. Remove or switch off the battery so there’s zero chance of the motor kicking on while you’re working. Flipping the bike upside down or using a repair stand makes the job much easier.

Clean and inspect first

Before tightening, check that the axle and dropouts are clean. Grit in the threads can throw off your torque and make the nuts loosen faster.

Make sure washers or spacers are all there and in good condition, especially any torque washers with tabs that lock into the dropout. Put everything back in the same order it came off, and replace anything worn or missing.

Wheel Alignment and Placement

Proper tightening actually starts with proper placement. Make sure the wheel’s axle is fully seated in the frame slots on both sides. The flat sides of the motor axle should be flush against the dropout – no gap.

If you have disc brakes, ensure the rotor is between the brake pads and not pressing on anything. If you removed the wheel, guide the axle back in carefully along with any washers (as shown in the image above) and verify that the wheel is centered and straight.

If your e-bike uses a torque arm, install it onto the axle now (the axle goes through it) and attach its bracket to the frame, but leave its nut/bolt slightly loose until after the axle nuts are tightened, then tighten the torque arm bolt.

By preparing everything ahead of time, you’ll have a smooth process when you go to actually tighten the nuts.

How to Properly Tighten E-bike Hub Motor Axle Nuts

Now let’s get into the step-by-step process. Follow these steps to tighten your e-bike’s hub motor axle nuts correctly and safely:

Safety First – Power Off and Stabilize the Bike

Make sure your e-bike is turned off and remove the battery if possible. This eliminates any chance the motor could unintentionally kick on.

Flip the bike upside down, resting it on the handlebars and seat (place a towel or padding to protect displays), or secure it on a bike repair stand. A stable bike will prevent accidents and help you apply torque evenly.

Align the Wheel and Axle

Before tightening, check that the wheel is fully inserted in the dropouts. The axle should sit all the way into the slots on both sides, and the wheel should be centered between the frame stays or fork legs.

If you have disc brakes, ensure the brake rotor is properly aligned within the caliper (not rubbing the caliper body). If the bike has gears, make sure the axle is in place so the chain and derailleur aren’t twisted. In short, the wheel should be in its correct position exactly as it will ride, with nothing cockeyed.

Position Washers and Torque Arms

Install any required hardware on the axle before the nuts. Most e-bikes will have at least a flat washer on the outside of the dropout, and many have anti-rotation washers with a little tab that fits into a hole or slot in the dropout.

Make sure those tabs are indeed slotted in correctly on each side (one common spot is inside the dropout or on the outer face). These washers keep the axle from spinning under power, so they’re important.

Also, if you have a torque arm, slide it onto the axle and orient it to attach to the frame, but don’t fully tighten its clamp or bolt yet. You’ll secure it after the axle nuts are done. 

Double-check that no washer is missing; a missing inner washer can cause the nut to bottom out and not actually clamp the wheel, or lead to binding issues.

Hand-Tighten the Axle Nuts

Take each axle nut and thread it onto the axle by hand (clockwise to tighten). Do this for both sides. Screw them down until they are finger-tight against the washers/frame.

Hand-tightening first ensures the nuts aren’t cross-threading and that everything is sitting correctly. At this stage, the nuts should be snug enough that the wheel won’t fall out, but of course not fully secure yet.

Tighten Evenly in Small Increments

Using your wrench, begin tightening the nuts gradually and evenly. Don’t crank one nut down all at once. Instead, give one side maybe a half-turn or a few firm pulls, then switch to the other side and do the same. Alternate sides two or three times as you bring them up to tension.

This alternating technique ensures the axle pulls in squarely and the wheel remains centered, preventing one side of the axle from hanging halfway out. It also helps maintain even pressure on both dropout sides. As you do this, you’ll feel the nuts getting tighter and the wheel clamping in solidly.

Apply the Proper Torque

Now tighten each side to the recommended torque or final tightness. If you’re using a torque wrench, set it to your manufacturer’s spec (for example, 35 Nm which is common for many rear hub motors).

Use a suitable socket or crowfoot attachment to engage the nut (on the side with the cable, a crowfoot adapter or an open-end wrench attachment is helpful since a normal socket might not fit over the wire).

Tighten until the torque wrench clicks or indicates you’ve reached the set torque. Then do the other side. If you don’t have a torque wrench, you can still get pretty close by feel: tighten the nut firmly with your regular wrench, essentially “as tight as you can get it with one hand on the wrench” for an average adult. 

A good guideline from experienced riders: about 30 ft-lbs (≈40 Nm) of torque feels like a 30-pound push on a one-foot-long wrench. In practical terms, that’s very snug: use strong pressure from your arm, but do not jump on the wrench or use excessive body weight.

If your wrench is shorter than a foot, you might have to push a bit harder to achieve the same torque. The nut should feel extremely solid and should stop turning – that’s when you know it’s tight enough.

Don’t Overtighten

While tightening, be mindful not to go overboard. Once the nut is no longer moving with firm force, you’ve likely hit the right tightness. Cranking beyond that can start to stretch threads or crush parts.

If you hear creaking or see the washer deforming excessively, stop. Remember, more is not always better. Proper torque is key. If you’re around the 35–40 Nm range (or the “one good pull” tightness), you’re done.

As a check, look at the axle and dropout: the axle’s flat side should be flush in the slot and the washer tight against the dropout. If the wheel is hard to turn after tightening, you may have overtightened or a washer is misplaced causing binding – you’d need to loosen and inspect.

Final Checks

Now that the nuts are tight, do a quick check of the setup:

Wheel Security: Try to wiggle the wheel side-to-side – it should not shift at all in the dropouts. Everything should feel solid.

Wheel Spin: Lift the wheel (or if the bike is inverted, just spin it) to ensure it rotates freely. It should spin without wobble. If you hear the brake rubbing, the wheel might be slightly off-center – loosen and readjust if needed.

Torque Arm: If you have a torque arm, tighten its mounting bolt now (this often uses a small wrench or Allen key). The torque arm should be firmly anchored to the frame and snug on the axle.

Motor Cable: Check that the motor’s electrical cable isn’t twisted around the axle. The cable usually has some slack; make sure it’s not pinched and that its connector (if you unplugged it) is reconnected securely. Never allow the cable to wrap around the axle; if the axle were to rotate, that could shear the wires.

Clean Up: Pop any protective caps back over the nuts if your bike has them. These caps keep dirt out of the threads and make it look neat.

With these steps, your e-bike’s hub motor axle nuts should now be properly tightened! The wheel is clamped securely and you’re ready to ride.

It’s wise to re-check the nuts after your first ride or two (especially if you just changed a tire or installed a new wheel). Sometimes things can settle slightly, so a quick snug-up may be needed. But if done right, they should stay tight for many miles.

Tips to Keep E-bike Hub Motor Axle Nuts Tight (and Avoid Common Mistakes)

Tightening axle nuts is straightforward, but a few extra tips can help ensure they stay tight and trouble-free in the long run:

Re-check After Initial Rides

It’s good practice to check the axle nuts after the first few rides whenever they’ve been loosened and re-tightened (like after fixing a flat or doing maintenance). They can occasionally loosen slightly as everything “beds in.”

A quick re-tighten after ~5–10 miles is a smart safety check. Many riders also periodically give the nuts a once-over (for example, during routine cleaning or before a long ride) to ensure they haven’t vibrated loose.

Use Threadlocker for Persistent Loosening

If you find that your axle nuts keep coming loose over time (despite proper torque), you might consider applying a medium-strength threadlocker (like Loctite Blue) on the axle threads.

This compound prevents vibration from loosening the nuts. One experienced builder suggests using plenty of medium threadlocker so you can tighten to a snug level without it backing out.

Important: Only do this if you are comfortable with a bit more effort when loosening the nuts in the future, as threadlocker will make them a tad harder to remove.

Avoid high-strength (red) threadlocker, since you might not be able to remove the nut without heat. Also, if you use threadlocker, the threads should be clean and dry (no oil) for it to bond effectively.

Lock Washers or Nordlock Washers

Some e-bikes come with lock washers or serrated washers that dig in and prevent loosening. Ensure any lock washer is placed correctly (usually under the nut, biting into the surface).

If your nuts are plain and you’re facing repeated loosening, you could add an appropriate split lock washer under the nut or even invest in Nord-Lock washers designed to resist loosening. Keep in mind, however, that a proper torque and threadlocker usually suffice.

In one case, riders found that regular serrated flange nuts can slip on hardened torque plates, so a Nord-Lock (which uses two serrated pieces) might be more effective if needed. These are more advanced solutions if you have a persistent problem.

Avoid Overtightening, Use Spacers if Needed

As mentioned, over-tightening can cause issues. If you ever notice that when you really crank down the nut your wheel doesn’t spin well or the motor seems to bind, double-check the assembly.

Sometimes a missing washer or spacer means the nut is pressing on a moving part (like a bearing cover or freewheel) when it shouldn’t.

The fix is to add the proper washer/spacer between the axle shoulder and dropout so that when you tighten, you’re clamping the axle to the frame, not squeezing the hub internals.

In general, tighten firmly but stop at “good and tight.” You shouldn’t need a three-foot breaker bar on a bicycle axle nut!

Use the Right Tools and Technique

A common mistake is using an incorrect tool or technique that leads to partially tight or damaged nuts.

For example, using pliers or an undersized wrench can round off the nut corners, preventing you from ever getting it tight enough. 

Always use a properly fitting wrench/socket. Also, tightening the nuts evenly (as we did in the steps) is key – if you clamp one side down fully before the other, the axle might not seat correctly on the opposite side. Alternating is the way to go.

Leverage and Force

If you’re not strong enough to tighten the nut adequately with a short wrench, don’t be tempted to leave it loose.

Instead, use a longer wrench or a breaker bar for more leverage, or better yet, a torque wrench. You want it tight enough that you couldn’t turn it further without significant effort. For reference, “nice and snug” for most people corresponds to the recommended torque.

If in doubt, it’s safer to slightly over-shoot to the higher end of the torque range (say 40 Nm instead of 35) than to be under and have things come loose, as long as you don’t exceed what the hardware can handle.

Torque Arms for High-Power Setups

If your e-bike is high-powered (mid to high thousands of watts) or you ride it hard, a torque arm is practically a must. It relieves the axle nuts of taking all the motor’s twisting force.

Always install torque arms as instructed, and if one torque arm is provided, consider adding a second on the other side for very powerful motors. This doesn’t eliminate the need for tight nuts, but it helps keep the whole system secure and can save your frame if a nut ever did loosen.

Dropout Condition

Keep an eye on your frame’s dropouts. If you notice any damage, elongation of the slot, or deformities where the axle sits, address it immediately. Tightening a nut against a deformed dropout might not hold well.

In steel frames, torque plates or replacing the washer can help. In aluminum frames, damage can be more serious. Never ride if the dropouts are compromised (get a bike shop’s advice).

By following these tips, you’ll maintain tight axle nuts and avoid the pitfalls of both under- and over-tightening. It’s a simple thing, but it makes a huge difference in safety.

Tightening Hub Motor Axle Nuts on a Long-Tail Cargo E-Bike

Long-tail cargo e-bikes deserve special mention. These are the sturdy e-bikes built to carry heavy loads or passengers (think extended rear racks, child seats, etc.). The axle nuts on a cargo e-bike are under extra stress due to the increased weight and often a more powerful motor. Here’s what to keep in mind for these haulers:

Higher Loads, Higher Stakes

A long-tail cargo e-bike might carry an extra 50–100+ pounds of cargo or a second rider. All that weight, combined with the motor’s torque, puts immense force on the rear axle.

This means the axle nuts not only have to hold the wheel in, but also bear the brunt of extra vertical and twisting forces. Proper tightening is even more critical in this scenario – you do not want a loose axle when you’ve got your kids on the back or groceries loaded up.

Use the Upper End of Torque Specs

If a range is given (say 35–40 Nm), err toward the higher end when tightening a cargo bike’s axle nuts (closer to 40 Nm). In practice, that means really ensure it’s very snug.

Cargo e-bikes often come with larger axles/nuts (like 19 mm nuts on M14 axles) which can handle a bit more torque. Still, follow the manufacturer’s guidelines. The key is you want those nuts tight enough that there’s virtually no chance of them loosening under heavy use.

Dual Torque Arms or Upgraded Hardware

Many cargo e-bikes are equipped with a torque arm, and some even have one on each side.

Always reinstall and secure the torque arms properly when working on the wheel – they are critical safety components for these bikes. If your cargo e-bike didn’t come with a torque arm, consider adding one (they’re available aftermarket).

Also, using heavy-duty Nord-Lock washers or locknuts could be beneficial in keeping the nuts tight over time, since the constant jostling with cargo can encourage loosening. Essentially, reinforce anything related to the axle on a cargo bike.

Frequent Checks

Making it a habit to check your long-tail’s axle nuts more frequently. For example, if you do a weekly family ride or delivery run, give the nuts a quick inspection/tug each time.

The peace of mind is worth it. It’s not uncommon for cargo bike riders to check the axle security every few rides, due to the higher consequences of a failure.

Mind the Dropouts

Cargo e-bikes often have beefed-up dropouts or even bolt-on dropout reinforcements. Ensure those are in place and not damaged. If your bike uses replaceable dropout inserts or plates, keep them tight as well. The combination of tight axle nuts and sturdy dropouts is what keeps everything safely together.

In summary, a long-tail cargo e-bike is an amazing utility machine, but it puts your axle nuts to the test. Treat tightening and maintaining them as a top priority. The last thing you want is an axle coming loose when carrying precious cargo. 

By tightening properly and checking often, you’ll keep your cargo e-bike safe and reliable even under heavy loads.

FAQs

How tight should e-bike hub motor axle nuts be?

Aim for 35–40 Nm (25–30 ft-lb). That’s “very snug” with a standard wrench. Heavy cargo/high-power setups can go to the top of the range; don’t exceed spec.

Do I need a torque wrench?

Recommended for accuracy. No torque wrench? A one-foot handle with ~30 lb push ≈ 40 Nm. Use a crowfoot on the cable side if a socket won’t fit.

Why do my axle nuts keep coming loose?

Usually under-torque, missing/misplaced anti-rotation washers, or tired threads. Fix with proper torque, blue threadlocker, quality lock/Nord-Lock washers, and a torque arm on higher-torque builds.

Can over-tightening axle nuts cause damage?

Yes—stripped threads, bearing bind, bent/aluminum dropout damage. Stop at spec; if the wheel stops spinning freely after tightening, back off and check washer/spacer stack.

How often should I check axle nuts?

Recheck after the first ride post-service, then periodically (weekly or every few rides). Inspect more often for long-tail cargo e-bike loads, off-road, or high-power hubs.