Torque plates (often called torque arms) are crucial safety brackets for hub-motor e-bikes. They attach to your bike’s dropouts and prevent the motor’s reaction torque from spinning the axle out of place. Without them, a powerful hub motor can “spread” or crack aluminum dropouts (or distort steel ones), risking wheel ejection. In practice, you pick a torque plate based on your motor’s power, your bike’s frame (steel vs aluminum), and the type of dropout. High-power motors and soft frames always need beefier torque plates, while low-power kits on steel forks might get by with minimal reinforcement. The rest of this guide explains what torque plates do and how to choose the right one.

What Torque Plates Are and Why They’re Essential

A torque plate is simply a metal bracket that bolts to your hub-motor axle and bike frame to take the twisting force off the dropouts. In effect, it holds the axle flats securely and transfers the motor’s torque into the frame, instead of letting that force rip open the dropouts.

For example, a torque plate may hold the axle 1 mm away from the dropout and use bolts to tie into the dropout plate, so the axle cannot rotate under load. This is far stronger than relying on the axle flats alone. Any strong hub motor generates high torque in reverse when pushing the bike forward. If that torque isn’t managed, the dropout can deform or fail. 

In tests, typical dropouts “spin out” at only ~60–90 Nm of torque without a plate, while adding a solid torque arm can raise that threshold above 150 Nm. In other words, with a proper torque plate, your dropouts can withstand much more force. 

Even if your current motor is modest, torque plates protect against unexpected abuse (like loosed nuts or hard starts). They are especially essential on high-power e-bikes and bikes with weaker forks or aluminum dropouts.

In short, a hub-motor torque plate is not optional on a powerful kit: it prevents the worst-case failure of your bike’s frame. For lower-power geared hub motors (≤500 W), a small torque washer inside the dropout may suffice, but for mid- and high-power motors (≈750 W and above) a full torque arm/plate is strongly recommended. 

Figure: Grin Tech’s V5 torque arm (steel plate) installed on front and rear dropouts. The arm bolts to existing frame eyelets near the axle.

SEE ALSO Torque Sensor vs Cadence Sensor: Which Is the Better Choice for Ebikes?

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Matching Torque Plates to Motor Type (Front vs. Rear)

Front vs. Rear Dropouts

Front fork dropouts are usually steel or cast and are generally thicker than many modern rear dropouts (often aluminum). However, bicycle forks were not originally designed to resist motor torque. Even steel forks can crack if the forces get high. By contrast, rear dropouts on quality steel frames can handle more torque, but most light bike frames use aluminum rear dropouts that are relatively weak.

As a rule of thumb, use a torque plate for any front hub motor above a few hundred watts, and for any rear motor if you have aluminum dropouts or a high-powered motor. In practical terms, many e-bike builders add at least one torque arm to every front hub conversion. For rear motors, you check your dropout thickness: if it’s >8–9 mm steel, a 750 W kit might work without one, but any thinner aluminum or power above ~1000 W warrants a plate.

Grin Tech’s tests found that a typical 36 V/20 A (≈750 W) motor on a flat steel rear dropout might not need an extra arm, but any setup with >1000 W, aluminum forks, or regen braking definitely does. Note also that front-hub e-bikes with regenerative braking see forces in both directions, so they especially benefit from torque arms on both sides. 

Geared vs. Direct Hub Motors

The rule of thumb is similar. A geared hub under ~500 W usually relies on axle flats and torque washers, but a direct-drive hub at 750 W or more needs a torque arm based on frame strength. Some sources suggest at least one torque washer for every motor, even small ones, and always use a torque arm once you exceed about 500–750 W or swap to a lightweight aluminum fork.

Quick Summary (front/rear)

Front hub: Almost always put on a torque plate (forks are weak).

Rear hub: If frame dropouts are steel and motor <750 W, one plate might suffice; if rear dropouts are aluminum or power is high, use one or two. In any case of doubt, adding a torque arm is a cheap insurance against a far costlier dropout failure.

SEE ALSO Comprehensive Guide to Ebike Motors

Choosing the Correct Material (Steel, Aluminum, Chromoly)

Torque plates come in different metals.

Steel

Steel is the most common and reliable material. Many quality torque plates use stainless or chromoly (4130) steel. In fact, high-end designs even use hardened 17-5 stainless steel inserts for the axle slot. Steel plates are heavier but are strongest under load. For any motor above ~1000 W, a steel plate is safest. 

Aluminum

Aluminum torque plates exist and are lighter, but they aren’t as strong. Aluminum (often 6061 or similar) is fine for low- to mid-power builds (<500–750 W) where weight is a concern. They also resist corrosion better. However, aluminum fatigue can be an issue under repeated stress, so avoid aluminum plates on very powerful kits. A common approach is to use aluminum for small commuter bikes and steel for heavy-duty or DIY kits.

Chromoly

Chromoly (chromium-molybdenum) is actually a high-strength steel alloy, often used in frames. If a torque plate is made from chromoly, you can treat it as steel – it has excellent strength-to-weight. In practice most commercial torque arms use stainless or mild steel, but chromoly is a known steel option.

Plate Thickness

No matter the metal, thickness matters. A 5 mm (3/16″) steel plate is a good minimum for serious torque arms. Thinner 3 mm arms only add ~20–30 Nm of resistance over having no arm, which is modest. So look for a plate at least 4–6 mm thick (or plate doubled up) for heavy motors. (Some DIY clamping arms use two 3 mm plates bolted together, but be careful the bolts can shear.)

In summary: use steel (or chromoly) plates for high-power and rough use, and aluminum plates only on lower-power setups. Always pick a well-made, thick plate from a known supplier, since cheap thin copies may fail prematurely

Dropout Compatibility: Slotted, Vertical, or Horizontal

E-bike frames come with different dropout styles, and your torque plate must fit the style. The three common types are slotted (quick-release), vertical (wheel drops straight down), and horizontal (wheel slides fore/aft).

Slotted/Q-R Dropouts

These have a little “lawyer lip” at the end of the slot for quick-release wheels. Many torque plates can’t sit flush if that lip is in the way. In that case, you’ll need a thin spacer or special “C-washer” that fits inside the lip so the plate can sit flat on the dropout. Some torque arm kits include lock-washers or custom spacers for this purpose.

Horizontal Dropouts

These are common on fixed-gear or some road bikes (the axle slides in/out). When using a torque arm here, position it so that the motor’s forward torque pushes the axle deeper into the dropout, not out of it. (Grin’s designs flip the arm orientation for this purpose.) If your torque arm has an asymmetrical mounting (like a curved slot), mount it in the correct direction – mounting it backwards could actually pull the axle outward under power

Vertical Dropouts

These are common on modern bikes (mountain and many road frames). Vertical dropouts inherently prevent the wheel from moving fore-aft. You still attach the torque arm so that forward torque drives the axle into the dropout. Many newer torque arms can be flipped for either orientation. For example, Grin’s V4 arm has an axle plate that “can flip” to fit either horizontal or vertical dropouts.

Other

For thru-axles or uncommon designs, you may need a custom solution. But most front forks and rear frames have either QR-slotted or vertical dropouts.

The key is to match the arm to the dropout style. Some arms are “slot-shaped” for QR forks, others clamp around a tube for smooth-fork eyelets. If your bike has mounted fender/rack eyelets near the dropouts, a bolt-on arm can use those holes. If not, a clamp-on arm attaches with stainless steel hose clamps around the fork or frame tube (discussed below). The Grin V5 arm, for instance, uses existing eyelets for a neat install on both front and rear dropouts.

Always ensure the torque arm actually contacts the dropout correctly. If needed, a little filing or a washer can help the arm slide fully onto the axle flats. In short, choose an arm/plate made for your dropout style and use any included spacers or washers so it sits flush against the metal.

Dual Torque-Arm Setups for High-Power Motors

When your e-bike has a lot of torque – for example, very high wattage or dual-motor setups – builders often use two torque plates: one on each side of the wheel. This shares the load and adds redundancy.

In fact, if you’re using a very thick one-piece arm (like 1/4″ steel), one arm per side is usually enough by itself, but a second arm “never hurts”. For thinner or single-arm kits, doubling up is recommended. 

For the most extreme cases (multi-kilowatt motors or strong regen), you can even preload the arms. This means loosely positioning two arms on one side and tightening one slightly ahead of the other, so one arm takes torque in the forward direction and the other catches any reverse torque. Grin suggests that technique for regen e-bikes.

In practice, standard e-bike kits often come with one arm per wheel. But if you’re pushing 1500 W+ or plan to reuse the bike for other high-torque motors, consider installing two arms on the same axle (one pointing forward, one backward) for maximum safety.

Installation Considerations (Bolt-On vs. Clamp-On)

Torque arms attach to the bike in one of two ways: bolt-on or clamp-on.

Bolt-On (Eyelet-Mounted)

These arms use the bike’s existing bolt holes – typically the small threaded eyelets for fenders or racks near the dropouts – to secure the arm. For example, Grin’s V5 torque arm is designed to bolt to a fender eyelet on the frame. Bolt-on arms look neat and are very secure once installed. The downside is you must have an eyelet in the right place; otherwise, you can’t use this style.

Clamp-On (Hose-Clamp)

These arms (like Grin’s V4/V6 models) come with stainless-steel band clamps that wrap around the fork or chainstay tube. They fit almost any frame or fork without extra holes. Clamp-on arms are a bit bulkier and may require tightening the hose clamps very firmly. It’s a good idea to protect your frame’s finish with a strip of tape or heat-shrink tubing between the metal clamp and paint.

Regardless of type, a few tips apply: orient the arm correctly (so torque pushes the axle in, not out), slide the plate fully onto the axle flats, and tighten everything very securely. Any play or slippage is dangerous. The hardware usually includes lock-washers or “C-washers” to lock the arm onto the axle. After tightening, double-check that the arm is snug and that the axle nuts are torqued down. 

Hose-Clamp Tip

Grin Tech recommends using small pieces of heat-shrink tubing over the stainless band to keep it from digging into paint. Also, if your torque arm uses multiple clamps (some designs have slots for 2–3 clamps), use at least two clamps for redundancy.

Orientation

One classic mistake is mounting the arm on the wrong side. If the arm sits on the front side of a fork, motor torque can actually pull the axle forward and out. Always mount so that when the motor applies forward torque, the arm braces it into the fork or frame.

Top Torque Plate Brands and Models

There are several well-known torque arm/plate products on the market. Below are a few to consider:

Grin Technologies (Canada)

Grin is often cited as making the highest-quality arms. They offer multiple models (V2 through V7) for different mounts. For example, the V5 is a steel arm that bolts to eyelets, the V6/V4 use clamps for eyelet-less frames, and the V7 is a beefy arm for regen setups. All use 1/4″ thick stainless plates or hardened inserts. Grin arms are pricier but well-tested. Many riders consider them worth the price for serious builds.

E-Bikeling (US)

E-Bikeling sells “Universal Laser-Cut Torque Arms” (versions S and P) that are popular budget options. These are clamp-on steel arms (around 3 mm thick) for M12/M14 axles. They include clamps, C-washers, and hardware. Reviews say they work well for medium-power kits.

NBPower & Others (China)

Various generic brands (often on Amazon or eBay) sell universal torque arm kits. For example, NBPower offers a clamp kit rated for 3000–5000 W motors. These are usually stamped 3 mm steel arms with hose clamps and C-washers. They’re cheap and generally get the job done, but their thin steel means serious builders often double them up or replace with thicker plates.

DIY/Aftermarket

Some kits or users improvise plates (even using crescent wrenches or custom-cut plates). If you go DIY, follow thickness advice (>5 mm steel) and bolt quality precautions

When choosing, match the arm to your axle size (M12 vs M14) and dropout style. Read reviews or ask if possible. As a rule, favor kits that specify plate thickness and material. Thicker, hardened-steel arms (like Grin’s) will outperform no-name thin ones. And remember: any arm is better than none on a high-power motor

Chart: Typical Torque Plate Recommendations By Motor Power and Frame.

FAQs

Do I really need a torque plate?

Yes. Any hub motor can exert large torque on the axle. Without a torque arm or plate, even a moderate system can rip apart aluminum dropouts or bend steel slots. Experts agree that above about 500–750W (especially on aluminum frames or front forks), you should install torque arms.

How many torque arms should I use?

For most e-bikes one arm per hub is standard. But on very high-power setups (or if using thin stamped arms) you should use two per wheel. This spreads the load and adds safety, especially if you regenerate. If your kit includes one, consider doubling up with a second arm on the opposite side.

Does frame material change my choice?

Absolutely. Aluminum dropouts are much weaker than steel or chromoly. If your fork or frame is aluminum, use a torque plate even for modest power. On a strong steel frame, low-power kits (<500W) might get by with minimal bracing, but any big motor should still have one. In general: steel frame = good but still add arms for high power; aluminum frame = always add torque arms