Tongsheng Mid-Drive Motors: TSDZ2, TSDZ8, TSDZ16 & Torque-Sensing Conversion Kits

Tongsheng mid-drive motors stand out from other e-bike conversion options because they deliver genuine torque sensing (not just pedal rotation detection), support an active open-source firmware (OSF) community, and come at a lower price point than comparable Bafang kits. Whether you’re building a lightweight commuter or a hill-climbing trail bike, understanding the differences between the TSDZ2, TSDZ2B, TSDZ8, and TSDZ16 is the first step.

TSDZ2 vs TSDZ8 vs TSDZ16: Tongsheng Motor Comparison

Model	Power (Nominal / Peak)	Weight	Max Torque	Bottom Bracket	Typical Use	Approx. Price (kit)
TSDZ2	250W / 500W	7.9 lb	37 ft‑lb (50 Nm)	BSA 68–73 mm	Commuting, light off‑road	$350–$400
TSDZ2B	250W / 500W	8.0 lb	37 ft‑lb (50 Nm)	BSA 68–73 mm (integrated torque sensor)	Same as TSDZ2, improved sensor	$370–$420
TSDZ8	500W / 750W	7.7 lb	55 ft‑lb (75 Nm)	BSA 68–73 mm	Higher torque for hills or cargo	$450–$500
TSDZ16	750W / 1000W	8.8 lb	74 ft‑lb (100 Nm)	BSA 68–73 mm (includes throttle)	Steep climbs, heavy loads	$500–$600

All models are mid‑drive units with a removable battery connection and fit standard English‑threaded bottom brackets. Check your frame’s shell width before ordering.

Why Tongsheng’s Torque Sensor Matters More Than Cadence Sensing

Most entry‑level mid‑drive kits (and many hub motors) use a cadence sensor — they ramp up power as soon as you start pedaling, regardless of how hard you push. Tongsheng motors use a strain‑gauge torque sensor built into the bottom bracket spindle. It measures the actual force you apply to the pedals in real time.

Rider outcome: Assist feels exactly like a natural extension of your leg power. Climb a hill by pushing harder, not by spinning faster. You get immediate response without the sudden “surge and coast” feel of cadence‑based systems. On technical singletrack or stop‑and‑go city riding, this predictability means better control and less wasted battery energy.

The TSDZ8 and TSDZ16 use the same sensor design but with larger internal gearing to handle higher torque loads without sacrificing the natural pedal feel.

Open‑Source Firmware (OSF) – Unlocking Custom Tuning

Every Tongsheng motor ships with a factory firmware that limits performance to legal Class 1 or 2 settings (20 mph assist cutoff). The open‑source firmware project (often called OSF for TSDZ2) replaces the stock controller code to give you full control over:

• Assist levels: Define up to 10 power curves mapped to torque input.
• Speed limit: Set any cutoff (or remove it, where legal).
• Regenerative braking: The TSDZ2 and TSDZ8 can apply mild regen through the motor when you brake – recovers some energy and extends pad life.
• Display options: Customize what shows on the stock KT‑LCD3 or SW102 displays, or switch to a Bluetooth‑enabled controller for phone tuning.

Installing OSF requires a wired programming cable (about $15) and a Windows PC. The community provides precompiled hex files for common riding styles. Warning: OSF voids Tongsheng’s warranty and may not meet local e‑bike class regulations. Use at your own risk.

One realistic branch you’ll face: After flashing, if the display shows an error code like “E07” (communication failure), you likely selected the wrong display variant file. Stop riding immediately, re-flash the correct hex file for your display model (KT‑LCD3 vs SW102), then test again. If the error persists, verify the cable connection between motor and display — a loose pin can also cause the same symptom.

Installing a Tongsheng Mid‑Drive Kit – What to Expect

A typical conversion takes 2–4 hours for a mechanically comfortable rider. Here’s the sequence:

Tools You’ll Need

• Crank puller (compatible with your cranks)
• Bottom bracket tool (for your existing BB, usually splined or Park BBT‑22)
• Torque wrench (0–50 ft‑lb range)
• Allen wrenches (4, 5, 6 mm)
• Cable ties, electrical tape

Step‑by‑Step Outline

1. Remove cranks and bottom bracket – Clean the shell threads.
2. Install the Tongsheng motor – Use the supplied lock ring and torque it to 30–35 ft‑lb (check your kit’s specs). The motor’s axle must sit flush against the frame. Branch: If the motor housing does not sit flush (i.e., there is a visible gap of more than 1 mm), stop and check for debris in the threads or an incorrect lock ring orientation. A thin spacer (supplied with some kits) may be needed for frames with slightly wider shells. Do not over-torque to close the gap — this can crack the motor housing.
3. Mount the battery – Most kits include a bottle‑cage mount on the downtube. Position it so the cable reaches the motor without tension.
4. Connect wiring – Motor‑to‑battery (XT60 or Anderson connector), motor‑to‑display (six‑pin JST), and optional throttle if included (TSDZ16). Route cables along the frame and secure with zip ties.
5. Install the display – Typically a handlebar clamp mount. The KT‑LCD3 or SW102 shows speed, battery level, assist mode.
6. Adjust chainline – Tongsheng motors place the chainring 2–3 mm further out than a standard bottom bracket. You may need to shift the front derailleur or use a chainring offset. For single‑speed or IGH setups, this is rarely an issue.
7. Test and verify – Spin the crank backwards until the torque sensor zeroes, then ride slowly in low assist to verify smooth engagement.

Concrete verification step: After your first 50‑yard ride in assist level 1, stop pedaling completely and coast for 10 feet. The motor should cut power within one second. If the motor continues to push you after you stop pedaling, the torque sensor hasn’t zeroed correctly. Power off the motor, spin the cranks backwards 3 full revolutions, then ride again. Normal behavior: assist engages within a quarter crank turn of starting to pedal and disengages immediately when you stop.

Common Fitment Note: The TSDZ2/2B/8/16 all require a BSA (English) threaded bottom bracket with a shell width of 68–73 mm. Italian, BB30, or press‑fit frames need an adapter (available from third‑party sellers). Carbon frames: consult the OSF forum for torque limits – the motor housing can crack fragile shells. If you have a carbon frame, tighten the lock ring to 30 ft‑lb maximum and use a thin rubber gasket to avoid scratches.

Tongsheng vs Bafang: Price, Performance, and Trade‑offs

Factor	Tongsheng (TSDZ2)	Bafang BBS02 / BBSHD
Base price (kit)	$350–$400	$500–$650
Torque sensing	Yes (built‑in strain gauge)	No (cadence only)
Max torque	37–100 Nm (model dependent)	80–120 Nm (BBSHD)
Weight	7.7–8.8 lb	8.8–9.5 lb
Noise	Quieter (gears, less whine)	Slight gear whine under load
Aftermarket support	Large OSF community	Larger hardware spare‑parts market
Durability	Good for moderate use; internal clutch can wear on high‑mileage cargo	Very robust; rated for heavy loads

Trade‑off: Tongsheng gives you a more natural riding feel at a lower price, but Bafang offers higher peak torque and a wider network of replacement parts. If you are building a heavy cargo bike or plan to ride aggressively on steep hills every day, the BBSHD’s extra durability may justify the added cost. For a lightweight commuter, gravel bike, or trail bike where feel and efficiency matter, the TSDZ2 or TSDZ8 is the better value.

Failure mode to watch for: The TSDZ2’s internal one‑way clutch can slip or fail after 3,000–5,000 miles of continuous high‑torque use, especially on loaded cargo bikes. Symptoms: a metallic clicking sound when you pedal hard, or the crank spins freely without engaging the motor. Replacement clutches cost about $15 and require pulling the motor apart. If you plan to use a TSDZ2 for heavy hauling, budget for a clutch replacement every 1–2 years, or consider stepping up to the TSDZ8/16 which have beefier clutches.

FAQ

Can I use a Tongsheng motor on a carbon‑fiber frame?

Yes, but only if the bottom bracket shell is a standard BSA threaded 68–73 mm. The motor housing is aluminum and can stress carbon laminate if over‑torqued. Tighten the lock ring to 30 ft‑lb max and use a torque spec indicator. Many riders install a thin rubber gasket between the motor and frame to avoid scratches.

What battery voltage works with Tongsheng motors?

All models accept 36V or 48V nominal batteries (42V–54.6V fully charged). The factory firmware automatically detects voltage. Higher voltage (48V) gives more top speed and power, but requires a battery with matching BMS. Do not use 52V or higher without OSF modifications – the stock controller may overheat.

Is the OSF firmware difficult to flash?

It requires a Windows computer, a programming cable (no soldering needed), and following a step‑by‑step guide. The community provides ready‑to‑use binary files. Most first‑timers complete the flash in about 20 minutes. The main risk is selecting the wrong display variant (KT‑LCD3 vs SW102) – double‑check the file name before uploading.

Tongsheng mid‑drive motors offer a compelling mix of torque sensing, OSF flexibility, and affordability. For most riders looking to convert a bike without breaking the bank, the TSDZ2 or TSDZ8 delivers a natural, efficient ride that’s hard to beat.

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