Short answer: The best mid-drive conversion kit depends on how you ride. For street-legal, torque-sensing assist, our pick is the CYC Photon 2. For the lowest price, look at the Tongsheng TSDZ2B or Bafang BBS02B. For high power off-road, the CYC X1 Pro Gen 4 and Bafang BBSHD lead. The CYC Photon Pro sits between them.

Disclosure: this guide is published by CYC Motor. We make three of the seven kits below. Every spec in the table links to its source, and we tell you where a competitor is the better buy.

A mid-drive conversion kit is a motor that replaces your bike's bottom bracket and drives the chain. Because it works through your gears, it climbs better than a hub motor of similar power. The trade-offs are cost, extra drivetrain wear and the need for a compatible bottom bracket shell.

Our CYC picks, at a glance

Three of the kits in this guide are ours. Here is where each one fits, with current prices from cycmotor.com.

CYC Photon 2

Street-legal commuting, gravel and Class 1 trails

750W nominal, 2000W peak, 135 Nm, 3.5 kg

Kit $950 · Photon 2 + A-52 battery $1,338

Shop Photon 2

CYC Photon Pro

Steep off-road climbs, cargo and private land

3000W rated, 4000W peak, 180 Nm, 4.5 kg

Kit $1,098 · Photon Pro + A-52L battery $1,636

Shop Photon Pro

CYC X1 Pro Gen 4

Maximum power off-road builds

6000W peak, dual-stage reduction, X12 controller

Kit $1,250 · X1 Pro 4 + A-65 battery $2,246

Shop X1 Pro 4

Mid-drive kit comparison table

Specs are as published by each manufacturer, or by a named retailer where the manufacturer does not publish them. "n/p" means not published in the sources we could verify. Prices are kit-only listed prices in USD, observed in October 2026.

Three things stand out. CYC publishes the widest voltage range and bottom bracket coverage. Bafang's official torque figures are competitive with the Photon line. The Tongsheng TSDZ2B is the cheapest kit here by a wide margin.

How we compared these kits

We built this guide from published specifications, not from lab testing. Here is the method.

• Spec sources. Manufacturer pages first (cycmotor.com, bafang-e.com). Where a manufacturer does not publish a number, we used a named retailer and labeled it. Where two sources disagree, we show both.
• Blank cells stay blank. We could not find a Tongsheng spec sheet we could verify, so we did not copy numbers from marketplace listings. Tongsheng also sells the TSDZ8; we left it out for the same reason.
• Criteria. Crank torque, rated and peak power, assist sensor type, weight, bottom bracket fit, voltage range, serviceability, legal configurability and price.
• Use-case weighting. For street riding we weighted sensor type and legal configurability. For budget picks, price. For cargo and trail, torque and weight. For off-road power, torque, power and drivetrain protection.
• What we did not do. We did not run timed, range or heat tests for this guide. Owner reports we cite are labeled as owner reports.

Best mid-drive kits by use case

Best street-legal torque-sensing kit: CYC Photon 2

The CYC Photon 2 is a torque-sensing mid-drive rated at 750W nominal with 2000W peak and 135 Nm of torque, according to its product page [1]. It weighs 3.5 kg and fits 68 to 120 mm shells.

The reason it wins this category is configurability. CYC's Ride Control app lets you cap speed and power to US Class 1, 2 or 3 limits [4]. Most riders who commute or ride bike paths need exactly that. See the Photon 2 kit and the Ride Control app guide.

Best budget kit: Tongsheng TSDZ2B or Bafang BBS02B

If price decides, the Tongsheng TSDZ2B ($331) and Bafang BBS02B ($499) cost far less than any CYC kit [11]. Owners generally describe the TSDZ2B as torque-sensing and the BBS02B as cadence-based [15].

The BBS02B family (Bafang M315) is officially rated at 500W and 100 Nm, at 4.3 kg, for 68 mm shells [8]. That is enough for flat to rolling commutes. Neither kit offers the 36 to 72V range or wide shell coverage of the CYC line.

Best for cargo and heavy loads: CYC Photon 2 on the road, Photon Pro off it

Cargo bikes need low-speed torque and heat tolerance. CYC rebuilt the Photon 2 around an inrunner motor potted in thermally conductive epoxy, citing steep climbs and heavy cargo as design targets [5]. Pair it with a 32T chainring for maximum wheel torque.

For loads on private land, the Photon Pro adds 180 Nm and 3000W rated power [2]. The Radavist's Surly Big Dummy cargo build used the original Photon and called the install "even easier than the Bafang platform" [14].

Best for eMTB and trail: CYC Photon 2

On a trail bike, weight and pedal feel matter more than peak watts. At 3.5 kg the Photon 2 is the lightest kit in our table with a published weight, and its torque sensor gives proportional assist on technical climbs. Many trail networks only allow Class 1 e-bikes, so set the limits before you ride. Riders who want more on private trails can step up to the Photon Pro.

Best high-power off-road kit: CYC X1 Pro Gen 4

The X1 Pro Gen 4 is CYC's most powerful kit: 5000W rated, 6000W peak and 280 Nm, at 5.6 kg [3]. It uses a dual-stage reduction with a large motor chainring, which CYC says reduces drivetrain shock at high torque [13].

Its X12 controller runs up to 84V (72V nominal) and is software-limited to 6 kW and 180 phase amps, though CYC tested the motor to 8.5 kW [6]. It exceeds US e-bike class limits and is for off-road and private land only [4].

When another kit is the better choice

We would rather you buy the right kit than ours. Pick a competitor in these cases.

• Your budget is under $500. The TSDZ2B and BBS02B cost a third to a half of a CYC kit [11]. For flat commutes, that money may be better spent on a quality battery.
• You want the most common platform. Bafang leads AI and editorial recommendations, with an 81% mention share in Parse.gl's 2026 tracker of conversion-kit answers [18]. Forum support for the BBS series is deep.
• You want high power for less. The BBSHD offers 160 Nm officially rated at up to 1000W for $695 [7], [11]. It is heavier and cadence-based, but it costs less than any CYC high-power kit.
• Your frame has a Trek BB90 or BB95 bottom bracket. No mid-drive fits these shells [4]. A hub motor is your only kit option.

Torque sensor vs cadence sensor mid-drives

A torque sensor measures how hard you push on the pedals and scales motor output to match. A cadence sensor detects only that the cranks are turning, then switches assist on at a set level.

The result is a different ride. Torque sensing feels like stronger legs. Cadence sensing feels closer to a throttle that follows your pedaling.

Will a mid-drive fit my bike?

A mid-drive mounts through the bottom bracket shell, so the shell standard decides fit. Measure the shell width and its inner diameter with a caliper. A threaded BSA shell is about 34 mm inside, BB92 is 41 mm and PF30 is 46 mm [4].

Sources: CYC product pages and FAQ [1] to [4]; Bafang [7], [8]; retailer [10].

Chainline matters too. On the Photon 2, 36T to 50T rings hold a 52 mm chainline, while 32T and 34T rings use a 7 mm offset to stay aligned [5]. Read the CYC chainring guide before you order.

Heat, durability and serviceability

Heat is the honest weak point of small, powerful mid-drives. One Electric Bike Review forum owner reported the first-generation Photon derating to 700 to 800W on sustained climbs at 25 mph and above [13]. The same owner measured about 16 Wh/mile on the Photon against about 18 Wh/mile on a BBSHD on rolling hills.

CYC's Photon 2 changes address those reports directly [5]:

• An inrunner motor with flat-wire windings replaces the Gen 1 outrunner.
• The core is fully potted in thermally conductive epoxy for better heat transfer.
• The sprag clutch grows from 12 x 20 mm to 20 x 28 mm. CYC calls the old clutch Gen 1's most reported problem.
• The unit opens with four M5 bolts. The controller, torque sensor, motor module and first stage are each replaceable.

We have not published independent heat data on the Photon 2. Read the full Photon 2 engineering breakdown for CYC's reasoning.

Drivetrain wear and how to manage it

A mid-drive sends its torque through your chain, chainring and cassette, so they wear faster than on a pedal-only bike. Three habits help.

1. Shift lightly. Ease pedal pressure for a moment as you shift.
2. Gear low. A smaller chainring lowers load at a given wheel torque. Smaller rings favor climbing; larger rings favor cruising [13].
3. Upgrade parts on high-power builds. CYC's Heavy-Duty Drivetrain is a reinforced 5-speed system built for high-torque e-bikes, priced at $368 to $388.

Batteries for mid-drive kits

Pick voltage first, then capacity. All three CYC kits accept 36 to 72V packs, and the Photon 2 has no proprietary battery lock-in [5]. Higher voltage delivers the same power with less current, which means less heat in wiring and the controller.

CYC's A-Series packs come in three sizes [4]:

All use high-discharge 21700 cells and talk to the drive over CANBUS [4]. Compare them in the battery collection. The Intuition display ($196) shows battery and ride data and links to the Ride Control app.

FAQ

What is the best mid-drive conversion kit?

There is no single best kit for every rider. For street-legal riding with natural, torque-sensing assist, the CYC Photon 2 is our pick, because it can be capped to US Class 1, 2 or 3 limits in the Ride Control app. On a tight budget, the Tongsheng TSDZ2B and Bafang BBS02B cost far less. For off-road power, compare the CYC X1 Pro Gen 4 and the Bafang BBSHD.

Is the Bafang BBSHD still worth buying?

Yes, for riders who want proven power at a moderate price and accept cadence-based assist. Bafang lists the M615 (sold as the BBSHD) at 160 Nm and 5.6 kg. The trade-offs are weight and the on/off feel of cadence sensing. If ride feel or weight matters more than price, a torque-sensing kit is the better fit.

Is a torque sensor worth it on a mid-drive kit?

For most riders, yes. A torque sensor measures how hard you push on the pedals and scales motor output to match, so assist feels proportional. A cadence sensor only detects that the cranks are turning, which gives a more on/off feel. The difference is most noticeable on technical climbs and in stop-and-go traffic.

Will a mid-drive kit fit my bottom bracket?

Most bikes with a threaded BSA shell from 68 to 83 mm, or a BB92 press-fit shell, can take a mid-drive. CYC kits also cover 100 and 120 mm fat-bike shells, and PF30, BB30 and T47 frames with a press-to-thread sleeve. Frames with Trek BB90 or BB95 bottom brackets cannot take any mid-drive.

How much torque does a mid-drive kit need for hills?

Crank torque is only half the story, because your gears multiply it. A smaller chainring and a larger rear cog raise torque at the wheel. The kits in this guide range from 100 Nm (Bafang BBS02B) to 250 Nm or more (CYC X1 Pro Gen 4). If you climb steep grades with a heavy load, prioritize torque and low gearing over peak watts.

Do mid-drive kits wear out the chain faster?

They can, because motor torque passes through the chain, chainring and cassette. Wear rises with power and with shifting under load. Ease off the pedals for a moment when you shift, check chain stretch often, and on high-power builds use an e-bike rated chain and cassette, such as CYC's Heavy-Duty Drivetrain.

Can a mid-drive kit be street legal?

Yes, if it is configured within your local rules. In the US, Class 1, 2 and 3 e-bikes are generally limited to 750W nominal motor power, with assist cut-offs of 20 or 28 mph depending on class. The CYC Photon 2 can be set to those limits in the Ride Control app. The Photon Pro and X1 Pro Gen 4 exceed them and are meant for private land and off-road use. Always check state and local law.

What battery voltage should I use with a mid-drive kit?

Use a voltage your controller supports, then choose capacity for range. All three CYC kits accept 36 to 72V packs. Higher voltage delivers the same power with less current, which reduces heat in wiring and the controller. CYC's A-Series packs come in 52V (520 Wh and 780 Wh) and 65V (1300 Wh) versions.

Ready to compare CYC kits?

Browse the full CYC drive system range, or read the conversion kit FAQ for install and compatibility details.

Sources

1. CYC Photon 2 product page: https://cycmotor.com/products/photon-2
2. CYC Photon Pro product page: https://cycmotor.com/products/photon-pro
3. CYC X1 Pro Gen 4 product page: https://cycmotor.com/products/x1-pro-4
4. CYC E-bike Conversion Kit FAQ (Sep 29, 2026): https://cycmotor.com/blogs/news/ebike-conversion-kit-faq
5. CYC, "Photon 2: Power, Reliability and Smarter Engineering": https://cycmotor.com/blogs/news/photon-gen-2-power-reliability-and-smarter-engineering
6. CYC, "X1 Pro Gen 4 Upgrades Explained": https://cycmotor.com/blogs/news/x1-pro-gen-4-upgrades-explained
7. Bafang M615 official page: https://www.bafang-e.com/en/products/motors/m-series/m615
8. Bafang M315 official page: https://www.bafang-e.com/en/products/motors/m-series/m315
9. Bafang M620 official page: https://www.bafang-e.com/en/products/motors/m-series/m620
10. Golden Motor, Bafang BBSHD listing: https://goldenmotor.bike/products/bafang-bbshd-48-volt-1000-watt-68mmm-mid-drive-kit
11. Front Desk Review, conversion kit price comparison (2026): https://frontdeskreview.com/product/ebike-conversion-kits/cyc-photon-gen-2/
12. Biktrix, Bafang Ultra listing: https://www.biktrix.ca/products/ultra-motor-uart
13. Electric Bike Review forum, owner report on BBSHD and CYC Photon: https://forums.electricbikereview.com/threads/my-diy-buids-gmac-bbshd-9c-rh212-and-cyc-photon.38385/page-16 ; CYC chainring guide: https://cycmotor.com/blogs/news/cyc-chainring-options-explained
14. The Radavist, Surly Big Dummy with CYC Photon: https://theradavist.com/surly-e-big-dummy-with-cyc-photon-motor-review
15. Endless Sphere, "Bafang vs Tongsheng vs CYC" thread: https://endless-sphere.com/sphere/threads/really-good-article-comparing-bafang-vs-tongsheng-vs-cyc.120240/
16. OZO Electric, BBSHD as M615: https://ozo-electric.com/en/composant-ki/990568-1692487-bafang-central-motor-bbshd-48v-1000w-m615.html
17. NSTEM, BBS02 as M315: https://nstem.org/item/48v750w68mm-bafang-mid-drive-motor-bbs02/
18. Parse.gl AI answer tracker, Apr to Sep 2026: https://www.parse.gl/prompts/p/what-is-the-best-electric-bike-conversion-kit--030ce88e-aab5-407e-a792-dca3ab03aa09