The GNG BB-drive, which has some issues that can be fixed with parts upgrades, but its affordable price has recently made it popular. 15mm belted primary on the left, with a bike chain secondary.

GNG, an affordable 1,000W Mid Drive Kit

January 21, 2013

We have waited to write about the GNG kit because it proved to be immediately popular (’s leader Eric stumbled across the new GNG site in Aug 2012, about six months ago), and the inevitable upgrades that endless-sphere builders added were rapidly defining the strengths, weaknesses, and limits of this handy kit. Bottom-Bracket (BB) drives have really taken off this last year, and for good reason. The prices for the basic parts have come down, and the selection has improved too.

Part of the reason is because of a type of BMX bike called a “trials” bike, which is used for performing stunts (shown here with rider Danny MacAskill). They frequently have pedal crank-arms that hold a freewheeling chainring onto the BB. By putting two chainrings on a freewheeling BB…a motor can drive one of them, while the other chainring drives the rear wheel. This arrangement allows the motor to power the bike without the pedals moving. The GNG kit does not require an extra-wide pedal-axle, which is unlike some other BB-drive kits.




The biggest benefit of a BB-drive is that it is an inexpensive way to give the motor the use of the bikes gears. Whether you are limited by a legal street E-bike power-cap, or you have an unlimited-power off-road E-bike, external gears allow the motor to stay in its higher RPMs, so it’s not necessarily drawing high amps, or generating excess heat in the first place.

The EGO is an Austrian BB-drive that is a powerful and high-quality system, and has been around for a while, but…it is expensive (EU 2400, $3000 USD…Yikes!). The Cyclone is from Taiwan (which also has lots of hills), and although it is somewhat more affordable than the EGO, it is still pricey for the entry-level quality of parts you get, along with many customer reports of how noisy the system is.

A Chinese exporter called GNG recently began packaging and selling a brushless 48V BB-drive that they advertised as a 450W system. To the inexperienced buyer, that sounds weak, and we suspect it is advertised this way to sell in the many countries that have a 500W power limit for E-bikes.

The controller has been verified to put out a stock unmodified max power of 22-Amps, and since watts are “volts times amps“, that makes this a continuous 1,000W system. Plus, since this system applies its 1000-watts to the BB, the fact that this motor is using the bikes gears, would give it the same performance as a much more powerful “one-speed” hubmotor built into the wheel.

The GNG primary reduction uses a toothed belt from the motor to a jackshaft, and this runs quieter than the Cyclones metal-geared primary reduction. The stock belt is much looser than needed, and has a tensioner wheel to take up the slack. It is not spring-loaded, and you simply adjust the proper tension and then bolt it down.

The stock design has way too much “wrap” around the 14-tooth motor-drive pulley, and experimenters have verified that the excessive wrap uses up around 100W, even when its just spinning unloaded. The excessive wrap is there to help keep the belt from slipping when applying the full 1000W to the small pulley. Here is a graphic to show what I mean.




A quick e-mail to the customer service department of the famous Gates drive systems company provided professional engineering advice. Experimenter “LightningRods” then ordered custom laser-cut sideplates for the GNG mounting bracket that would allow the jackshaft to have its position adjusted, so as to properly tension the primary belt/chain without any wrap at all (these plates also allow a larger diameter pulley than the stock 80-tooth, which helps the motor RPM reduction). This lowered the parasitic power loss of the primary belt down to a more reasonable 10W.

However, now you have fewer pulley-teeth engaged, and if you apply high power, the belt will slip, leading to an early belt death.




If you run this kit with the advertised 48V, the motor will be spinning so fast that you cannot add pedaling when you are at the top speed (bikes are often designed for a cadence of 80-RPMs at the pedals). Two solutions for this have been tried.

You could run it at 36V with a different controller, which makes it a well-balanced USA street-legal 750W system. When doing this, the slower motor RPMs (due to the lower volts) will allow you to pedal along with the motor. Adding pedaling will greatly extend your battery range, and make your motor and controller run a little cooler. The GNG company will swap-in a 36V controller at no extra charge if they are informed at the time the kit was ordered. The other option is to swap-in larger diameter chainrings while keeping 48V.

So is the GNG kit ALL good? to be honest, there are several weaknesses. It’s actually quite a nice kit at 750W (@ 36V / 20A). It has a reasonable top speed on the flats, and you can downshift the bike to tackle the hills. The kit is only $400 plus shipping…just add a battery, add a charger, and a bike (near $1000 total, plus a bike, when a significant 15-Ah battery is added).

The mild steel mounting bracket has arrived bent for some buyers (due to rough handling by the shipper?), and it flexes a little when using 2,000W. Both of these points indicate that the bracket’s not quite as strong as it should be. Because of this, there are now custom sideplates available that are specifically designed to be stronger (found here at, and these plates also allow proper tensioning of the belt/chain without any idler needed.

If you add more power by raising the stock 48V or the 22A, the narrow 15mm wide primary belt will begin skipping, and then quickly shred. Several off-roaders have upgraded the primary to a chain-drive, which is noisier, but then…it can handle 3,000W without trouble. The example in this pic is using #25 chain (there are also examples using #219 chain). The large sprocket is bolted directly to the side of the stock pulley, and the small 12T drive-sprocket is from an 8mm shaft that is bored out to 10mm. Notice the idler wheel is barely deflecting the chain so drive losses will be low.




The stock belt is only 15mm wide, and builders immediately looked into a 20mm or 25mm wide belt-and-pulley set, so a fairly quiet belt could handle more power. But it’s not an easy swap-in. The stock 14T drive-pulley is a part of the motor-shaft, and must be ground off first. That is not easy to do yourself properly, and a machine shop can be expensive. One builder found that if he sanded the sharp edges off of the rough-cut stock 14T pulley, the belts lasted longer.

There are a wide variety of small sprockets that can be used on a GNG motor-shaft that has been turned down to 10mm, 12mm, or 0.500-inch. However, we have not yet found a good 20mm wide pulley with a small enough tooth-count, in order to make up for the removal of the deep idler belt-wrap. (the search continues, since a primary belt would be much quieter than a chain)

One major point in favor of the GNG kit (besides the affordable price), is that the custom Bottom-Bracket freewheel holder uses affordable and available off-the-shelf 16T freewheels, and this freewheel is the one part that is likely to need replacement about once a year with frequent use (almost forgot, the toothed belt is likely to need replacement every few months).




Also, the motor appears to handle 72V X 30A = 2,100W quite well (and 40A intermittently), because it is an inrunner that has the hot stator coils attached to the aluminum motor shell, which helps it shed heat under heavy loads. Until the arrival of this affordable motor, most E-bike non-hubs were either too expensive, too small, too wide to fit between the pedals, or didn’t shed heat well.

It’s just frustrating to find that this GNG motor-shaft and drive-pulley are one piece, when a 12mm diameter shaft stub (or 1/2-inch) would open up an entire world of opportunities for experimentation and using this motor in other applications.




So…what’s the final verdict? This is not a plug-and-play system like the popular hub-kits. It’s more involved and also technically challenging to install it properly on a bike. But, in my humble opinion…it’s better and more affordable than the Cyclone, and it’s definitely much more affordable than the very expensive EGO.

Bosch and Panasonic have produced very high quality BB-drives for the power-restricted global markets. But I doubt North American customers will pay a high price for a low-power 250W system, no matter how nice it is (like the Bosch and Panasonic).

If you are happy with 750W, you are mechanically handy, and you live around a hilly region, this might be the kit for you (you will save money by getting the lower voltage 36V battery, but you must use a 36V controller with it). GNG will swap the 48V controller for one that already has a Low-Voltage-Cutoff (LVC) set for a 36V battery, so ask before ordering, and then check it when the kit arrives before plugging in the battery.

The stock kit is 1,000W (and when you apply 1,000W to the bikes gears is a LOT of fun!), but it definitely wears out belts too quickly. It really needs a 20mm-25mm wide belt with de-burred pulleys and proper primary belt tensioning. If you perform a simple mod to the stock 9-FET controller, you can easily raise the max amps to 30A, which would provide around 1500W, but…if you do this…add a cheap temp probe to the controller so you can stay at least one step away from frying anything. And be aware at 1000W+ you will need to upgrade the primary drive to a chain, unless you don’t mind replacing belts often.

Link to buy the GNG BB-drive from this article. forum discussion about the GNG.

Discussion about changing the primary drive to a chain.




Here is a 16-minute video of a GNG kit being dis-assembled.


Written by Ron/Spinningmagnets, January 2013

Grew up in Los Angeles California, US Navy submarine mechanic from 1977-81/SanDiego, Hydraulic mechanic in the 1980's/Los Angeles, Heavy equipment operator in the 1990's/traveled to various locations, Dump truck driver in the 2000's/SW Utah, Water Plant operator since 2010/NW Kansas

  • snellemin

    Great article!

  • ElectricBIke

    Really nice informative article. Now i really want to buy one of these and covert a full suspension mountain bike of mine.

  • Michael Backus

    Thanks Spinning Magnets for an excellent review of the GNG mid drive. I’m Lightning Rods from the E-S Forum. I’m still communicating with Gates Corp as well as Pfeifer Industries in search of replacement pulleys for the GNG. I am also looking into having a custom motor spindle machined to replace the one piece pulley/spindle that the unit comes with. This will simplify the installation of either sprockets for chain drive or better quality pulleys to retain the quieter belt drive.

    About half of the people purchasing my adjustable brackets are converting to chain drive. Chains still need to be tensioned and an idler adjuster adds noise and robs power. The way it seems to be breaking out is that the off road riders seem to be going with chain primary drive and the street people want to solve for the belt for the advantages of low noise and no chain mess.
    The GNG is a great value and with the application of a bit of hot rod re-engineering I’m convinced that it can be a game changer in the e-bike business.

    • ElectricBIke

      Lighning rods…feel free to provide links or info on your products here. You are providing a service to the electric bike world :)

  • Paul H

    GNG have released a 2nd generation version of their brushless mid drive system.
    They’ve listened to feedback and replaced the pully system with a chain drive:

    Endless-Sphere discussion:

    • BasilPrayer

      do you know of any users of the 2nd generation? Because the ES users had some pretty nasty comments on the gng quality and out of the box failures.

  • Cyclebutt

    Once I’ve installed the adjustable sheets, including a roller type idler as pictured with the chain drive, I’m expecting to more than double (hoping 4x) belt life. Chain drive primary may indeed be the final solution for this interesting new mid drive kit.

  • Steve

    I’m amazed at how hard it is to get accurate information from anyone. I have a Micargi Mustang GTS stretch cruiser (single speed coaster brake) Can anyone tell me if this mid mount setup will fit or work?? My front fork is a springer (NIX Front Hub, my wheels are 68 spokes, nix rear. Now will the mid setup work or how many components must be changed or replaced???? Thanks to anyone

  • skyungjae

    How do you remove the 12T freewheel on the end of the jackshaft?

  • parajared

    A cheap simple mod that helps this kit quite a bit is to just buy a BMX half link for the side that goes to the BB. It makes things quieter, more efficient, and eliminates the need for a chain guide. I bought a half link for $2.

    Also after I dived in, I didn’t find that grinding the shaft down to 10mm with an angle grinder was as hard as it looked.

  • skyungjae

    It’s too bad the 150mm bottom bracket spindle isn’t suitable for any moderate off road or rough terrain riding.

  • Eric P

    Hi, thanks for the write up on the gng mid drive kit. I purchased the same
    kit, except I asked for a 36 volt controller which they substituted for the 48.
    I’m new to electric biking and I have some questions that I’m hoping you can
    give me some guidance with.

    First off my wife and I have been avid (loaded) touring riders for years,
    but age and some health issues have slowed us down. After pushing my wife’s
    bike up a mountain in Provence, France last May we came home and bought her an
    IGO, 36v, 10 ah, 250 watt mid drive 8sp. We changed pedals, tires, bars and
    seat. Best gift I ever got her, and me. After 20 years of sand bagging I could
    ride just about as fast as I wanted. If it was uphill or a stiff head wind she
    sometimes waits for me. Awesome! Best of all we easily get 50+ mile rides in
    with battery to spare. Obviously she pedals some, but I was still very
    impressed with the range, which is better than advertised. If the IGO fit me I
    (I’m 6’4″) I might have got one myself.

    So I decided to park my trusty old Trek 520 and bought a titanium
    Motobecane cross bike that I set up for touring, so that I could stay ahead of
    my wife. That left the Trek just collecting dust, so I decided to make it a
    project. We got a good deal on a spare IGO 36 volt battery and that is the main
    reason for choosing 36 volts for the gng kit, so that we could share batteries
    and chargers.

    I just completed the basic mechanical installation, I replaced the drops
    with an MBT bar and an 8sp shifter (on the left bar). The bike rides fine but I
    want a larger chain ring than the 36 that the gng comes with. Looks like there
    is room to add another chain ring, and I left the derailer on. What I can use much help with is the
    electrical components (or lack thereof).

    Questions: Sources for electrical connectors. I would like to find a
    battery connector same as the IGOs, but any advice is welcome there.

    A battery level indicator so that I have a clue as to how much charge is
    left. And how does it connect to the harness?

    Brake switches/levers. I am currently using the bar and brakes from my

    I would like to have the option (like my wife’s IGO) to twist the throttle
    or just pedal and choose between several power settings. My wife found holding
    the throttle open tiring and almost exclusively uses the hall sensor on the
    pedals to activate the motor. I prefer drops and with a pedal sensor I would
    probably convert back to drops.

    I’m sure I’ll have more questions as I get further into this but answers to
    these would help much.

    Thanks for your help,

    Eric Pekrul

  • Stinni

    Thanks for a great article/review, I’m sold! one question though, is it hard to get the right size toothed belt for GNG mid drive? does GNG sell a lot of spares?

    • spinningmagnets

      There have been several lengths of belt used, depending on various pulley tooth-counts that have been tried. The different sizes have proven to be fairly easy to buy online, and they arrive just a few days later in an envelope. Here’s the thread (it’s long, but the info is in there):

  • Eric Fahlgren

    I just received this kit, ordered it based on this review (and many others on this site, thanks guys). I ordered it on Wednesday evening, had an e-mail conversation with Jon Chan at GNG on Thursday, received the box on Saturday using the EMS option (“Speed Post Shipping”) via USPS here, near Los Angeles. The box was sort of munched, but the GNG guys had packaged the contents quite well and the box could have taken a whole lot more damage without compromising the contents.

    Contents are as described above, but with the addition of a plastic mud guard on the motor/drive assembly. I’ll report back after installation and testing.

    • spinningmagnets

      Thanks for posting, Eric. You might want to consider starting a build-thread over at endless-sphere in the “non-hub” section. That way others can benefit from your experience, and you can also see the other builds that use a GNG as the basis for their E-bike:

  • Coomkeen

    I know this is an old thread, but hope someone is still around.
    This looks like it could be the kit for me, but I want to fit it to an ICE Recumbent Trike.
    Anyone tried it, or see any problems?


  • PSA

    I installed my kit, but the chain keeps on coming off. Any advice? Does this picture look like it is set up right?

    • ElectricBIke

      post this on the endless-sphere forum where many users have bought this kit.

  • WW

    where cab I buy 1,000W Mid Drive Kit?

  • Michael Zimmermann

    Hello, I installed a GNG 650 watt with primary chain lately, and found following problems:
    primary shaft was sticky due to untrue axle seats – after trueing the seats on a lathe, the fit was so sloppy, some epoxy had to fill the gap. The two shaft bearings seemed to be also of bad quality, judging from turning them in my hands – and I thought a grease nipple (see picture) between them might help, getting the best out of them. Both free wheels were noisy because of rough manufacturing and little grease. The large primary sprocket is very rough and this is causing most of the noise. One hour of filing and brushing yielded a smooth finish and greatly improved noise level. I added an idler on the primary side taken out of a regular bicycle chain tensioner and re-cut the teeth to the 8mm spacing of the chain – but, I guess this one will not last long due to the high speed. The large primary sprocket was whobly, but three additional hub screws fixed that. The bb axle also was badly machined, and I needed a spacer to lign up both sprockets on the secondary reduction. The primary chain width seems to be a mismatch – a bit to wide for the sprockets. A standard 8x3mm roller chain will be too narrow, however. Quality roller chains have closed smooth barrels – GNG version has barrels with a seam – likely to cause some noise. The cut outs of the primary sprocket were up to 2mm off center – 1 hour of filing to fix this. The kit to frame mount via hose clamp did not look “cool” – I made a custom bracket instead – see picture. The good news: the motor has plenty of power and made me smile when I took the bike out on the road for the first time.

  • RC

    How do you mod the controller to put out 1500 watts? Is the current 2015 controller still the same? Thanks!

    • ElectricBIke

      yuo have to buy a new controller…..there are plenty of 40 -60 amp 48 volt ebay controllers on the market

      • RC

        Do I have to buy a new controller because the 2015 unit cannot be modded? Can you give me a few item numbers? I don’t know what to look for.

    • Matt G.

      You can mod the shunt in the stock controller to allow more amps. I believe the stock controller is shunted at 22amps. You can safely run that up to about 30-35amps max. More than that an the motor phase wires start to cook. I haven’t done this myself so I can’t speak from experience, but it’s possible that modding the shunt will mess with your LVC on the controller, so you may wan to use a battery with a BMS, or a watt-meter to watch your pack.

      There’s a bunch of info on this on Endless-Sphere, so you may want to look there for more details.