GMAC Motor System

  • The GMAC motor system was developed in conjunction with Grin Technologies and Mac motors, and is the premier lightweight, high-powered, regenerative-capable electric assist system. Featuring:
    1. An 8.6 lb rear hub motor with up to 100 N-m of torque - higher than any hub-motor (and almost any mid-drive) e-bike on the market!
    2. 28mph top speed, up to 40 mph for speed-unlimited software settings.
    3. Variable regenerative braking - increase your range by 10-15% while virtually eliminating brake pad wear
    4. A 750 watt-hour frame-locking battery with cells from Tesla, with an upgraded even higher-capacity Sanyo battery available
    5. The Phaserunner/Baserunner motor controller, a state-of-the-art motor controller from Grin Technologies that provides immense power, top speed boost, and customizable motor response in a tiny package
    6. Cycle Analyst V3 for unprecedented diagnostic and control precision
    7. Sempu Torque Sensing Bottom Bracket (Square Taper - Inquire for Other Options)
    8. A revolutionary motor axle that fits modern bicycles perfectly, with no risk of the motor's torque damaging your frame (not thru-axle compatible)
    9. A 2-year warranty on the motor and battery, and a 3-year warranty on all other parts

    Price includes professional installation at our Seattle shop. If you're outside of the Seattle area, we can ship it to a local bike shop for professional installation, and will provide $100 in labor credit for that shop and detailed instructions and phone support.

  • Motor
    1,000 watt (2,000 watt peak) planetary geared brushless DC hub motor with cassette freehub body, locked clutch, and 10mm (135mm OLD) axle with splined torque arm interface. 8.6 lbs, 36 spoke hole, manufactured by Mac Motor. 10T/8.1 rpm/V winding speed (8T/10 rpm/V available upon request). Thermistor equipped
    Weatherproof, locking enclosure 52V 15 amp-hour frame mount (Hailong) with Tesla 5.00 Ah 21700 cells (14S 3P cell configuration). 30A max discharge/15A max charge. Upgrade available: 52V 21 amp-hour Panasonic 18650GA 14S 6P battery with, 35A max discharge/20A max charge
    2.5A 58.8V (100%) charger with mini-XLR plug, UL certification. Upgraded Cycle Satiator available (up to 8A charge current, user programmable)
    Baserunner/Phaserunner Field Oriented Controller from Grin Technologies. 40A/50A max battery current, 80A/96A max motor phase current for maximum torque (Baserunner/Phaserunner). Field weakening for unlimited top speed. 0.6 lbs
    Grin Tech Cycle Analyst V3 WP; shows precise system diagnostics and allows for advanced control schemes like pedal cadence sensing, cruise control, power limiting based on motor temperature, etc
    Thumb (Left, Right, or Universal) - doubles as regenerative braking power signal when brake is depressed
    Brake Cutoff
    Single glue-on reed switch or inline cable switch
    Torque Arm
    CNC Milled Aluminum 2-Piece Splined
    CUSMADE waterproof 1910 motor connector, XT60 battery connector, JST crimpable control connectors
    Spokes & Nipples
    13G/14G single butted pillar stainless steel (Svandik T302+), Pillar brass nipples
    Sun Ringle Rhyno Lite (20”, 26”, & 29er sizes), CR18 (700c sizes), Helix TR25 (650b sizes), eyeleted, brushed or black sidewalls, black
    PAS/Torque Sensor
    Torque Sensing Bottom Bracket (Sq. Taper - Inquire for other options)
  • The basic GMAC system is activated by the hand throttle. When you squeeze the brakes, the system will go into regenerative braking at a set percentage of maximum torque (default: 25%), and in this case the throttle sets the brake level, where depressing the throttle with the brakes activated increased the motor's braking torque up to 100%.

    Each system is limited to the road-legal top speed of 28mph. However, with the speed limiting removed (a simple procedure), the top speed varies with wheel size. 20” version = 28mph+; 26" = 32mph+; 700C and 29er = 35mph+. The Phaserunner controller can also increase the top speed beyond these limits (via field weakening) if desired.

    The battery life varies based on numerous factors (the power level used, the rider’s weight, the amount of pedal assistance, cargo, terrain, wind, etc). Even a cargo-bike rider using full power can expect at least 20 miles to a charge, and you get 75+ miles on a standard bike using lower power settings, smart regenerative braking, and pedaling normally. Most folks report a battery range between 25 and 45 miles.

    The total system weighs 19 lbs, but it replaces your rear wheel, which weighs about 2 lbs. So it will add 17 lbs or so to your bike, but the power it gives you will offset its weight 20 times over!

    The GMAC requires a bike with:

    1. 135mm rear dropout spacing (almost all mountain bikes, most hybrids, and some road bikes have this)
    2. Enough room to mount the battery in the main frame triangle
    3. Water bottle mounts on the downtube
    4. Disc or rim brakes on the rear
    If you have any questions about whether your bike meets these criteria, check out the links above. If you’re still unsure, call us at (206) 588-6546, or send an email to We’d love to help!


    We suggest having this system professionally installed at our Seattle shop, which is included in the retail price. If you're outside of the Seattle area, we can ship it to a local bike shop for professional installation, and will provide $100 in labor credit for that shop and detailed instructions and phone support. If you'd like to install it yourself, please contact us for instructions and a potential discount.

    The motor and battery come with a 2-year warranty, and all other parts come with a 3-year warranty. Essentially, that means that any damage not caused by an accident or misuse is covered. See the full warranty here.

    It really comes down to how well you, the battery’s owner, care for it. With that said, you can expect a full 500 cycles with the standard charger before the battery life drops to 80% of its original capacity. But with the "Cycle Satiator" charger, you can extend that number to 1,000 cycles or more. We warranty the battery for 2 years with some stipulations (see warranty section for more information).

    From completely flat, the standard battery takes 6 hours to charge. However, the Cycle Satiator can recharge the battery in just 2 hours!

    Nope. But don’t leave it plugged in for too long (24 hours or more). It keeps the cells from dropping down to their resting voltage and prematurely ages the pack.

    No! Actually, it's best to not completely discharge the battery. We suggest you simply recharge the battery overnight after riding, regardless of whether it's completely dead or not.

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