The Grin All-Axle Hub Motor

The Grin All-Axle hub is a direct-drive motor series we designed to be universally compatible with all the varieties of quick-release and thru-axle mounting standards that exist in the bike world these days. It solves the compatibility problem between hub motors and modern bicycle frames, it provides the benefits of direct drive without the traditional heft, and it simplifies installation with integrated torque arms and torque sensors. 

Features

• Both FRONT and REAR models available
• Both regular width (27mm) and Fatbike models (45mm) available.  
• Lightweight 4.0 kg for regular / 6.0 kg for fabike, vs ~6kg and ~9kg for comparable generic DD motor
• 0.35mm Laminations for low motor drag when pedaling unassisted
• Integrated Torque Arm with secure frame mounting clamp
• Uses 32 Spoke Holes for vastly more in stock rim options
• Min 18mm Disk Caliper Clearance fits most (but not all) calipers without spacers
• Statorade Compatible with side cover injection port
• Available in both metallic silver and black anodized finish
• Designed and Assembled in Canada

Rear Specific

• Built-In Torque and PAS Sensor. No need for bottom bracket torque or cadence sensors
• Support both Shimano HG and SRAM XDR cassettes, with XDR for wide range 11-12 speed
• Fits Most Rear Dropout Standards (135mm quick release, 12x142 Thru Axle, 12x148 Boost Thru Axle, 170&190 Fatbike, 177&197 Thru-Axle Fatbike)

Front Specific

• Fits Almost All Front Fork Standards (100mm and 135mm Quick Release, 12mm, 15mm, 15mm Boost, and 15mm x 150 Thru-Axle)
• Compatible with Single Side Installation on many trike and quad vehicles

Models

There are 5 distinct mechanical models of the All-Axle motor currently in production summarized in the table below. 

Model	Weight	Stator Width	Axle Bore	Frame / Dropout Compatibility
V2 Front	4.0 kg	27mm	20mm	Only recommended for old 20x110 mm Thru-Axle suspension forks, or single side applications requiring 20mm axle mount.
V3 Front	4.0 kg	27mm	16mm	Slotted Dropouts: 100mm, 135mm Thru Axle: 12x100, 15x100, 15x110, 15x150  Single Side
V3 Fat Front	6.0 kg	45mm	16mm	Slotted Dropouts: 135mm Thru Axle: 15x150  Singled Side
V3 Rear	4.3 kg	27mm	12mm	Slotted Dropouts: 135mm,145mm (tandem), 160mm (Santana) Thru Axle: 12x142, 12x148 (Boost), 12x157 (Superboost), 12x167 (Santana)
V3 Fat Rear	6.3 kg	45mm	12mm	Slotted Dropouts: 170mm (4" Tire), 190mm (5" Tire) Thru Axle: 12x177 (4" Tire), 12x197 (5" Tire)

Axle Adapters and End Caps

Technical Specifications

 

 

	Regular (27mm) Model			Fat (45mm) Model
	Slow (8T)	Standard (6T)	Fast (5T)	Slow (5T)	Standard (4T)
kV	7.5 rpm/V	10.0 rpm/V	12.0 rpm/V	7.2 rpm/V	9.0 rpm /V
Phase to Phase Resistance	268 mΩ	145 mΩ	100 mΩ	155 mΩ	102 mΩ
Phase to Phase Inductance	680 uH	380 uH	260 uH	-- uH	-- uH
Hysteresis Drag Torque	0.6 Nm			1.0 Nm
Eddie Current Drag Torque	0.0005 Nm/rpm			0.0008 Nm/rpm
Spoke Flange Diameter	214 mm			214 mm
Flange Spacing	49 mm			67 mm
Magnetic Pole Pairs	23			23
Motor Weight	4.05 kg (8.9 lb) Front / 4.30 kg (9.4 lb) Rear			6.0 kg (13.2 lb) Front / 6.2 kg (13.6 lb) Rear

User Manuals

3D CAD Models

We have made available full 3D models and drawings of the front and rear motors with various adapter sets in order to facilitate vehicle integration.  

 

 

 

 

Videos

Motor Speed

The Standard Grin All-Axle Motor is currently produced with three different windings; a slow 8 turn stator, a standard 6 turn stator, and a fast 5 turn stator. Ignoring potential limitations of your motor controller, all three motor winds are capable of producing exactly the same torque and power outputs, so the recommended motor model depends on your desired vehicle speed. The faster wind motors are more appropriate for small wheel diameters and/or lower battery voltages, while the slower motor winds are more common with larger wheel sizes and higher battery voltages.

The following table shows the unloaded speed of each motor winding at common battery voltages in 20" 26", and 29" (700c) wheel sizes.

Unloaded Speeds of All-Axle motors (27mm Stator)

	Slow 8T Wind (7.5 rpm/V)			Standard 6T Wind (10 rpm/V)			Fast 5T Wind (12 rpm/V)
	20” Wheel	26” Wheel	29” Wheel	20” Wheel	26” Wheel	29” Wheel	20” Wheel	26” Wheel	29” Wheel
36V Battery	26 kph	34 kph	37 kph	34 kph	45 kph	50 kph	41 kph	54 kph	60 kph
48V Battery	34 kph	45 kph	50 kph	46 kph	60 kph	67 kph	55 kph	72 kph	80 kph
52V Battery	37 kph	49 kph	54 kph	50 kph	65 kph	72 kph	60 kph	78 kph	87 kph
72V Battery	52 kph	67 kph	75 kph	69 kph	90 kph	100 kph	83 kph	108 kph	120 kph

 

The 45mm Fatbike Motors are available in two winding options, a slow 5T stator and standard 4T stator. In general, the bottleneck for power and torque capability of these larger motors will be the phase current limit of the Baserunner or Phaserunner motor controller. This table shows the unloaded speed of both fatbike motor windings at common battery voltages in 20" 26", and 29" (700c) wheel sizes.

Unloaded Speeds of Fat All-Axle motors (45mm Stator)

	Slow 5T Wind (7.2 rpm/V)			Standard 4T Wind (9 rpm/V)
	20” Wheel	26” Wheel	29” Wheel	20” Wheel	26” Wheel	29” Wheel
36V Battery	24 kph	31 kph	35 kph	30 kph	39 kph	44 kph
48V Battery	32 kph	42 kph	46 kph	40 kph	53 kph	58 kph
52V Battery	35 kph	45 kph	50 kph	43 kph	56 kph	62 kph
72V Battery	48 kph	62 kph	69kph	60 kph	78 kph	87 kph

The top speed under any kind of load is going to be less than this value, and we recommend using our motor simulator for exact performance details of any given combination of motor, battery voltage, and controller model.

Motor Power

The standard All-Axle motor uses a 27mm wide 205mm diameter stator and has similar continuous power and torque capabilities as other direct drive hub motors of this size. However being optimally designed for weight reduction it has less metal mass to absorb heat. Under heavy loads the core temperature will rise at a faster rate than you would see on an otherwise identical but heavier hub, and for those reasons we recommend Statorade in the motor when used in more demanding applications.

The table below shows both the continuous and 5 -minute power capability of the motor at various RPMs with and without Statorde motor coolant. Notice again that the motor winding speed does not impact the power capability of the motor, this table holds true for all three winding options. 

 

The fatbike motor with the 45mm stator has a greater power capability. The projected values based on extrapolation from the 27mm motor data are summarized in the table below. This may be subject to change on completion of wind tunnel testing of the fat motor's thermal dissipation characteristics.

 

For a more detailed understanding we recommend using our motor simulator or trip simulator applications to properly predict the capability of this motor in any specific usage scenario.

Single Side Applications

A unique feature of the front All-Axle hub design is its ability to work in applications requiring a single side mount. This allows the side wheels of trikes and quads to be readily electrified for the first time, and is especially popular with tadpole trikes running an internal gear hub rear wheel.

Unlike front bicycle forks where there are industry standards (admittedly a lot of standards, but standards at least), the wheel mounting strategy on trikes is all over the map, and unique adapters are required for most vehicle models. We've taken the approach of using the disk caliper mount as an anchor point to hold the wheel and lock the axle against rotation.

Catrike	The popular catrikes are ideal for the V2 Grin Hub motor because they already use a 20mm spindle, and they adopt the rear ISO2000 disk caliper mounting standard for both the left and right wheels.
Terratrike	The terratrike rovers also have a 20mm spindle, but they use a front ISO disk mount and the shaft has a shoulder that prevents the hub from sliding on as far as would be ideal. We accommodate the terratrike axles with a two-piece torque arm that provides the necessary spacing for where the motor fits in place.
Icetrike	This adapter bolts onto a custom machined All Axle Hub Motor to allow for single side mounting to the spindle of certain Icetrike tricycles. The two-piece adapter secures the motor axle to the trike frame via the disk caliper mounting holes. This adapter requires a shim insert to step down the ID of the motor axle to 12mm.
Greenspeed	The Greenspeed trikes use a smaller 12mm diameter spindle and have a disk caliper location with Rear IS2000 caliper placement. We have a similar 2 piece arm that can be flipped 180 degrees for working on either side. This also requires a shim to step the axle ID down to 12mm.
HP Velotechnik	The popular german brand HP Velotechnik makes trikes that all use a 12mm spindle but use a post mount rather than an ISO disc mount. To fit the All-Axle motors on these trikes, we have a disc caliper mounting block that repositions the brake outwards to align with the motor and increases the radial offset for a larger 180mm rotor. The torque arm in this setup is secured to the two fender bolts via a stainless steel plate rather than to the caliper mount.   The hardware for the left and right side models are similar, differing only in the direction of bend on the stainless torque arm plate.
DIY	The splined arm is available by itself for doing DIY mounts on other vehicle types. The two bolt holes allow you to interface with a separate flat plate of metal that can attach under the disk caliper or other frame location on the frame to lock the axle from spinning.

 

 

One Side or Both?

A trike with dual Grin hub motors can be insanely powerful and will be able to rocket up the steepest hills with amazing efficiency, but it is also quite expensive to do a full conversion with two specialized motors and motor controllers. You can also run a tadpole or delta trike with just a single side wheel motor and leave your original wheel on the other side. In general this does not result in any lopsided steering or handling issues and allows for a ligher weight and more economical conversion.

Wheel Lacing

Unlike most hub motors, the All-Axle uses 32 spoke holes rather than 36 spoke holes in order to fit the much larger availability of 32 hole rims. The spoke holes are paired sufficiently close that there is NO NEED to have the spokes cross over. With a radial lacing the spokes have an effective angle that is the same as a regular hub with a triple cross. That said, you are free to do a single cross lacing if you prefer the look.

One not-so-obvious detail is that the spoke flange of the All-axle motor is designed for the spokes to be laced with the elbows in and the head facing outwards. The flange has a couterbore for the spoke head on the outside, and is wide enough apart (49mm, vs 25mm for typical motors) that there is sufficient triangulation with all spokes elbows in. If the wheel is laced with the spoke elbow facing outwards, it results in a bending force on the flange that pushes the entire center of the side plate outwards by 1-2mm. This can result in the motor axle developing play to slide left and right. 

Version History

The original V1 All Axle hub motor was in limited production from 2013 until early 2019 and used a large 45mm ID thin section bearing on the side covers and was available in front only. This allowed for a generous amount of room for the heavy gauge phase wires to pass through the axle, but the thin section ball bearings could have short lifespans in setups with frequent exposure to the elements.

In the spring of 2019 we released an updated V2 Grin motor design based on feedback and experience. This updated model has the motor cable exiting on the disc side of the motor rather than the non-disc side to facilitate single side installations, and it uses a wider 35mm ID ball bearing standard with a custom tooled lip seal to prevent ingress and statorade egress. These changes increased the overall motor weight a small amount, but the improved robustness and versatility was worth it.

In January 2024 we updated to a V3 motor design. In the V3 front motors, the ID of the axle was reduced from 20mm to 16mm in order to have more clearance from the disc rotor for the cable exit. And the rear motor was upgraded from a PAS only sensor in the cassette to full torque sensing, the torque arm spline interface was improved, and a wider 45mm fatbike motor variant was added to the mix as well. 

 

Differences Between V1 (2013-2019) and V2 (2019+) and V3 (2024+) Front Grin Hubs

Property	V1	V2	V3
Main Bearing	45x58x7 (6809)	35x55x10 (6907)	Same as V2
Bearing Seal	Standard Dust Seal	Double Lip Seal	Same as V2
Cable Exit	Non-Disk Side	Disk Side	Same as V2
Axle ID	20mm	20mm	16mm
Torque Arm	Non-Disk Side	Non-Disk Side	Same as V2
Connector	Anderson +JST SM	HiGo L1019	Same as V2
Side Plate Seal	Sillicone Sealant	O-Rings	Same as V2
Statorade Compatibility	So-so (can leak through bearings)	Excellent	Same as V2
Weight	3.95 kg	4.05 kg	4.1 kg
Magnets	N35UH	N40SH	Same as V2
Thermistor	10K NTC, Beta 3950	10K NTC, Beta 3950	10K NTC, Beta 3450

 

 

Summary Differences Between V2 (2023) and V3 (2024+) Rear Grin Hubs

Property	V2	V3
Freehub Style	Shimano HG Mountain	Shimano HG Road, or SRAM XD
PAS Poles	12 Pulses / Revolution	9 Pulses / Revolution
Torque Sensing	None	Yes, 28.3 Nm/V
Thermsitor	10K NTC, Beta 3950	10K NTC, Beta 3450
Available Adapter Sets	Quick Release: 135x9 Thru-Axle: 142x12, 148x12	Quick Release: 135x9, 145x9, 160x9 Thru-Axle: 142x12, 148x12, 157x12, 167x12
Torque Arm	2 Lobes Only	2 Lobes plus 4 splines

 

In addition to the mechanical changes we also updated from N35 to N40 grade magnets in the move from V1 to V2. Stronger magnets allow the motor to produce more torque for hill climbing with less heat loss, but they also increase the drag of the motor when riding without power. In our original design we erred on having lower rolling drag because at the time we felt this was more important than efficiency on hill climbs, but the Virtual Electronic Freewheeling feature in the Phaserunner/Baserunner controllers has shifted the balance and we switched to a higher strength magnet.

 

As a result the V2 and V3 motors spin about 5% slower than the V1 models. They have about 10% more drag torque but they can also climb hills with 10% less heat generation.

Motor Colour

We originally launched the V2 front motor in both a shiny silver and black anodized finish, and continue to offer both types. With the introduction of the rear motor having a wide number of variants (3 winding speeds + 3 cassette types), we decided to only list these rear motors in black in order to keep the total SKU count from getting out of hand.   

Our original production of side plates used low silicone ADC5 alloy that would anodize to a jet black colour very well.  However, due to issues with the injection molding facility we were no longer able to get the plates made with ADC5 after 2023.  Since March 2024, all the motor side plates are made with a more conventional die casting alloy that does not anodize quite the same.  The result is more of a dark grey colour than a true black.  

V3 Model Update Summary

In December 2023 we rolled out significant design update to both the front and rear All-Axle motor models.  This was driven by two primary motivations:
1) To resolve the recurring issue of customers experiencing cable damage on front motors due to the small clearance to the spinning disk rotor. 
2) To add both torque sensing functionality and SRAM-XD/XDR driver support to the rear motors. 

Changes to the Front Design

Axle: The front motor now uses an internal 16 mm bore rather than the 20mm bore of the original design. This gives us 2mm more room for the cable to clear the disk rotor. Unfortunately, it also means that the V3 front motor is no longer compatible with 20mm axles.  The bicycle industry has long ago moved away from the original 20mm thru-axle fork standard to 12 and 15mm axles instead, so for most this is of almost no consequence. However, we will continue to make the V2 motors available for people who do require compatibility 20mm forks or single-side installations. 

Adapters: All of the axle adapters for the V3 motors are different as they must fit into an 18mm recess and not a 20mm ID. We are clearly labeling each adapter set on our store as either a V2 or V3 model to reduce uncertainty, and will always carry a large stock of the V2 adapters to support customers over the years as they move their V2 motor from one bike to another.  

Changes to the Rear Design

Freehub: The most significant change is the migration to a new freehub supplier that has options for integrated torque-sensing, rather than our original freehubs that only had basic magnet PAS encoder. There are three options now available

• Shimano HG Torque - This model uses the industry standard Shimano HG freehub body, but using the road rather than mountain standard. By default we are including a 1.5mm spacer to support the more common mountain cassettes, which should be removed if used with a Shimano road cassette.
• SRAM XDR Torque - The option for a SRAM XDR driver gives the ability to use high-end 11, 12, and 13 speed 1x cassettes that have super wide range and a small 10 tooth gear to simplify pedaling at high speeds. Both XD and XDR cassettes are compatible (XD with an included spacer)
• Shimano HG PAS - For those who don't need a torque sensor in their substance, we're planning in 2024 to also offer a less expensive version that has just a basic PAS sensor like our original rear hubs.

These sensors communicate with an internal circuitboard that generate a 0.8V signal at rest, which increases up to 4V as maximum torque is applied. The circuitboard also generates an equivalent 2 wire PAS output to support motor pedal cadence sensing and most importantly back-pedal regen

Torque Arm: The torque arm looks the same externally but internally it now features a set of internal splines in between the two screw holes, providing higher spinout resistance in anticipation of future higher motor models. 

Motor Adapters: While the original rear motor had adapters for the three most common dropouts (135mm quick release, 142x12 thru-axle, and 148x12 boost thru axle), the V3 rear motors envision a much wider assortment of adapter sents, including -

• 145x9mm quick release for regular tandem bikes 
• 157x12mm superboost thru-axle for mountain bikes
• 160x9mm quick release for Santana Tandem bikes

Disk Spacing:

Finally, the V3 rear all-axle motors are sized so that a 1mm disc spacer is required to correctly position the disc rotor in the bike frame. This increases the caliper clearance to the side plate from 18mm to 19mm which greatly increases the number of brake calipers that will fit without rubbing. 

Changes to Both Front/Rear

Thermistor Beta: The 10K NTC thermistor has been changed from one with a 3950 Beta constant to a 3450 Beta constant. This allows for better resolution and accuracy when measuring high motor temperatures, as there is a more discernable voltage change. Most hub motors from other manufacturers that have a thermistor include one with this Beta value, and it is already supported in our Cycle Analysts (V3.15 and later FW) and motor controllers. 

45mm Stator for Fabikes: A more powerful motor option using a 45mm stator instead of a 27mm stator was introduced for better fatbike support. This increases the hub flange spacing making it easier to lace into fatbike rims, and it naturally increases the power and weight of the hub too. The front fatbike motor will work with 135x9mm quick release and 150x15 thru-axles, while the rear fatbike version will support 170/177 dropouts for 4" tires, and 190/197 dropouts for 5" tires. 

 

Background

The All-Axle motor has been a long development project for Grin to produce a direct drive hub motor that was lightweight and compatible with all Thru Axle and quick release fork standards. The idea first took roots in 2010 when we were impressed with the performance of large diameter direct drive hub motors being imported from china, but increasingly frustrated with the poor mechanical tolerances and bike fitment. While prototyping these mechanical improvements we also saw considerable opportunity to reduce the mass of the hub without affecting the torque output.

These earlier videos filmed from Ken (owner of a Calgary based ebike store) as he was passing through town in 2010 show the early development and thought process:

Since then we've gone through a number of design revisions, enhancements, mold toolings, and several pilot production batches while working out many kinks along the way. The hub was really put to the test in several touring trips (such as 2013 cargo biking Vancouver to San Francisco, and the 2018 Sun Trip solar bike race) and has finally come of age in 2019 with the V2 model when we switched to a wider and more rugged bearing, cable exit on the disk side, and a move to o-ring seals rather than silicone sealant for the side plates and screws for more consistent mass production and easier servicing. 

Marine Motor - PAUSED

UPDATE: The Marine Motor development was paused in 2022 as Grin needed to focus on updates to our core ebike kit offerings and manufacturing capabilities. We hope to resume this project in full capacity in 2024 and will email everyone who has expressed interest once we re-embark on this project. The marine motor axle design has been fully re-engineered to be stackable so that 2 or 3 motors can be added end to end.

We are actively developing a Marine version of our All Axle motor for people interested in electric sailboats conversions. The ~4kg motor can directly replace a much more massive diesel engine, and it is perfectly matched to drive the shaft 1:1 with no transmission required. Our standard width Grin motor with a 27mm wide stator can effectively replace an 8 horsepower engine, while a fatter 45mm stator option could replace a 12 hp diesel. This should broadly cover most sailboats with the 24-32 foot realm, or larger vessels if you don't mind being under powered.

We are planning to do a pilot launch of this motor in summer 2021 and are currently looking for potential pilot customers in BC lower mainland or Vancouver Island. Ideally these are people who have an existing sailboat with an inboard engine that is due for replacement, and with the drive shaft still in place. If that situation rings a bell and you have a strong interest in going electric, please fill out the google form below:

Where to Order

The Grin All Axle hub motors are available in stock at our shop in Vancouver and our distribution partner Grintech.eu in France, and also sold through dealers all over the world, including ebike-solutions in Germany, BikeToTheFuture in Switzerland, and BikeSwift in the USA