{"id":2416,"date":"2026-07-14T05:08:40","date_gmt":"2026-07-14T05:08:40","guid":{"rendered":"https:\/\/speed-reducer-gearbox.com\/in-wheel-motor-planetary-reducer-compact-drive-for-evs\/"},"modified":"2026-07-14T05:08:40","modified_gmt":"2026-07-14T05:08:40","slug":"in-wheel-motor-planetary-reducer-compact-drive-for-evs","status":"publish","type":"post","link":"https:\/\/speed-reducer-gearbox.com\/hi\/in-wheel-motor-planetary-reducer-compact-drive-for-evs\/","title":{"rendered":"In-Wheel Motor Planetary Reducer: Compact Drive for EVs"},"content":{"rendered":"
\n

An in-wheel motor with a planetary reducer is the most compact and direct form of electric vehicle propulsion: the motor and gearbox are housed entirely within the wheel hub, driving the wheel directly without any driveshaft, differential, or half-shaft. This architecture eliminates the mechanical losses and packaging complexity of a central motor and long driveshafts, enables independent torque control at each wheel for traction control and active torque vectoring, and frees up the vehicle underbody for battery or cargo space. The planetary gearbox that makes this possible must fit within the wheel rim while still providing the ratio and torque density to match the motor output to the wheel speed.<\/p>\n

\"In-wheel<\/p>\n

Packaging Constraints of In-Wheel Drive<\/h2>\n

A 16-inch (406 mm) rim leaves a usable internal diameter of approximately 300\u2013340 mm after accounting for the tyre bead seat and the structural rim. An 18-inch rim allows 360\u2013400 mm. The planetary reducer \u2014 ring gear, planets, sun gear, and carrier \u2014 must fit within this diameter while delivering the required torque to the wheel hub. The ring gear is typically integrated with the wheel hub structure, eliminating a separate housing component and reducing weight. The motor stator mounts to the suspension upright, and the motor rotor connects to the sun gear input shaft of the planetary stage.<\/p>\n

Ratio and Torque Requirements for In-Wheel Applications<\/h2>\n
\n\n\n\n\n\n\n\n\n\n
Vehicle Type<\/th>\nTarget Wheel Torque<\/th>\nMotor Peak Torque<\/th>\nRequired Ratio<\/th>\nMotor Peak RPM<\/th>\nWheel Top Speed<\/th>\n<\/tr>\n<\/thead>\n
Passenger car, 18″ rim<\/td>\n2 000 N\u00b7m<\/td>\n250 N\u00b7m<\/td>\n8:1<\/td>\n12 000 rpm<\/td>\n210 km\/h<\/td>\n<\/tr>\n
Electric bus, 22.5″ rim<\/td>\n15 000 N\u00b7m<\/td>\n500 N\u00b7m<\/td>\n30:1<\/td>\n6 000 rpm<\/td>\n100 km\/h<\/td>\n<\/tr>\n
Forklift, heavy-duty<\/td>\n30 000 N\u00b7m<\/td>\n800 N\u00b7m<\/td>\n37:1<\/td>\n3 000 rpm<\/td>\n25 km\/h<\/td>\n<\/tr>\n
Mining haul truck, giant<\/td>\n500 kN\u00b7m<\/td>\n5 000 N\u00b7m<\/td>\n100:1<\/td>\n1 500 rpm<\/td>\n50 km\/h<\/td>\n<\/tr>\n
AGV warehouse robot<\/td>\n500 N\u00b7m<\/td>\n50 N\u00b7m<\/td>\n10:1<\/td>\n6 000 rpm<\/td>\n15 km\/h<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Wheel torque = motor peak torque \u00d7 ratio \u00d7 efficiency. Top speed = motor rpm \u00f7 ratio \u00d7 wheel circumference.<\/p>\n<\/div>\n

Unsprung Mass: The Critical Design Constraint<\/h2>\n

In conventional vehicle dynamics, the mass of components that move with the wheel \u2014 the wheel, tyre, brake disc, hub, and half-shaft \u2014 is called unsprung mass. High unsprung mass worsens ride quality and handling because the wheel cannot follow road irregularities as quickly when it is heavy. Adding a motor and planetary gearbox to the wheel significantly increases unsprung mass \u2014 a typical in-wheel motor system adds 15\u201325 kg per corner compared with a central motor arrangement. This is the primary reason in-wheel motors have not become mainstream in passenger cars despite their conceptual elegance: the ride and handling compromise is significant on normal road surfaces.<\/p>\n

The compromise is more acceptable in applications where ride quality is less critical \u2014 commercial vehicles, buses, agricultural machinery, and industrial vehicles. The EPB high-precision torque planetary gearbox<\/a> with its high torque density (high torque per kilogram of gearbox mass) minimises the unsprung mass penalty, and the EPF economy flange output planetary series<\/a> provides a cost-effective option for commercial vehicle in-wheel applications where precision is less critical than torque capacity and durability.<\/p>\n

\"In-wheel<\/p>\n

Bearing Arrangement for Hub Integration<\/h2>\n

The planetary reducer in an in-wheel motor must serve double duty: it provides the gear ratio, and its output bearing arrangement supports the wheel load. A conventional vehicle wheel bearing consists of a double-row tapered roller bearing or angular contact ball bearing that carries both radial load (vehicle weight) and axial load (cornering force). The planetary output carrier serves as the inner race of this bearing, with the ring gear or hub housing serving as the outer race. This integration saves weight and axial length but requires careful design to ensure the bearing preload is maintained through the full temperature range \u2014 thermal expansion of aluminium hub components relative to steel gears changes the bearing preload as the system heats up during driving.<\/p>\n

\"In-wheel<\/p>\n

Sealing and Environmental Protection<\/h2>\n

An in-wheel motor and planetary reducer are exposed to road splash \u2014 mud, water, salt, and tyre spray \u2014 that is far more aggressive than the environment seen by a nacelle-mounted motor or a gearbox in a machine room. IP67 is the minimum sealing requirement; IP69K (high-pressure wash-down at 80\u00b0C) is specified by some truck and bus manufacturers who pressure-wash vehicles regularly. The seal must also handle the constant rotation of the wheel and the articulation of the suspension \u2014 the seal interface between the rotating hub and the fixed suspension upright must accommodate 5\u201310 mm of axial and radial movement from suspension travel without compromising the IP rating. For comparable sealing challenges in marine environments, the HSRV stainless steel worm gearbox<\/a> demonstrates the sealing approach used in submerged or wash-down exposed drive applications.<\/p>\n

Frequently Asked Questions<\/h2>\n
\n
\n1. Why don’t all electric vehicles use in-wheel motors?+<\/span><\/summary>\n
The primary obstacles are unsprung mass (adding 15\u201325 kg per wheel degrades ride and handling on normal roads), packaging (fitting motor, gearbox, brakes, and bearing in the wheel rim is extremely tight, especially for passenger cars with small wheel diameters), and durability (the hub environment is harsh \u2014 high vibration, shock loads from potholes, and road contamination exposure). These challenges are manageable in buses, trucks, and off-road vehicles where ride quality standards are different and wheel diameters are larger.<\/div>\n<\/details>\n
\n2. What ratio does an in-wheel planetary gearbox need for a city bus?+<\/span><\/summary>\n
A city bus travelling at 80 km\/h with 800 mm outside tyre diameter has a wheel rolling at 80 000 \u00f7 (\u03c0 \u00d7 0.8) \u00f7 60 \u2248 530 rpm. If the hub motor peaks at 3 000 rpm, the required ratio is 3 000 \u00f7 530 \u2248 5.7:1 \u2014 achievable in a single planetary stage. For the heavy torque demand at bus stop acceleration (15 000+ N\u00b7m at the wheel), a two-stage planetary with 10:1\u201315:1 total ratio and a 1 000\u20131 500 N\u00b7m motor is more appropriate.<\/div>\n<\/details>\n
\n3. How is regenerative braking handled in an in-wheel motor system?+<\/span><\/summary>\n
The motor operates as a generator during deceleration \u2014 torque is applied to the wheel to slow it, and electrical energy is recovered to the battery. The planetary gearbox is back-driven in the same direction as normal driving; the gear mesh sees the same torque and speed as during driving. Friction brakes remain as a backup and for emergency stops; the control system blends regenerative and friction braking to maximise energy recovery.<\/div>\n<\/details>\n
\n4. What is the expected overhaul interval for an in-wheel planetary reducer?+<\/span><\/summary>\n
In clean automotive applications with sealed, oil-bath lubrication, the reducer should last the vehicle life without scheduled internal overhaul. The oil is sealed at manufacture and not a service item. Wheel bearings are the most likely service item at 150 000\u2013200 000 km depending on loading and road conditions. The planet gears and sun gear, operating well within their fatigue limits in most applications, rarely fail before the bearings.<\/div>\n<\/details>\n
\n5. Can an in-wheel motor be used in a vehicle with suspension travel above 200 mm?+<\/span><\/summary>\n
Yes \u2014 off-road vehicles with long-travel suspension use in-wheel motors with flexible power leads that can accommodate the full suspension travel. The gearbox and motor are fixed to the unsprung mass (wheel carrier), and the suspension spring and damper operate between the wheel carrier and the chassis in the normal way. The power leads route through a protected channel in the suspension linkage and must be specified for the full bending cycle count of the suspension travel over the vehicle life.<\/div>\n<\/details>\n<\/div>\n
\n

Speak with a Planetary Drive Specialist<\/h3>\n

Share your torque requirement, ratio, and application environment \u2014 our team at Condell Park NSW returns a sized recommendation and stock check within one business day. No obligation.<\/p>\n

\n
\n
ADDRESS<\/div>\n

27 Harley Crescent
Condell Park NSW 2200<\/div>\n

\n
PHONE<\/div>\n

+61 2 9708 3322<\/p><\/div>\n

\n
EMAIL<\/div>\n

sales@speed-reducer-gearbox.com<\/p><\/div>\n<\/div>\n

Send Enquiry →<\/a><\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"

An in-wheel motor with a planetary reducer is the most compact and direct form of electric vehicle propulsion: the motor and gearbox are housed entirely within the wheel hub, driving the wheel directly without any driveshaft, differential, or half-shaft. This architecture eliminates the mechanical losses and packaging complexity of a central motor and long driveshafts, […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[2917],"tags":[],"class_list":["post-2416","post","type-post","status-publish","format-standard","hentry","category-electric-vehicles"],"_links":{"self":[{"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/posts\/2416","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/comments?post=2416"}],"version-history":[{"count":0,"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/posts\/2416\/revisions"}],"wp:attachment":[{"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/media?parent=2416"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/categories?post=2416"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/tags?post=2416"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}