Honda NBC110 Component Material Analysis – A Space for My Projects, Thoughts, and More…

This post covers a simple analysis of the major component weights and raw materials of a 2016 Honda NBC110 motorcycle, acquired from a crashed donor bike purchased to provide parts for my daily rider. Missing from the list are the rear wheel and sprocket, cylinder head (located elsewhere at the time of writing), battery, and various other small components and fasteners.

For reader reference, the NBC110 (Seen below) is a 110cc commuter motorcycle with an 8hp 4-stroke SOHC engine, four-speed transmission with automatic clutch, and an enclosed chain final drive. It is a member of the SuperCub lineage, which Honda have been producing since the late 1950’s.

Material Breakdown and Costs

The measured weights sum to a total of 79.865kg, approximately 18kg short of the 98kg rated dry mass of the vehicle. For each component, an estimate was made of its primary, and secondary material fractions by weight, e.g. 70% steel, 30% aluminium. Tertiary and further materials were included in the spreadsheet where appropriate but were not used for the breakdown due to their minimal contributions.

Steel makes up the majority of the total at approximately 60kg, with aluminium comprising 9.44kg, plastic 7.64kg (Primarily Polypropylene), and copper 0.853kg. This leads to an estimated raw material cost of $66.3USD, predominantly (~75%) made up of steel and aluminium in equal amounts, and the remainder divided between copper and plastic. Raw material market prices were taken from (1) and (2).

(1) Daily Metal Price: Free Metal Price Tables and Charts

(2) Polypropylene (PP) Price Index, Trend, Chart, Cost, News

Weight Fractions by Component Category and Considering an Equivalent Electric Vehicle

One motivating factor behind this analysis was to better understand the design impacts associated with a switch to an electric vehicle (EV) drivetrain, from one built on the traditional combustion engine (ICE). In particular, the achievable range of electric vehicles is an often-cited concern due to the poor energy density of chemical batteries when compared to petrol. Even taking into account the inefficiencies of a petrol engine (75% loss under good conditions), mechanical work out per unit mass is still in favour of petrol by a factor of 10-20 (3kWh/kg vs 0.15-0.3).

One of the key advantages of electric drivetrains however is the comparatively high-power density and torque characteristics of modern electric motors, which allow for significant reductions in the size and complexity of the driveline. This can make space to pack additional battery capacity, helping to erode the gap between real world electric and ICE vehicle range.

In order to access the impact on vehicle weight, we first determine the required battery capacity to deliver a range equivalent to that of the standard 4L fuel tank (~250km). With a density of 0.75kg/L and an engine efficiency of 25%*, the equivalent stored useful energy of petrol is 9kWh. This corresponds to a battery mass of 30-60kg.

*Transmission loss is assumed to be similar to electric motor inefficiency, so it is ignored for simplicity.

From the below chart, it is apparent that the primary engine components (Engine, exhaust pipe) make up some 24% (23.1kg) of the total 98kg vehicle weight. This aligns with the rated engine weight of ~25kg, which suggests a cylinder head weight of around 2kg. Auxiliary engine components (airbox and throttle body, wiring looms and throttle cable, electrical components, fuel pump) making up another 5% (4.73kg). The fuel tank itself, which was not included in the auxiliary components category, makes up an additional 2.35kg.

Electric Motor Weight Estimate

Eliminating the engine and associated systems will thus save approximately 32kg, however the weight of an equivalent power electric motor and controller must be included for fair comparison. Of the many commercially available options, the specifications of several are outlined below, for both mid-drive, and hub (In-wheel direct-drive) configurations, with rated powers from 1-8kW continuous. The electric motors compare favourably, delivering specific powers up to almost 0.65kW/kg, over three times that of the 110cc engine (0.18kW/kg). Motor specific power does vary significantly however, with as low as 0.091kW/kg for a 1kW hub motor, likely due to the low RPM of a hub motor, and size scaling limitations at lower power.

For the EV case, a reference 6kW motor with a specific power of 0.6kW/kg is used (10kg motor mass). This specific power is on the high end of the options considered, however this can be justified for several reasons:

The weight of the fuel tank was not included in the engine categories, which gives a 2.35kg margin for the EV case to account for the controller and any other required components.
While the NBC110’s engine is rated at 5.8kW, sustaining such output is damaging. Electric motors by comparison are not impacted by operation at their rated powers, and can even reach much higher peak powers without damage. For this reason, it would not be unfair to compare the ICE against a smaller electric motor.

Comparing the ICE vs EV Vehicle Case for Equivalent Range

Finally adding up the vehicle components for the original ICE driveline compared to EV equivalents, we can see for the optimistic 300Wh/kg battery capacity case, the total vehicle weight only increases by 8kg (8.2%) from the original 98kg. This represents a replacement of the 25kg engine and 7kg associated components, with 30kg of batteries, and a 10kg electric motor, retaining the original power output, and 250km expected range.

For the150Wh/kg lower bound for battery capacity, the impact on weight is much greater, increasing to a total of 136kg to maintain the 250km range*. Such a weight is still within the range of typical motorcycles however, and so even in this case the 250km range could be maintained.

*Because of the poor drag coefficient of motorcycles, at high speed the majority of driving power goes towards overcoming air resistance, so we can plausibly neglect the impact of the additional battery weight on range.