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I ride Honda CD-100 SS, a 100cc motorcycle.

Does increasing the wattage of the headlight bulb affect the mileage(fuel efficiency) of the motorcycle? If it does please explain how.

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up vote 1 down vote accepted

If you're not increasing the load on the engine then mileage(fuel-efficiency) remains unaffected.

  • Primary source of electrical energy on Honda CD100SS is the magneto, an alternator that cuts magnetic flux from permanent magnets.
  • This alternator generates AC following the principle of Electromagnetic Induction
  • A battery is used as the source of DC. Battery gets charging current from AC generated from magneto after going through Rectifier-Regulator circuit.
  • AC so generated is fed through a Rectifier/Regulator, which performs AC-to-DC conversion, clipping higher voltages etc.
  • In most Indian motorcycles headlight is powered by AC coming out of regulator.

Coming to your question, when you replace say a 35W(12v) bulb with 50W(12v) then new bulb will not glow to its full capacity.

However, if you rewind the stator-coil to produce more current then technically more load is on the engine. This load from stator(magneto) will always be there whenever engine is on.

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Not by any amount you can measure, no. The power consumed by the bulbs are such a small fraction of the total that you would not notice it, unless you are adding multiple spotlights or going all retro-mod, maybe, like this pic from the Telegraph:

enter image description here

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