Is it legal to ride a bicycle with a self-installed motor around California?
<p>I'm going to California for a few weeks, largely the San Francisco and Los Angeles areas, and to save money (and time considering LA traffic) I plan to bring a bicycle with me and use that and public transport to get around.</p>

<p>Seeing as a lot of the rides are long and hilly, and I have a good deal of electronics experience, I'm strongly considering mounting a motor to the bicycle to make my commute a bit easier. <strong>Would a bicycle with a motor manually attached be street legal in California, specifically in Los Angeles and San Francisco?</strong></p>

<p>There are state laws pertaining to the operation of motorized bicycles (Vehicle code 21207.5. </p>

<blockquote>
  <p>no motorized bicycle may be operated on a bicycle path or trail,
  bikeway, bicycle lane established pursuant to Section 21207,
  equestrian trail, or hiking or recreational trail, unless it is within
  or adjacent to a roadway or unless the local authority or the
  governing body of a public agency having jurisdiction over such path
  or trail permits, by ordinance, such operation</p>
</blockquote>

<p>However, <a href="http://www.leginfo.ca.gov/cgi-bin/displaycode?section=veh&amp;group=00001-01000&amp;file=100-680" rel="nofollow">section 405</a> of the vehicle code distinguishes motorized bicycles and motor-driven cycles. Per 405:</p>

<blockquote>
  <p>A "motor-driven cycle" is any motorcycle with a motor that displaces
  less than 150 cubic centimeters. A motor-driven cycle does not include
  a motorized bicycle, as defined in Section 406.</p>
</blockquote>

<p>It does not matter if you do it yourself.</p>

united-states california traffic driving vehicle