Look at the H4 halogen bulb, top tab is straight up in a USA car but the bulb is slightly twisted. the shield is not flat.
But if you look in your motorcycle headlight you will see that the tab is offset which makes the bulb and shield level which makes for a flat beam.
You're taxing my memory about all of this Dave, and you might well be correct. I haven't seen an original Honda bulb in a long time, and I didn't pay attention when I removed my G6 the other day. The below is from memory, so it may not be accurate because as we all know, memory is not always the best technical resource.
The flat beam pattern is the motorcycle standard everywhere except North America, which is part of why Honda sells the proprietary bulbs here- I think, see below.
North American headlamp housings and motorcycle headlamp housings do not have the upper tab notch in the same location due to different lighting regulations in North America compared to almost everywhere else, and is part of the reason why many motorcycle have these different bulbs that don't match what is in our cars in North America. Many motorcycle have these different bulbs by the way, it isn't just the ST1300.
North American automobile headlamp housings have the notch for the bulb base upper tab at exactly 12:00. A North American automotive 9003 bulb base installs with the upper tab to match at 12:00, but the bulb is mounted to that base offset- I thought that it was 15°, which provides the up-tilt of light on the right-hand side. In a motorcycle headlamp housing the notch for the bulb base upper tab is not at 12:00. It is slightly offset from 12:00. This is because most other countries outside of North America use standard automotive bulbs in motorcycle headlamps. This offset notch in the motorcycle headlamp housing causes the automotive bulb to be orientated so that the bulb filaments are rotated back to horizontal when they are installed in a motorcycle headlamp housing. This cancels out the up-tilt and results in a flat beam pattern. The flat beam pattern is so that the motorcycle headlamps meet the anti-glare requirements of all countries regardless of what side of the road they drive on.
These LED bulbs are made to the automotive standard, not the motorcycle standard, so they will have the bulb mounted off-set on the base as well when they are in the 9003 specified orientation. When they are installed in a motorcycle headlamp housing, this offset is cancelled out the same as it is with the 9003 bulb. These LED bulbs can be rotated in their base to fine tune the beam pattern as one wishes however. Again, from memory, this was an intended design feature so that these bulbs could be used in the automotive markets of both left-hand and right-hand drive countries, not to suit the motorcycle industry.
You now have me wondering how much of the above I am misremembering. Some of it is from reading posts that
@spiderman302 has made over the years. Maybe he can chime in and correct whatever I have stated that is wrong for the benefit of us all, as long as he doesn't make me stand in the corner for getting it wrong.
As a side-note, I preferred the flat beam because I found that these bulbs are so bright that when I had the right-hand up-tilt and I was traveling on a multi-lane road to the left of other vehicles at night, these bulbs shined so brightly in the mirrors of the vehicles that I was passing that I was blinding the drivers of these vehicles going in the same direction. Having a flatter beam pattern helped avoid this and did not detract from illuminating road signs in any significant way.
