I've been looking at upgrading my R2 P45t headlight bulbs to H4 P43t ones on my R2 headlight assembly. I'm aware that there are H4 lamps with P45t mount, but there are not as many options available as H4 P43t lamps. So I've found out there seem to be P43t to P45t adapters such as these, or those from alternative manufacturers.
That'd be a perfect fit. Yet doing some more research, there seem to be some claims that these adapter are not optimal. For instance, in this forum:
Source: http://www.candlepowerforums.com/vb/showthread.php?347775-R2-vs-regular-h4-bulbs
Source: http://www.triumphrat.net/classic-vintage-and-veteran/636402-brighter-headlamp-2.html
Source: http://www.st1300.us.com/showthread.php?t=357
Source: http://britbike.com/forums/ubbthreads.php?ubb=printthread&Board=23&main=42437&type=thread
In summary, the adapters reportedly put the filament of the H4 P43t bulbs in a non-optimal location relative to the reflector, which results in an equally non-optimal focus point. However, there is no mention of by how much or in which way, and whether that could be corrected somehow. Particularly the latest statement mentions "could move the bulb off the focal point", which would indicate there has been no testing made to back these claims.
On the other side of the fence, one of the final replies from that last thread states:
Source: http://britbike.com/forums/ubbthreads.php?ubb=printthread&Board=23&main=42437&type=thread
And also http://dastern.torque.net/Mods/H4mod.html shows a mod to drill some recesses on an R2 headlamp fitting to accommodate the 3 tabs of a P43t bulb. That would locate the filament more or less at the same position as the adapter (perhaps 1-2 mm more into the reflector). No mentions of
That same page points at how tilting the bulbs can affect focus (http://dastern.torque.net/Mods/H4tilt.html), but there is no mention of what the optimal filament distance to the reflector is.
Finally, looking at side to side pictures of H4 P43t + adapter vs. R2 P45t, it appears to me that the filaments sit at the same height in both bulbs –roughly, the filaments are shaped differently. I'll try to post some pictures when I've removed the bulbs from my car later on.
In any case, given that this forum is where the experts live, I thought they could shed some light into this (no pun intended!).
Thanks!
That'd be a perfect fit. Yet doing some more research, there seem to be some claims that these adapter are not optimal. For instance, in this forum:
No. There is no way to make a regular H4 bulb (with its P43t base) fit or work correctly in a lamp designed to take R2 bulbs (P45t base). There are "adaptors" around -- they don't work.
Source: http://www.candlepowerforums.com/vb/showthread.php?347775-R2-vs-regular-h4-bulbs
Likewise, I'd advise against buying lens/reflectors that take the P45t bulb fitting (locates in the reflector with a series of lumps and bumps); fitting a P43t bulb with a "P43t to P45t adaptor" makes for a poorly-focussed bulb.
Source: http://www.triumphrat.net/classic-vintage-and-veteran/636402-brighter-headlamp-2.html
The P45t to P43t adaptor rings don't work -- they fail to put the bulb's filament in the correct place relative to the optic, and so the beam focus is grossly upset.
Source: http://www.st1300.us.com/showthread.php?t=357
2. Lens/reflector and bulb makers go to great lengths to ensure any bulb is on the focal point of any lens. Using the adapter (just so you can use the 'wrong' bulb) could move the bulb off the focal point of the lens, and you'll end up with the dreaded 'black hole in the middle of the beam'.
Source: http://britbike.com/forums/ubbthreads.php?ubb=printthread&Board=23&main=42437&type=thread
In summary, the adapters reportedly put the filament of the H4 P43t bulbs in a non-optimal location relative to the reflector, which results in an equally non-optimal focus point. However, there is no mention of by how much or in which way, and whether that could be corrected somehow. Particularly the latest statement mentions "could move the bulb off the focal point", which would indicate there has been no testing made to back these claims.
On the other side of the fence, one of the final replies from that last thread states:
To update, I have been able to test a selection of P43t H4 bulbs using adaptors in place of P45t H4 bulbs-which resulted in no apparent changes to the headlamp's beam pattern or focus, so as far as I'm concerned the adaptors do seem to work OK.
Source: http://britbike.com/forums/ubbthreads.php?ubb=printthread&Board=23&main=42437&type=thread
And also http://dastern.torque.net/Mods/H4mod.html shows a mod to drill some recesses on an R2 headlamp fitting to accommodate the 3 tabs of a P43t bulb. That would locate the filament more or less at the same position as the adapter (perhaps 1-2 mm more into the reflector). No mentions of
That same page points at how tilting the bulbs can affect focus (http://dastern.torque.net/Mods/H4tilt.html), but there is no mention of what the optimal filament distance to the reflector is.
Finally, looking at side to side pictures of H4 P43t + adapter vs. R2 P45t, it appears to me that the filaments sit at the same height in both bulbs –roughly, the filaments are shaped differently. I'll try to post some pictures when I've removed the bulbs from my car later on.
In any case, given that this forum is where the experts live, I thought they could shed some light into this (no pun intended!).
Thanks!