the front opening dropouts are fine but.....i've always wondered what if any advantage they had?
Over your current arrangement? I don't know - I haven't tried your current arrangement.
For a singlespeed, using track ends means you need to move the wheel forward and derail the chain from the chainring before you can get the wheel back out of the slot. With a front-opening dropout you just release the wheel and move it forward and out.
With track ends and a derailleur, you pull the wheel back and out of the slot against chain tension, then I'm not sure what happens next. Do you need to pass the wheel back in front of the derailleur? My feeling is that it makes wheel changes more awkward, but again, I haven't tried that setup. I know the Karate Monkey uses a similar arrangement.
When I've used a derailleur on my Kilauea (which had track ends fitted by the previous owner) I used a DMR chain tug / mech hanger, which moves with the axle. That's awkward too.
alignment was required with each wheel fitting....even with the adjuster type screws
That shouldn't be the case: just pull the wheel back to the adjusters and fasten the quick release. If the frame alignment's good (and it should be) you don't need the adjusters - and anyway, aligning the wheel only takes a second.
and if the rider won't be experimenting with wheelbase length changes.....then the vertical dropout is the way to go
unless (as in your case) you want to keep your options open for fixed or singlespeed without a tensioner.
a track end just offers a simpler option.
I don't see why it's simpler - the slot opens to the front or to the rear.
It does offer the posibility of a shorter wheelbase, if that's important to you, and it means you can use a chain tug for extra security.
and.....if the wheel every slips forwad, there is a finite end.
That's true, but if the wheel slips, the tyre will hit the chainstay before the axle leaves the dropout. The wheel shouldn't slip, of course. You could run the axle hard up against the front of the slot on your bike, but it doesn't look as though the derailleur hanger was placed with that in mind.
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