Doug Deacon is the font of wisdom and experience in this area, other than perhaps the maker of your turntable.
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The only problem with using a 1" vs 1/2" belt is the ability to manufacture a pulley that would properly fit the shaft length of most commonly used motors. Obviously as pulley length increases, run-out error at the crown of the pulley is magnified if there isn't adequate shaft length on the motor to correctly "support" the additional mass of the longer pulley. Also, one needs to have adequate belt tension, and I think this might become trickier with the longer pulley.
That said, I think belt length depends on factors such as the diameter of your pulley, drive type (DC or AC), as well as motor pod design, turntable shelf design, and a host of other factors. I generally shoot for around 44" in circumference, but I also have been fiddling around with an idler pulley to increase wrap around the pulley and the platter simultaneously, so I've been trying to position my motor pod/pulley as close to the platter as possible, hence necessitating longer belt lengths.
My best advice is to cut a few different lengths, and listen for yourself. The differences will be fairly apparent - vibration suppression, available belt tension, tracking of the belt on the pulley/platter, overall noise floor, so-called "PRaT", etc are all affected by belt length. Good luck.
1. I haven't tried different lengths but the factors mentioned by Richard (Palasr) must all come into play. With so many competing factors, the "optimal" length is likely to be a compromise and quite specific to each setup. His advice to try several lengths was sensible.
2. Haven't tried Kapton, but the stripped holographic mylar I described in a thread a couple of years ago is superior to any other tape I *have* tried. Is there a source for Kapton tape that would work? I wasn't able to find one (several years ago).
3. Subject to the cautions noted above, wider tape provides a greater surface contact area with the platter and capstan. This should reduce slippage (good) but may also provide greater transmisibility of motor vibrations (bad). You win some...
4. Yes. ;-)
Frankly, I suspect that *any* decently implemented tape drive will perfrom so much better than whatever you're using now that these distinctions will seem insignificant, at least at first. Just do it and enjoy. Time enough for fussing after your ears adjust to the more lifelike rhythmn and drive you'll undoubtedly hear.