Even though I started this thread, I still don't have a GNG (yet). Here's my take on belt/chain primary on the Gen-1 from reading dozens of GNG builders reports.
The belt is quieter than the chain. If you don't mind a little chain noise, just start out with a chain primary and make some kind of a cover for it, to keep out dirt and make it as quiet as it can be. If you want the performance of 60V/72V, and going to 35A/40A/45A...just plan on starting out with the chain, whether it's a DIY #25 or the upgraded LightningRods #219 kit (available soon).
If you want the quietness of the belt, the engineering data suggests that a GT2 belt that is 20mm wide and has a minimum of 18T should work great and last a long time. I think there is a very big market for a 48V system that is fairly quiet. I suspect the #219 primary will be quieter than the a #25, due to thin #25 sprockets "ringing". I also suspect that once a proper safety/dirt cover is developed, the noise level from the primary drive (whether #25/#219/GT2 belt) will be improved a surprising amount.
If you have a stock kit, and you want it to continue to run until the upgraded components are available: hand sand the sharpness off of the stock belt driver teeth, buy a Goodyear belt as the next replacement, adjust the phase amps (full power at top speed, but no wheelies from a stop), and limit the max amps (I know, hard to do when there is so much fun available on tap at the flick of a wrist).
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Concerning the holding power of the "soon to arrive" GT2 belt-primary. the stock 14T has five teeth fully engaged at any given time (if you remove the excessive-wrap idler that consumes 100W), and they are 15mm wide.
The 18T driver should have SEVEN teeth fully engaged. Two more teeth out of five is a 40% increase in holding power. Now, take that resulting 'torque holding' limit, and multiply it by another 30% increase in belt/pulley width (5mm wider than 15mm). 100% of stock belt power X 1.40 = 140% of stock, X 1.30 = 180% stronger than the stock set-up.
By going to an 18T driver, the diameter of the pulley is large enough we can use a larger belt-tooth, like the 8mm pitch instead of the 5mm. The Gates belt data PDF states "...[GT2-8mm has]
Twice the HP capacity as HTD®...", sooo...take 180% and double it = 360% better torque capacity than the stock GNG.
Not sure about epoxy when it heats up at 7000w. There is JBweld that is better suited for motoparts, but will see.
