It depends a bit on what you're trying to do with it, are you racing on a track, or just bashing with it? That being said, 80/56 sounds like WAAAYYY too tall a gear ratio, even for playing around. I'd start with something more like a 4.12 FDR(which you can get with an 88T spur & a 48T pinion, assuming you're using 64 pitch gears), it may not be the perfect FDR, but that should be a reasonable starting point(for either racing or playing), should run much cooler & longer that way....