Possibly looking for some rims

[ScottieJ]

I think your best bet would be to upgrade the rear shafts rather then change the wheels, I can't imagine a lighter wheel will really help that much.

[twiss]

I agree with scottie, if you are snapping shafts when the wheels touch down I would either a) stop slamming the wheels into the floor while they are spinning or b) replace the shafts with some that won't snap

I would replace the wheels if (for example) you were on spacers as well and had a short lifespan for wheel bearings, in which case you would get wheels with more offset (and remove the spacers) to reduce the pivot stress on the wheel bearings