what causes my spur to be swiggly?

[BrianG]

blueb8llz: 86:21 is 4.09:1 ratio with a shaft to shaft distance of 22.2mm. A 58T spur and 14T pinion will be really close, but the shaft to shaft distance will be 30.16mm, so be sure that the motor can be adjusted that far.

brijar: 90/15 is 6:1 ratio. The 58T Jato spur and 10T pinion at 5.8:1 is the closest you'll probably get. IMO, 10T pinion is really small, and you'd probably be better off sticking to the 90/15 TBH.