I suggest you check the starting current of your motor, to see whether a 10A relay is sufficient. Regarding the snubber, I'm not an expert in this area, but 10nF sounds way too small to me, I suspect you need at least 1uF for a motor of that size.
There are vendors of alternative arc-suppression devices who claim that snubbers are useless in high-power applications, for example http://www.arcsuppressiontechnologies.com/Documents/Lab%20Note%20103%20-%20NOV2011%20-%20Snubbers.pdf.