Just got my new orion 10.5. I was using the gearchart.com but I dont think its right. I found a 94t 64p spur. Im trying to get to around 5.5 ratio. The 94t spur is smaller than the stock 87t 48p. Any how does anyone have any idea what would be a good starting point for the 94t 64p spur for the 10.5 orion. Thanks in advance