Was that tested on a SkyRC 2s type of tester? If so, 10.5 amps is way high for a 17.5. Cut that in half. You're going to get two different answers from the community. Some are setting 17.5s around 40 degrees of timing. The 40 theory being that the motor will have more torque. Others will say closer to 50 degrees - the thinking being that these motors have so much torque anyway that you don't lose anything by cranking more amps into them and getting more overall RPMs.

I use a SkyRC 2S for my initial setting, looking for between 4.5 and 5 amps. On some motors that happens at 42 degrees and on others it takes closer to 50 degrees. SkyRC testers are ok, but are tested without load on the motor. It is a good way to get a quick starting point or make a quick adjustment at the track. Inertia dynos help to see real differences in motors and timing settings. I use both, so the SkyRC between 4.5 and 5 amps is usually close to where each motor ends up on the Mini-Pro dyno. The Mini-Pro provides evidence on how to gear two motors differently (4.5 to 5 amps on an X-Factor will produce a different torque curve than a R1 Shorty) and which motors are slightly better than others.