Strange Vibration

My 98GP has a strange vibration in the steering wheel between 105 and 115 km/H. This vibration is not present below 105 or above 115. Any ideas?

My bet would be a tire is slightly out of balance.

The tires are just three weeks old. They are Toyo brand. I bought those because I had two on the front 18 months ago after the belt on the original was out of place so I decided to make a complete set. I'll return to the shop next week.