Why does my tire shake?

Best thing to do is have the tires balanced and rotated and ask them to inspect the CV axles https://partimages.genpt.com/largeimages/719837.jpg while the tires are off the vehicle, Because if the wheel weights came off one of the tires it will come in and out of balance at a certain miles per hour every time. If they determine the axle needs replacement you can check that estimate here www.repairpal.com/estimator put in your vehicles info and choose axle shaft replace and if you need to find a shop www.repairpal.com/directory

The most common cause of high speed tire shakes is going to be wheel balance, but that is not to say that tire balance is the ONLY factor that can cause that vibration/shake. Other factors such as out of round tires, tire wear (cupping), U-joints, and various loose or damaged front end parts can cause vibrations/shakes as well. Here at Top Tech Automotive/Newbill's Alignment we do a thorough alignment check that fully diagnoses issues such as this, and will get you back on the road in no time.

I once owned a car that also began shaking at higher speeds only to find my wheel... not tire... was out of round.

I had the same issue it was the left tire rod but they call it the left arm controller or something like that. Around 50bucks at oreillys and mechanic put it on for 30 bucks..