Wheel balancing issue

So this isn't exactly Prius-specific, but I figured it was a good place to start. I have one of those cheap Harbor Freight Bubble Balancers for static balancing wheels. Got it because I use winter tires on my Prius, and didn't want to waste a ton of money and time getting them on and off twice a year, but the convenience of replacing my regular tires whenever I want. But no matter what I try, I cannot get repeatability on that balancer. I have confirmed the main shaft is straight (though a tiny variance to one side or the other shouldn't matter), I have used bubble levelers to check that the ground I put it on is flat on all planes, I have checked the tip of the shaft for burrs and irregularities, I have centered the bubble precisely after having it all set up, but it just doesn't work. Typically, the bubble will lean in the same direction every time, regardless of how the tire is put on. I have confirmed, to my satisfaction, that it is an issue with the cone, since rotating the cone causes the bubble issue to rotate as well (I never rotate the cone with a weight on it). However, with no tire on the cone, I can place a 1/4oz weight on the rim and watch it respond very precisely.

If anyone else here does their own balancing, I'd love to know if there's anything I'm missing before I junk this thing. Also, if you have a reputable bubble balancer that you like, I'd also love some suggestions if I give up on the HF model. Not going to spend $300 on a Coats brand, but I'd be willing to do more than the $50 I spent at HF.

Thanks.

 

So to clarify, I have 4 rims, and 8 tires. I also would need this when I get new tires due to tire damage or wear (I drive 30-40k/yr).

Exstudent: I mount my tires at home. I've had tons of problems in the past with being unable to get tires in a timely manner, and losing my car for a day getting work done. I work long hours, so I typically have to drop my car off for the day and find another way to make my 60mile commute to work while it's getting done. Unmounting/mounting my tires at home is incredibly convenient for me. I have also have numerous issues with tire mounting and balancing quality including, but not limited to: excessive/fraudulent charges, mounting irregularities, improperly balanced wheels, damage done to car while not in my care.

Tankyouong: I actually removed the ring and springs last night before I posted this. I had a vague notion that the issue might have been caused by one spring being too short/long/taught which might be throwing the level off. I did notice a difference without the ring, but still had problems. Very good chance that the problems I encountered with that was due to not having the tire perfectly level on the cone (which is what that ring is supposed to be for). Aside from simply eye-balling it, do you have any good tips/advice to make sure it's 100% properly seated without the ring? I'll probably give that another go.

Thanks to everyone who commented.