Wow. There is some really good, hardly ever found, information in this thread about proper tire balance. I am fanatical about tire balance and was cruising the net for information and came across this site.
Hennessy, is spot on in many ways here. Fact: You can balance an egg, but it won't roll down the road smoothly. Think about that. So, if the tire is not indexed on the rim correctly, it could create an out of round situation. Match the low/high spot of the tire with the low/high spot on the rim. If you have too perfect of a rim, though, it may not result in much improvement. Also, be sure the beads are seated properly. If they are not, they will mimic an out of round condition. Road Force reading are subjective: A snow tire should produce low road force figures - under 10 lbs. Think about it - they are soft and pliable. A low profile tire on a large rim? Not likely. They are harder, inflexible, and likely will result in higher road force figures. What's too high? Well, that depends on your vehicle. Vehicles with tight suspensions need lower road force figures. Larger vehicles with a suspension that isn't "sport tuned" can get away with higher road force figures. As an example, I run a 2014 Ford Explorer Sport. I can "feel" road force variation when the values are above 17lbs. Keep in mind that I'm in tune to the entire situation. Your average Joe may never notice it. My Blizzak snow tires road force at 4, 6, 8 7. My summer tires are Bridgestone and they are 8, 9, 12 and 17 I'm in the process of replacing the 17 now. My "standard" on this vehicle is 10lbs. or less. Again, it varies, widely, based on your vehicle. Don't assume road force is what is causing the shakes. You need to be certain what follows is done correctly before you assume an assembly with a road force figure of 17 is causing your "shakes."
Mounting the assembly - either use a bullseye collet from Hunter, or the appropriate adjustable collect from Haweka to BACKCONE the rim to the balancer. Tapered cones are hit or miss - mostly miss. Using a wingnut on the front is not as precise. You should insist on the use of a flange plate - a plate with fingers that mimic the mounting of the rim, by the lug nuts, to the hub. The idea with the cone, and the flange plate, is to exactly mimic the mounting setup you have on your car - hub bore and the lug nuts. If you don't, you're back to my analogy of the egg. You can balance an egg, but it won't roll down the road smoothly. YOU MUST BE CERTAIN THE ASSEMBLY IS CENTERED; OTHERWISE, EVERYTHING ELSE IS MOOT! Perform a centering check on the balancer before you move forward with road force and balance calculations.
Balance. Using a Hunter Road Force machine, turn OFF Smart (DUMB) Weight. Also, turn OFF the blind and rounding function. The balancer needs to be dialed in so it shows the TRUE static and couple readings. No rounding. Perform the balance in the standard mode - Smart (DUMB) Weight off, no rounding and no blind. Attach correction weights as indicated. Then, put the balancer in JUST static mode. If there is more than .25oz, apply correction weight based on the static output.
If you follow the above, you will have eliminated nearly 100% of the potential issues from the assembly (tire and rim) that lead to a vibration.
BE SURE THE ASSEMBLY IS CENTERED BEFORE YOU DO ANYTHING!
If you discuss the above with a shop, and they stare at you, or try to talk you out of it, thank them for their time and quickly walk away. It will take some time to find someone that will go through this; however, once you do, you will be happy the FIRST time they balance/road force/index. Not after the 4th comeback.