Trying to get an "A" model that doesn't shimmy is like trying to find a smooth shopping cart at WalMart.
Breakout force, tire pressure, type of tire and weight on front wheel all affect.
I had a lot of experience with a Velocity trying to eliminate shimmy which is a much more difficult issue due to no weight on wheel and lower breakout forces (you can't go too tight as the wheel slides in turns)--Also, there's no stops so when shimmy gets a good wiggle going it can literally destroy the fairing and even the fork assembly. My eventual fix was a locking nosewheel. (Here's a link)
http://www.velocityaircraft.com/news...eel%20Lock.pdf
Breakout force--Grummans, Velo, RVs, etc all call for at least 22lbs of pull before the fork moves. Get the nosewheel off the ground and pull with a luggage or fish scale at (or even with) the axle. On an RV you can go significantly higher--your only concern is to keep it loose enough that the nosewheel swivels in flight otherwise you'll have an uncontrollable rudder out front. We've got a few RVs here with 30+ pounds on the pull with no adverse affect. This is the most common issue as they tend to loosen up over time. Take several readings as it will vary.
Tire pressure--key here is amount of rubber on the runway. On some tires as you increase the pressure, the tire eggs and lower/outer portions of the tire no longer contact the ground. The small amount of wobbling this can cause may initiate a shimmy. (Less side to side movement resistance)
Weight on wheel--larger engines and constant speed props get more tread on the nosewheel contacting the surface as well as providing more movement resistance.