Increasing nose tire drag with low air pressure or bearing drag, will result in an increased tendency for the nose wheel to tuck under during a botched landing.
It seems to a pretty common for there to be misunderstanding with some of the terminology used when describing things related to the nose wheel so here is a little clarification.
The reason lower nose wheel tire pressure reduces the tendency of shimmy isn't because it is increasing the rolling resistance (though that probably has some influence). It is because it is increasing the contact footprint of the tire on the ground/runway.
If you use a high tire pressure, the tire doesn't compress very much and there is very little contact area of the tire on the ground. In a severe case the contact area might only be 1" wide (laterally). This provides very little scrubbing resistance on the ground. I.E., there is much lower resistance to it pivoting in the yaw axis, so it will be much more susceptible to shimmy.
There is a balance point regarding having enough pressure for the amount of weight on the nose wheel but not having too much, and Walt is correct that getting the nose pressure too low can reduce the safety margin from a failed nose gear, but arbitrarily pumping the tire up to a high pressure can induce serious problems as well.
Also, proper pressure is not going to be the same for every A model RV, because they have different engine / prop combinations, and other variables which cause differences in C.G. (that is why the tire pressure range mentioned in the SB is so wide).
Aircraft loading is a factor as well.
A lot of nose tire pressure, a lower than ideal nose fork breakout friction, and an aft C.G. landing are the perfect storm for having a severe nose wheel shimmy event.
All of the factory 2 seat A model RV's have had the nominal nose pressure established visually with the airplane parked on a smooth level surface.
The pressure is adjust until there is about 1/2" of contact area of tire lifted off the ground surface on each side. This leaves a generous footprint of the tire in contact with the ground
-Side bar- The shimmy I am talking about here is the lateral pivoting movement of the nose fork in a resonant manner.
The forum is full of conversations with people taking about nose wheel shimmy where they were actually talking about the fore/aft shimmy that the
leg can make in certain situations. usually caused by excessive drag in the nose wheel bearings/seals, and out of round tire, and out of balance wheel assembly, or a combination of any number of these.
The conversations often diverge into people giving advice for one when the question was actually about the other. Adding to the problem is that because there are two different actions where the same term is often used, a person sometimes doesn't seem to be sure what problem they even have..... all they know is someone saw them land and said they had a nose gear shimmy.
Bottom line.... if you feel something that is pretty violent when the nose wheel first touches down.... it is nose fork rotational shimmy that you are dealing with. It should be fixed before the next flight or you could cause some serious damage.