I have a suggestion that could be brought up as an alternative.
Form a committee from the 4x4 users at the Evan's Creek Focus group meetings (that way PNW4WDA members and non-members can have input) to create a set of ratings and recommendations for the invididual trails, that can be put on signs and maps. The recommendations can include difficulty levels, tire sizes (maximums or minimums), width, wheel base, availability of lockers and winches etc.
Similar to what was done at Elbe. For example, Rainier Vista has a recommendation of 36" tires or larger, dual lockers and a winch. Sunrise has a recommendation of 31-33" tires and a single TAD.
At Evan's the 198 could have a recommendation of (for example only) 78" wide, SWB, 35" tire minimum and dual lockers, rated difficult. The 519 could say Offroad tires recommended, rated easy.
You get my point that proper signage and documentation made readily available to those who do and do not take advantage of the internet can help to prevent unnecessary damage.
We've been over and over the fact that tire size alone does not cause damage, it's the driver. Larger tires only have the potential to cause more damage. It's also well known that most bypasses are caused by vehicles (including quads) that end up in places where they don't belong, or up against obstacles that they cannot handle. Keep the right people on the right trails and we have fewer problems.
This is an alternate approach to providing the USFS with tire size limits or width limits for the park and to me (whatever that's worth to you) this is a better alternative for everyone.
President, Faithwheelers Offroad Club