So true Jeep School. There really is no "official" trail rating system in California other than the Forest Service's "green, blue, and black (circle ,square, and diamond)" system. Most Trail ratings are based upon Off-Road publications like Charles Wells books. My club finds these rating to be highly inaccurate and too much on the conservative side. Many of these writers base trail difficulty on how difficult it was to get their stock SUV through the trail. The FS and state parks base their ratings on how difficult is is to get their stock 4x4s through.
Much like others have done, my club came up with our own trail rating system. We stayed with the simple 1-5+ system that many others use, but chose to be more specific with terrain descriptions and vehicle requirements. These trail ratings, along with our "newbies guide to joining runs", has really made it easier for new members and trail masters alike to organize and conduct runs.
1) Graded Dirt Road: Still passable by most high-clearance 2wd vehicles, however caution is required and lower speeds may be necessary. Small rocks (less than 5”) may be embedded in road surface. Some steep grades possible. May be muddy if wet.
2) Formed Track: Not passable by standard passenger vehicles. High clearance preferred, 4WD preferred. Steep grades present, larger rocks embedded in trail (less than 7”). Some loose trail surfaces and shallow water crossings possible. Sand and dry washes may challenge available traction requiring lower air pressure. Trail may be narrow and require backing to allow other vehicles to pass. Mud or snow may make traction difficult.
3) Formed / rugged Trail: High Clearance SUV or Truck required with low range gearing. Trail will be very rough and heavily eroded, with large, loose rocks present and steep, loose climbs requiring good traction and driver skill to negotiate. Wheel placement critical. A spotter may be needed to get through obstacles with minimal damage. Skid plates required, along with larger tires (31”+) necessary to prevent damage. Deeper water and mud crossings possible. Parts of the trail may be entirely in a wash, with loose sand and large rocks present. Possibility of rock ledges, and crossed axle obstacles. Good suspension articulation required to maintain traction. Sand Dune conditions may exist. Aggressive all-terrain or mud-terrain tires highly recommended. Low tire pressure necessary. 4-lo required for most of the trail.
4) Challenging Trail: High clearance modified vehicle required. Not within the capability of a stock vehicle without damage. Trail likely in river / wash bottom or narrow canyon with very large rocks present. Deep mud possible requiring aggressive tires and higher speeds. Water crossings in excess of 24” possible. Heavily rutted and crossed axle terrain present, with large ledges and very steep hills with embedded and loose rocks. Body protection, especially rocker protection, required to prevent damage. Stronger (or spare) axle and steering components necessary. Winching and extraction possible. Aggressive 33” tires, at least one locking differential, and flexible suspension required. 35” tires and dual locking differentials recommended.
5) Extreme Trail: Heavily modified vehicle with very experienced driver required.
Extreme rock crawling, with very large ledges and waterfalls present requiring winching. Body and drive-train damage likely. Very cambered terrain may cause roll-overs. Water crossings may be hood high, and mud may be very deep and heavily rutted. Rocks over 36” high encountered frequently. Vehicles will require heavy modifications. 35” tires required, along with front and rear locking differentials in upgraded axles. 37” tires recommended. Experience driver will be challenged by highly technical obstacles.
5+) Beyond extreme: Custom vehicle, very experienced driver required. Competition level vehicles on insane terrain with frequent roll-overs and drive-train damage. Full custom vehicles with massive axles, 37”+ tires, very low gears, 1 ton drive-train, custom chassis, and full roll cages with harness belts. Beyond the realm of most full-bodied rigs.