AGF Field Guide No. 07

Trail Difficulty Is More Than a Number

A trail rating describes the hardest unavoidable part of a route—not the average mile. Learn what the obstacles look like, what makes them worse, and why the same trail can feel completely different in two vehicles.

The AGF Scale

Read the Rating Correctly

The class reflects the most difficult obstacle you cannot reasonably bypass. A mostly easy road can still earn a higher rating because of one shelf, climb, ledge or water crossing.

1

Improved Road

Maintained gravel, graded dirt and broad access roads with predictable surfaces.

  • Usually suitable for ordinary passenger vehicles in dry conditions
  • Low clearance may still matter after storms
  • Expect dust, washboard and potholes
2

Scenic 4WD

Rougher two-track with embedded rock, shallow ruts, mild grades and limited room.

  • High-clearance vehicle strongly preferred
  • Four-wheel drive may be needed when wet or loose
  • Careful tire placement matters
3

Low Range

Technical terrain where contact, wheel lift, recovery or vehicle damage becomes realistic.

  • Low range and durable all-terrain or mud-terrain tires expected
  • Recovery points and recovery equipment required
  • Spotting and line choice become important
4

Serious 4x4

Large, steep or highly exposed obstacles requiring substantial clearance and experienced judgment.

  • Lockers, armor and larger tires may be necessary
  • Body, driveline and rollover risk are real
  • Travel with capable partners and a recovery plan
Illustrated Obstacle Atlas

What the Trail Actually Looks Like

These diagrams are intentionally simple. Use them to recognize the obstacle category, then evaluate its height, depth, slope, exposure, surface and available bypasses.

Usually Class 1–2

Graded Dirt Road

A broad, maintained surface with drainage, shoulders and enough width for normal traffic. It can still include washboard, dust and potholes.

Difficulty jumps when: rain softens the road, potholes hide sharp edges, washboard reduces control or snow blocks the crown.

Usually Class 2–3

Embedded Rock

Rock fixed into the roadbed rather than loose on top. The tire must climb it or the vehicle must straddle it without striking the differential or belly.

Difficulty jumps when: the rock is taller than axle clearance, angled toward a sidewall or positioned where there is no clean line.

Exposure Multiplier

Shelf Road

A narrow route cut into a hillside with a bank on one side and a drop on the other. Technical difficulty may be modest while consequences are high.

Difficulty jumps when: the road narrows, the outside edge crumbles, oncoming traffic appears or the driver cannot see the outside tire.

Usually Class 2–4

Off-Camber Section

The road tilts sideways, shifting weight toward the downhill tires. The vehicle may feel worse than the actual angle, but soft edges and tall loads matter.

Difficulty jumps when: the downhill side is soft, a rut increases lean, the vehicle is top-heavy or the line also climbs or turns.

Traction Test

Cross-Axle Obstacle

Opposite wheels compress while the other pair unloads. An open differential may send power to the tires with the least traction.

Difficulty jumps when: suspension travel runs out, a wheel lifts, the obstacle is on a climb or momentum would create a hard landing.

Clearance Trap

Deep Rut

Parallel trenches force the vehicle to ride inside the rut or balance on its edges. The center ridge can contact differentials, exhaust or skid plates.

Difficulty jumps when: the rut is deeper than axle clearance, the sides collapse, steering cannot climb out or water hides the bottom.

Depth Is Only One Variable

Water Crossing

Moving or standing water can hide holes, rocks, soft sediment and a damaged exit. Current can move a vehicle before water reaches the intake.

Difficulty jumps when: water is fast, visibility is poor, the bottom is soft, the exit is steep or depth approaches vulnerable components.

Surface Changes Fast

Mud

Mud ranges from a thin slick layer to deep suction. Tire tread, vehicle weight and the firmness below the surface matter more than color alone.

Difficulty jumps when: ruts swallow axles, the base disappears, the route slopes sideways or repeated traffic turns the exit into a wall.

Momentum Is Not a Plan

Loose Climb

A grade covered in gravel, shale, sand or loose rock. Tires dig and move the surface instead of pushing against a firm roadbed.

Difficulty jumps when: the climb steepens, there is a turn, wheelspin creates holes or stopping leaves no safe restart.

Geometry Matters

Turnaround Limitations

A dead end, blocked route or failed obstacle becomes serious when the trail is too narrow to turn around. Reversing may be the only exit.

Difficulty jumps when: wheelbase is long, visibility is poor, trailers are involved, the edge is exposed or multiple vehicles must reverse.

Vehicle Capability

Why the Same Trail Feels Different

No single modification defines a capable vehicle. Geometry, traction, durability, weight, driver judgment and trail conditions work together.

WB

Wheelbase

A shorter wheelbase turns tighter and usually improves breakover angle. A longer wheelbase can bridge holes and feel more stable, but it needs more room and may drag its belly over crests.

CL

Clearance

Look beyond the rocker panel. Differential clearance, belly height, approach angle, departure angle and breakover angle determine what actually contacts the terrain.

T

Tire Size

Larger tires improve obstacle rollover and raise axle clearance. The gain under the differential is only half the increase in tire diameter, and added size can strain gearing, steering and brakes.

L

Lockers

A locker keeps both wheels on an axle driving when one unloads. It can turn a wheel-lifting obstacle from a momentum problem into a controlled crawl—but it cannot create grip on every surface.

XP

Driver Experience

Good drivers read terrain early, place tires deliberately, use low range smoothly, know when to spot and turn around before a small problem becomes a recovery.

WT

Weight + Load

Roof tents, tools, water and spare parts change braking, suspension travel and center of gravity. A heavily loaded build may have less usable clearance and more off-camber risk.

One Obstacle. Three Experiences.

Vehicle Setup Changes the Margin

Stock Crossover

Limited Margin

  • Long overhangs and low underbody components
  • Road-focused tires may struggle on rock or mud
  • Electronic traction aids need wheelspin to react
Stock High-Clearance 4x4

Useful Baseline

  • Low range and better geometry improve control
  • Factory tires and steps may still be vulnerable
  • Driver line choice remains the deciding factor
Built 4x4

More Margin, Not Immunity

  • Larger tires, lockers and armor expand options
  • Extra weight and height create new limitations
  • A bad line can still break expensive parts
Trail Rating + Current Conditions + Vehicle + Driver = Actual Difficulty
Before You Commit

The Thirty-Second Field Check

Stop before the obstacle, get out and inspect it. The best recovery is the decision that prevents the vehicle from becoming stuck or damaged.

Look For

  • The highest point, deepest hole and softest edge
  • A tire line that protects differentials, rocker panels and sidewalls
  • Where the vehicle will lean, unload a tire or lose visibility
  • A safe place to stop, reverse or winch if the attempt fails
  • Whether the obstacle continues around a blind corner
  • Room for every vehicle in the group—not just the lead rig
A Rating Is Information—not Permission.

Trail access, closures and legal vehicle use must be verified separately. Stay on the designated route, avoid creating bypasses, and leave the trail in better condition than you found it.