Trail difficulties are listed as a number next to each trail title. Any sort of rating system is subjective, so a "10" on our scale might not be the hardest trail in Arizona, but rather the hardest by comparison. Below, you can see what each rating level is like, and what the vehicle requirements are for each level of difficulty. Click images to enlarge.
Wide and graded dirt roads with minimal elevation gain, remoteness factor, and fear factor. Suitable for low clearance except after rain. May have some washboards but typically accessible by every type of vehicle.
Trails with a "2" rating will typically be semi-maintained roads (like forest service roads). Usually wide and graded although could have sections where it is narrower and rougher. Expect washboards and wash crossings where sand could be encountered. Enough room to pass 2 vehicles. Low clearance can do most trails although not recommended after rain. See trail description for case-by-case basis.
Rougher and narrow, these trails may be semi-maintained roads with rocks and washboards. Trails are typically wider but have sections where sharp drop offs and steep terrain could be encountered. Steep climbs and wash crossings make high clearance vehicles preferred. Stock vehicles with good clearance (like a Tacoma or a Wrangler) will do fine.
Majority of "4" rated trails will be narrow and rough. Two vehicles should be able to pass at most points. Expect long, semi-remote trails with long stretchs of sandy river bottoms and steep drop offs in the mountains. High clearance and 4-wheel drive needed. Stock vehicles should be fine on most of the trail but could scrape. Water crossings possible, especially after rain. Washouts likely.
Trails in this category will be long, rough, and remote. High clearance and 4-wheel drive required. More aggressive vehicles favorable. Stock vehicles can make it with careful driving but expect pinstripping and possible scrapes underneath. Trails are often narrow and rutted, where backing short distances may be required to pass other vehicles. Expect steep hills with dropoffs. Water crossings possible which could make trail impassable after rain.
Most of "6" rated trails will be slow-going and rough, where 4-Low may be needed most of the time. Large sections of rocks (like creek bottoms) with no bypass possible. Expect tight turns and narrow trails with steep dropoffs. Backing required to pass. Aggressive vehicles should have a small lift (at least 2") and larger tires which should be aired down. Deep sand possible in dry washes and mud/water possible after a rain storm.
Trails with a "7" rating require serious vehicle modifications like a lift (3"+), larger tires (31"+), and skid plates. Lower vehicles could scrape. Expect lots of ruts, rock ledges, and washouts on the trail. Prior 4x4 experience helpful and 4x4 recovery equipment not a bad idea.
Bordering on the edge of difficult, trails with an "8" rating require aggressive vehicles with lots of clearance and 4-wheel drive. Recommended 4" lift and 31"+ tires. Skid plates and lockers useful. Expect sections of ruts and rock ledges where rock stacking and/or good articulation is necessary. Water crossings up to 12" possible with the trail being impassable following a recent storm.
These are difficult, meaning experienced drivers in a capable vehicle required. Expect lots of rock crawling over boulders in 4-low. Only the most aggressive vehicles should attempt. Recommended 5"+ lift with 33"+ tires. Lockers, skid plates, hi-lift jack, and other equipment useful. Stacking rocks and using a spotter may be needed. Expect long, loose, and steep hills with dropoffs. Lots of trail erosion possible in the form of washouts and ruts. ATV's and smaller vehices should be skilled and use extreme caution.
The "10" rating is reserved for the most difficult trails which require the most capable vehicles and a seasoned driver. Serious vehicle modifications required. Massive lift (6"+), large tires (35"+), roll cage, winch, and other recovery items required. Not recommended for ATV's, UTV's, or dirtbikes due to steep and rough terrain. We've not come across a "10" yet but we haven't done much hardcore wheeling.