When you first start mountain biking, you’ll probably notice signage on the trail with a white or green circle, a blue square, or a black diamond (or two) on it. These shapes and colors are parts of North America’s mountain biking rating system and are used to tell bikers how difficult a trail is. Once you know what these shapes and colors mean, you can ensure you only ride on trails that fit your skill level, setting you up to have a more enjoyable experience while reducing your risk of injury.
Key Takeaways
- Understand the colors: White = easiest, Green = easy, Blue = intermediate, Black = advanced, Double-Black = expert only.
- IMBA sets the standard: The IMBA Trail Difficulty Rating System has been the norm across the U.S. and Canada since 2008.
- Difficulty factors: Narrower trails, steeper grades, larger obstacles, and taller technical features raise a trail’s rating.
- Ride within your limits: Picking the right rating keeps rides fun and reduces the chance of injury.
- Test every level at WildSide: Our Smoky Mountain park offers 20 trails—from white circle to double black—and a jump park for added thrills.
What Are Mountain Biking Rating Systems?
Like ski trail ratings, mountain biking rating systems usually contain a variety of colors and symbols that quickly communicate the difficulty of a trail to a mountain biker. For example, in North America, a white circle indicates that the trail is the easiest you’ll encounter, while a double-black diamond tells bikers that the trail is extremely difficult.
Around the world, you can find a variety of mountain biking rating systems, but for the most part, each system takes the same factors into account to determine how difficult a trail is. For example, a trail’s width, average grade (meaning how steep the trail is), maximum grade, tread surface, obstacles, and technical features usually factor into a trail’s rating. Some trail rating systems outside of North America may also include fitness level in their rating.
What Mountain Biking Rating System Does North America Use?
The primary mountain biking rating system used in North America is the International Mountain Bicycling Association (IMBA) Trail Difficulty Rating System. This rating system was created in 2008 and has become standard in the United States and Canada.
Around the world, countries have different trail difficulty rating systems that use different mountain biking symbols and colors to signify the difficulty of a trail. For example, parts of Great Britain rely on the MTB Trail Grading System, while other parts of Europe use the Single Track Scale.
Though different rating systems often have similarities with the IMBA system, it’s still important to check a country’s particular rating system before you go mountain biking outside of the US or Canada. Doing so makes sure you don’t end up on a trail that’s past your desired difficulty level.
Understanding Mountain Biking Trail Colors From the IMBA Trail Difficulty Rating System
-
White Circle — Easiest
Beginner-friendly trails, designed for new riders, families, or gentle cruises.
- Width: 72″ or more
- Grade under 5%
- Smooth, surfaced tread; no obstacles
Perfect for learning basic bike handling without technical stress.
-
Green Circle — Easy
Accessible trails with mild challenges for newer riders.
- Width: 36″ or more
- Grade up to 15%
- Unavoidable obstacles up to 2″
Great for building confidence and fundamental skills.
-
Blue Square — More Difficult
Intermediate terrain that demands balance, focus, and controlled speed.
- Width: 24″ or more
- Grades often exceed 15%
- Obstacles up to 8″; narrow bridges and TTFs to 24″
Expect unavoidable technical sections and variable tread.
-
Black Diamond — Very Difficult
Advanced trails with steep, rough, and highly technical sections.
- Width: 12″ or more
- Loose rocks and abrupt elevation changes
- Obstacles up to 15″; technical features to 48″
Recommended only for riders with strong technical skills and high fitness.
-
Double Black Diamond — Extremely Difficult
Expert-only terrain with high-consequence, unavoidable features.
- Width as narrow as 6″
- Steep grades over 20%
- Unpredictable tread and huge technical features
Only for fully confident, experienced riders.
IMBA Trail Difficulty Rating System Chart
Looking for a quick breakdown of the main features of each type of IMBA mountain biking trail? Review our chart:
White Circle — Easiest
- Trail Width
- 72" or more
- Tread Surface
- Hardened or surfaced
- Avg. Trail Grade
- Less than 5%
- Max Grade
- Max 10%
- Obstacles & TTF
- None
Green Circle — Easy
- Trail Width
- 36" or more
- Tread Surface
- Firm and stable
- Avg. Trail Grade
- 5% or less
- Max Grade
- Max 15%
- Obstacles & TTF
-
• Unavoidable ≤ 2" (50 mm)
• Avoidable may be present
• Bridges ≥ 36" (900 mm)
Blue Square — More Difficult
- Trail Width
- 24" or more
- Tread Surface
- Mostly stable; some variability
- Avg. Trail Grade
- 10% or less
- Max Grade
- Max 15% or greater
- Obstacles & TTF
-
• Unavoidable ≤ 8" (200 mm)
• Avoidable may be present
• Bridges ≥ 24" (600 mm)
• TTFs ≤ 24" (600 mm), deck >½ height
Black Diamond — Very Difficult
- Trail Width
- 12" or more
- Tread Surface
- Widely variable
- Avg. Trail Grade
- 15% or less
- Max Grade
- Max 15% or greater
- Obstacles & TTF
-
• Unavoidable ≤ 15" (380 mm)
• Avoidable may be present
• Loose rocks possible
• Bridges ≥ 24" (600 mm)
• TTFs ≤ 48" (1,200 mm), deck <½ height
• Some sections may exceed criteria
Double Black Diamond — Extremely Difficult
- Trail Width
- 6" or more
- Tread Surface
- Widely variable & unpredictable
- Avg. Trail Grade
- 20% or more
- Max Grade
- Max 15% or greater
- Obstacles & TTF
-
• Unavoidable ≤ 15"
• Avoidable may be present
• Loose rocks possible
• Bridges ≤ 24"
• TTFs ≥ 48", deck unpredictable
• Many sections exceed criteria
Go Mountain Biking in the Smoky Mountains at Wildside
If you’re looking for mountain biking trails near Pigeon Forge, Wildside can help. Our adventure park features 20 trails with difficulties ranging from beginner all the way to double black diamond, ensuring beginner and advanced riders can be challenged as much or as little as they want to be! We also have a jump park for adrenaline junkies, various manual and electric bike rentals, and over 11+ miles of trails for mountain bikers to explore.
Learn more about our mountain bike trails and rental options today!