Trail Difficulty Guide

Our friends at the International Mountain Biking Association have created a stellar rating system for trail difficulty.  The IMBA system encompasses trail grade and surface as well as natural obstacles and technical features, and is intended to rate only technical challenge, not physical exertion.  BMA has adopted the IMBA ratings for our trail guide, and also provides a more detailed TAC rating for those who really wanna geek out with a combined system for Technical, Aerobic, and Coolness factors.

Do you disagree with BMA's rating choices?  We'd love to hear your feedback!  Send us an email at trailinfo@bouldermountainibike.org.

Easiest

white circle

White Circle

Easy

green circle

Green Circle

More Difficult

blue square

Blue Square

Very Difficult

black diamond

Black Diamond

Extremely Difficult

double black diamond

Double Black Diamond

Trail Width

72" or more 36" or more 24" or more 12" or more 6" or more

Tread Surface

Hardened or surfaced Firm and stable Mostly stable with some variability Widely variable Widely variable and unpredictable

Average Trail Grade

Less than 5% 5% or less 10% or less 15% or less 20% or more

Maximum Trail Grade

Max 10% Max 15% Max 15% or greater Max 15% or greater Max 15% or greater

Natural Obstacles and Trail Technical Features (TTFs)

None

Unavoidable obstacles 2" tall or less

Avoidable obstacles may be present

Unavoidable bridges 36" or wider

Unavoidable obstacles 8" tall or less

Avoidable obstacles may be present

Unavoidable bridges 24" or wider

TTF's 2' high or less, width of deck is greater than 1/2 the height

Unavoidable obstacles 15" tall or less

Avoidable obstacles may be present

May include loose rocks

Unavoidable bridges 24" or wider

TTF's 4' high or less, width of deck less than 1/2 the height

Short sections may exceed criteria

Unavoidable obstacles 15" tall or greater

Avoidable obstacles may be present

May include loose rocks

Unavoidable bridges 24" or narrower

TTF's 4' high or greater, width of deck is unpredictable

Many sections may exceed criteria