IMBA has come out with a method for rating mountain bike trail difficulty in the book Trail Solutions: IMBA’s Guide to Building Sweet Singletrack. It’s called the IMBA Trail Difficulty Rating System (TDRS) and, despite its flaws, it seems to be a pretty good start at standardizing trail ratings.
First off, IMBA makes a great distinction between technical difficulty and physical difficulty. The TDRS is only concerned with technical trail difficulty since physical difficulty can be objectively communicated through trail length and elevation change information. I totally agree.
IMBA outlines a number of things to consider when coming up with a difficulty rating like natural obstacles, psychological factors (like sheer cliffs on the side of the trail), and tread surface. They also recommend rating trails relative to other trails within the area or region, which I don’t really agree with. I mean, if we’re going to come up with a rating, why not have it translate from state to state and even country to country?
This is certainly an issue with other terrain difficulty rating systems like those used at ski resorts. Arnolda14 pointed this out in his recent comments and it’s certainly true: a black diamond slope at Beech Mountain in North Carolina won’t really compare to the black diamonds at Vail in terms of difficulty. I ran into this myself when I first moved from Georgia to North Carolina. The “easy” Colorado MTB trails according to the guidebooks I read were shockingly difficult compared to the “advanced” trails in Georgia. When I moved back east I experienced the same thing in reverse – every trail seemed overrated.
I really like most of what IMBA is trying to do with the TDRS and I’m interested to see how it catches on. Perhaps we could have users vote on difficulty ratings on singletracks using the IMBA criteria (outlined below) and see what we come up with. What do you say?