In reply to Damo:
> Yep
> And not only that, the conversions have changed over time. I'm in Australia, have only climbed a little rock in the UK and none really in the US. But what constitutes '5.9' in the USD has ranged from 17 to 21 at various times in the 20 years I've been climbing! So I'm very wary of any mountain rock graded 5.9 as I can always grunt my way up a 17 but might easily fail totally on a 21.
In reply to Jonny2vests:
> YDS is the weirdest because not even guide book authors can agree on a definition.
YDS has some interesting historical artifacts that can make grades strange, especially in the above-mentioned 5.9 range.
Originally, YDS was a closed system from 5.0 to 5.9 -- so 5.9 was the hardest climb that someone could do. Of course, it took a fair bit of ego to climb something and then say it was the "hardest possible" so a lot of tough stuff would get graded 5.8 or 5.8+ as well. So routes that were done and graded in the early days could be far harder than one might expect and still be graded in the 5.8 - 5.9 range. And, as we all know, once a route has been given a grade it takes a LOT to change the historical grade of a route, even if it has become quite a sandbag.
Also, originally YDS was a "single hardest move" grading system. (Comparable to the technical grade of a UK trad grade). Over the last 15-20 years, this has generally evolved to being a "overall difficulty of the climb" type grade, taking into account hardest move, sustained series of moves, rests available, overall sustained work needed for the climb, etc. This can, also, make comparing grades in YDS across generations of climbs (and climbers) tricky.
(I expect there was probably a similar situation with HVS/Extreme before Extreme got extended into E1, E2, etc. But I don't know the history of UK grading as well as I do North America.)
But, if you are climbing in North America, and you are climbing a route that was first climbed before (about 1990) and the grading is in the 5.8+ to 5.9+ range, take a good look at it before getting on it. There's a local 5.8+ route that I went after with a few friends... a couple of them on-sight in the low 11s and project low 12s, but could only get the crux by pulling on a draw. (The route is very well protected, with a bolt at the crux, and only the one very hard move -- the rest is a bit stiff for the grade, but ok. So... maybe a VS 6A climb.