Originally Posted by BushwackerinPA
triple just causing shifting problem and most MTB doubles can be geared pretty low. 24/36 with a 11-36 cassette on 26er is a great way to start, for a 29er 24/34 12-36 would probably great. Another reason for doubles in much increased clearance over trail rocks and logs which you have less of out there but still some. 36x11 on 26 inch wheel at 100 rpm is 25 mph. Trust me you will be no where near 25 mph on any singletrack while trying to pedal. your lowest gear(24 F 36 R)if you run a 11-36 rear cassette is about 100 rpms at 5 mph. the other thing you need to realize is climbing on a MTB is quite often not as steep as roads climb because the dirt would fall apart if it was. ...
I'll start w/ where I agree w/ Bushwacker:
Clearance. Do the trails you will ride regularly feature lots of large rocks, square-edged-obstacles, & logs?
If so, you probably would be well advised to skip the 40+ tooth front ring and go with a double setup like Bushwacker recommends.
The majority of Moab locals, for example, ride single or double ring front setups, due to the near omnipresence of sandstone outcroppings & large rocks riders have to constantly grind & "leverage" themselves over.
I must admit I have to scratch my head at the assertion that offroad climbs tend to be less steep than road climbs. Never mind the 30%+ walls you'll find out on the UT slickrock, I've climbed dirt trails in the 25-30% range on three continents, and with the exception of Lombard St. in SF at 27% (which has been made a pedestrian zone, so the cars don't get stuck) I cannot recall another pitch this steep that road engineers have bothered to pave (roads with sustained pitches over 20% are scarce enough that the Giro organizers have had to resort to racing up gravel roads to Plan de Corones in recent editions).
If you're looking predominantly at woodland trails with lots of flow, or lots of long, consistently graded double track descents & climbs, I see no reason why you should limit yourself to a double, unless you score a killer deal on a bike set up that way.
4 out of 5 all-mountain component kits offered by Santa Cruz, for example, feature triples. Properly set up they work well.
You mention that climbing isn't your strength: 24F/36R rear on a double is pretty much the same gear as 22F/34R you'd likely run on a triple, but of course the triple still offers you the option of "going big" and running the 36R if you chose, plus a 42 or 44 big ring to hammer down long, sustained downhills - in case you're an impatient type like me, who often feels that gravity needs help ;~>
My personal philosophy of "broader range = broader smiles" is clearly the polar opposite of the singlespeed mindset Bushwacker is coming from.
As for YOU, you indicate that you like a triple on the road, and aren't a flyweight climber type.
On this basis, I'll go out on a limb and encourage you to likewise go for the widest gear range allowed by local trail conditions.
As I've gotten older, I've extended the gearing range on *all* my bikes, and as a result I experience far less knee pain than I did even in my teens & twenties when I used to climb with a straight-block on the road.
Some guys seem to be blessed with indestructible joints: if they're happy grinding on an SS, God bless 'em.
For those less blessed, there are always more rings.