Finally got a bike.......

[IndyIan]

I agree. 10, 11, 12 is all marketing. What matters is the ratio difference between the smallest & biggest (e.g. 10-42 = 4.2:1). Once you get 9 or 10 gears, the steps between ratios are plenty small enough that having more (like 11 or 12) is totally irrelevant. In fact, it's counterproductive as it makes the sprockets and chain thinner and less durable, and the derailleur tuning more sensitive, and the cog heavier.


Reasons:
1. The stress/wear on any cog is divided by the # of teeth engaged. Bigger cogs = more teeth = less wear.
2. Bigger cogs are heavier.
For these reasons, the big cogs can be made of Al without wearing out too fast while staying light.
That said, 50+ tooth cogs seem excessive. A 30F - 42R is low enough that the max slope is limited by traction not gearing. And those super big cogs require derailleurs with long cages, especially when the small cog is a 10 or 11.

For real steep climbs, these bikes with bigger diameter tires and longer reach frames can get grip that makes a 30f-52r ratio useful. For 150lb xc racers with clipless pedals on their race bike and skinnier tires, they probably can get away with a less low gear and are limited by rear grip. For those of us with less power to weight and flat pedals, I still find the odd time I could use a slightly lower 1st gear on my trail bike with 22f-34r and a 26" rear wheel on a tricky spot. My kids design some trails that seem initially impossible but with some attempts and perfect line choice its kind of amazing to me what we can get up eventually.