Lately I have sen a few pics and videos,on YouTube, that show a view of the rear cassette. I have noticed that the largest cogs is SIGNIFICANTLY bigger that the second last one.
Can someone help me understand this? I know it give more climbing ability but...
Thanks!

Some cassettes are marketed with that as a feature - they combine fairly closely spaced cogs so you get close-spaced gear ratios in normal riding with one really large 'bail-out' cog to use when climbing really steep grades. The idea is that for the rare particularly steep grade you won't care if you've got exactly the right gear - you just want a low enough gear so you won't have to walk.

Some people like the idea - others don't.

You mean like this? They've had 'em for a while.



Like prathmann said, some people really love 'em, others don't. When I'm bogging down climbing a hill, I like my downshifts to be meaningful, but not too wacky.

The freewheel that ThermionicScott shows above are a 'cross over' freewheel with granny. Cross over gearing, not to be confused with cross chaining, uses a 10 to 12 tooth difference in the front chainrings. You downshift from 7 to 6 to 5 to 4 in the large chainring, then shift 4 to 3 to 2. If you need to really go low, you can make a very large jump to 1 on the freewheel. By that time, you are probably going slow and won't really notice the very large jump. This type of gearing can be combined with front triple to very good effect. If done properly, the gears outside of the cross over are duplicated so you don't need to ride in a cross chained combinations.

The seven speed freewheel is probably the most number of gears you want to use for a cross over system. It works very, very well with a 5 speed freewheel. As you get to 8, 9, 10 and now 11 gears, the steps between gears is so small that you can run up and down the cassette while only worrying about the extremes.