Newbie in need of some help please....
 

Just bought my K2 Attack 2.0 about 2 weeks ago. got it for a steel because the crank needed replacing. I replaced the crank with a Truvativ 175mm crank with a 48/38/28 cog set up. After replacing this i can to find my derailleur wasn't up the the challenge of using all three gears (the new middle gear is 2 teeth smaller then the old largest gear). So i'm in the market for a new front derailleur but i don't know what im looking at or where to start. Some research i did is telling me a Shimano 105 but apparently it makes a differnce what your cog setup in the back is and i can only find setups for 9 and 10 speed in the rear and triple fronts when i need a 8 speed rear triple front. does this rear cog suggestion make a difference?

This is best asked in the Mechanics Forum

Excellent idea. Moved to Mechanics.

1. Are you sure your existing front derailleur can't be made to work? What happens if you move it up on the seat post to clear the new larger big ring?

2. Do you know why the crankset on your bike needed to be replaced?

3. Is it possible to replace the chainrings on your new crankset with some smaller chainrings that will work with your current front derailleur?

4. A 105 front derailleur is going to give you fits trying to make it work. The cable pull direction is wrong and the cable pull requirement won't match your mountain bike shifters precisely.

A 48/38/28 seems a little on the large size for a full suspension trail bike. But if that's what you wanted then fine. The more normal size for trail bikes is 44/32/22. The set you got sounds more suitable for a cyclocross bike.

The front derailleur should be fine but it will need to be moved up on the seat tube slightly to work with the new setup and then play with the final cage angle and cable adjustments a bit. There are also limit screws on the derailleur that will need to be adjsuted to suit the new crankset. Also you'll require a new chain since your big ring is so much bigger than the old ring that you would end up jamming things up if you try to move to a big to big gearing combination.

As for how to set things up go to www.parktool.com and click on the parts of the bike you're interested in learning about.