hi l am looking upgrade my forks on my felt 620q
been looking at Marzocchi MX Pro LO Air 100/120mm Travel Fork
any good using it for medium trails and single track
also love the frame on this bike you can chuck it any way
so will changing the forks hinder this
and what is air cartridge in the forks?
thanks
malc

The MAGURA Laurin ( $440 ) looks BEST for your bike (pricepoint.com).

l would not put more than 20mm more travel on a bike than what it came with. So as yours came with 80mm of travel you want a for with 100mm of travel tops. Any more and it will completely change the geometry and handling/feel of the bike that you like so much. l suggest something like this Rock Shox Recon (http://chainreactioncycles.com/Models.aspx?ModelID=25827). It has adjustable travel 85 - 130mm and a lock out feature.

Hope this helps

80mm of travel is more than enough for single track and medium trail riding. If you just can not help yourself, look at rock shock or marzochi. xc forks. Any will work just fine. Air cartridge is an alternative to spring loaded forks. It works the same way by offering resistance to impact.