"I'm wondering will changing from a 44t to a 48t give me back that difference? a bit extra would be nice as I'm spinning fast now to keep up with the roadies."
Yes it'll make a difference, but not quite as much as you are hoping for I'm affraid. You'll still be working pretty hard to keep up with the road crowd. Road bike big rings usually start at 52T for a compact crank set and go up from there. With a 12-28 road cassette and 700c tires they're still going to have more potential than you will. If they are fit enough to use the full potential of their drive train, you'll get dropped. But a 48T would help some.
Also would my front derailleur (shimano XT) work ok with this?
Maybe, depends on the exact model of the derailleur. However, all XT derailleurs have maximum capacities betwee ALL the chain rings. The maximum capacity of most Shimano front derailleurs is 22T. This means that the maximum difference between the big ring and the small ring can be 22T before you start having problems. Also the max difference between each ring is 12T. So assuming that your current crank is set up with the standard 22/32/44 rings you'd likely need to replace your small and middle ring as well to keep things running smoothly. For a 48T set up your minimum middle ring size would be 36T in keeping with the 12T max difference. That would make your minimum small ring requirement a 24T. However the 24T would exceed the maximum 22T capaicity of the standard derailleur, so you'd have to bump the small ring to 26T to make it work properly. That's why Shimano's standard set up for a 48T big ring crankset is a 26/36/48T combo. This would also require you to clamp the derailleur higher on the seat tube as well. The reason behind this is the derailleurs limited capacity to lift or drop the chain from gear to gear. Exceed the maximum capacity and you'll either end up with the chain dragging on the cage when in the small ring, or your won't be able to get up into the big ring if the derailleur is set low enough to prevent it.
"48t or bigger in 4 bolt 104mm seem to be fairly rare, cheapest i have found is $69 at Chainreaction. Anyone know of a better deal?"
Can't help you there. While not as rare as some, they deffinately aren't that common. And when you do find them, as noted, they're usually rather spendy. And keep in mind the above, you'll need to go to bigger small and middle rings to keep things working properly. So it'll likely be a bit more expensive than you initially thought. It's deffinately doable, but it's not just a matter or replacing the big ring. There's a little more to consider than that.
Good Dirt
