wow, that's a good deal on that bike. i don't know the terrain there, but i second the suggestion of 48/17. let me rephrase that. play around with some different chainring sizes, but keep the 17 tooth cog. up to a 49t chainring, i believe, using a 17t cog will give you the best skid patches. to put skid patches simply, if you're not sure (use the search as well, there are some other good posts to read on the subject, plus diagrams and calculators)...different ratios will cause your rear wheel to stop at different points when you lock it up, due to the number of wheel rotations per crank rotation, causing different amounts of wear, depending on how many places the wheel stops at. 17t cogs are the best size cog since the ratios tend to yield the most skid patches, but you can play around.