Originally Posted by Raiyn
What are you running as a cassette now? Also if you're running 35 mph on a MTB on the flats 
you should just look at getting a real road bike because there's no way you're pushing that kind of speed on dirt
Please read more closely - 35 downhill. I have test-ridden road bikes and am not at all comfortable on them. I like the bigger wheelset and higher gears, but simply cannot sacrifice stability and durability. Even the Cyclocross bikes aren't sturdy enough for my liking. My stock big chanring is is 42t and I'm just wondering if there's a larger 'stock' chanring I can move up to without rebuilding the entire drivetrain. I have a 9-speed cassette that came with it (Giant Rainier). Apologies if I did not specify this is a commuter bike, not a pure dirt bike.