I am just now getting into cycling and I have a few questions about how I might do a couple of things. One would be are there any upgrades I can get that will increase my overall speed? Somewhere to start anyhow? I have looked at crankshafts and I currently have 48 tooth and I was wondering if I should go bigger. I have a mountain bike but all I can find that is any bigger is for road bikes. Can you rig that? Thanks for any help.