Beginner road bike for heavy person?
Alright I'm new to the whole biking scene and I need some advice from people who may have been in my position.
First of all I'm 19 years old, 6'3" 280 pounds, and I'm looking for a nice bike that I can ride around to lose weight. Currently I have a diamondback sorrento mountain bike that I ride around on but I'm wanting to try something built for smooth roads rather than off roads. I've heard that riding at a higher psi with smooth road tires can make a difference coming from aggressive knobbed tires, but I'm not sure whether or not to buy a pair or just keep the MTB and upgrade to a road bike? What I'm worried about if I do get a road bike is whether or not it will be able to support my weight. Would there be any significant difference between riding a MTB and a road bike for someone my weight? Also, what kind of road bike should I look for? I was looking at a cheap 149$ takara kabuto on amazon, but I saw a post here saying I should spend a little more for something higher quality. I'm in college and don't have a lot of money to spend, probably max around $300. I was also thinking of buying one off of Craigslist. I saw a 25$ cyclone racer but I've never heard of the brand.. Right now I'm really just looking for a nice short term road bike to get into cycling and to improve my healthy.
Sorry if this is a little long, I'm just kind of clueless right now.