Although road bikes have regained some of their popularity in recent years, there can be no doubt that mountain bikes dominated the market throughout the 1990s and the early 2000s. It seemed that the industry just couldn't make enough of them, and they sold like hot cakes. So chances are that you may already have an old mountain bike stashed away in your basement, garage, or backyard. Due to their very nature, mountain bikes don't make great road bikes. They tend to be heavier, their fat tires generate rolling resistance, and they lack the high gearing needed to go fast (something you'll miss when, for example, you are riding with a strong tailwind). Mountain bikes come with flat handlebars (or handlebars with a slight rise), but these offer a limited number of holding positions, something that can lead to hand numbness on longer rides. And finally, there is no way to attach a frame-mounted rack on mountain bike with rear suspension.
Thanks and Regards,