I recently started cycling again after a long absence. I bought a cool old Raleigh mountain bike at a garage sale, but after I spent a lot of money fixing it up, finally figured out it was too small for me. I traded that bike in for a bigger, like-new 1996 Gary Fisher Nirvana hybrid, but after riding it for the first time today I am totally bummed - the hybrid tires really aggravated my TBI (traumatic brain injury - i had two concussions in 2007.) I didn't have any problem with the Raleigh's tires, or with my wife's' older Trek mountain bike. My questions are: Can I switch the hybrid tires I have for Mountain bike tires? How expensive would that be? And should that solve the problem of creating a smoother ride that doesn't jostle me around as much.