Im looking at buying a new pedal bike. I've used the same 10 speed since my teens. Its done well for me, but its time for something new. Im not really concerned about a mountain bike, as most of my riding will be black top related, but i would like to be able to use a somewhat aggressive tire for some grass and dirt trails. Im not really into bikes, so i dont want to spend a ton of money either. The last time i got one new, i remember just sizing them by the size of the tires. Now it seems its by the seat post. Is it just the feel of it, or is there a proper way to size the bike you need? Whats the deal with the front shocks? Are they actually necessary?