How to choose a bike I'm a new cyclist and I'm looking for a new bike primarily for recreation and also for fitness. I would like a mountain bike mainly because I like the style and the fat tires! However, I won't really be doing much if any trail riding. I did some research to try and determine the right size bike for me and based on my 5'9" height and my 29" inside leg I found that I needed an 18" or medium sized mountain bike. However, when I went to the store to check them out, it seemed like the 18" or medium bikes were quite small, and I felt like I wouldn't be comfortable on something like that.

So I was wondering if mountain Bikes, by design, are somewhat smaller than road or hybrid bikes due to the way they are ridden?  If I'm not intending to do any actual mountain biking with it, would I be OK buying a larger size? I'm assuming that when riding trails etc. most riders are standing in the pedals rather than sitting on the saddle, but I'm guessing I'll spend more time in the saddle when I'm riding, which makes me feel like a larger bike would be best for me.

Just looking for some guidance here so I don't make a bad decision. Thanks
Whenever I am asked a question like yours, I invariably ask back: "what are you going to do with that bike?".

As 90% of the time the answer is "dunno", the obvious suggestion is "go for an economical model that fares decently in most situations, then when you have found out what your cup of tea is and you still love biking, go for a more expensive choice".

And this advice is based on my own experience: in the times where having a mountain bike was cool, I rode an old 3 speed, steel frame from the '60s, my father's legacy. It was not cool maybe (nowadays we would call it vintage), but served my purpose.

Then for my first chosen bike in the early 2000s I went for a BSO city bike, sub brand of a major brand. Again, it was not fancy or cool, but I rode about 15 thousand km on it (including a holiday in the central Italy Apennines), discovering that what I like to do with bikes is commuting and touring.

Then my first serious bike was, and still is, a touring bike. I also own a cheap city bike, just because I don't trust leaving my touring model in an unguarded garage for thieves to pick up.

A friend who asked my advice in the past ignored it and went for a cool, expensive, full suspension off road model  (where we live the max rise is about 40 m and the only off road, except BMX tracks, is gravel roads in the countryside). He admittedly rode it for a bare 40 km and then sold it after 10 years to make room in his garage.