Firstly, that question seems to be commonly asked on here in new members, so if you scroll down the new members chat page till you get to the bottom, there's a search box. Use that before posting new topics. Secondly, theres a lot of reasons to get either 20" or 26" or even 24". 20" bikes (known as mods) are usually smaller, lighter and easier to chuck around. But I have always found their not so good for a lot of static moves (compared to a 26"). Most people who start trials end up getting a mod simply because it seems to be easier to learn on. 26" bikes (stock) are usually ridden by taller riders. To me, stocks feel more stable than mods but less flicky and agile. I've always found that rolling moves (such as hooks and taps) are easier on stocks as theirs more room to move around on. Stocks are usually heavier so when you ride them you probably would get tired easier, but its all preference to which you want to ride. Thirdly, topics like this aren't very helpfull to be honest. All they do is annoy a lot of people on here because your asking such a vague question. You should structure your post a lot better and ask a lot more questions to get the answers your after. It doesn't matter how tall you are, tall riders can ride mod and short riders can ride stock. It's all preference. But the majority of stock riders tend to be a bit bigger than mod riders Report it then?