Originally Posted by
rms13
Your inseam and the stand over of the bike are about the least important part of fit. Use this fit calculator. It will give you a ballpark idea of what size bike you should be on.
Bike Fit Calculator | Find Your Bike Size | Competitive Cyclist
Of course if you are new and looking for a bike the best bet is visit a LBS and let them fit you. Getting the right fit is personal because people have different proportions. Some have long legs, some have long torso, some have long femurs, some have long wrists and everything can effect fit. I'm 5'11 and I ride a 54 quite comfortably but many people my height ride 56 or 57.
But to answer your question, for me a bike is too big when I feel too stretched out. If you can't reach the brakes/shifters comfortably it's too big.
This is probably right, I am 5' 9 and I like to feel stretched out, so it is probably different for everyone. I dont like to ride smaller than 58cm. Now I ride fixed gear and I like to ride 58 cm, but if I ride a geared road bike I can go 60 cm no problem. I also have a 56 cm fixed gear I ride a lot but I feel not as comfortable as I do on the 58.
So you should follow some guidlline that you might read but ultimately you need to feel comfortable and that is probably a personal thing in the end.