also do you think i should go for the tiagra as the size is also better for me, but is 50 pounds more
also most other websites say my height should get a 50cm frame so what should i go for.
I would say a 50cm might be too big for you if you are only 155cm (5'1"). I'm roughly 158cm, and both of my bikes are 45cm and 48cm respectively. I would think you would be more in that range.