froggya

hi there all,
I have bought a giant crx4 2nd hand, done around 2000km, I would like to change a few things. Could someone help me.
I would like to find some data on the front derailleur which comes with the crx4 I know it is a clamp on
but what is the diameter 28.6mm, 31.8mm, 34.9mm, mine is an acera x but what size, I know I could remove it and check but I would like to avoid it if poss. If wanting to upgrade what should I get cosidering it has a triple ring, which lead me to my next question.

I want to change the crank, I have a Shimano TX71 28/38/48T 8 speed I want removable chain rings
a)I would like a 26-39-52-crank how should I proceed as I am confused
I realise this would be a custom job, I can get the chain ring from harris cyclery and other but what crank would I need or should I forget it and get a Shimano Ultegra Triple 52/42/30 or similar which will mean replacing the bb anyway, basically what are my choices.
b)I have a un25 bb I know it is 68mm width but what is the spindle length 107, 109, 113, 115, 118, 122.5, 127.5 mm ? I want to upgrade what should I go for because eveything I read tells me it is a very basic bb.
thanks for all your help guys

froggya

In case someone gets the same problem, I have found out that bb spindle length is 122.5mm and front derailleur clamp is 31.8mm