Chainset

Doombrain
Doombrain Posts: 360
edited July 2011 in Road buying advice
I need a little help choosing the correct chainset please.

I have Ultegra 6700 double which i want to swap out for something a little lighter, something like the SRAM red or FSA carbon type.

question is i'm not sure if a) the bottom bracket will fit b) what the 170, 172.5 & 175mm relate to?

TIA

Edit: OK, 170mm etc relates to arm length
edt:Spindle - ISIS (BB-108mm)?
LOL road riding.