Is it a Planet X one? The one I took to Italy was and it's vast. I fitted my bike, cycling shoes, helmet, all my cycling clothing, tools, a ton of bars and gels, and bottles of energy drink powder in it. Still had space so chucked in some more shoes and sandals. There was still space left in it but I nearly gave myself a hernia trying to lug the thing about railway stations as it was. Stairs were not fun.
On David's recommendation I looked at the Decathlon ones, now badges B-Twin. More compact, with a solid base, a clamp to hold the front forks, and some wheels to tow it about.
If anybody (probably taller and stronger than me which should narrow it down a lot
) wants the Planet X one let me know. If you're big enough to manage the size
then it's a decent bag with loads of internal pockets.