I keep hearing people saying:
The bike weight isn't a problem, rider is.
My girlfriend is only 48 kg, and a mtb hardtail usually 13-15kg (full suspension would be more like 18kg for an older one), which is already 25% of the total mass.
Is there any huge difference going from 15kg bike to 7-8kg?
I would like to acknowledge the points that others have made:
- Cycling/pedalling skills (sorry, not applicable in this question, but good to know)
- Weight/Cost/Performance dilemma (choose 2 out of 3, and this question chose Weight+Performance)
- Power output / Acceleration and Speed difference with respect to Bike Weight's difference
Edit: It is performance vs bike weight, please avoid adding other unknown parameters. It is worth mentioning those for the benefits of other cyclists, but please do not focus on unknown variables.
Edit2: I agree that in real world, you need to take into account other variables. However, my approach is focusing at the bicycle (not cyclist, and in my subjective view, I certainly cannot tell my gf to get fit to ride the bike I made for her...), then whatever components is not feasible for "real-world", replace it with inexpensive alternatives.