You dont need a super light frame to get a build under 15lb. That's almost like a regular midrange build these days. I had a 6kg rim brake build around a ~950g frame a few years ago. And that's with everything- pedals, bottle cages, computer mount. It was heavily compromised though- carbon saddle, garden hose Tufo tubular tires- it was kind of awful to ride.
It's all about picking the right components. My suggestions?
- Frame- something with a round seatpost so you have cheaper options there. Rim brake is getting tough as there are less and less options. The innovation/investment is in disc.
- Wheels- not hard at all to find sub 1200g wheelsets these days. You don't even have to compromise much on width/depth. You can prob find sub 1000g wheels if you're willing to compromise on performance (I wouldn't)
- Tires- I might just not have known about better options when I did my build but I don't think you have to compromise here. BRR has the info to let you find the best compromise of weight, rolling resistance and puncture protection:
https://www.bicyclerollingresistance.com/road-bike-reviews?orderby=weight Shouldn't be an issue for you to find 23c tires under 200g/axle that aren't complete trash.
- Cranks- not hard to find ~400g crank arms. I have Extralite chainrings and they are OK. If you can go 1x, even better.
- Groupset- mixed bag; mechanical rim is the lightest but eh. Carbon rim brake surfaces just suck and turn your wheels into wear items. I would def look into disc, not sure if hydro or cable is lighter. Again go 1x if you can
Etc. You can def get under 15lb without sacrificing much of anything; I'd wager you can even get under 14lb if you are very careful. I will say it is very nice to have a bike that "holds speed" so I would also factor aero in...... aero & rolling resistance take over pretty early so I think it's worth eating a few grams for stuff like rim depth, faster tires etc will make for a more enjoyable experience. My bike is prob 1kg heavier now but it is so much faster and nicer to ride. My next build splits the difference with the best of both worlds.
