> Bicycle racing has produced a lot of people who think weight matters on bikes. It does in races, but weight isn’t a substantial factor for people who ride at normal speeds.
Weight is still a substantial factor if you ever have to go up or down stairs with your bike.
Or even up or down hills. I could stand to lose quite a few pounds, and it's far cheaper to lose 20 pounds of me than 20 pounds of bicycle, and while I love my good old steel Surly, there's an obvious difference riding my aluminum road bike and a very obvious difference when I've test-ridden modern carbon bikes.
An additional couple of pounds on the bike is only a couple of %, and you're not going to notice it. Wind, tires, positioning, how you're feeling, and road surface matter more. Anything less than a pound and you're talking the difference between a full small waterbottle and an empty one.
Doubling the bike weight, you might notice in the speed, you might not. You might notice it in the handling/feel, you might not. Adding 8kg of panniers to my bike doesn't noticeably slow me down.
Personally, I'm just as fast up hills on a 12kg gravel bike with fat, supple tires (650x42), a rack and fenders as I am on the 8kg carbon 700x25c boneshaker tires.
And I'm faster going down, because I'm not shaken all to hell.
Weight is also a substantial factor in the wheels and tires. I experimented heavily with everything from 26x1.25" tires to 26x2.25" tires, with light tubes all the way to thorn proof tubes with that green goop in them (Man I was sick of flats...). The difference in the speeds I was able to attain not just from rolling resistance but to the amount of weight I had to spin was huge.
I settled eventually on 26x1.75" tires with a solid center tread and kevlar lining. They were amazing on road (commuting) and worked well in other situations too. For context, I was riding 12mi/day commuting to/from work in Reno NV back in the mid 2000's. Rode a steel framed Specialized Rockhopper that was converted to a fixed gear tank- not your average fixie. Featured trekker bars, an MTB sized IRO hub, cliffhanger rims, racks front and back, the works. Best bike I ever had.
Saving weight on a bike becomes exponentially more expensive the lighter the bike becomes. Sure, it helps not to buy the cheapest, heaviest model you can find at Walmart, but how many hundreds of dollars is worth to save another kilo or two to carry up a flight of stairs?
It’s bulk that makes navigating stairs with a 10kg bike worse than a sack of groceries…well and that the geometry of a bike changes with changing orientation.
In a domestic space a bicycle is an awkward piece of metal.
10kg is a pretty light bike. My steel city bike weighs 17kg, and some of those pretty dutch style citybikes with sturdy steel fenders can weigh over 20kg
Weight is still a substantial factor if you ever have to go up or down stairs with your bike.