Originally Posted by
sam_cyclist
I recently test rode a 2014 Giant Defy 2 and 2015 Giant Defy 1. The shop weighed both bikes at my request and the Defy 1 weighed more than a pound less. It's also about $500 more expensive.
I did a bit of climbing and obviously, I didn't notice any difference in my ability to climb with either bike.
I'm wondering if getting a bike "significantly" lighter, say 3 or 4 pounds lighter or more, would make a noticeable difference either in overall handling characteristics and especially in how quickly I can climb hills.
The impact proportional to total weight.
For example, together my bike and I weigh 165 pounds so loosing a pound of bike weight would increase my speed up the steepest hills 165/164 = 0.6% which is 22 seconds for each hour of climbing I do.
4 pounds would be a full 2.4% faster and knock nearly a minute and a half off an hour climb.
On flat ground the results aren't significant (rolling resistance is constant and power to overcome it linear so most of your power goes into overcoming aerodynamic drag proportional to the square of velocity with power to overcome its cube) and not enough energy goes into acceleration for that to matter.
This is a bit of a hypothetical question as I don't plan on spending several thousands of dollars on a road bike, but I'm wondering how much of a performance advantage I would gain from a bike which is 3+ pounds lighter than the Giant Defy 2 I test rode.
Mostly it'll look nicer and be more pleasant to hoist onto your repair stand unless you race, are in the mountains, and have a build conducive to climbing (about 2 pounds per inch is a good target).