I’ve been using the weight of my gravel bike (10kg) as an excuse to why I’m so crap at getting up Hills on it but based on the website below if I keep all the details the same and on a 10% gradient it says it only takes an extra 5w to keep the same speed going from an 8kg bike to a 10kg bike. I’m feeling rather disappointed my excuse seems to no longer be valid.
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If ~4 pounds of bike weight only equals 5 what’s than I guess that’s why so many obsess over 4-5 watt differences between tires and wheels, etc.
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Yeah, weight matters less than we have often assumed. When you then include the fact that most rides include up AND down directions, it matters even less for most applications.
This is the reason that most consider aerodynamic effects to be more significant and important to address, even if it comes at the “cost” of more weight.
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I thought it would be double that and be more in the 10w range for 2kg.
Say I climb a hill at 350w at 68kg, that is 5.14w/kg
If I add 2kg (now 70kg), then it takes 360w to do 5.14w/kg (360w/70kg=5.14)
Obviously the gradient and the CdA matters, but I imagine at 10% that wouldn’t be an issue.
Am I missing something?
I love how the pro’s toss their spent gel wrappers just before a climb. Yeah, that 0.03 grams weight savings will put you across the finish line first, buddy.
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Well, placebo effect could well be more “real” in a case like this than the physics.
Our minds are silly things far too often 
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I suppose its also down to rider weight and FTP. 2kg will be a bigger percentage of their total weight in the case of a smaller rider and 5w might also be a greater proportion of their FTP; then at a competitive level equipment weight might be more important 
The down never makes up for the up bc the high speeds going down run into higher drag.
The other thing is how 2 different speeds are averaged.
eg,
1 mile climb at 10mph = 6:00
1 mile descent at 20mph = 3:00
It would seem that since you did half the ride at 10 and have at 20 that your ave would be 15 but it’s not.
The average is 2 miles at 9:00 which is 13.3mph. This is because you spend less time at 20 than you did at 10. To average 15, you’d have to do 6 min at 10 and 6 min at 20. But since 20 is faster, you only do 20 for 3 min in this example.
WRT bike weight savings, a 6kg bike weighs 75% as much as an 8kg which is a big difference. But when rider weight is included (70kg as an example) the total weight is 97.4% (a pretty small difference).
Sure, and I am not saying that it is equal or balances. Just that people often ignore the other side of the equation. Like many things, it’s not purely negative in all lights.
I get what you’re saying and I agree. Sidenote, I remember feeling like it always did balance out bc when I rode in TX, my avg speed was always roughly the same, 20-20.5mph. I moved to CO and then I had to adjust to the fact my speeds were slower. Same when I moved to Cali. The hills were suddenly a big enough impediment that my avg speeds were impacted.
You’re missing:
- 8 kg of bikeweight, and
- an OP that is either more heavy than 68 kg and/or has less power to use than 350 watt
But yes, for that gradient for us mortals things like cda and rolling resistance can be ignored. So X% more system weight or X% more watts would have the same result of an X% faster climbing time.
So maybe repeat the calculation with somebody around 90kg, using 250watt ;-). Then 5 watt or 2kg would indeed be roughly the same 2%.
When climbing at 10% gradients, weight matters exactly as much as ‘we’ assumed 10, 20, or 100 years ago. Yes: when including the down, or smaller gradients, old assumptions have been proven wrong by a better understanding of mostly aerodynamics. But in the context of the OP’s question that’s not really relevant… 
Gotcha. I was actually using my own body weight and bike weight and power up a 5-8 minute climb, but I see how the numbers shift at higher weight and less power.
Edit: I’m only 63kg and my road bike is 7kg
Thanks for the replies. Just to clarify I was using 60kg as body weight which is accurate. Being that I’m pretty light I thought 2kg increase would make much more of a difference so I’m feeling a bit personally attacked by this website as it’s basically telling me it’s all in my head 
.
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Yeah I’m usually ~57kg so figured with a lower system weight overall, bike weight becomes more important as its a bigger percentage than it is for someone a lot heavier like 75kg or something.
These days though it seems like you can generally get a bit of both, aero wheels are lighter than stock. As a lightweight rider I only worry about going “deep” as I have concerns about being thrown around in the wind.
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Always.
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I expected a bigger difference at that weight
Same 
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I wonder what difference inertia makes. Especially if you’re climbing slowly - if very slowly, you basically have to accelarate the bike from a full stop with every pedal stroke. That isn’t so much a concern if you’re climbing at a higher, constant speed.
Investing in general health, a coach (be it nutritional, sports, rehab, PT) and training, will get you further and faster everywhere. Plus you get to learn yourself quite a bit.