Originally Posted by
FBinNY
You guys are over thinking it to death. There are tons of variables, so graphs like this are based on averages with other variables held constant. This isn't a precise statement of any change, just an approximation of the net effects.
Exactly, I agree.
Originally Posted by
Inpd
Great thread and good post.
Oh oh. I have an important question that will destroy some people's dreams. Does the graph and discussion above also extend to bike weight not just rider weight?
If so, what does the graph look like for dropping 1kg (2.2 pounds) of your bike?
My understanding is that it will only minimally (barely) improve speed on the flats but will help when climbing.
Originally Posted by
FBinNY
Do you go fishing, if so, you've opened a can of worms and should hang out for some free bait.
First of all, as I mentioned earlier, this is simply a rough approximation of net effect of weight change. So bike or body, it's all the same thing.
OTOH there's plenty of opinions, and some science, on the differences between weight changes on the body, bike or wheels. Lot's of debate on the subject, comparable to a chain lube debate, and few meaningful answers. There is a general consensus, that weight reduction at the rim counts double (supported by good science) for purposes of acceleration, but not for climbing or constant speed riding. There's also some (not as much) consensus that weight on the bike counts a bit more than on the body, reflecting the fact that riders move the bike around under them (I buy into this, but consider it to be subtle).
Also, think about what happens when climbing steep grades at low speed and cadence. The bike undergoes decent size speed changes with each pedal stroke, so the effects of weight are slightly greater than at constant speed. Then there's "feel". Lighter bikes feel lighter and snappier, that may produce a placebo effect that helps riders ride as if it actually made a difference. IMO- for whatever reason, losing 5#s off a bike feels like a bigger difference than losing 5#s off your body.
Throw all of this into the hopper, and draw your own conclusions, and maybe tweak the overall graph a bit, but it's just another set of small variables so don't assign it more value than it deserves.
The rule of thumb here, and in similar discussions, is that the science can get you to the right city, and even (maybe) to the right ball park, but if you think it can get you any closer than that you're kidding yourself.
Certainly there is something to this, but it can be difficult to separate all the many variables. For example, me + road bike + all the cr@p I carry when I ride is probably 220-225 lbs., whereas me + mountain bike + all the cr@p that I carry is probably 250 lbs. So yes, it is harder to climb with the mountain bike, but part of that comes from riding on dirt, part from the big fat knobbies that I have on that bike, and so on.
As an aside, a friend told me about this quasi-experiment (but I never saw it in print anywhere) where weight (maybe lead in the seat tube) was added to a bike without the knowledge of the rider, and the rider was asked to indicate at what point the extra weight was noticeable. Supposedly professionals could identify changes on the order of a few ounces, whereas freds like myself could only identify changes on the order of a few pounds. So if that is true, there is also a great deal of subjectivity when it comes to perceived effort (at least for freds like me).