Weight distribution of bike

gemship

Okay I just came back home from a Two hour ride, went to town and put at least 4 pounds of groceries in my milk crate. I definitely notices a difference out the saddle sprinting on the flat roads. All the wieght up high just makes the bike feel more flexy but I still accelerate about the same. That same wieght feels easier to ride with when in the saddle and not straddling the bike side to side so much.

dabac

Tha javeling thrower analogy isn't applicable at all because the thrower and the javelin are two separate components - launcher and missile.
The skier analogy is only vaguely applicable because of the differences in operator - equipment interface. The skier is attached around his lower leg and has to exert all control through that pivot point - even small masses getss a massive leverage.

The bike rider OTOH has pedals, saddle and bars quite nicely distributed - nowhere near as much leverage to overcome as compared to the skier.

The thing is that if we're talking about the CoG of the bike shifting because of the actual weight of the components, then their individual contribution gets so smeared out that you really need to be ultra sensitive to notice anything. Things like rigidity becomes more important than actual weight or CoG.
But sure, if you have a choice, having the weight lower is better than having it higher. Don't expect to notice anything as long as you remain seated though.

Going from a heavy sus fork(w/ lockout) to a rigid fork IS noticeable, but first when you're really throwing the bike around.

Saus

dabac, while I do not agree on what can be noticed, at least you answered the question - weight distribution toward the bottom is preferable to weight distribution toward the top. Thanks for being the first person actually to respond to what was asked.

On a road bike of very light weight, a heavier saddle will be noticed - especially over a long ride.

Dietmar

How often do you want to read the same answer? Mikesbytes already answered you, twice, but it seems that you don't like his answer. So you keep asking until someone gives you the answer you want to hear?

Seriously, Mike is right, given reasonable restrictions on weight distribution, the change in center of gravity of the bike with rider will be tiny. Such small changes will not have a discernible effect on the handling of your bike. Just think about how "different" your bike handles if you raise your saddle by half an inch, which is a manipulation that has an effect on the center of gravity that is at least one order of magnitude higher than the one of switching frames and wheels around in order to lower the center of gravity.

Dietmar

Nonsense. It essentially doesn't matter how lightweight your bike is, given that the rider is much heavier, and it is the system rider+bike that matters.

Saus

Thank you all for your input. Enjoy the season.

dabac

Low is good, but rigid is better.
I do a fair amount of utility riding, and hanging a basket from my rear rack will be much more influential than hanging the same basket from my handlebars.
At the bars, between my hands, the basket moves pretty much in unison with me if I'm riding out of the saddle.
On the rack there's an obvious delay in response as flexing in the rack will have the basket continuing to travel towards one side while the rest of the bike is about to begin tilting towards the other side.
But even a heavy pannier on a flexy rack doesn't really call any attention to itself as long as I ride seated.

But when you are talking about the bits that actually make up the bike they're all rigid enough as not to cause any swaying anyway.
And since they're distributed over the whole bike the differences in CoG attainable by different componentry choices must be limited indeed.

artemidorus

Not one post on this thread has even approached a demonstration of this hypothesis, nor has any appropriate secondary source been cited.

We all very happily shove 50-150kg on the very tops of our bike frames.

I think that following the general maxims of "aerodynamic is good" and "lightness is good", particular with regard to the rider, you'll be set up to go as fast as anyone else of similar fitness.

__________________
"All that we see and seem is but a dream, within a dream..."

gemship

Happily shoving wieght on the top of my bike frame, now that's a laugh. Grateful maybe, that I could muster the strength to run a few errands with my billygoat commuter rather than drive. No doubt in my mind that sprints are harder the cornering is ever so slightlier lazy when loaded up with a good 15 pounds over the rear wheel. Yeah I must be sensitive because I notice it but admittedly more so out of the saddle and riding. How does that not answer the op's post. Maybe the differences are small but if you can feel it then its there.

artemidorus

Of course, it feels different. The question was not whether it could be felt, but whether it was "important".
"Important" to me means altering the efficiency of pedalling, or reducing the cornering ability. No-one has offered any proof or convincing argument that it makes one jot of difference to efficiency or cornering ability, other than that things might feel different.

__________________
"All that we see and seem is but a dream, within a dream..."

dabac

As long as I remain seated it doesn't matter squat, but if I'm out of the saddle, tilting the bike left/right as I pedal - then gear carried in lowriders definitely has less of an impact on how the bike feels than a similar weight carried in a handlebar basket. The higher up, the bigger the arc that the extra mass has to travel across.

Same basket hung on rear rack is worse, despite the load being lower.
My theory states that this is because of the flexing in the rear rack. Basket hung at front is higher but more rigid - it still moves in sync. Basket hung at flexy rear sort of overshoots the turnaround angle, which certainly can be felt at the bars.

I am quite confident that this is the truth when carrying stuff on the bike, so presumably the same principles(low is good and rigid is good) should apply to the bike itself.
But whether it is possible to shift the CoG around enough on a bike by the careful selection of components for this to be noticeable is another question entirely.
I find it unlikely, but then unlikely opinions aren't exactly rare when it comes to the finer nuances of bike characteristics.

Dietmar

Go here for more details, if you can handle the theoretical mechanics. Short version: Yes, lower center of gravity leads to a more stable bicycle, unsurprisingly. Does it matter in the context we are talking about in this thread? No.

P.S.: The above website also has free software for bicycle stability calculations.

crater

Instead of asking the correct question of "how noticeable is a heavy seat vs a light one" saus has asked a very dubious question. He then gets irritated because he isn't getting an answer applicable to the real question. I don't know anybody intentionally strapping weight to their bike to make it more fun, high or low. I think a saddle that is comfortable will make a more fun ride for any length. I don't believe you will feel a difference in handling between a 120 gram saddle and one like mine weighing twice that. Do yourself a favor- strap a innertube to the rails of your saddle then climb a hill. Roll back down that hill, leave the innertube on the ground and do the climb again. I couldn't feel a difference on my Vitus carbon 3 or my Giant TCR with my tool bag that certainly weighs more than 100 grams.