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ideal (?) weight distribution sitting, standing, stem lngth(9 posts)

ideal (?) weight distribution sitting, standing, stem lngthFez
Nov 11, 2002 6:30 AM
much has been written about weight distrib. i know all about saddle fore/aft, kops, etc. this is all about cycling while in the seat.

but what is ideal stem length that puts the weight distibution for best climbing? is it usually 100 for smaller frames, 110 for med, 120 for larger ones? or is there a more scientific method based on individual geometries of frames?
Your very question gives the lie to KOPS. We do this thingbill
Nov 11, 2002 7:10 AM
with a plumb bob when we're static, and then when we ride we're all over the place. And then there's crank length, and shoe size, and cleat position, all of which will effect the way that the lever functions.
But your question is about stem length. Stem length is about cockpit dimension, reach, handling, and weight distribution, which are related to varying degrees. Obviously, a longer stem will increase your reach and place more of your weight over the front, but the stem also is a lever by which your bars turn the steerer. If the length is too little, small changes in the handlebar orientation will have an outsized effect on steering, leading to instability. The stem also probably to some extent is a suspension system, so that a longer stem will absorb more road shock.
Geometry, your own physical dimensions, and how you ride the bike can matter to all of this stuff. There is a school of thought that a properly sized frame and a properly oriented saddle will always yield a 110 mm stem, but I think most agree that anything between about 100 and 130 is acceptable.
no such thing....C-40
Nov 11, 2002 9:08 AM
When you stand, the weight distribution will shift dramatically toward the front wheel. Body position will affect the weight balance far more than stem length. Body position when standing is not dictated by stem length. If your stem is too short though, you might contact the bar with your knee, if you lean too far forward.

If you are pedaling correctly, you should not be placing a significant amount of weight on the bars. For maximum power over a short duration, the arms may be used to pull up on the bars as the feet push down.
no such thing....Fez
Nov 11, 2002 9:44 AM
Here is a simplified example.

Bike A setup has 54.5cm top tube, 115 mm stem.

Bike B setup has 56cm top tube and 100 mm stem.

Seat/head tube angles are the same on both frames, standover is within acceptable range on both.

Just wondering if the stem length was a factor on a standing climb. Does the longer stem actually put more weight distrib over the front wheel? Is this desirable?
When you stand on a climb, you are not necessarily puttingbill
Nov 11, 2002 10:29 AM
more weight over the front wheel (regardless of stem length). When you stand, your center of gravity is going to shift forward of your saddle along the axis of the top tube, as far as that goes, but because the bike is angled upward your weight could still be balanced between the wheels exactly the same. Theoretically. I could see that it depends on how straight you stand up, whether you keep your butt over the saddle, how much you are pulling up on the bars, even whether you are spinning versus mashing (mashing will cause you to exert more oppositional forces by pulling up more, although I guess it could be a net zero), etc. Those are a lot of variables to predict how a 1 cm difference in stem length would matter, although I could see that, at the extremes of length, a too-short stem would leave you with too short a cockpit and not enough leverage to provide oppositional force to the pedals without shifting your weight all the way forward and banging the handlebars, and too long a stem would force you over the bars with the weight too far forward to leave your rear with enough traction. Or something like that.
Given the number of variables, I still don't think that a couple of cm would make very much difference in the abstract so that you could predict an outcome. Not to say that it wouldn't matter; I just think it would be very individual.
it's the wheelbase, not the stem length....C-40
Nov 11, 2002 3:17 PM
The idea that stem length contributes to a significant change in weight balance is incorrect. Very little weight should normally be supported by the bars and stem in the sitting position.

In your example, the most significant difference in the weight balance would be due to the longer wheelbase that results from the longer top tube. This difference will also be quite small, about 1.5%, with the longer wheelbase frame having slightly more weight on the rear wheel.
it's the wheelbase, not the stem length....commuterguy
Nov 12, 2002 11:53 AM
I thought I had read that weight should be evenly spread across the seat, cranks and bars. That would have 33% on the bars, no?

Some of the explanations for back pain while riding point to a stem that is too short/too high, which prevents the rider from stretching and puts too much weight on the saddle. Am I mistaken?
I think you're mistaken...C-40
Nov 12, 2002 2:57 PM
If the saddle is positioned properly, the majority of a riders weight should be on the saddle and the cranks, not the bars.

A shorter stem changes the arm angle in relation to the torso and creates a slightly more upright position, but it should not cause back pain (maybe crotch pain). I can use a 90-110mm with no discomfort. A 120mm on my current frame increases the angle between my arm and torso enough to cause shoulder pain. A stem shorter than 100mm would still be comfortable, but my knees and elbows would overlap in the drops and the amount of weight on the saddle would likely increase due to the more upright riding position.

Read up on the subject at peterwhitecycles.com. I don't agree with all of these ideas, because I'm convinced that the KOP position can be adjusted to enchance torque or cadence.
re: ideal (?) weight distribution sitting, standing, stem lngthDINOSAUR
Nov 11, 2002 9:42 AM
First: Make sure your KOPS is dialed in (or whatever method you use to position your saddle). Then see how your stem feels when you ride, is it too long or too short? You want to be a little bit spread out on your bike for aerodynamics. If you have an incorrect stem length your body will let you know.

Then handlebar tilt comes into play. For climbing I like to ride in the hoods and honk and pull back on the bars and use my upper body. For descending I want to be low and spread out, but not too spread out or it will tweak my lower back whan I hit rough spots on the road. I can push forward and support myself with my hands in the hoods. Just a couple of degrees in tilt one way or the other makes a big difference.

What I did is carry a couple of hex tools and dialed in my position while I was riding in very small increments.

You can't nail down a perfect stem length as it has to do about the size of your bike and your anatomy, no one size fits all. Just find what feels good for you. Then you get into stem rise and I don't want to go there as it gets very confusing....you have to experiment and try different settings but keep track of what you did so you can duplicate a setting, as sometimes you go back to where you started out. And don't make too many changes at once or it can lead to injury.....