Weight Distribution
 

I always hear how having the seat fore/aft too far forward can cause too much weight on hands and shoulders.

Can't this also happen from too short of a stem, alternatively?

The idea in saddle fore/aft is to get one's center of gravity close to dead above the BB axis. This keeps you from sliding forward or back on the bike, helps you stand to pedal or cushion your butt from road pounding, and tends to use your balance to reduce the hand force needed to hold you up.

After yu get this aspect in equilibrium, then set your bar reach and height.

Thanks for the response.

Usually I hear people talk about KOPS, but you are saying to get your center of gravity over the BB, not your knee over the pedal spindle?

I am 71.25 inches tall with a 32 inch true rider's inseam, both without shoes on. I have a long torso and short legs. It is my understanding that people with long torsos for their body need longer stems, and people with longer limbs for their bodies need shorter stems.

Im wondering if I need a longer stem. I know with the standard setup of the hoods being level with the top of the handlebars, I have to bend my wrists up to have my hands on the shifting levers in the drops.

Thanks for the help.

A too short or high stem is likely to create too much of a weight bias toward the back. It can also create too much pressure on your hands, arms, and shoulders. Ideally your weight will be supported by your core spinal musculature and not your arms. Your arms should rest lightly on the bars without carrying much weight at all. The center of gravity changes depending on how aggressive your posture is and a lower center of gravity is generally desirable on a bike. If you think of the bottom bracket as a pivot point then an aggressive racing posture is rotated forward and down with the saddle much higher than the bars and with short 60mm saddle setback. A lazy sight-seeing posture set up is rotated backward with the bars relatively high and saddle lower moved backward with perhaps 80mm setback. People often mistakenly presume that a lazy sight-seeing posture is more comfortable but depending on a riders age, proportions, weight, and strength that isn't necessarily true. Typically noobs will start with the lazy posture and as their strength improves move forward and down. Professional racers typically have their bars about as low as they can get them and the longest stem available.

If you stand balanced on the pedals while coasting along on a flat road in a fairly aggressive posture hovering just over the saddle with all of your weight supported by your legs and spine with hardly any weight on your hands then you can sort of determine where your hands/bar and saddle setback naturally need to be relative to your body parts. For example you can remove one hand from the bars and imagine the ideal spot to rest it. You can briefly set your arse on the saddle and determine if it's too far forward or back.

Your wrists should be straight not bent and so you rotate the bars to achieve that. The position of your hoods relative to the bar top is unimportant unless they're so low you slip off them.

Yes, but for different reasons. It's about torque - you can get the same number with a high force on a short lever, or a low force on a long lever. Your upper body weight creates a forward torque moving you towards the bar, and you need an equal but opposite torque resisting that to stay at the same angle. With your hands closer the lever arm is shorter, so there's more weight on them.

Yes

I don't often interfere with fitting threads but there are various claims made here, mutually contradictory and as well as I can tell as a non-fitter cyclist who has studied physical mechanics, are mechanically wrong.

Can it happen from too short a stem - No. Bending the elbows more with a shorter stem, the torso has the same angle and therefore the same center of gravity, but of course it's easier to hold your weight up with your hands closer than farther away. Keeping the arms the same on the other hand moves the balance back and up, which would reduce the weight on the hands. Physiological effects may increase (or sometimes reduce) pressure on the hands, but those effects are not invariant amongst all individuals.

KOPs has no effect on the weight distribution between the saddle and bars. It changes the direction of force from the legs. It also has another effect, that Clem von Jones alluded to.

The torque lever arm would be operant while riding out of the saddle and leaning forward, but sitting in the saddle the force vector from pedals pushes back from the bars, not towards them.

I agree. Arms are most relaxed with nearly straight elbows and wrists. If the stem is so high/short that the elbows need to be acutely bent to maintain an athletic back angle, the lower back and arms will be in conflict. Fatigue and pain will develop from the wrists through the shoulders, upper back, and neck.

No! That is all backwards. The seat to BB relationship is all about your position relative to the best power, comfort and aerodynamics of your body. Same with handlebars. After those are in place, your weight is where it is relative to the BB and more important, the wheels. If that is not optimum for handling, then that frame doesn't really suit you. (My weight ends up being far enough forward of the BB that I have my customs built with rear triangles as short as feasible and longish front centers.)

My feeling is that the bike is a tool to support my riding, not vice versa. (Although this forum is "Fitting Your Bike" so perhaps I am in the wrong place. I should be in 'Getting Your Bike to Fit".)

Ben

Interesting. I always thought that the more bent arms within reason the better. I just changed from a 90 to a 105 st em because my arms were too bent and I felt like it was too much pressure on my hands. I wondering if this will work now that I read this since my arms are still slightly bent, but less so than before.

You're right Ben. For one thing, having the center of gravity over the BB would only balance you if you were coasting. Pedaling, you'd need to balance somewhere forward of the BB (because that's where you're pressing down, not at the center). But my point is not important because it's not about balancing your center of gravity.

But what if, when fitters say "center of gravity" they're using a term of convention and really mean something else? From that viewpoint, if you rephrase Road Fan: "The idea in saddle fore/aft is to get one's position correct relative to the BB axis". To me, that seems absolutely correct and everything else he said follows. That would agree with you also wouldn't it, since your position for power depends on setting the saddle relative to the pedals.

The other factor is top tube reach* front wheel feels lighter if its moved ahead of the riders C Of G..

off the shelf frame proportions usually figure that in for standard sizes.


*Plumb line through the BB is the dividing line .. 'reach' Ahead, 'set back' Behind.

Great replies. I don't really know the best way to set my fore/aft. I tried to look in the mirror to figure out where my weight look distributed, but that didn't help. Are there any measurements I can take to figure this out?

Because of my long torso, and being 210 pounds, it seems I have a bit of weight I'm carrying in my upper body. I hope I can get fairly comfortable, regardless.

I also want to throw in that I have mild scoliosis. My reach is longer with my left arm. Do you guys have any recommendations to help with that?

But energy spent maintaining balance over the bike is energy not available for propelling the bike.

While I maintain that center of gravity dead over the bottom bracket is not necessary, it's a starting point. The idea is to be far back enough so the core can support the forward-bent torso with minimal help from the arms. This doesn't apply to track sprinters and time trialists. A road rider, however, can't afford to the energy needed to support the upper body for hours at a time with his arms and shoulders. The weight-centered approach lets the stronger core muscles do most of the work.

Look at your knees, which work sort of like elbows. Would your rather stand for an hour on slightly bent knees or deeply bent knees? Would you rather finish your pedal stroke with slightly bent knees or deeply bent knees?

You bend your knees and elbows for power when that's what you need, but nearly straight is more relaxing.

Have you tried setting your fore/aft so that your knee is directly over the pedal spindle when the pedal is at 3 oclock? I've never set fore/aft any other way...and since my frame is the right size, that works for everything else. Think about how many pedal strokes you perform...having the fore/aft set up for your knee is the right thing to do. Changing stems (shorter/longer / higher/lower) and handlebar angle is the correct way to fix your hand placement and overall fit, in my opinion. If you can't get that dialed in, then your frame is massively incorrect for you. Anyone saying to slide your saddle foreward or backwards to fix your reach, I wouldn't listen to.

The Myth of K.O.P.S.

The Myth of K.O.P.S. An Alternative Method of Bike Fit

by Keith Bontrager

originally edited by Doug Roosa
HTML and additional editing by Sheldon Brown
Minor edits and a few comments by John Allen

[h=2]Editor's notes at the time it was published:[/h]Exploding myths is tough work. People don't want to believe that their ideas about how things work or how things should be are wrong. Keith Bontrager tackles one of our primary beliefs about bike fit: that aligning the rider's knee over the pedal spindle is critical for proper positioning. He shows that there is no physiological basis for it. His dismissal of that rule, and his alternative method of bike fit, is based on quite a bit of anatomical study and a lot of practical experience in fitting riders to his custom-built framesets. Some of the ideas in this article may be initially hard to grasp, but if you bear with it, you will derive an understanding of an approach to bike fit that considers the needs of the rider in all riding positions, not just the seated one.
-Doug Roosa.

Thanks for this!

Thanks for the replies.

There seems to be a lot of debate into what goes into a good fit.

It would be nice if there was a detailed explanation with formulas for a fit, other than just the KOPS method. If I put myself at KOPS, I will need the seat all the way forward, but will need a long stem for my long torso.

If I get a longer stem, won't that bring my knee forward? If it does, it would be hard to set the fore/aft correctly before getting the stem length correct, I would think.

Also, is there anything I can do fit wise to compensate for the scoliosis?

Thanks in advance.

Bump