Stem length and bike handling
 

I think I get the approach for overall fit by starting with saddle height and fore/aft position using the balance method, then stem length.

At this point, I am not sure about how to identify stem length. I ride with the bar typically 2" below the saddle, even at being 70. Old school memories say the bar should be hiding the front hub with the hands in the most comfortable position on the bars.
I move my hands a lot as drops tend to be supportive of multiple hand locations. Riding the hoods is kinda new to me with a couple of C&V bikes now sporting Ergo's. The result is seeing the hub more often.
OK great, big deal! But the real question is how is the handling of the bike impacted by where your hands are relative to .... what? With head angles and variations of off-set, where is the best location for you hands for the most neutral handling relative to what reference point(s)?

I don't know if this answers your question, but longer stems are more stable and shorter stems are more twitchy. I wouldn't worry about hiding the front hub view. Do what feels comfortable or get a bike fit. I fought getting a bike fit, but when I finally gave in and got a bike fit, it was the best money I have spent on my bike.

Don't do the visualization thing trying to hide the hub unless you know that every other part of the geometry of this bike is the same as a previous bike you think you had a successful fit that happened to give you this sight line.

I change the stem length to get my arms in a comfortable position that has some bearing with how aero and stretched out or not that I want my normal position to be. What some old wisdom or calculation says doesn't concern me one bit if I'm comfortable some other way.

Yes the length of stems might change up your perception of stability and responsiveness, but I doubt it's much more than just slightly noticeable.

Fitting theory says that with hands on the hoods or deep in the drops, the upper arms should make an approximate 90° angle with a straight torso. For me, that works out to my elbows being just in front of my knees with hands on hoods and horizontal forearms. For me, that position does hide my front hub.

Stem length will change depending on frame top tube measurement / reach. Modern bikes in XC / MTB / Gravel etc have pushed the envelope to have slacker head angles, longer top tubes and shorter stems to improve stability at speed etc.

Every bike is designed to have neutral handling with the rider in the 'optimal position'. Variations from that are sub-optimal for neutral handling. The optimal positions for a city bike differ from a race bike. A custom bike will be designed for neutral handling given your body measurements & for the style of riding you prefer. In mass produced bikes, the task transfers from the builder to the buyer - to find the style and size that puts the body in the optimal position.

Given that 'optimal' is the theoretical perfect position, a question becomes: How much will neutral handling be affected with changes to designed optimal? The answer is different for each person.

Consider this example. I have a friend close in body size that likes my 60cm bikes (approx12cm stems). I have a 58cm frame with short top tube and 14cm stem. It feels a bit long for me, but my friend literally cannot ride it, finds it unstable.

As to how will a long stem affect handling?
I would answer that if a long stem puts the body in an optimal position on the bike for neutral handling (or nearly neutral) the effect will be minimal.
But why does the frame require such a long stem? Maybe a small frame and requiring saddle setback/long stem for your body dimensions. How will saddle setback affect pedaling position? Some racers in the pro ranks ride small frames with saddle setback and longs stems. They can tolerate the larger saddle to bar drop.
For drop handlebar road bikes a stem length of 10 -12cm is the nominal range across typical commercially sized bikes

That's why good frame builders are in demand. Science and a touch of art. And in mass produced bikes, bike fitters can be invaluable.

I remember watching this a while back..may be worth a look

"80mm stem was utterly terrifying." :rolleyes: I have never felt much of a difference between short stems vs long stems, and now prefer a slightly shorter stem. I currently run a 90mm stem, and live in an area with steep hills, and curvy roads, The shorter stem is not, "utterly terrifying", even at speeds up to 45mph. You may, may feel a difference initially, but after riding a short time, less than a day's riding, you won't notice it.

Rather than take the video too literally, I view it more as an illustration of the limiting cases...trends to expect at either extreme. Whether it gets a little scary would depend on how squirrely the bike is at it's design center. The OP asked a question..this offers some info...dwiwyw
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If you can comfortably.maintain the same torso angle while sufficiently supporting your upper body without holding the bars, you probably got the stem length about right.

It's not your position that makes it feel twitchy. It's simply that you turn the bars less and it turns in more. It's like a car with a small steering wheel vs a bus steering wheel. If you ride bikes back to back you will notice. If you run a short stem for a while you get used to it. It's more noticeable at slower speeds like climbing.

I have never noticed any concerns with handling as a result of stem extension. I adjust stem extension based on comfort and whether my hands keep drifting back, away from the hoods. I don’t use or see any sense in arbitrary points like bars obscuring the axle.

I bought an inexpensive gravel bike online. It's a flat bar. One problem is the reach. It's about an inch less than my HT Mtn bike, which I've been riding on gravel routes. My old bike fits like a champ. Based on my measurements, switching from a 110mm stem to a 130mm would do the trick.

My question is what's the downside?

I'm not an aggressive rider. I keep my weight back, whenever I'm going fast.

Downside is that all the replies above your question will just confuse everything from here down. Start new threads for new questions when you aren't the OP.

Agree. Stem length principally affects weight distribution and bike fit. It's an error to think of a stem as a rudder determining how quickly the bike responds to steering input. At anything above the equivalent of jogging speed, you're steering by leaning and not by turning the handlebars.

Stem length (and its consequent effect on frame fit) does not have a set and stone approach because we are all made up of different proportions. The average torso to inseam balance is 45%. Anyone above or below this figure will need to be more precise with finding their ideal top tube + stem length. There are several other factors to consider such as your arms, pelvic bone, hip insertion and angle, lumbar spine strength/condition, etc etc that we are simply all left to figure this out with our own specific bike geometries.

The original stem length set by a manufacturer is a good starting point for not only what sort of person they envisioned riding their bike, but riding styles as well. Feeling the need to go significantly shorter or longer in stem length (lets say 30mm or more in variance?) Indicates to me that you are

A. Different in proportion than average
B. Not using the bike for its intended purpose.

This does not always mean that going significantly.longer or shorter is indicating toward poor bike choose. Case by case circumstances.

A very short stem might feel slightly more agile at very low speeds. A very.long stem might feel more stable at very high speeds. The differences exist and are to be considered, but the primary factor will always be how you are supposed to distribute your weight over the bike.

IMO stem length has a minimal effect on fore/aft weight distribution, because the amount of body mass being moved forward and backward is much greater in the case of saddle (most of the body mass) versus the handlebar (perhaps 10% of the body mass).

Aside from possible discomfort resulting from stem too long or too short, the only effect (IMHO) of stem length in steering is leverage. The bike turns or enters a turn based on rotation of the steer tube. A long stem results in less effort for a desired rotation, but more handlebar motion. Perhaps this would feel sluggish compared to a shorter stem that requires a little more force, but less motion to begin a lean toward the direction of turning. I would probably think the steering response in the short-extension case is more snappy, the bicycle can be "flicked" from side to side.

Hmmm. I agree with the results you describe in your last paragraph, but I don't see how an optimum stem length has any clear dependency on body geometry and proportions, beyond a commonly-known guideline on elbow bend, used to position car steering wheels and motorcycle handlebars. There are of course books used by ergonomics experts to understand the averages of human proportions and common human physical abilities, for example in designing tools and workstations, but how do you relate that stuff to bicycle operation?

Is neutral handling based on weight distribution or on rise and fall of the head tube as the steer tube is rotated? The existing of the common equation, which may not be the whole story, for "neutral" geometry (see Talbot's book on designing and building your own frame, from 1979) talks about setting fork offset for a given head angle and wheel diameter.

I am not a frame builder and the 'common equation' (have not read Talbot) details of HTA, fork offset, frame size, steerer length, stem length, wheel size, tire selection, etc - as regards neutral handling are not my expertise. Instead of singularly the 'fore/aft weight distribution', I believe that the rider's position on the bike has to be complementary to the frame design to achieve neutral handling. That should include rider's height, flexibility, and preferred arm extension - but (obviously) the rider's fore/aft distribution is a huge factor.

How important is neutral handling? For just riding around - probably not important at all. Descending a twisty road at speed (my first 1.5 mi of every ride) begins to show the effects of bike design and position.

I may not be able to explain all the elements well, but when I ride it (twisty and at speed) I can feel it. My DeRosa, Mondia, Falcon, and 1 of th Pinarellos handle like a true racer with neutral handling. The other bikes may also have neutral handling but are not as race performance oriented so the benefits are not so dramatic. Example = the Bridgestone CB-0 (step thru city bike, designed for upright upper body) handles better at very slow speeds in stop&go situations than the DeRosa.

Also worth noting - a bike can be comfortable, a great rider, accommodate a range of positions and not have neutral handling. Especially, where the roads are flat and/or mostly straight. If one rides1 or 2 bikes, you may readily adapt your style to a specific bike. I ride a bunch of bikes and find it harder to 'adapt' riding style to each one. Maybe that's why each is distinctive for this old man. Variety is the spice of my bicycle life..

The equation from Talbot is

Y= R * tan((90deg - head angle)/2)

where Y is the fork offset or rake (inches), and R is the wheel radius in inches. If your head angle, radius, and for offset satisfy this condition, you have "Neutral Steering."

So for my 1952 Rudge the wheel is 347 millimeters and the head angle is 73. My offset for neutral steer is 2.04 inches. However, the Raleigh spec for the bike says the offset is 2.5", which according to the Talbot book means my bike is "slower than neutral." I am not sure what neutral means.

I can calculate the trail for this bike, to be 39.7 mm. I can also calc the trail if it satisfied the neutral condition of Y=2.04". That would be 51.9 mm. So "less neutral" or "quicker than neutral" correlates to less trail. What else does it mean? I don't know.

While these discussions seem to offer insight, if what the terms mean is not agreed to by the participants, I can't see where my intent to help anyong else can possible be effective. If we ever do stop talking in circles, we will never know it.

It's seems that whatever Talbot was trying to say has no connection to what we here on BF are trying to say.

slower than neutral -
to me that would mean,
(talking drop handlebar road bikes),
a long front-center measurement.

As opposed to 'faster than neutral',
which would be a short front-center.

Let me find 3 pics to visually show what I think it translates to in the Real World.

vintage bikes are good examples given: level top tube, mostly straight tubes, visually simple, = enhancing frame design over aero frame designs or such things today.
long front-center on a large touring bike custom designed for stability in gusty wind conditions in flat TX & OK.

https://cimg6.ibsrv.net/gimg/bikefor...8f00f61b0.jpeg

Below a bike with short front center, possibly accentuated due to a likely head-on crash and stiff replacement fork not used in original build. Straight line stable, no hands with easy balancing, but lightning quick steering. Some would say twitchy.


https://cimg8.ibsrv.net/gimg/bikefor...f8728c849.jpeg

As to which bike is best example of neutral, I will pass. Above are extremes.

dies the equation take into account the change in handling effect from varying tire sizes.....say from 23mm to 38mm?



( sorry if this is too far off stem length topic of thread, but a handling and control issue )

Formulas might give you some context to discuss things in terms of numbers. But what is neutral on one bike still might might feel more or less stable on another geometry bike that is also at a neutral calculation.

I don't think that formula gives any useful comparison among different geometry frames. It just tells you how much different a frame and fork is from the bikes original design and components.

I have used everything from 32mm to 100mm with flat and drop bars on my bikes.

The 100mm stem is alot more compliant and stable at speed. It doesn't like being hustled around tight turns. Prefers a smoother more gentle line. Not much benefit in going significantly shorter for faster handling. Not the point of the stem. It's mainly a factor of fit. I like using a single piece forged stem over the cheaper welded stuff. Handlebars will also speed up or slow down the handling. Try getting used to a pair of handlebars your shoulder width.

All in all I noticed more of a difference than except trying stems between 40 -100mm on my road bike .