Metric that takes into account stem and handlebars for handling?

[cyan]

Is there a quantitative metric for 'handling' that takes into account not just the trail (http://yojimg.net/bike/web_tools/trailcalc.php) but also the stem length, bar reach, bar width (and even stem spacers?), as we know all of these other things affect handling?

If so, what's the formula to calculate it?

[fa63]

Trail, BB drop and wheelbase have the most impact on handling. Stem length etc. are all secondary in my experience, and the body adapts to changes in those very quickly (assuming we are not going to the extremes, like running a 60 mm stem on a 60 cm frame). But no stem is going to make a bike handle right, if the wheels aren't in the right place to begin with.

[vqdriver]

I wouldn't put too much effort into it. Unless you're using extreme sized parts It won't make much difference, and in those cases you're probably on the wrong size frame.

[yinzerniner]

Originally Posted by cyan

Is there a quantitative metric for 'handling' that takes into account not just the trial (http://yojimg.net/bike/web_tools/trailcalc.php) but also the stem length, bar reach, bar width (and even stem spacers?), as we know all of these other things affect handling?

If so, what's the formula to calculate it?

No real mathematic variable can accurately quantify the steering feel, but a combo of trail/rake/head angle with stem and handlebar sizes can probably get a somewhat accurate guesstimate as to how a bike will handle at different speeds.

Good article here going into steering nuances vs measurements.
https://cyclingtips.com/2015/03/how-...-and-handling/

[oldpotatoe]

Originally Posted by cyan

Is there a quantitative metric for 'handling' that takes into account not just the trail (http://yojimg.net/bike/web_tools/trailcalc.php) but also the stem length, bar reach, bar width (and even stem spacers?), as we know all of these other things affect handling?

If so, what's the formula to calculate it?

Considering that the human body isn't static, but flexible, at various points and 'hinges(elbows, waist, knees, hips, ankles, wrists, etc, etc.) and that the cyclist moves around on the bike all the time when riding..doubt there's a 'formula'..

Some small 'c' constants that are 'starting points', like kops, but 'comfort' is thrown into the 'equation or formula', and that's 100% subjective.

[quickfeet]

Realistically the only place you would feel a handling difference from stem length is in a parking lot. There just isn’t enough steering with the bars to have it affect performance IMHO.

Mtb and CX are different animals though.

[David Tollefson]

From a frame designer's perspective... An important factor keeps getting left out of the "handling" equation: weight distribution. The balance of front-center and chainstay length relative to where the rider's center of gravity rests while riding. Stem/bar length are resultants of the rider's morphology (their contact points) and the desired handling characteristics.

[spoonrobot]

It sounds like you're looking for the cockpit version of steering angle.

I think there's some merit to this but I haven't done the thinking or math to come up with anything myself.

These are two posts I bookmarked when I was researching this for my drop-bar MTB. I was trying to figure out the ideal combo for stem/reach/width for later 2010s 29er geometry.

Google Groups discussion on steering angle

PVD's take on stem length

[Mzilliox]

and what would discovering this accomplish? I dont see an application...

[yinzerniner]

Originally Posted by Mzilliox

and what would discovering this accomplish? I dont see an application...

The only realistic circumstance for the OP is "I found a blingy stem and bar combo that's different lengths than what I have / am used to. How much will it effect steering and handling since I can't test them out before buying."

And the answer always is; it depends on a lot of different variables and you can't shortcut a definitive answer from online responses without real world experience.

[dddd]

I've fitted (the best that I could) a great number of drop-bar bikes for my own use, many of which were well less than ideal in terms of frame sizing.

This for two reasons, firstly that my proportions are of the long-legged bias (so few frames offer an ideal fit), and secondly that most of these bikes were bought used, to likely be used for a relatively brief period before being sold (or not).
I thus gave myself the benefit of test-riding just short of "tons" of bikes and keeping the few (many?) that somehow "worked" in the real-world context of riding, out on the roads and/or trails.

The first thing (other than frame size, stack and reach) that I had to give consideration to was whether the bike had any chance of working off-road, which mainly had to do with the front-center dimension (distance of the front axle from the bottom bracket) and especially the tire clearances.
Those two variables naturally also weighed heavily on the desired weight distribution and on the stem length that would be needed.

I didn't give much thought to including trail dimensions, as these weren't often published and the fork rake might be unknown and more work to measure. I observed that headtube angle and fork rake have some tendency to have been adjusted to each other, though the trail is known to vary significantly from one bike to another. So I would simply test the bike without concerning myself with trail figures.

The end result of many such tests informed me that on most bikes, the stem length can affect the handling over the longer term (i.e., even after I'd ridden it for hundreds of miles).
Some road frames will have poor dynamics while sprinting when the stem length is changed just 1cm beyond a certain point, and this can, at the extremes, mean a stem longer than 10cm or shorter than 11cm.
Again though, this is on frames that were not ideal in terms of frame size (when the actual stack and reach figures were looked at).

I have yet to ride a production bike that handled poorly with it's factory-original stem length, even when the reach was a little off the mark, but a wrong-fitting bike never seems to handle as well whether I'm swooping corners at speed or sprinting uphill.
Some lower-level bikes such as the ubiquitous late-1980's Schwinns that curiously came with 8cm stems mounted to 58cm frames clearly benefited from longer stems that allowed the reach I needed to support my upper-body weight while sprinting/climbing, but the handling wasn't doing anything weird (with either the original 8cm or my 10cm stem) while I was descending a twisty road or sprinting (geometry on those BTW was 74STx73ht).

I did figure out that, for whatever reasons (weight transfer being one), a longer and lower stem tends to add stability, and vice-versa, which often allowed me to make conclusions about whether a needed (for fit) stem change would lead to better or worse handling. So a bike that already felt on the twitchy side would likely be a poor choice for me if it also measured up as needing a shorter and/or taller stem.

But since the body's dimensions are complex in terms of weight distributions about the various pivots/joints/hinges, as oldpotatoe surmised I concur that an all-inclusive formula seems like a near-impossible proposition at this time.

Hats off to the folks who struggle with the scientific side of the fitting game, I've had my fun with it but only at the "fun" level.

Editing here, note that stem length and headtube angle can also have a significant effect on a rider's drafting safety and efficiency in terms of the chance of touching tires with a leading rider's bike.
I suspect that many bikes have some bias in this regard toward achieving a shorter front-center. And one of my best-handling bikes ever (in overall terms) actually achieves the shortest front-center that doesn't quite burn holes in the toes of my shoes! That old bike, though built for someone else (and shown as before I put my preferred saddle on it), somehow does everything right, so is pictured below. It really deserves a good repaint and parts upgrades!