Does narrowing handlebars always reduce reach?

[biwa]

Many posts online say narrower bars reduce your reach and if >2cm narrower you may want a longer stem to compensate.

Is that always true? Doesn't it depend on how wide your shoulders are? If your shoulders are as wide as the original bar width, doesn't narrower bars actually increase your reach to the bars (visualize the triangle formed as you move)?

Or is there some anatomical details I'm missing that'd defeat my argument?

[Hexsense]

If you keep your shoulder stationary, bring hands closer together only from elbow to hands without moving the shoulder. The reach is reduce, right?
Now, try again but move from the shoulder. Try to thrust the shoulder forward to make it narrower. You don't only make the hand spacing narrower. But even the distance between both elbow reduced as well. Does that increase reach instead of reducing it?

While deemed as bad form, you can thrust or fold the shoulder forward to fit narrower bar and longer reach. Real shoulder width is fixed. But effective shoulder width that matter to the bike posture isn't.

[BigBoyND]

Depends on shoulder width. If your bar is wider than your shoulders, then narrower will decrease reach (need longer stem). If your bar is narrower than shoulder width then it will increase reach (need shorter step). It's an arc that maxes when you're arms are straight forward.

But enough of the theory and let's see what this means in practice.

Average arm length for a male is 63cm. Average shoulder width 46cm.

Let's say you go from a 460mm handlebar to a 380mm bar, so each arm moves in 4cm, which is a huge change.

630-630mm*cos(arcsin(40mm/630mm)) = 1.3mm

So even if you go from a 460mm bar to 380mm to only need a 1mm shorter stem. Keep the stem you have.

Edit: edited the math (thanks for the correction)

[biwa]

If you keep your shoulder stationary, bring hands closer together only from elbow to hands without moving the shoulder. The reach is reduce, right?
Now, try again but move from the shoulder.

When you bring your hands closer together (assuming along the same horizontal line), you'll need to extend/move forward your elbow/upper arm to do that, so effectively the reach is longer.

Try to thrust the shoulder forward to make it narrower. You don't only make the hand spacing narrower. But even the distance between both elbow reduced as well. Does that increase reach instead of reducing it?

Isn't thrusting your shoulders forward the same as an adjustment of your body to a longer reach?

[biwa]

Depends on shoulder width. If your bar is wider than your shoulders, then narrower will decrease reach (need longer stem). If your bar is narrower than shoulder width then it will increase reach (need shorter step). It's an arc that maxes when you're arms are straight forward.

But enough of the theory and let's see what this means in practice.

Average arm length for a male is 63cm. Average shoulder width 46cm.

Let's say you go from a 460mm handlebar to a 380mm bar, so each arm moves in 4cm, which is a huge change.

630-630mm*cos(sin(40mm/630mm)^(-1)) = 8.3mm

So you would have to go from a 460mm bar to 380mm to need a 8mm shorter stem. Unless you're making such a large jump, you can probably keep the stem you have.

What is sin(40mm/630mm)^(-1)? You mean arcsin(40/630)? EDIT: actually, by that calcuation, the distance change is much lower than 8.3mm, more like 1.3mm. And the trigonometry here is not so right.

[maxim809]

So you would have to go from a 460mm bar to 380mm to need a 8mm shorter stem. Unless you're making such a large jump, you can probably keep the stem you have.

noooooooez

you need to factor what happens to the rider's hip angle when they go narrow bars

narrow bar often means the rider is sitting up more

Increasing the stem length is one way to correct this. Tweaking stack/setback/cleats can also be a thing. So to OP's question, yes narrower bars can decrease reach.

Regarding shoulder width, that is a starting point, but people's elbows splay differently, people have different levels of flexibility, and the way how each person's shoulder blades interact are different while on hoods vs drops...

So the most important thing to start with is the rider's goals and work forward from there. Normally when narrow bars are discussed it's for aero. But it's not always the fastest without the right fit. Especially if you're sitting up more, or unable to get your head dropped from skeletal/muscular limitations around the shoulder blade area.

[Hexsense]

Isn't thrusting your shoulders forward the same as an adjustment of your body to a longer reach?

For me, it's otherway around.
I don't thrust because the reach is too long. But I do it automatically to reduce the shoulder (and arm) width on a bike with narrow bar, regardless if my stem is short or long.

Then, since thrusting the shoulder increase my effective arm length, I'm more comfortable with longer stem.

If you keep your shoulder stationary, bring hands closer together only from elbow to hands without moving the shoulder. The reach is reduce, right?
Now, try again but move from the shoulder.

When you bring your hands closer together (assuming along the same horizontal line), you'll need to extend/move forward your elbow/upper arm to do that, so effectively the reach is longer.

I don't keep it horizontal.
When my hands are wide, shoulder are relaxed.
Then when I try to make myself narrower, the shoulder fold forward to reduce width automatically. My hands now join at a farther spot. That should pair with a longer stem to take back the increased arm length.

That said, I trend back from narrow bar back toward moderation these day. From 36cm bar to a more standard width 38cm. My shoulder/neck are more relaxed with 38cm bar than 36cm.

[smokva]

Depends on shoulder width. If your bar is wider than your shoulders, then narrower will decrease reach (need longer stem). If your bar is narrower than shoulder width then it will increase reach (need shorter step). It's an arc that maxes when you're arms are straight forward.

Exactly, depends on your shoulder width and bar widths of new and old bar.
If old bar = shoulder width than new narrower bar will reduce reach.
If old bar > shoulder width than new narrower bar will increase reach, upt to bar=shoulder, after that it will start to decrease
If old bar < shoulder width than new narrower bar will reduce reach even more.

All of that is theoretic, in practice there might be more factors which influence reach....for example when you decrease bar width you might want to change your torso angle to get more aero which will also have impact on reach. This might make you move the saddle a bit.
Anyway...the only way to really know is to try, and readjust saddle and reach (stem) after installing new bar. If you are changing bar model good chances are you'll need another stem anyway.

[BigBoyND]

630-630mm*cos(sin(40mm/630mm)^(-1)) = 8.3mm

So you would have to go from a 460mm bar to 380mm to need a 8mm shorter stem. Unless you're making such a large jump, you can probably keep the stem you have.

What is sin(40mm/630mm)^(-1)? You mean arcsin(40/630)? EDIT: actually, by that calcuation, the distance change is much lower than 8.3mm, more like 1.3mm. And the trigonometry here is not so right.

Arcsin and inverse sign are the same function. You're right I should've written it sin^(-1)(40/630) which changes it to 1.3mm. In which case the change is negligible and the OP should not change stem length

[maxim809]

running a theory thru an equation is not practice, it's still theory

practice is actually trying several bar widths on your same bike

[alanyu]

Average arm length for a male is 63cm. Average shoulder width 46cm.

I think this value is based on the o-o measurement for custom suits, rather than the c-c value for bar width.

[darnellrm]

running a theory thru an equation is not practice, it's still theory

Geometry is not a theory.

[smokva]

[/quote]

Geometry is not a theory.
[/quote]

Not practice eaither

[Hexsense]

Average shoulder width 46cm.

I think this value is based on the o-o measurement for custom suits, rather than the c-c value for bar width.

And since arm is at least 5cm thick each shoulder. Would that mean shoulder socket width where the movement happen is 36cm on average or narrower?

[alanyu]

Average shoulder width 46cm.

I think this value is based on the o-o measurement for custom suits, rather than the c-c value for bar width.

And since arm is at least 5cm thick each shoulder. Would that mean shoulder socket width where the movement happen is 36cm on average or narrower?

How do you get 5 cm thick each shoulder? To me it is 45 o-o and 39 c-c. If the average c-c is 46cm, why no/few brands make 48 and 50 c-c dropbars? Moreover, with avg. arm length 63cm, even considering small hands like 15cm, it will simply yield 46+63*2+15*2 = 202cm arm span , if you insist 63 and 46 both are correct values for avg. arm length and avg. c-c shoulder width.