Does narrowing handlebars always reduce reach?

[Hexsense]

How do you get 5 cm thick each shoulder?

guess work. But I guess the inside to inside shoulder width to be 36cm, not c-c which you think it is 39cm.

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.

Yeah the number sounds off. Like way too big for global average men. Global average men height in 2020 was 176.5cm. So wing span of 2 meters as average sounds off.

Based on your number, 45-39=6cm. So it's 3cm each arm when considering c-c vs o-o.
But (do we really)* rotate at the center of the shoulder socket? Shouldn't it be i-i (inside to inside, to exclude arm width at the shoulder completely) -> and hence, bigger delta when considering i-i shoulder width?

()* part : genuine question. I really don't know this. So please correct me.

[BigBoyND]

The 46cm is likely o-o. So it overlaps with some of the arm length from the other chart. These are averages I found online in 5 second, not rocket science precision.

Anyway, I used these numbers as rough approximation. So whether reach changes 1.3mm, or 1.0mm or 1.5mm, doesn't mean much. The point is that you don't need to get a different stem length.

[alanyu]

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.

Yeah the number sounds off. Like way too big for global average men. Global average men height in 2020 was 176.5cm. So wing span of 2 meters as average sounds off.

Based on your number, 45-39=6cm. So it's 3cm each arm when considering c-c vs o-o.
But (do we really)* rotate at the center of the shoulder socket? Shouldn't it be i-i (inside to inside, to exclude arm width at the shoulder completely) -> and hence, bigger delta when considering i-i shoulder width?

()* part : genuine question. I really don't know this. So please correct me.

During my dynamic fitting, the fitter first measured the width of bone top point around the joint (I don't know what should it be called academically), when I stood naturally with arms down. This is 39cm and I refer it as c-c width. After that, I was required to gently stretch out my arms forward and to hold a straight bar. The width of the same bone point was measured to be 38cm. Based on these, the fitter initially suggested 38/39 c-c bars, and after pedalling on fitting bike with different setups, he suggested me 38 c-c for Gran Fondo and 36 for rides shorter than 100 km. 36 c-c aero bar was and is hard to source out and I do long rides more than short rides, so I opted for 38.

If this can help.

[maxim809]

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

Geometry is not a theory.

Okay fair, now please validate the equation from BigBoy for us on how it maps to real life.

Tactic knowledge being overruled by GIGO and fancy formulas is what I am trying to get people to see and understand. The formula is only as good as the person concocting it.

In the end, I agree with smokva in that the only way to really know is to try for yourself.

[Roadbiker10]

Don't know about shoulder width. But from measuring alone, on two different bikes I've changed from 42 to 38. The difference was 0,5cm in reach.

[BigBoyND]

Okay fair, now please validate the equation from BigBoy for us on how it maps to real life.

Tactic knowledge being overruled by GIGO and fancy formulas is what I am trying to get people to see and understand. The formula is only as good as the person concocting it.

In the end, I agree with smokva in that the only way to really know is to try for yourself.

That was very basic trigonometry and using average proportions we end up at an estimate of 1.3mm change in reach. What is GIGO about it?

The point of the "fancy" formula wasn't to be exact, but to show that we're an entire order of magnitude off from the next stem size in change and that's if you switch from very narrow bars to very wide ones, or vice versa.

[darnellrm]

Okay fair, now please validate the equation from BigBoy for us on how it maps to real life.

Tactic knowledge being overruled by GIGO and fancy formulas is what I am trying to get people to see and understand. The formula is only as good as the person concocting it.

In the end, I agree with smokva in that the only way to really know is to try for yourself.

That was very basic trigonometry and using average proportions we end up at an estimate of 1.3mm change in reach. What is GIGO about it?

The point of the "fancy" formula wasn't to be exact, but to show that we're an entire order of magnitude off from the next stem size in change and that's if you switch from very narrow bars to very wide ones, or vice versa.

BINGO

[maxim809]

I'm really trying not to call you out this way.... cuz I hate to put people on the spot (I'm being honest) but have you tried various handlebar widths while keeping the stem length the same?

If so, at what increments have you swept?

[TriJoeri]

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)

Sorry to bring up an older thread, but I got my Factor Ostro with 420mm bars and I want to move down to 360mm like I have on my gravelbike.

If my arm length from shoulder to wrist is 480mm (hypotenuse). Then for half a bar width for the new bar of 180mm (opposite side), the angle is sin^-1(180/480) which is 22 deg. Then the reach would be cos 22 deg * 480mm which is 445mm.

For the older bar the angle is sin^-1(210/480) which is 26 deg. Then the reach would be cos 26 deg * 480mm which is 431mm.

The difference is then 13-14mm longer reach for the narrow bars?
Not saying you're wrong but I'm trying to figure out my stem length before I order my cockpit but 1mm in difference or 13mm difference in stem length is a bit discrepancy in either mine or your calculation haha.

[BigBoyND]

The way youre calculating the angles suggests that both of your shoulders are in the center of your chest. You're not incorporating shoulder width anywhere. Once you do, it brings those "22deg and 26deg" much closer to zero where each degree has a smaller impact on Cos.

[sigma]

Okay fair, now please validate the equation from BigBoy for us on how it maps to real life.

Tactic knowledge being overruled by GIGO and fancy formulas is what I am trying to get people to see and understand. The formula is only as good as the person concocting it.

In the end, I agree with smokva in that the only way to really know is to try for yourself.

That was very basic trigonometry and using average proportions we end up at an estimate of 1.3mm change in reach. What is GIGO about it?

The point of the "fancy" formula wasn't to be exact, but to show that we're an entire order of magnitude off from the next stem size in change and that's if you switch from very narrow bars to very wide ones, or vice versa.

This was my conclusion as well. I used to ride 44cm bars which is my shoulder width. I went to 42 then slowly 40. Now to 38 on some bars. I made the shift more of a function of where I often had my hands while climbing - on the inner parts of the flat part of the bar. As I was doing this, I worked with my fitter on the reach issue as I had the same question. Theoretically should not be an issue, but in practice lots of moving parts. Swapped the trainer bars to 38 for the winter. Once I factored in where put my hands most of the time (hoods) and the longer reach of 9270 di2, I left the stem measurements alone in the end after experimenting with a few different lengths. Caveat - I live in the Rocky mountains most of the year, so climbing a lot which puts me in a different position than folks riding flatter and shorter courses like crits. If I were in that case, I would be tempted to add some length to lower the torso even more, but I would not do this in the mountains where I prefer to climb slighty more upright. Last point, handling especially on the descents. Quite different with narrower bars. Takes a bit of practice to get used to the new balance points.