Changing Stem Length after bike fit

Discuss light weight issues concerning road bikes & parts.
wingguy
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by wingguy

RussellS wrote:
Thu May 03, 2018 10:28 pm
The only thing that matters regarding aerodynamics on a bike is the amount of surface area going into the wind. How you achieve the minimal surface area is irrelevant.
Absolutely not true, for aerodynamics on the bike or for any other kind of aerodynamics.
Long and low or short and fat.
I can't even envision a short and fat position. How do you make that happen? :P

by Weenie


guyc
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by guyc

wingguy wrote:
Fri May 04, 2018 7:42 am

I can't even envision a short and fat position. How do you make that happen? :P
I've seen that at a few sportives :lol:

morganb
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by morganb

Since the Obree position is somehow relevant to fit and aero on a standard road bike, everyone knows the fastest position is laying down with your feet in front of you and a fairing around you.

morganb
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by morganb

But back to the OPs question, I think it's best to used your fit as a reference more than an absolute. I've gone 2cm narrower in bars and 1cm longer in stem since my last fit along with marginally lower and am just as comfortable, but my initial fit was pretty far away from where I am now.

Mr.Gib
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by Mr.Gib

wingguy wrote:
Fri May 04, 2018 7:39 am
Mr.Gib wrote:
Thu May 03, 2018 11:21 pm
wingguy wrote:
Thu May 03, 2018 8:48 pm
Mr.Gib wrote:
Thu May 03, 2018 4:26 pm
Overlooking the "generally" qualifier, longer and lower is not more aerodynamic. Having a very high handlebar, perhaps as high as the seat, and a shorter stem is much more aerodynamic.
I'm sorry what?

Unless you're referencing the Obree tuck I'm really not sure where this could possibly have come from. And if you are referencing the Obree tuck, it obviously has zero to do with a usable or sustainable road riding position. :noidea:
Exactly. The areodynamic superiority of this position is massive. Obree won using much less power.
Exactly, It's a pointless and daft thing to say in the context of road riding.
That's interesting, people said Obree was daft. But what he proved that is relevant in the context of road riding, was that bent elbows are faster. In fact, he didn't really prove that as it was pretty much common knowledge. What Obree showed was what could be gained by maximizing this position. I think it is obvious that I am not suggesting setting up a road bike to acheive the Obree tuck.

With the massive industy (manufacturers and consumers) investment in aerodynamics for the road, I can't imagine why optimizing the body, the part of the system that has by many magnitudes the greatest influence on aerodynamics, would ever be considered pointless.

Here's another one for you - assuming a fixed saddle height, which is more aerodynamic - peddaling with the toe down or with the foot level? No idea of the answer, but I am curious (with appologies to the OP for the hijack).
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

Hexsense
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by Hexsense

RussellS wrote:
Thu May 03, 2018 10:28 pm

The only thing that matters regarding aerodynamics on a bike is the amount of surface area going into the wind.
No. Shape matters, a lot.
Tilted cylinder 's Drag Coefficient (fore arm straight down in drop) is a lot worse than a straight ahead cylinder (forearm horizontal in drop) even without talking about the frontal area (which bent elbow with horizontal forearm also have less surface area of arm expose).

The were also some (informal) talk about belly actually fill the gap in the torso area make the shape more aero for the same surface area... which obviously not helping as much as the belly fat harm ability to sit in lower position.

DCcyclist
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by DCcyclist

Doesn't steering become less responsive as you increase the stem length?

This is a helpful discussion because I had removed spacers about 1cm and never changed my stem length. Should I get a longer stem and why?

AJS914
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by AJS914

When you remove spacers the reach effectively gets longer so you could potentially get a shorter stem if needed. It's probably just a few mm though so you probably don't need a full cm shorter stem.

wingguy
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by wingguy

Mr.Gib wrote:
Fri May 04, 2018 4:11 pm
I think it is obvious that I am not suggesting setting up a road bike to acheive the Obree tuck.
Just as it is obvious that simply stating without context, in a discussion of road riding positions, that a very high and very short stem is better aerodynamically than long and low is pointless, counterproductive, and fundamentally bad advice.

Mr.Gib
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by Mr.Gib

wingguy wrote:
Fri May 04, 2018 10:20 pm
Mr.Gib wrote:
Fri May 04, 2018 4:11 pm
I think it is obvious that I am not suggesting setting up a road bike to acheive the Obree tuck.
Just as it is obvious that simply stating without context, in a discussion of road riding positions, that a very high and very short stem is better aerodynamically than long and low is pointless, counterproductive, and fundamentally bad advice.
What you say is true but, as opposed to presenting it as simple universally applicable advice, I am working from the assumption that the readers on this forum will pause to contemplate the seemingly radical suggestion, and synthesize the context in their thought process (just as you did).
It is a suggestion designed to compel the reader to contemplate more implications of handlebar location, and help them to avoid pointless, counterproductive, or fundamentally bad advice.

It is thoughtful of you to protect those readers who may not get my point, but I was not writing for them.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

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themidge
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by themidge

Obree still has a flat back in his poistion, so I'm not sure why you're all arguing about this. If you look at photos of riders doing time trials in days gone by (before the invention of the TT bike, think Anquetil, or early Hinault) then they still have a very aggressive position, but with quite high handlebars, they achieve that position by bending their elbows. These days riders have lower handlebars but the same back angle.
Also, the analogy of the child on a sit-up-and-beg bike being more aero than Indurain is slightly meaningless because the child, by sitting bolt upright, acts like a sail, which Indurain does not because he is tucked in low. The child is probably still more aero because they're so small, but that's about as far as it goes.

Long and low looks cool too, who wants to look like Graeme Obree?

jih
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by jih

DCcyclist wrote:
Fri May 04, 2018 6:56 pm
Doesn't steering become less responsive as you increase the stem length?

This is a helpful discussion because I had removed spacers about 1cm and never changed my stem length. Should I get a longer stem and why?
Not really less responsive. Less twitchy I’d say.

I guess technically less responsive, but in a good kind of way.

Depends what you ride now of course. Most modern racing frame geometries seem to be made with a 110-130 stem length in mind.

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