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Changing Stem Length after bike fit

Posted: Thu May 03, 2018 6:09 am
by quadzilla
Maybe like 3 months ago I got a bike fit (best upgrade I've ever made) but at the time I was out of fitness and very unflexible. As I am now in my road race season, I am in better shape and stretching has made me significantly more flexible. For reference, during my bike fit I could barely touch my toes, now I can grab the entire top of my foot with my entire hand. During the fit they recommended a 120mm stem and thats what ive been riding since. Becuase of my increase in flexibility I want to go for a longer stem 130 maybe. Will this mess up the rest of my fit? i don't wanna get another fit soon becuase it was very expensive. I'll most likely buy a cheap kalloy stem, test it for a few weeks then evaluate. any opinions?

Changing Stem Length after bike fit

Posted: Thu May 03, 2018 6:09 am
by Weenie

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 6:45 am
by TonyM
The bike fit has to be seen as a baseline from where you can/should experiment depending on your fitness level, goals etc....

Try the new stem length!

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 3:37 pm
by Rick
My advice would be go ahead and try it. I have switch stem-lengths numerous times in experimentation.
But you have to be honest with yourself. It is not only about your flexibility. Power-output and long-term comfort come into play even though longer-lower seems generally better from the aerodynamics.

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 4:26 pm
by Mr.Gib
Rick wrote:
Thu May 03, 2018 3:37 pm
longer-lower seems generally better from the aerodynamics.
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.

It is more a question of in what position can you hold your torso and arms, and where do your handlebars need to be to acheive this so you can control your bike with comfort. If you feel too cramped or you are not happy with the angle of your upper arm/elbow bend when you "get low", then you may be happier with a longer stem. On the other hand maybe you are better off just bending your elbows more.

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 7:00 pm
by Rick
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.
Well, just look at some pics of a professional in time trial position, and make your own assessments ;)

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 7:36 pm
by AJS914
I say try it. One centimeter is not a huge amount.

One thing of remember is that different stems have different clamp lengths. If the new stem clamp is wider then you need to remove spacers. If shorter, then add. It may be easier to get the same exact brand of stem.

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 7:53 pm
by Zakalwe
Have you got any spacers you can lose first? You won’t get much lower with a longer stem, just have to stretch your arms further

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 8:44 pm
by jih
Just do it. Stems aren’t that expensive and easy to change back if you don’t like it.

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 8:46 pm
by quadzilla
Thanks for the answers and opinions.

In terms of spacers I actually have quite a few. The but my saddle height is 801mm and my frame size is 56 so I still have quite a large saddle to bar drop. The reason i want a longer stem is to make the "aero on the hoods" positions more comfortable. I already ride with my arms reasonably bent with little back pain and it can sometimes feel like I need to use lots of core and shoulder strength to be aero on the hoods. It kinda feels cramped aero on the hoods.

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 8:48 pm
by wingguy
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:

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 10:28 pm
by RussellS
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?
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. Long and low or short and fat. Makes no difference. Surface area hittig the wind is what matters. A child on a tricycle is more aerodynamic than Miguel Indurain was on his time trial bike. Because the child sitting straight up had much less surface area hitting the wind than Indurain did in his most tucked aero position.

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 10:52 pm
by 2lo8
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.
I'm not an aeroweenie, but I'm pretty sure that isn't right. There's reasons why rims are wide, tubes are foil shaped, helmets have funny shapes, people wearing socks on the outside of their shoes, velomobile fairings, mantis position etc. As far as body position complying with UCI regulations, that might be more or less true as a basic rule of thumb.

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 11:21 pm
by Mr.Gib
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.
Image

But the laws of aerodynamics remain, only regulations and what an athlete's body might do change. At any given position of the torso, the more a cyclist can fold up the arms, the more aerodynamic they will be. In other words, keep the torso constant and raise/shorten the bars for better aerodynamics. Of course the obvious question each rider must ask is whether they are comfortable in that position for the required period of time.
Rick wrote:
Thu May 03, 2018 7:00 pm
Well, just look at some pics of a professional in time trial position, and make your own assessments ;)
Another way to look at a good time trial position is to consider that the bars are set as high as they can go for that position. If the bars were raised further the cyclist would be forced to raise the torso. Now the bars could go lower without affecting the position of the torso, but it would open up the arms increasing aerodynamic drag.

So to the OP, my answer to the question about stem length is it depends what you are trying to achieve. I assume that like most of us you are trying to find the right balance between comfort and aero for your body and the type of riding you do. No chart will give you that, so feel free to experiment. Just don't assume that longer and lower handlebars automatically equates to better aerodynamics.

Re: Changing Stem Length after bike fit

Posted: Thu May 03, 2018 11:45 pm
by 2lo8
Mr.Gib wrote:
Thu May 03, 2018 11:21 pm
But the laws of aerodynamics remain, only regulations and what an athlete's body might do change. At any given position of the torso, the more a cyclist can fold up the arms, the more aerodynamic they will be. In other words, keep the torso constant and raise/shorten the bars for better aerodynamics. Of course the obvious question each rider must ask is whether they are comfortable in that position for the required period of time.
If you want to toss regulations out the window, there are far more comfortable and more aerodynamic positions that don't require your torso to be aerodynamic though and your arms wherever you want them.

Re: Changing Stem Length after bike fit

Posted: Fri May 04, 2018 7:39 am
by wingguy
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.

Re: Changing Stem Length after bike fit

Posted: Fri May 04, 2018 7:39 am
by Weenie