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PostPosted: Wed Jan 25, 2012 1:22 am 
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Posts: 261
if i wanted t go slightly longer and higher is there any set extra stack i need to add for going from a 100mm stem to a 110 or 120?


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Posted: Wed Jan 25, 2012 1:22 am 


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PostPosted: Wed Jan 25, 2012 6:35 am 
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wassertreter wrote:
I'm getting numb parts when I'm sitting on the saddle's nose. Still working on a better position while sitting centrally.

I sit far enough back on the saddle that my perineal area is accomodated by the downward curving "sweet spot" of he saddle, even though the nose is level or slightly turned up. It seems a little counter intuitive, but if your saddle nose is up, it helps slide you back where the saddle is wider and softer and curves down. Once you get up on the nose it is narrow and hard!


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PostPosted: Wed Jan 25, 2012 1:32 pm 
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Location: South Carolina
beardking wrote:
if i wanted t go slightly longer and higher is there any set extra stack i need to add for going from a 100mm stem to a 110 or 120?


Maybe, but if you keep the same stem anlge, the HB center will be higher. You may find though that by coming up a bit, and not much, maybe 1cm, that you are able to flatten out more.

HUMP

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PostPosted: Wed Jan 25, 2012 5:20 pm 
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bricky21 wrote:
phourgenres wrote:
I have been fitted in a more upright position, and I feel like I have a lot more power than I did before. So now I pose the opposite question from before. Why go low? Is it just for aerodynamics?

One advantage that I have found besides the extra power (now that my handlebars are higher), is that when I do come out of my saddle to sprint or climb I have more stability, because I no longer have to crouch over when Im pushing hard on my pedals.

I am so confused now... :noidea:

Thoughts?


The other good reason for going low is to lower your center of gravity which improves bike handling.


Errr, no! This is a common misconception + center of gravity is simply not a big issue on a bicycle.
A bicycle will not provide lateral support like a 3 or 4 wheeled vehicle. It leans into the corners because it has to be in line with the forces acting on it, inertia and gravity, to stay up..
On a three or four wheeled vehicle the center of gravity needs to stay low to enable high speed cornering because the centrifugal force will want to tip the vehicle over. A bicycle leans into a corner and is assisted in traction by the centrifugal forces pushing it into the ground.
A bike/rider with a lower center of gravity will react slightly quicker to input though, mainly because the length of the lever decreasing. Sort of like a pencil falling over faster than a broomstick.
(The center of gravity of a cyclist is usually 800-1000mm above ground so changing the position to be 10-20mm more upright would not make any significant change anyhow)

/a

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PostPosted: Wed Jan 25, 2012 8:27 pm 
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andy2 wrote:
bricky21 wrote:
phourgenres wrote:
I have been fitted in a more upright position, and I feel like I have a lot more power than I did before. So now I pose the opposite question from before. Why go low? Is it just for aerodynamics?

One advantage that I have found besides the extra power (now that my handlebars are higher), is that when I do come out of my saddle to sprint or climb I have more stability, because I no longer have to crouch over when Im pushing hard on my pedals.

I am so confused now... :noidea:

Thoughts?


The other good reason for going low is to lower your center of gravity which improves bike handling.


Errr, no! This is a common misconception + center of gravity is simply not a big issue on a bicycle.
A bicycle will not provide lateral support like a 3 or 4 wheeled vehicle. It leans into the corners because it has to be in line with the forces acting on it, inertia and gravity, to stay up..
On a three or four wheeled vehicle the center of gravity needs to stay low to enable high speed cornering because the centrifugal force will want to tip the vehicle over. A bicycle leans into a corner and is assisted in traction by the centrifugal forces pushing it into the ground.
A bike/rider with a lower center of gravity will react slightly quicker to input though, mainly because the length of the lever decreasing. Sort of like a pencil falling over faster than a broomstick.
(The center of gravity of a cyclist is usually 800-1000mm above ground so changing the position to be 10-20mm more upright would not make any significant change anyhow)

/a


Wouldn't a bike that's easier to turn equate to a better handling bike? It's noticeably easier to take fast lines threw tight corners when I lower my upper body vs. riding upright on the hoods.


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PostPosted: Wed Jan 25, 2012 9:39 pm 
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If you think it's better handling it is - for you.

But how do you know that it's easier to turn due to the up/down shift in the c of g?

My guess, and it's just a guess since I have not seen you on the bike, is that it's because of the change in the distribution of weight:
A lower position usually means that you put more weight on your hands, thus shifting your center of gravity forward. Loading up the fork tends to stabilize the steering, but also as you turn the bars the load swings around the inclined steerer axis, it will turn the fork. Sort of like power steering..
The more trail you bike has the more the wheel flop and thus the higher the tendency of the increased load to swing around the axis. High(ish) trail bikes are typical in modern small carbon frames fork with their often slack steering angles mated to standard 43-44mm offset forks.

Anyhow that's my initial hypothesis :noidea: .

/a

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PostPosted: Wed Jan 25, 2012 10:28 pm 
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andy2 wrote:
If you think it's better handling it is - for you.

But how do you know that it's easier to turn due to the up/down shift in the c of g?

My guess, and it's just a guess since I have not seen you on the bike, is that it's because of the change in the distribution of weight:
A lower position usually means that you put more weight on your hands, thus shifting your center of gravity forward. Loading up the fork tends to stabilize the steering, but also as you turn the bars the load swings around the inclined steerer axis, it will turn the fork. Sort of like power steering..
The more trail you bike has the more the wheel flop and thus the higher the tendency of the increased load to swing around the axis. High(ish) trail bikes are typical in modern small carbon frames fork with their often slack steering angles mated to standard 43-44mm offset forks.

Anyhow that's my initial hypothesis :noidea: .

/a


You ask some good questions. I guess I don't know the exact reason why my bikes corner better when I lower my upper body. I've always assumed that the lower the center of gravity the easier the bike is to turn. That's what I was taught, and never doubted it because it made sense and it worked.


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PostPosted: Thu Jan 26, 2012 8:29 am 
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hey, could you guys have a look at my fit, I posted about it here and would like thoughts on it
viewtopic.php?f=3&t=98908
thanks


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PostPosted: Tue Feb 07, 2012 6:24 am 
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Location: San Diego
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PostPosted: Sun Feb 12, 2012 12:57 pm 
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It's some time since i posted in this topic but I'm now finally running the 130stem instead of the 110. After some riding on the rollers I have to say it feels better. I'm going to try it outside next week to find out if the handling is still ok but I don't really have any doubts on that issue.

The 110 stem is still in stock for classics and mountain rides. If not useful it's going on the mountainbike.

Thx for the advice Hump and others! :thumbup:

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PostPosted: Wed Feb 29, 2012 10:57 am 
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Joined: Tue Apr 12, 2011 8:08 am
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Location: Pedal Square
Ok I can report back now after riding with the saddle back for some time -- interestingly that seems to help prevent the forward slipping, and lets me sit with the seatbones on the saddle nicely planted. My hypothesis is that my position was too far forward in the first place, so the centre of gravity was not properly over the saddle.

Interestingly I also find it very easy to spin the pedals in the more back position, which seems to be contrary to popular belief that setback is better for mashing. Anyway, probably just another indication that my initial position was not optimal.

Haven't done any climbing yet, though. The mountain roads are not in condition yet.

The guidance for finding my new position is Steve Hogg's "Point of balance" -- http://www.stevehoggbikefitting.com/blo ... oad-bikes/" onclick="window.open(this.href);return false; although I'm admittedly conducting it rather sloppily.

Next step: "How to ride in the drops like the pros", my goal is being able to comfortably do "all out" over 20km in the drops within a few months, and over 40km in fall, for taking part in TTs with a road bike classification. Might open another thread for that.

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