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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 04-25-06, 08:42 PM   #1
sloppy robot
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the roadies got me all bugabooo..

im reading this thread over there.. trying to figure out fit.. and the claim is.. the steeper the seat tube angle.. the shorter the Tops tube can be to get the same fit..

i.e... a 74 degree s-t with a 53 t-t is similier to a 73 degree s-t with a 54 t-t..

what i want to know is.. wouldnt it be the opposite? the steeper the seat tube.. the closer your seat is to the head tube? help me here.. this **** is ****ing me up.. baxtefer.. i saw you over there chiming in.. feel free to help a brudda see the light..

edit: heres a quote summing it up: For every 1deg increase in seat angle, you can subtract ~1cm of toptube, and for every 1deg decrease in seat angle, you can add ~ 1cm of top tube.
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Old 04-25-06, 08:45 PM   #2
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That's assuming that you're going to keep your position relative to the cranks the same. So you'll be more set back on the seat post.
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Old 04-25-06, 09:02 PM   #3
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Originally Posted by endform
That's assuming that you're going to keep your position relative to the cranks the same. So you'll be more set back on the seat post.
endform nailed it.
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Old 04-25-06, 09:11 PM   #4
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Originally Posted by dolface
endform nailed it.
is this some KOPS **** youre talking about? ah.. i kinda get that.. my first mistake was reading the roadie forum
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Old 04-25-06, 09:13 PM   #5
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I was thinking about this too. I rode a road bike for 20-something miles and my arms, elbows and hands were killing me. I was first thinking it was seat angle/positioning, but all was good. The bars were a lot higher than what I ride on my track bike. I usually ride about a 55-56 roadbike and 54ish track frame with a really long stem so I get my weight forward. This was a 54cm specialized allez sport along these lines
I started thinking about top tube length. My track bike is just about square, or a little under. 54c-c seat tube and 53 top tube. To complicate matters, the geometry is obviously compact. I don't know anything about the virtual geometry, but the way I see it-- given identical measurements (seattube length c-c and top tube length), virtual or not, the post would extend from that geometry at an angle effectively lenthening the top tube on a bike with a more relaxed seat tube angle.

This would explain why I have elbow pain. I was too stretched out, and more of my weight was placed on my arms. That and the roadies were having a lot of trouble keeping up when I left cruiser mode.
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Old 04-25-06, 09:20 PM   #6
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Originally Posted by chuck_norris
That and the roadies were having a lot of trouble keeping up when I left cruiser mode.
oh..snap, dawg... hammer time!

the double negatives of this all is what messes me up
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Old 04-25-06, 09:23 PM   #7
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Originally Posted by sloppy robot
is this some KOPS **** youre talking about? ah.. i kinda get that.. my first mistake was reading the roadie forum
Edit: I swear to God I just typed something out that wasn't even english. **** it, I give up.
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Old 04-25-06, 09:54 PM   #8
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Originally Posted by sloppy robot
is this some KOPS **** youre talking about? ah.. i kinda get that.. my first mistake was reading the roadie forum
Sort of, just think of it as butt over bb.
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Old 04-25-06, 11:07 PM   #9
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When you make the seat tube go straight up and down, you are not moving the seat forward, but rather moving the bottom bracket back.

Basically bike fit works like this. First, put your butt and bottom bracket in the proper relationship. Then adjust your handlebars forward, backward, up or down to get the right comfort/fit/aerodynamics you desire. Whatever you do (and here's where I really question my fellow roadies judgement) do not move the seat forward or backward in order to change your reach to the handlebars. If your handlebars are too far or too close, use a longer or shorter stem.

A person's torso remains the same length no matter how far forward or back their but is sitting over the bottom bracket. So a person who needs a 56cm top tube needs that same top tube length regardless of their seat tube angle.
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Old 04-26-06, 12:49 AM   #10
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Originally Posted by MrCjolsen
do not move the seat forward or backward in order to change your reach to the handlebars. If your handlebars are too far or too close, use a longer or shorter stem.
this is true.

Quote:
Originally Posted by MrCjolsen
A person's torso remains the same length no matter how far forward or back their but is sitting over the bottom bracket. So a person who needs a 56cm top tube needs that same top tube length regardless of their seat tube angle.
this is not necessarily true. (unless you mean total reach, not top tube length)

steepening the STA, while keeping the same saddle height and saddle-on-rails position, effectively moves the saddle forward.
the saddle should be moved *back* on the rails to maintain a the proper knee/leg/pedal position.
this effectively lengthens the top tube.
in other words, a 73 degree STA with a 56cm TT and a 74 degree STA with a 55cm TT *may* give the same reach, with the same bar/stem combo. obviously this depends on your saddle height - to the tune of approximately H*sin(1) cm, per degree change in STA (where H=saddle height).

or, put it this way:
given two frames with identical 56 cm TTs, but one with a 73 STA and one with a 74 STA, you'd put a 1cm *SHORTER* stem on the 74 STA to maintain the same reach.
shorter stem affects weight distribution, affects handling, yaddayaddayadda.

you get my point

Last edited by baxtefer; 04-26-06 at 01:31 AM.
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Old 04-26-06, 06:57 AM   #11
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With regard to the fwd/aft position of the saddle, I think that there's an amount of personal preference involved as well. I've tried KOPS. I've also tried keeping the nose of my saddle within 6-8 cm aft of a vertical line extending from my bottom bracket spindle.

Every time I do any of these things, I find that I'm jost not as comfortable as I am with my saddle pushed as far forward as it will go. For some reason, my butt wants to be as close to directly over the bottom bracket as I can make it. Whenever I move my seat back, my butt is more sore and my legs feel lke they have less power.

Also, that rule where the view of your front hub is supposed to be blocked by your handlebars also doesn't work for me. That rule would make my stem an inch and a half longer than what is comfortable for me.
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Old 04-26-06, 07:03 AM   #12
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Quote:
Originally Posted by MrCjolsen
With regard to the fwd/aft position of the saddle, I think that there's an amount of personal preference involved as well. I've tried KOPS. I've also tried keeping the nose of my saddle within 6-8 cm aft of a vertical line extending from my bottom bracket spindle.

Every time I do any of these things, I find that I'm jost not as comfortable as I am with my saddle pushed as far forward as it will go. For some reason, my butt wants to be as close to directly over the bottom bracket as I can make it. Whenever I move my seat back, my butt is more sore and my legs feel lke they have less power.

Also, that rule where the view of your front hub is supposed to be blocked by your handlebars also doesn't work for me. That rule would make my stem an inch and a half longer than what is comfortable for me.
it sounds like you're on the wrong sized frame.
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Old 04-26-06, 09:44 AM   #13
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My fixie is a 56 and my road bike is a 58. It's the case with both of them. And I know that anything larger would be way too big for me. I like being directly over the pedals.

The type of riding you do makes a difference as well. Setback is great for sprinting and racing. But triathletes go for a more vertical seat tube. They get on their bikes and ride at a steady pace for 100+ miles. That's more like what most non-racing roadies do on a regular basis. If I'm riding a century I'll take a cue from triatletese over road racers any day.
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Old 04-26-06, 11:58 AM   #14
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Moving the saddle fore and aft brings different muscle groups into focus. When mashing low RPMs up a steep climb seated, you'll tend to move your butt back on the saddle to work the glutes and hamstrings. For fast spinning the butt tends to move forward. Its the type of riding and riding style that affects base fore/aft saddle adjustment and knee to pedal spindle relationship.

Last edited by pigmode; 04-26-06 at 12:18 PM.
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Old 04-26-06, 12:13 PM   #15
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Quote:
Originally Posted by MrCjolsen
My fixie is a 56 and my road bike is a 58. It's the case with both of them. And I know that anything larger would be way too big for me. I like being directly over the pedals.

The type of riding you do makes a difference as well. Setback is great for sprinting and racing. But triathletes go for a more vertical seat tube. They get on their bikes and ride at a steady pace for 100+ miles. That's more like what most non-racing roadies do on a regular basis. If I'm riding a century I'll take a cue from triatletese over road racers any day.
uh, not really.
sprinters (at least track sprinters) prefer a more vertical seat tube. it puts them over the pedals for more power. see dolface's yellow 3Rensho or shant's makino.

triathletes (and time trialists) do use steeper seat tubes. However, they don't do it because it's more comfortable on 100+ mile rides. They do it because they want to get aero, but still be able to transfer power. dropping onto aero bars closes your hip angle and reduces power. scooting the saddle forward by steepening the STA re-opens the hip angle and allows you to get more aero, and to increase power transfer.
on top of that the steep STAs of tri-bikes changes the muscle groups used - more quads, less hanstrings so you can save then for the run.
and tri-bikes generally suck for any kind of climbing.
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