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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 01-22-09, 10:02 PM   #1
kfm
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track/road frame geometry

i want to design a frame with road geometry. does anyone have specific information as to how geometry is factored (beyond the assumed)? i've looked around the web a bit, & it seems like most frame builders work off of standards that they tweak a little here an there. i'm curious, because otherwise the process seems very abstract. lower bottom bracket, more fork rake, longer stays, looser seat & head tube angles... but how do i figure out how much (given my inseam & size).

thanks
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Old 01-22-09, 10:06 PM   #2
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I am guessing better responses may await this question in the frame building sub forum. those guys are pretty helpful.
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Old 01-22-09, 10:12 PM   #3
kfm
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yup, i posted it there as well.
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Old 01-23-09, 02:01 AM   #4
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there are lots of different takes on geometry...

"Eddy MerckxCenturyGeometry",Lemond,European,Italian,Classics,
Sloping,Compact,Crit,blah blah....

have fun...

http://en.wikipedia.org/wiki/Bicycle...Frame_geometry
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Old 01-23-09, 02:33 PM   #5
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Typical road geometry is 73 degree head tube, 73 degree seat tube with 40-45mm rake depending on how you want to tweak the trail. This is "all-around" road geometry, and has been more or less the standard for a long time because it works. The 73 degree seat tube keeps things a little more comfortable because it means inherently longer chainstays and fits a large amount of riders for fore-aft seat position. The 73 HT/40-45mm works very well for how one would want a road bike to handle on the road. The greater-BB drop (lower BB height) means more dampening inherent in the longer stays, as well as lower center of gravity which is much desired when doing long, winding descents.

Steepening the head tube and seat tube/lessening the rake results in a tighter wheelbase, more stiffness inherent in the geometry (a steeper HT/less rake will give less dampening and more road feel up front, while also stiffening the front end; a steeper ST/shorter chain stay means more of the "acceleration-happy" feel and less dampening) and more "criterium" geometry, less suited for riding all day in the saddle. Crit geometry is somewhere between traditional road and traditional track geometry.

Read the geometry chapter of the Paterek Manual for Framebuilders for a good expansion on all this stuff. Also, Dave Moulton's bike blog is a good resource, as is frameforum.org
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Old 01-23-09, 08:11 PM   #6
misha misha
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great info
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Old 01-26-09, 05:55 AM   #7
kfm
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Quote:
Originally Posted by andre nickatina View Post
Typical road geometry is 73 degree head tube, 73 degree seat tube with 40-45mm rake depending on how you want to tweak the trail. This is "all-around" road geometry, and has been more or less the standard for a long time because it works. The 73 degree seat tube keeps things a little more comfortable because it means inherently longer chainstays and fits a large amount of riders for fore-aft seat position. The 73 HT/40-45mm works very well for how one would want a road bike to handle on the road. The greater-BB drop (lower BB height) means more dampening inherent in the longer stays, as well as lower center of gravity which is much desired when doing long, winding descents.

Steepening the head tube and seat tube/lessening the rake results in a tighter wheelbase, more stiffness inherent in the geometry (a steeper HT/less rake will give less dampening and more road feel up front, while also stiffening the front end; a steeper ST/shorter chain stay means more of the "acceleration-happy" feel and less dampening) and more "criterium" geometry, less suited for riding all day in the saddle. Crit geometry is somewhere between traditional road and traditional track geometry.

Read the geometry chapter of the Paterek Manual for Framebuilders for a good expansion on all this stuff. Also, Dave Moulton's bike blog is a good resource, as is frameforum.org
excellent, thanks
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Old 01-26-09, 11:28 AM   #8
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Quote:
Originally Posted by kfm View Post
i want to design a frame with road geometry. does anyone have specific information as to how geometry is factored (beyond the assumed)? i've looked around the web a bit, & it seems like most frame builders work off of standards that they tweak a little here an there. i'm curious, because otherwise the process seems very abstract. lower bottom bracket, more fork rake, longer stays, looser seat & head tube angles... but how do i figure out how much (given my inseam & size).

thanks
Try this:

Bicycle Geometery 101
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