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Old 10-08-07, 02:41 AM   #1
tarmenel
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Bike Geometry and XC

Hi all,

I did a search throught the forum and didn't find anythin on bike geometry other than tons of links on the Genesis system of GF. Well I'm trying to aquire more knowledge in the technical department which is sorely lacking in my corner. Tried google but got completely sidetracked on the framebuilding side of things. What I want to know is what should I be looking for in the geometry of a bike for XC. I'm average height 1.84m not sure what the inches work out to but I'd like to learn more about the geometry of various bikes and what the differences mean. Any link to the basic's of the geomerty and how it effects riding and riders would also be appreciated.

Thnks
Hilton
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Old 10-08-07, 04:39 AM   #2
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Here's is a condensed and probably shabby explanation. Steeper head angles, make the steering quick, responsive and agile. Too steep, and the bike get's twitchy, and braking can be an adventure. Shorter chain stays keeps weight over the wheel when climbing out of the saddle, but the bike get's a little less stable, and doesn't trail as well. Top tube length affects the riders position, comfort and distribution of weight on the bike. seat tube angle affects the relationship of the rider to the pedals.
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Old 10-08-07, 05:13 AM   #3
tarmenel
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how will these angles and tubed lengths be effected by the rider's height. I mean would a taller rider want a more stable position because he's "top" heavy so would shy away from the shorter chain stay, but then a taller rider would also be heavier so pulling extra weight up the hill would greatly benefit from a shorter chain stay. How would the top tube effect the position, comfort and distribution? What would the calculations be again by the height of the rider for the top tube and also if XC riding would benefit from shorter or longer top tube lengths. I can understand for racing you may want "twitchier" steering or is this more rider specific, obviously a more experienced rider may be able to handle this twitchiness far better than a newb.
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Old 10-08-07, 05:28 AM   #4
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Originally Posted by tarmenel View Post
how will these angles and tubed lengths be effected by the rider's height. I mean would a taller rider want a more stable position because he's "top" heavy so would shy away from the shorter chain stay, but then a taller rider would also be heavier so pulling extra weight up the hill would greatly benefit from a shorter chain stay. How would the top tube effect the position, comfort and distribution? What would the calculations be again by the height of the rider for the top tube and also if XC riding would benefit from shorter or longer top tube lengths. I can understand for racing you may want "twitchier" steering or is this more rider specific, obviously a more experienced rider may be able to handle this twitchiness far better than a newb.
you can discuss the theory all you want, simply comes down the test ride and what suits an individual.. 2 people of the same dimension may well choose 2 different syles and sizes of bike for the same purpose..
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Old 10-08-07, 05:38 AM   #5
tarmenel
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I seem to be finding that the geometry found on a bike just as confusing as the 10th grade stuff I suffered through. Is there no website that breaks it down advantages over disadvantages. i understand that no two riders are the same but surely there must be a consensus and from there you can tweak the setup to your type of riding. I mean unless you get a bike built custom most of us will be stuck with what the manufacturers churn out. Their measurements must be based on some sort of theory?? If not they could just throw a bike together on random measurements
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Old 10-08-07, 06:40 AM   #6
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Originally Posted by tarmenel View Post
I seem to be finding that the geometry found on a bike just as confusing as the 10th grade stuff I suffered through. Is there no website that breaks it down advantages over disadvantages. i understand that no two riders are the same but surely there must be a consensus and from there you can tweak the setup to your type of riding. I mean unless you get a bike built custom most of us will be stuck with what the manufacturers churn out. Their measurements must be based on some sort of theory?? If not they could just throw a bike together on random measurements
bikes aren't just thrown together, they've been developed over time empirically. Theres a big difference between the mountain bikes of 20 years ago and now. Stays are shorter, top tubes are longer, stems are WAYYY shorter, fork rakes are higher, seat tubes are shorter, head tubes are longer, theres a lot of differences, and they've developed through rider feedback and what sells best. there is really no theory to it.
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