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Bicycle frame geometry explainar

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Bicycle frame geometry explainar

Old 01-14-16, 06:29 AM
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bikingman
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Bicycle frame geometry explainar

Hello frame builders,

I'm looking for a comprehensive guide to frame geometry. Wondering if there are any pdfs available for download.

Ideally, the guide will have explained the different geometries of a bicycle, and what they mean for the rider. Preferable, the guide covers a range of bicycle type options, such as utilitarian bikes, recreational bicycles etc etc.

The type of language Iím looking for is, "number 2 refers to the bottom bracket height. Raising and lowering the bottom bracket with affect the handling of a bicycle in opposition to each other. Increasing the height of the bottom bracket from the ground will decrease stability and increase pedal clearance, and v.s., dropping the bottom bracket height will have the opposite effect.

Background: I'm developing a small frame builders workshop in Kenya, and would love a comprehensive manual for the guys to consult for frame design.

Thanks you in advanced!

Daniel
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Old 01-14-16, 06:57 AM
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there was a book(I think) written by a professor for his bicycle construction class. It's mostly about stability because they all built recumbents. Otherwise, unless I'm forgetting some resource, it's all hearsay, opinion, and lore
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Old 01-14-16, 08:36 AM
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These links may be useful.

The Geometry of Bike Handling

Bicycle Geometry 101 | Martin Manning
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Old 01-14-16, 09:06 AM
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Originally Posted by Scooper View Post
Nice articles. Learned more about BB height and fork trail. I'm just like the guy in the first article. Get the horizontal/virtual top tube length close and you're good to go. Didn't know much about how the rest affected handling.
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Old 01-14-16, 09:34 AM
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One aspect not to be found in any geometry guide I've seen is how the rider's fit and set up effects the handling. Also since all this is filtered through our brains and then regurgitated onto paper descriptions there is a fairly large range of description of the same otherwise handling. Just read enough magazine reviews and see the claims of this bike being more stable then that bike then when the specs are compared the numbers would suggest the opposite.

This is perhaps one of the more challenging aspects of frame building to understand and be able to translate from what your customer is asking to what they say after riding the complete bike (with the intended wheels, tires, bars and all). I've read that some builders feel that this ability isn't really understood by some without building many dozens (and dozens) of bikes.

It's like trying to fit a rider by numbers only (or by videos only) with no regard to flexibility, body mass placement, strength (and different strengths in different areas of the body) and rider reaction of discomfort (to name some of the intangibles). The guy I work for is one of the more experienced bike fitters in upstate NY and he sees other fitters who after doing a years worth (maybe a few dozen0 fits think they have a handle of how to fit. Then a couple years later these same fitters understand that there was a lot more they didn't understand after that first year.

I'll be interested to follow this thread and see more suggestions for geometry guides. After 35+ years of trying to understand this stuff and only building a few dozen bikes I have more to learn myself. Andy.
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Old 01-14-16, 08:51 PM
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I have to say that just because it's written down doesn't mean it's true. My road bike is exceptionally stable feeling. It has low-ish trail and the steering is really responsive, but that doesn't seem to affect the feeling of stability. The bottom bracket drop is about 8cm, which is said to promote stable cornering. I have no idea how to quantify these effects, it's all voodoo as far as I'm concerned
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Old 01-15-16, 12:18 AM
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Don't forget about looking into information on motorcycles. There is much to be learned from their as well. It doesn't relate EXACTLY to bicycle frame geometry, but it's relatable. Because speed multiplies the effect of differing geometries, you tend to see a larger range in motorcycle geometries based on intended use and desirable handling characteristics. The increase can help one to understand what going one way on the geometry scale does versus going the other way. With regards to bike fit, and how a rider is positioned on a bike, motorcycle weight distribution (with and without rider) can help one understand how this comes into play as well.
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Old 01-15-16, 12:28 AM
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Andy, this is a great suggestion, understanding the relationship between the geometry of a bike and the rider's bike fit; and how those relationships influence the ride. I myself have had experience with a "race fit" and, "comfort fit" on my road bike. From my inquiries, a race fit places the rider closer to parallel with the ground (aggressive), and a comfort fit places the rider closer to perpendicular with the ground (upright) - consider a TT position, v.s. an english cruiser.


It would be an interesting read to understand how a particular fit, influences a bike’s ride. Does a race fit, or moving the center of balance forward, cause tighter handling? Any ideas? Questions like this would be valuable to me, and perhaps many others.
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