Frame Geo Questions.

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1/19/2011 7:42 PM

Bottom bracket height?
Seat tube angle?
Headtube angle?

Can someone please explain how these affect riding.

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1/19/2011 7:46 PM

most frames there is going to be like a .5 difference between the headtube and seattube and bb height, but it doesnt really make a difference, some people say a steeper headtube gives you nose steez, but thats a bunch of bs. typically every frame as pretty much the same geo, just find one with a cs and tt you like.

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1/19/2011 7:48 PM

collin86 wrote:

most frames there is going to be like a .5 difference between the headtube and seattube and bb height, but it doesnt really make a difference, some people say a steeper headtube gives you nose steez, but thats a bunch of bs. typically every frame as pretty much the same geo, just find one with a cs and tt you like.

I was looking at a custom FBM, I know I want a short chainstay, just curious how this affects it. Thanks.

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1/19/2011 8:04 PM

Bottom bracket height moves your center of gravity over the bike. Higher feels twitch, lower feels more stable.

Seat tube angle affects how much room you have on the top tube so your seat doesn't get in the way.

Head tube angle affects how twitchy the steering is. Steeper makes you turn quicker, but it's also less stable.

11.5"-11.8" is the norm for BB height
69-71 degree is average for seat tube angles
74.5 and 75 degrees are the most common head tube angles.

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1/19/2011 8:08 PM

Kenealy wrote:

Bottom bracket height moves your center of gravity over the bike. Higher feels twitch, lower feels more stable.

Seat tube angle affects how much room you have on the top tube so your seat doesn't get in the way.

Head tube angle affects how twitchy the steering is. Steeper makes you turn quicker, but it's also less stable.

11.5"-11.8" is the norm for BB height
69-71 degree is average for seat tube angles
74.5 and 75 degrees are the most common head tube angles.

That was very helpful, but I'm not gonna get a ctustom FBM. Instead, I'm just gonna look for a white frame with a short chainstay, which is hard. But thanks, 'cause now I know smile

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1/19/2011 8:08 PM

collin86 wrote:

most frames there is going to be like a .5 difference between the headtube and seattube and bb height, but it doesnt really make a difference, some people say a steeper headtube gives you nose steez, but thats a bunch of bs. typically every frame as pretty much the same geo, just find one with a cs and tt you like.

How many frames have you owned to say .5 of a degree doesn't make a difference? Just wondering. I've owned three frames and the headtube angle does affect your front end quite a bit.

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1/19/2011 8:09 PM

dirtbmx33 wrote:

That was very helpful, but I'm not gonna get a ctustom FBM. Instead, I'm just gonna look for a white frame with a short chainstay, which is hard. But thanks, 'cause now I know smile

No problem. Don't quote me on the BB height, though. Someone needs to double check me on that.

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1/19/2011 8:10 PM

a triangle is 180 degrees

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1/19/2011 8:10 PM

Kenealy wrote:

Bottom bracket height moves your center of gravity over the bike. Higher feels twitch, lower feels more stable.

Seat tube angle affects how much room you have on the top tube so your seat doesn't get in the way.

Head tube angle affects how twitchy the steering is. Steeper makes you turn quicker, but it's also less stable.

11.5"-11.8" is the norm for BB height
69-71 degree is average for seat tube angles
74.5 and 75 degrees are the most common head tube angles.

dirtbmx33 wrote:

That was very helpful, but I'm not gonna get a ctustom FBM. Instead, I'm just gonna look for a white frame with a short chainstay, which is hard. But thanks, 'cause now I know smile

Kenealy wrote:

No problem. Don't quote me on the BB height, though. Someone needs to double check me on that.

Now that I think about it, it makes sense, I'm on your side with it.

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1/19/2011 8:16 PM

carjakester wrote:

a triangle is 180 degrees

Sum of all inner angles of a polygon = 180(n-2)
n is the number of sides in your polygon.

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1/19/2011 8:30 PM

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1/19/2011 8:34 PM

collin86 wrote:

most frames there is going to be like a .5 difference between the headtube and seattube and bb height, but it doesnt really make a difference, some people say a steeper headtube gives you nose steez, but thats a bunch of bs. typically every frame as pretty much the same geo, just find one with a cs and tt you like.

Easternbiker93 wrote:

How many frames have you owned to say .5 of a degree doesn't make a difference? Just wondering. I've owned three frames and the headtube angle does affect your front end quite a bit.

i ran 5 frames last year.

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