Frame Geometry

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6/4/2015 10:25 AM

So Ive been wondering why people are so anal about frame geometry. Im still on my first frame and I love it. Its got a 13in chainstay, 20.5TT, 75 degree HT. and whatever the rest of the specs are but those are the main specs if im right. So ive been looking for a frame like this and it seems difficult to find a frame with 13in dropouts without having a 75.5 degree headtube. And I was reading around and people are saying thats really extreme. I like to hit some decent sized dirt jumps but also ride alot of street and some park. So can someone give me some insight on if people are just being stupid or does .3 of an inch whereever really make that much of a difference? It seems kind of crazy for a frame to be "harder to spin" because it has a .5 longer chainstay, just seems ridiculous but I could be wrong and thats why im asking. Also, how do you think I would like a 75.5 HT angle coming from a 75. I know its all preference but give me a general answer.

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6/4/2015 10:41 AM

I'm not too knowledgable about geo but I think 75.5 degrees with 13" cs would be terrible for large dirt jumps. That's some extremely twitchy specs. The difference of spinning 13.5" would be made up for by having more stable landings. Someone else might be able to correct me if I'm wrong though.

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6/4/2015 11:22 AM

BB height and seatube angle make a HUGE difference aswell

I personally think BB height is as important, if not more important then TT Length and CS length

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6/5/2015 12:58 PM

I need help on my frame

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6/5/2015 1:36 PM

Check out s&m btm 75ht/13cs pretty sure

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6/5/2015 1:43 PM

I've had a few 75.5 if you like going big I wouldn't get it they get really twitchy going fast but if you like that slow combo line style you'll like it i personally would get a 75

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6/5/2015 6:45 PM

Anchorsaweigh wrote:

BB height and seatube angle make a HUGE difference aswell

I personally think BB height is as important, if not more important ...more

Seat tube angle does nothing at all as long as you adjust the top tube length accordingly. Aside from providing a reference point for top tube length, its purely aesthetic.

You can get away with some shorter chainstays as long as the bottom bracket heigth is lower. High bottom bracket with short chainstays is loopy as fuck.

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6/6/2015 6:53 AM

Ride bmx has a video on YouTube that explains frame geometry and how it affects your style

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6/6/2015 7:13 AM

ironmaiden666 wrote:

I'm not too knowledgable about geo but I think 75.5 degrees with 13" cs would be terrible for large dirt jumps. That's some ...more

I have 75.5 ht and a 13.5 rear or so and it works fine.

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