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Determining the top tube angle

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Determining the top tube angle

Old 10-22-17, 05:57 AM
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Determining the top tube angle

How do you determine the angle of the top tube? Where does the angle start? oh and btw does anyone know the top tube angle of the GT pulse? Thanks!
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Old 10-22-17, 06:19 AM
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We need a bit more information. Do you want the angle relative to the ground? Put the bike on level ground and use an angle finder. Do you want the angle of the intersection with the head tube and seat tube to determine miter angles? Whatever program you used to design the frame will provide those numbers.

The top tube angle of a particular frame will vary with the size of the frame. The head tube has to remain at the same height in each size frame, assuming the same size fork. The top tube length and seat tube length will change for various sizes, causing the top tube to be angled differently to meet the seat tube at the proper height.
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Old 10-22-17, 06:23 AM
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If you plot out where the top tube will go on the head tube and seat tube, the angle will reveal itself.
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Old 10-22-17, 08:20 AM
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antontoni- Do you understand trig? Do you have a level and a ruler? You can buy an electronic angle finder for $50. Andy.
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Old 10-23-17, 07:08 AM
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Thanks guys! I was thinking of having a frame built for me that looks like the GT Pulse. What kind of program is good for making a blueprint for a bike frame?
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Old 10-23-17, 08:47 AM
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Originally Posted by antontoni
Thanks guys! I was thinking of having a frame built for me that looks like the GT Pulse. What kind of program is good for making a blueprint for a bike frame?

For fooling around on the screen BikeCad is a very popular choice. I believe this still has a limited free version and a full fledged pro (as in cost $) version, the one that I use. Rattlecan is another design program that's bike specific. I believe it also has a free version.


But remember that it all starts with the rider/bike contact points and ends up there again. Andy.
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Old 10-23-17, 08:52 AM
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rattlecad is open source, if someone is selling it that's not good. I think that the web version of bikecad should be good enough to noodle out a design
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Old 10-23-17, 09:03 AM
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Top tube angle is measured from the horizontal. If the tube is straight the angle is the same anywhere you measure it. However these days many frames have curved top tubes, so all bets are off.

You can measure with a slope finder, or using some trig.
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Old 10-24-17, 05:32 AM
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If you're going to have someone else build the frame, there is no reason for you to design it. Tell the builder what type of frame you want and let them do the design part. There is no way I would build a frame for someone that came to me with a design they did themselves.
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