Is a 6 ft ramp with 60 degrees of arc a good 2nd ramp? the first one is 4 ft with 60 degrees.
I assume you're talking about second in a line of jumps . . . (not second you've built in your life).
It really depends on what kind of speed and gap distances you have.
In general, having gaps that match up pretty closely is the way to go. The height of the jump matters less than the gap you're clearing. Like in this drawing, if you cut the first set down to only 2 1/2 feet tall, but kept the same gap of 10 feet, then the speed you'd need to clear the 10 feet is still roughly the same as the speed for the next set that is 5 feet tall. I say "roughly" because a person's "body English" does matter (you can "soak up" a jump or "boost" it, with very different results).
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Unsecure image, only https images allowed: http://i255.photobucket.com/albums/hh138/upsetbmx/degreesofarc.jpg It's actually a pretty good way to think about ramps. You can have a really big ramp that is 60 degrees or a small ramp that is 60 degrees...
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