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is there any way to lock only the main triangle, while change any other parameters on the frame?
The lock frame feature described at: bikecad.ca/lock_frame will lock both the front and rear triangle. Within that tool, there are also options to address whether or not the handlebar and saddle angles should change. I assume this is what you are looking for. If you wanted to lock only the front triangle and not the chain stays and seat stays, then I don't think there is any reason you need to lock the front triangle at all. If the lock frame icon is turned off, there is nothing you can do to the chain stays and seat stays that will have any impact on the geometry of the front triangle. The main purpose of the lock frame tool is to lock the shape of the frame when a different fork length is applied or if the size of either the front or rear wheel is changed without changing the size of the other wheel.
My reason is, I want to reuse an old frame I built formerly. But only the main triangle with new stays, wheels, and new, longer fork, so this is why I need to lock the front triangle. My purpose I want to know the BB height after these change, but I want a specific head angel too, so kind a rotatitng the frame around front wheel axle. Meanwhile I found out, that I can lock the whole frame , change the fork and after change only the rear wheel size, thus I can see BB height and HA. Later I will find the stays position. Thanks
I would like to know if there is a way to do this? I have an old frame that someone would like to change the rear triangle and fork to accept larger tyres.
I want to rotate backwards around the bottom racket (simulating a longer fork). Then I will adjust the the bb drop and rear triangle accordingly.
There isn't a specific option for this within BikeCAD. However, if you take note of the current position of the rear axle in terms of X and Y coordinates from the bottom bracket. You can investigate how the geometry of the bike would change with a different rear end that positions the rear axle with some different pair of coordinates from the bottom bracket. In the example below, I've locked the frame and then shifted the rear end up and down by changing the Z dimension in the rear dropouts dialog box. The Z dimension controls how far the rear axle is fixed from the end of the slot. It primarily applies to track dropouts. Because the rear dropout has a vertical slot in this case, changes in Z correlate to changes in the Y coordinate of the rear dropout relative to the bottom bracket.
If you wanted to change the position of the rear dropout both vertically and horizontally, you could do it by angling the dropout slot in such a way that shifting the axle in and out of the dropout slot would change the position of the theoretical new dropout in both X and Y coordinates. If you'd rather isolate the X and Y coordinates, you could use a horizontal track dropout and shift the rear axle in and out to handle the X coordinate and change the rear wheel diameter to address changes in the Y coordinate.
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