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How do you figure out rear dropout angle...?

I am not sure what angle this is called... maybe rear dropout angle or cast angle? Anyway, I am just trying to figure out how you can figure out the angle between the chainstay and seatstay in BikeCad.

For example, see this picture... (sorry, I couldn't post the pic..just cut & paste)
Angle A, in the picture from the link above, is what I am trying to determine.

Chain stay - seat stay angle

This dimension is listed in the Frame tab of the Dimensions dialog box under the name Chain stay - seat stay angle. It is only available in BikeCAD Pro.

A follow up questions: How

A follow up questions: How would one change this angle in the dropout dimensions box? Since dropouts come with a set angle, i'd like to set it at say 45 degrees but the program seems to set it at an outcome based other frame dimensions. I can rotate it no problem but not change the angle.


Rear dropout angle

Although dropouts do come with an angular dimension, it is not always clear how that angle is measured.  In the case of socket dropouts, if you insert stays into the sockets the two stays should form the advertised angle.  That much we know.  However, we can't be totally sure that the vertex of that angle is necessarily aligned with the rear axle.  This is illustrated below.

The easiest way to change the rear dropout angle is to move the front end of the seat stays up or down along the length of the seat tube.  In BikeCAD, the end of the seat stays are measured from the top of the seat tube.  However, they can also be measured from the rear of the top tube, the top of the head tube, or the rear of the down tube.  If you are modeling socket dropouts, BikeCAD will automatically change the angle of the sockets to match the angle of the stays.  I realize that in real life dropouts aren't flexible like this, but I also didn't want to show an impossible situation where stays are being mashed into a socket from the wrong angle.

Where the rear end of the seat stays and chain stays attach to the dropouts is defined by Cartesian coordinates from the rear axle.  (In the case of slotted dropouts the rear axle is assumed to be slid all the way to the base of the slot.)  This is demonstrated below. These dimensions may not be supplied by the lug manufacturer.  However, you should be able to take these measurements yourself.

hi brent,

hi brent,

loving the program so far, and so far iam having less difficulty's and more fun than i thought i would, you should credit for that

but i just tried to find the drop out angle; in my bike cad pro there is a tab called primary demensions but i cant find the dropout angle?am i looking in the wrong place ?

thanks, mick

dropout angle

Thanks for the kind words.

I assume by dropout angle you are referring to the Chain stay - seat stay angle discussed above. You can find that under Frame >> Chain stay - seat stay angle as shown below.

The term dropout angle can be used in another context. In BikeCAD, this angle is defined in the input field Theta (θ). It is discussed at: bikecad.ca/dropout_slot_angle.

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