Cold setting a bicycle rear triangle



Sometimes it is desirable to change the spacing on the rear of a bicycle to fit a different hub or to upgrade an old frame to modern components.  Usually a bit of brute force is applied but this can be uncontrolled and easily lead to over doing it and to getting it lop sided.

To overcome this I use a modified spring compressor available from any car accessory shop and normally designed for compressing the springs in the suspension when fitting a new shock absorber.



The top item is the normal spring compressor and the bottom is the simple modification of reversing the hook arms to make the new tools.

The hooks on the new tool are simply placed over the ends of the chainstays and then cranked open with a spanner on the end.  This way you can apply a symmetrical and controlled force to get exactly the separation you wish.  It needs a bit of experimentation as when you release it the stays spring back.  For example setting the tandem rear triangle below from 135 to 145 OLN  required expanding to 175mm with the tool.  The beauty is you can work up to the right value bit by bit and control it to the mm.