Have a look at the original Plycycle here .

29 April 2013

Making the rear stays work...

On the first Plycycle the bottom rear stays came together with relative ease, it has become apparent that this was for several reasons. First, I didnt know it could be a problem area, but mostly because I had chosen to build the frame around 700c wheels with racing tyres which are very thin. I was also lucky in that the chain set I chose was a design with a large gap between the crank arms. Both of these factors allowed me to make the bottm rear stays straight and strong with no need for fancy shapes to get clearance.
However on the Plycycle Mk2, I have decided to use 26 inch wheels with slick tyres. These are essentially mountain bike wheels which are wider, even with the slicks on they are nearly twice as wide. Added to that the chain set i had planned on using (the Simano Alfine) has a relatively narrow clearance between the crank arms. I think I will have to look into an alternative crankset as I will need all the space I can get.
This drawing shows the problem, in order to make the new rear stays I am going to have to make the bottom rear stay a fairly complex shape. I may even have to set the wheel futhur back to make the space I need. I have already toyed with the idea of moving the botton bracket forward by an inch to help make more space, but this may compromise the cycling position.
I started to try and plan it out with some card board, and as things stand I would need a shape similar to the drawing above.
This is about as fat as I can get the bottom rear stay,
the fatter the better as it is a point of high stress in the frame.

From the side the geometry looks like it will all work out fine.

I like scribbling notes amd measurements down on bits of wood.

 I think the best way forward is to get the chainset, then work to that, otherwise it will all be a guessing game.