Originally Posted by
Wilfred Laurier
Because cables can only act in tension in a straight line, the main brake cable pulling straight up on the middle of a straddle cable straight across can create (theoretically) infinite tension in the straddle cable - the straddle cable will have a 'lateral' component to its movement and a 'vertical' component to its movement, and since there is very little of the vertical direction in a very short straddle cable, the tension needs to go very high to counter the tension in the 100% vertical main brake cable.
Yeah, I was probably trying to make the math simpler than it is. By pulling straight up on the center of the straddle cable, there would be a lateral movement at the cable ends, but I now understand that it wouldn't be a 1:1 relationship.