Task Summary
Straddles come in various different forms as shown below. Their general purpose is to provide a fixing point for the brake cable and to "straddle" the transverse cable from this centre point into each of the caliper arms. The closer the yoke to the tyre (or the shorter the transverse cable) the higher the Mechanical Advantage.
Straddles can be quite a fiddly exercise as, essentially, they are adding in another factor to the Mechanical Advantage of the braking system other then the straightforward compatibility issue between brake type and lever. Getting them into the right position takes feel and experience. But as a general rule you would position the yoke or bridge of the straddle next to the crown race on the fork.
One further issue with straddles is of course that the cables they hold will stretch, meaning that you will have to re-position them from time to time. If the cables stretch, it will lower the Mechanical Advantage and the brakes will feel less powerful.Self-Centreing
These straddles are often found on inexpensive entry level bikes and Cyclo Cross bikes.
Contemporary
These are found most commonly on hybrid commuter bikes Cycle Cross bikes in general.
WORKSHOP TIP: Make sure you place it around the same height as the crown race on the fork. It shouldn't be too high as the brakes won't be effective (too little leverage) nor too low as it may conflict with the mudguard or tyre.
