My 2006 Fuji tandem came with flat bars, 8sp triple and Tektro v-brakes, which worked very well. But I ride that bike a lot with my son and I changed to drop bars and used Ultegra 9sp STI brifters. Brilliant cheap conversion and the gears worked perfectly from the get go.

I got Travel Agents to correct the cable pull so that the v-brakes would work with the roadbike levers. Functionally the Travel Agents have been fine, even the setup process wasn't horrible. But the front brake squealed a lot, I imagine because the addition of the Travel Agent made a long lever even longer and much more prone to those high pitch high frequency vibrations, and because on a tandem the front brake is subject to some particular stresses.

I decided I needed to try cantilever brakes on this bike to get rid of the squeal. I've worked on lots of cantis over the years, they are always a bit fiddly to configure but I have been satisfied with their performance. I am familiar with the Sheldon Brown information.

Now I've installed Tektro CR720 cantilever brakes - on the front only so far. These particular brakes are quite nice out of the box. I was happy with the braking on my test ride: no squealing, right amount of travel at the lever etc. But in order to get the pads to contact the rim at the same moment I've had to set the straddle wire off-center - see the picture below.

My question is: how do I get that straddle wire centred? I've read thru a bunch of threads here on BF and have already tried putting the NDS spring in the top hole on the fork boss but it was just too stiff. Then I tried putting the DS spring in the bottom boss hole but it was just too weak. The middle holes are recommended by Tektro and work best for return and resistance at the lever. I have also wound the adjuster screws in and out as shown in the instructions but the calipers are so off-centre it made no difference.

Advice welcome.