Straddle angle for Tektro CR520 cantilevers

[rogerzilla]

These are traditional wide-profile arms with cable attachment points and frame pivots all in a horizontal line.  Is it correct that straddle angle doesn't make much difference for these?  I found them fairly ineffectual with Tektro pads, good enough in the dry with Kool-Stop salmons but still mediocre in the wet.  That was with the straddle just off the mudguard.  I suspect the Shimano drop bar levers pull too much cable for them, as they feel very firm.

[Torslanda]

What I have found through experience is the contact of the pads is just as important as the straddle.

The face of the cantilever must never go beyond the vertical and the pads must be squarely on the rim. After that set the straddle so it can't have an included angle of less than 90 degrees.

You will have a real problem with modern cantis on old narrow mountings as the pads won't hit square and you will need to find some older style CX type.

A framebuilder will be along shortly to give you the critical dimensions

[Brucey]

These are traditional wide-profile arms with cable attachment points and frame pivots all in a horizontal line.  Is it correct that straddle angle doesn't make much difference for these? 

yes that is exactly the case. Straddle height makes absolutely no difference to MA in this case. 

If you get the cable attachments up a bit (eg by taking spacers out of the brake block mounting) then you can make a small difference to the MA by lowering the straddle.

The levers that work best with these brakes are pre-DP ones, of which there are a few aero ones but  they are mostly non-aero. 1993-2008 STis and other DP levers are a little bit worse than that and newer model road STIs have a long (NSSLR) cable pull that makes them unsuitable for these brakes.

Really 520 and 720 brakes are meant for CX use, where mud clearance is very useful and a reduced MA is tolerated.

Mid-arm cantis offer much higher MA if the straddle is set low, but this comes with smaller running clearance.

cheers

[Brucey]

a graphical tool that can help you see what is what re canti geometry is here;

www.chapmancycles.com/cantilevers/

you can compare canti geometries using this tool. IIRC at one time the actual MA values were wrong by a factor of two but even so it still allowed a comparison with different canti brakes to be made.

FWIW a horizontal arm canti with 50mm arms and brake blocks set 25mm above the bosses has an MA of 1.  By contrast an 'old' DP caliper has an MA of ~1.5 (with the brake blocks set mid-slot) and a newer NSSLR one will have an MA of ~1.75 or so.

With a mid-arm canti (with ~55mm arms, such as BT-CX50/70) you can get to an MA of ~2 without very much difficulty. But if the bosses are set at a different height you will struggle to get anywhere near that.

cheers