Disc Brakes Front & Rear...
Hello all! I am looking for some information from anyone out there that has any feedback to share regarding the use of mechanical disc brakes front and rear. First,let me describe the set-up I intend to use. The tandem is a Cannondale MT 800. The fork is a "Fatty R". The wheels are 26" Velocity "Aeroheat" rims mated to DT Swiss 540 hubs. The spokes are DT Swiss alpine III (tied and sottered). The brakes are Interloc "dual bangers" (otherwise known as "WinZip" from Santana by-the-way) with 203mm rotors on both the front and rear. I know this is a bit of overkill, but I would rather be safe than sorry! What I am looking for is anyone that knows of any problems I will incure with this set-up. Will the 203mm rotor have enough clearence in the rear? Will this be to much stopping power, or is there such a thing as to much? Etc. Etc. Etc. Thanks for any input you can offer!
I've got disc brakes front & rear.
Setup: Spicer ti frame, 700c wheels, Nashbar steel fork with disk tabs. Shimano XT disk hubs, 36 hole. DT Swiss Alpine III spokes, 3 cross lace. No tying and soldering; I don't think it adds much & the Jobst Brandt book says it adds nothing. Brakes are avid mechanicals (road version) with 203 mm rotors.
My evaluation. It provides plenty of braking power. But the avid mechanicals, as good as they are have some issues which make them a little bit high maintenance.
-The road version still seems to require a lot lever pull and cable travel to activate them.
-If I try to set the pads closer to the rotor so that I don't have so much lever pull to engage the brakes, I find that the rotors brush the pads lightly while I'm riding, and this is annoying. It does this on the front (steel) and on the rear (ti).
-The cable pull problem was such a problem on the rear that I added a travel agent; that seemed to have solved the rubbing issues, and I have good braking power in the rear. But supposedly you don't need or are not supposed to use travel agents with the road version of the Avids.
-I don't have any clearance issues between the frame/fork and the rotors, although it was a little close in the rear with 203 mm.
-finally, disc brakes in general are heavy compared to other options, but you have great braking power and don't have to worry about rim heat or tire blowouts on super long, fast descents with disc braks.
We have an essentially stock Cannondale road tandem from last year with disk brakes (Avid mechanical brakes with Campy Ergo levers). They came with the bigger rotors (being disk brake illiterate, I don't know what they are, but the shop guy said "Wow you got downhill rotors!"). If the frames are similar you should be fine for fit.
As far as braking power, I have yet to do a massive 45+mph panic stop, but I can haul the bike down from that speed quick enough (one of our routes has a light at the end of a mile long descent) on a descent to make the future missus wonder if we're about to crash.
I've noticed the mushiness with the Avids and will be putting in the helper springs (travel agents?) to help the brake return the cable to a "ready" position. Not critical as we've been fine so far.
I have an Avid on the back of our CoMo with Campy Ergo levers. I also run the inline travel agent. The Travel Agent and "helper spring" are two different items. Some have placed a small spring over the cable where it attaches to the "arm" of the disc brake caliper. I've tried this and hated it. I was fortunate to find a longer spring adjustment screw for the Avid Mechanical. The first generation disc brake caliper uses a small fine threaded screw to adjust spring tension on the brake - the helper springs purpose is to increase this so that lever feel is better with such a long brake cable. Some company was giving this away at the Northwest Tandem Rally in Bend Oregon in 05 - actually at the Arizona Tandem table. I use the travel agent to reduce brake lever travel. The system works great.
A friend just picked up a new DiVinci with Campy Ergo Levers and the new 2nd generation Avid Mechanical discs front and rear. The disc caliper design eliminates the screw for spring tension - and i'm not sure how it's adjusted now. He does not have a travel agent inline and his lever travel is about the same as mine with similiar "tension". I'm going to be looking into the 2nd generation caliper so I can eliminate the inline travel agent as it's a hassle to set up when installing a new brake cable.
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