Rear racks have been problematic for those of us who like disk brakes. If your bike has the disk mount on the chainstay, most if not all standard racks will fit. But if the mount is on the seatstay, as on our Co-Motion and Cannondale tandem, then the only really good racks have been the Old Man Mountain Cold Springs and Sherpa. We have used a Sherpa with good results on both bikes. The drawback is that both mount via the skewer which makes wheel removal cumbersome. They also have an unconventional look if that matters to you.
I’ve posted more photos at my Flickr page.
Topeak also makes disk-specific rear racks, the Explorer and Tourist, which use built-in offsets at the eyelet to space the rack beyond the disk caliper. I have used the Explorer and it’s OK for a $35 rack, but not elegant. There are some threaded spacers out there from Jandd and others that allow you to mount a standard rack outboard of the disk caliper, but the rack ends up off-center and is dependent on the spacer.
Venerable rack maker Tubus recently came to the rescue with their Disco rack. It uses curved tabs at the lower legs to position the rack behind the caliper rather than outboard. Tubus includes a skewer to mount the rack through the hub if needed, but the rack mounted normally to our Co-Motion dropout eyelets. I mounted the fender stays to the same eyelet between the rack and frame for now.
The only downsides to me are the top shelf, which is narrow for a large racktop bag, and the $154 price tag (at least until Wiggle starts stocking it). The Disco is rated to a maximum of 20 kg. or 44 lbs., which might be a problem for some folks. We’d rather not carry 44 lbs. in the rear panniers so it’s fine by us. We’ll still use an Old Man Mountain Ultimate Lowrider front rack, by the way.
We’re going to test this rack on our upcoming honeymoon tour of Skyline Drive and the Blue Ridge Parkway, and I’ll follow up. For now, here’s a review from Bike Radar.
The Daily Randonneur 
The trick to the threaded spacers is to use them on both sides. That way the rack stays centered. Most of the tubus racks come with plastic spacers that will get you around disc calipers.
Hi Ed and Mary,
A clever arrangement for that tandem rack…but your top tube is begging for one of my new stickers:
“Oil Addiction Recovery Vehicle”
Tavis, let us know how it works out for you. On our Co-Motion tandem with 145mm rear spacing, we needed a 28mm spacer from Calhoun Bicyles plus height extenders from Tubus to barely clear the Avid disk caliper.
Putting one on both sides would have meant spreading the rack to 145mm+56mm more to center it. The included spacers from Tubus are a few mm each, nothing that would have worked in this situation. Have you actually tried what you suggest?
Have a look here:
http://www.calhouncycle.com/ProductCart/pc/viewPrd.asp?idcategory=69&idproduct=1327
As a long time Tubus and OMM rack owner I’m not surprised to see Tubus come out with an elegant disc brake rack solution.
I should note though that I find the OMM QR racks to add only 5-10 seconds to the process of changing a flat – virtually unoticeable. I even use their QR racks on my touring bike that has braze-ons simply because I like the design. I’ve abused an OMM Cold Springs rack for many years on paved and dirt road tours with only positive results.
I’ll be interested to read your thoughts on the Tubus Disco once you’ve had a chance to use it a while.
safe riding and happy honeymoon!
Vik
http://www.thelazyrando.com
Ed,
How much drop is there between the bagloops on the saddle and the top of the rack? Do you secure the bag to the rack or simply let it rest on top? If the latter, any problems with it moving around? I’ve got a Tubus Vega (minimalist rack) and wondering whether it will keep a Nelson LF away from my thighs. I have about 10 inches of drop between saddle loops and the top of the rack which looks to be slightly more than on your tandem.
Thanks!
ADM
Hello,
I’ve finally recorded my struggles with putting a bike rack on my classic Specialized Allez Pro road race bike:
http://rodgerswriting.blogspot.com/2011/11/bike-racks-on-classic-road-race-bicycle.html
The review of the Tubus Disco rack I eventually tried is here:
http://rodgerswriting.blogspot.com/2011/11/review-of-tubus-disco-bicycle-rack-on.html
It worked. But it was problematic on that bike. See the details and pics.