An Unconventional Speedhub: C-Dale MT2000 Tandem
|Cool... cleaning out the hard drive tonight, I found the text w/photo links to this write-up I put together and posted on the now defunct Rohloff Owners Club forums, not quite a year ago. I'm reposting here on MTBR for posterity's sake. This is mainly focused on the Speedhub setup, not the tandem build in its entirety. The build details have changed a bit, but the basics of cramming a Speedhub into this frame have not. |
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Here’s an unconventional Speedhub setup I’d like to share. What’s unusual is that I’ve adapted Rohloff's 135mm hub to fit the 145mm dropout spacing of a Cannondale tandem frame. I’ve written this post as a guide to anybody looking to do the same. And as usual, there’s a little bit of a story to go along with it.
This bike supposedly was born into a charmed life (you can read more about that here: Celebrity Mountain Tandem on eBay...), but interest waned. After years of neglect, I got my hands on it.
|Jumping ahead to the money shot, here it is today:|
Right off the bat, I regretted the fact that we couldn’t run a Speedhub on this frame. I accepted it, and accepted derailleurs back into my life. Anne became adept at kicking the chain into the granny ring when the bike wouldn’t shift down on a steep climb.
Besides the 145mm spacing, the Cannondale has very thick 10mm dropouts, so sticking 5mm spacers on each axle would have left me with no threads sticking out.
Spring came, and I was having a conversation with the guys at Rohloff USA. They suggested I take a look at Speedhubbing this bike again, using a bolt-on hub and their “Long” threaded axle plate. The long plate adds about 8mm of length to the non-drive (disc side) axle.
|I brought my frame into Rohloff’s shop, and we did some experimentation. Things began looking up. I ordered a long threaded axle plate from St. John Cycles, and found a used TS Speedhub already built into a matching tandem wheel from Alex at MTBTandems.com.|
This should be a simple project, right?
|As with any proper Speedhub conversion, I chose to drill out the frame’s cable stops. I’ve documented this process to death over on MTBR ((MkIII) Drilling Out Cable Stops...), but just a reminder to protect your frame against flying aluminum chips, mask the immediate area around the cable stop to protect against the cutting bit digging in, and, as always, wear eye protection.|
I slipped the spacers on to the hub, reoriented my shifter box…
…and found that the only possible shifter box orientation had the cables exiting STRAIGHT DOWN!
|Frustrated at this unforeseen roadblock, I contemplated running with this silly cable routing, versus converting the hub to non-disc and simply running a rear Magura HS33. But I posted a picture and my problem on MTBR for advice (Stumble: MT2000/Speedhub conversion; rear disc v. rim).|
BTW, I was pretty much dead set against using Rohloff's Speedbone or an alternate OEM2 configuration, unsure of whether the torque generated by such a heavily-loaded bike might damage the frame.
A couple of MTBR posters lent their two cents, got me thinking out of the box, resulting in this solution:
|On a bike with traditional 135mm dropout spacing, there wouldn’t have been room to orient the torque arm **inside** the dropout, as I did here.|
This is made possible by the 6mm+ gap between the Speedhub and the frame, filled in with four fender washers.
The next challenge was mounting the disc brake caliper. There’s practically zero clearance between the Speedhub rotor bolts and the inside face of the External Shifter, so shimming the rotor out was out of the question.
To compound the problem, the Cannondale’s disc brake tabs (1999 vintage, pre-ISO) are not flush with the inner face of the dropout, but recessed a few millimeters. This left me with a 12 to 13mm gap to bridge.
A visit to a local metal supplier got me a length of 3/8”x1/2” bar stock, which I drilled with two 6mm holes 51mm apart…
|…and cut down into a 9.5mm disc brake spacer. |
Note that I could *probably* increase the width of the bar stock to 1/2” and eliminate the additional round spacers you see in this next photo (between my aluminum block and the caliper adapter), but be warned that the rotor bolts arc very near to the black adapter, and I had to lightly shave some material off to prevent interference.
Because the hub is now offset to the drive side, the wheel requires re-dishing to move the rim closer to the non-drive side. I ran the numbers in a spoke calculator, and the tension difference was around 10%. Not bad. Two turns tightening the nipples on the disc side, two loosening turns on the drive side, and my wheel was re-centered, right where I needed it to be.
So this is what the whole package looks like, from behind:
|On to the drive side!|
Nothing could be done to increase the axle length over here. With the opposite side sandwiching ~6mm worth of spacers, I’ve still got a 4mm gap between the Speedhub’s locknut and the inside face of the dropout. I’m taking a gamble that the frame won’t mind being compressed this much.
|With the 145mm dropouts compressed down to about 141mm, this is how much threaded axle is left exposed.|