Disc brake modification on tandem bike

[AllenV]

This was a couple of years ago, but I thought you guys would enjoy seeing it.

I have a tandem bike in my stable ( three actually ). I use it for decently fast club rides and keeping weight and rolling resistance down matter as we climb the rockies around here with kid’s half my age.

The bike got caught up in a recall by Canondale to replace the original aluminum fork. A few had broken, with injuries. By the time I got wind of this they had run out of replacement forks but did agree to install a new carbon/aluminum fork. I got carried away with this unplanned upgrade and put on new, lighter, tubeless, wheels. Over all the bike came out 4 pounds lighter. Neat.

What you machinists care about is that the front brake disc did not fit onto the Shimano adapter needed for the hubs of the new wheels. The old wheels were 6-bolt and the new are CenterLock, splined.

Shaving a millimeter off the ID of the brake disc would allow a fit. But taking off too much threatened weakening the disc mounting. After some head scratching I decided to take the bold route and turn the disc on my 13x40 lathe. This is easily the most fragile item I have turned. Every bit of it has minimum mass. A thin stainless steel ring where the brake pads ride and a spidery anodized aluminum inner framework.

I managed to carefully mount it in the 3-jaw, pretty well centered. Spun it slow and shaved off that millimeter.

Here are photos.

 

[wrat]

I'm not ENTIRELY certain I understand what occurred or the dangers, but I'm happy it worked out for you.

Nice pics, too.

 

[MrWhoopee]

Nice to be able to deal with this sort of issue.
What do people without a machine shop in the garage do?

 

[TooManyWrenches]

Nice to be able to deal with this sort of issue.
What do people without a machine shop in the garage do?

Shimano made an adapter in the past. It's been a minute since I worked in bike industry, but I bet I could find the adapter somewhere. It's part number SM-RTAD05

 

[TooManyWrenches]

Shimano made an adapter in the past. It's been a minute since I worked in bike industry, but I bet I could find the adapter somewhere. It's part number SM-RTAD05

Oh I see that now. I would have just filed down the rotors to fit, but using the lathe is nicer and cleaner.

 

[AllenV]

Oh I see that now. I would have just filed down the rotors to fit, but using the lathe is nicer and cleaner.

Right. You can see the black spline adapter in the third photograph.
Filing would have worked just fine. But the lathe was right there. Turned out to be a dead easy job. My worry over bending/damaging the rotor was unfounded.

 

[bulgie]

Right. You can see the black spline adapter in the third photograph.
Filing would have worked just fine. But the lathe was right there. Turned out to be a dead easy job. My worry over bending/damaging the rotor was unfounded.

Nice bike! Good work on the disk hub hack too. I'm no PE but I'd call that totally strong. Even with the raised stakes from it being a tandem, and from it being a front brake, I'd ride it for sure. But inspect now and then for fatigue cracks. Easy, visual inspection, requires no disassembly, just look at it sometimes. But I'd expect, even if cracks appear, they'd grow slowly or even not at all, with no highly-stressed metal in the vicinity for the crack to propagate to.

Love the Rolf wheels. Have you considered a Gates belt to replace the timing chain? I hear there's decent room for weight savings, and no more oil, (& grime on your calf). Longer service life than chains too.

I'm a newcomer to belts, have bought the belt and sprockets but haven't built the frame yet! (Single, not tandem)

 

[AllenV]

Nice bike! Good work on the disk hub hack too. I'm no PE but I'd call that totally strong. Even with the raised stakes from it being a tandem, and from it being a front brake, I'd ride it for sure. But inspect now and then for fatigue cracks. Easy, visual inspection, requires no disassembly, just look at it sometimes. But I'd expect, even if cracks appear, they'd grow slowly or even not at all, with no highly-stressed metal in the vicinity for the crack to propagate to.

Love the Rolf wheels. Have you considered a Gates belt to replace the timing chain? I hear there's decent room for weight savings, and no more oil, (& grime on your calf). Longer service life than chains too.

I'm a newcomer to belts, have bought the belt and sprockets but haven't built the frame yet! (Single, not tandem)

A gates belt for the timing chain IS very nice. I have done all the math on that. If I remember correctly the total weight savings by doing that would be a bit over half a pound. Ultimately I decided that Gates drive represents the event horizon of a rabbit hole I do not want to go down with this bike. Gates drive would likely lead to installation of carbon cranks, for example. The cost of those ounces removed is just too high for a tandem that goes out 6 or 8 times a year.

The Rolf wheels are The Thing for tandems. The wheels that came off were DTSwiss heavy tandem touring wheels. Very stout but a challenge to accelerate.

Speaking of building frames, my first tandem was custom built for my wife and I in 1985, by my father. He was into a frame building phase, had done a few lugged steel singles for himself and wanted to tackle lugless construction.

 

[bulgie]

Speaking of building frames, my first tandem was custom built for my wife and I in 1985, by my father. He was into a frame building phase, had done a few lugged steel singles for himself and wanted to tackle lugless construction.

You're brave to ride an amateur's first tandem! But as so many threads here prove, hobbyists can do beautiful work, sometimes surpassing what the pros can do, with their requirement to make things profitably.

I started at Santana (tandem makers, for those who don't know) in '76 or '77, and did every task and subassembly dozens of times, sometimes hundreds, before I ever made a whole frame for myself. Classic apprenticeship model. So of course I tend to think of that as the only good and proper way to learn. Kidding! I've seen too many first efforts that came out spectacular, especially when the builder had a background in metal fab.

Later at Rodriguez (R+E Cycles), then at Davidson, and lastly at Ti Cycles (titanium), I was "the tandem guy". I might have made more tandems (several hundred, mostly all custom one-offs) than I have single bikes. When Bicycling magazine tested a Rodriguez I made (circa '81 I think), they called it the most "advanced" twofer they'd ever seen.

By '85 when your dad made yours, the advances in tandem design brought out by the likes of Santana and Rodriguez were getting widely known, so hopefully your dad didn't have to repeat all the mistakes of the bad old days of tandems. "Standing on the shoulders of giants" can actually limit you, if it keeps you stuck in the same old ruts of those who went before, but more often the people not educated in the old ways just re-make all the old mistakes. Lord knows, some of the "brilliant innovations" I came up with turned out to not be practical, or for whatever reason just died out. Now I take pride in doing things in old traditional ways, not trying to set the world on fire anymore.

I slightly regret not having made us a titanium frame when I worked at Ti Cycles, but now I'm back to lowly old steel in my home shop. I don't like welding aluminum, and hate the smell of epoxy so carbon fiber is out. Luckily not a weight-weenie anymore, a couple pounds isn't going to ruin my enjoyment of the ride. My steel Davidson from '89 is only 30 lb though, with clinchers (old-school, 36-spoke wheels), fenders and wide-range touring gears. For me and Laurie, that's like riding two 15 lb singles. (OK not really, but let me have my delusions.)

 

[MIkeMalibu]

We have more than 30,000 miles riding a Gates timing belt on our tandems. The benefits are no chain noise, no chain lube, no chain lag, and longer service life (also less weight). If you travel with a tandem, the belt is easier to deal with. The change over is a simple installation of two belt rings of the appropriate size and the matching belt.