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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 09-06-07, 11:59 AM   #1
born2pdl
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Interesting lightened drum brake

We occasionally descend things that require more than rim or disk brake to survive, so there's a dedicated drum (only) on the back of our trekt2k. I also don't want to wear my rolfs out, ever. An I'm an occasional weight weenie, and curious about brake alternatives, so I created a lighter drum brake for light duty tandeming.

Bought an extra arai drum ($30), put it on a lathe and removed the heat sink fins. Then I performed mental finite element analysis and swiss-cheesed the over done brake shoe metal. Then ground a bit of excess material from the backing plate. Its lighter, still not sexy, works fine. If I tour or decend anything significant, I'll put on my other (stock) drum.

Might have removed 1/2-3/4 pound. So what. Guess I had too much time on my hands.
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Old 09-06-07, 02:56 PM   #2
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It has already been done. Mel at Tandems East in NJ has been selling a modified Arai with the fins turned off for quite some time. I bought one in 2003. I don't know how long before that he was selling his modified Arai. Some say that the heat load is significantly diminished, some say that it was way overdesigned for a bicycle, since its original use was for a moped or something. I know mine has always been sufficient for our tandem use. I'd be interested in seeing your finite element results.
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Old 09-06-07, 03:21 PM   #3
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.......Then I performed mental finite element analysis and ....
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.....I'd be interested in seeing your finite element results.
We could schedule that MRI for tomorrow .
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Old 09-06-07, 08:11 PM   #4
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You mean like this:

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Old 09-06-07, 09:32 PM   #5
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Re-defined or de-finned Arai! Looks good!
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Old 09-06-07, 09:51 PM   #6
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The brake in that photo looks familiar.

I'm glad I didn't buy one of those square or octagon wheelsets. I'd have to re-invent the wheel too.
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Old 09-07-07, 07:07 AM   #7
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this is what i'd like to see...

a drum brake with the disc brake rotor integrated on it.
this is very possible if you have a lathe.

just a little bit of careful measurements using the stock ARAI brake shoe housing and AVID disc calipers mounted properly.

anyone up to this challenge?
could be an interesting winter project, eh?
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Old 09-07-07, 08:25 AM   #8
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Sounds interesting but why would you want to do that? A more elegant engineering answer would be to build a more robust disc brake as it would have the same weight and perhaps less complexity than the dual system.

Second issue is one of materials - the Avid disc is steel and is designed to flex to hit the static pad in the Avid caliper, whereas the Arai drum is aluminium and as such probably not the right material for a number of reasons. You would therefore have to machine some sort of disc adaptor. Another question is heat capacity. If you double heat inputs by having a disc and drum feeding heat into the same unit, the heat capacity of the unit won't improve. You will need to engineer some way of getting heat out of the assembly.

At that stage IMO you may as well go the whole hog and adapt a motorbike disc assembly. I guess a fully floating disc and cable driven hydraulic assembly that can stop a 200kg Fireblade and rider from 160mph repeatedly would be more than robust enough to stop a tandem going down a hill.
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Old 09-07-07, 08:35 AM   #9
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I also don't want to wear my rolfs out, ever.
Really??? If you think long-term, rims on caliper/canti/V-brake bikes are consumable items... like chains and brake pads and cables.

I know a former RAAM rider who considers replacing a wheel's rim to be about as ordinary as replacing a tire!

-Greg
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Old 09-07-07, 08:39 AM   #10
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Sounds interesting but why would you want to do that? A more elegant engineering answer would be to build a more robust disc brake as it would have the same weight and perhaps less complexity than the dual system.

Second issue is one of materials - the Avid disc is steel and is designed to flex to hit the static pad in the Avid caliper, whereas the Arai drum is aluminium and as such probably not the right material for a number of reasons. You would therefore have to machine some sort of disc adaptor. Another question is heat capacity. If you double heat inputs by having a disc and drum feeding heat into the same unit, the heat capacity of the unit won't improve. You will need to engineer some way of getting heat out of the assembly.

At that stage IMO you may as well go the whole hog and adapt a motorbike disc assembly. I guess a fully floating disc and cable driven hydraulic assembly that can stop a 200kg Fireblade and rider from 160mph repeatedly would be more than robust enough to stop a tandem going down a hill.

point well taken!

now this reminds me of a tandem i saw in my recent trip to Quebec City.
it is equipped with this electric hub, too bad i wasn't able to take a picture but here is the link to the hub http://www.bionx.ca/en/main/default/31.shtml
if we combine the the two parts above, we can probably make another segment of tandeming...
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Old 09-07-07, 09:42 AM   #11
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Braking is a waste of energy - literally. It converts hard-earned kinetic energy into heat. I try to brake as little as possible. We have an Arai drum but I removed it some time ago. We now rely on rim brakes. We decend some big hills & try to carry as much speed as we can. Our rims have about 10k miles on them & I can't see any wear.

My feeling is that if you regularly descend long hills with many tight switchbacks, or if you do loaded touring, you need a drum brake. Otherwise, rim or disc brakes work pretty well.
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Old 09-07-07, 09:58 AM   #12
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Braking is a waste of energy - literally. It converts hard-earned kinetic energy into heat.
Some noise also, but minimal energy there.

I'll bet these people wished that energy had been wasted differently . These really are quite ugly spills. Keep that in mind before viewing.

Not for the feint of heart
There has got to be a better way to come to a stop, ugly
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Old 09-07-07, 10:12 AM   #13
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Ouch! I don't ever want to experience that other than being a viewer.
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Old 09-07-07, 06:56 PM   #14
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The drum works well on long blind downhills, or pulling the trailer. I'm sure I could live without it in Indiana, but it has it's moments.
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