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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 02-27-14, 05:37 PM   #26
Ritterview
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Originally Posted by joe@vwvortex View Post
I've got dual discs - I had a rear with a front rim brake. I'll never not have a tandem with dual discs. I've done many long descents which required braking and many short steep and twisty descents that required even more braking.
The thing to do is to consider what you'd want if you were poised atop long, steep and twisty Mix Canyon Rd. I'd want front and rear discs. I think Bill McCready would want dual discs too.

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Old 02-28-14, 05:50 AM   #27
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Why would't Bill's technique work just as well on a bike with dual discs?

FWIW I ride a bike with dual discs but have retained the option of reinstalling the original V brake on the rear as a third brake if necessary.

Cheers,

Cameron
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Old 02-28-14, 08:16 AM   #28
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Originally Posted by Ritterview View Post
The thing to do is to consider what you'd want if you were poised atop long, steep and twisty Mix Canyon Rd. I'd want front and rear discs. I think Bill McCready would want dual discs too.


Pretty similar to Brasstown Bald.

We got down that without stopping with Dura Ace calipers, and a team weight of 350lbs.

http://www.strava.com/segments/614827
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Old 02-28-14, 09:12 AM   #29
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With rim brakes we had to stop twice on this. Some really steep sections at bottom that don't show on the graph. I am installing a rear disk and leaving the rear rim as a emergency brake.

http://www.strava.com/segments/613375

Anyone else use their jackets like a parachute on steep hills?

Wondering if a small parachute would work behind the Stoker? Or would it flap to much?

Half humor half serious question.

Has anyone does any serious descending with a kid trailer? At speed does it slow you down or just add to the freight train? What is the max speed that you have gone and felt safe with trailer?
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Old 02-28-14, 09:35 AM   #30
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With rim brakes we had to stop twice on this. Some really steep sections at bottom that don't show on the graph. I am installing a rear disk and leaving the rear rim as a emergency brake.

http://www.strava.com/segments/613375
This is where descending style comes into play. Looking at the satellite view of that, I think there would only be 3-4 hard brakes before the switchback at the bottom for us.

The faster you're willing to descend, the less heat is an issue for the brakes.



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Anyone else use their jackets like a parachute on steep hills?

Wondering if a small parachute would work behind the Stoker? Or would it flap to much?

Half humor half serious question.
Unzipping jackets, jerseys ( still attached at the waist so they don't flap wildly) and sitting up will slow your maximum speed a bit.
You need to get in the drops to corner though for added stability.

An actual parachute would be an entanglement risk. Not good in spokes.




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Has anyone does any serious descending with a kid trailer? At speed does it slow you down or just add to the freight train? What is the max speed that you have gone and felt safe with trailer?
We've pulled a burley trailer with a kid in the high 20's, and rolled down some small hills at 30mph or so. I wouldn't want to go much over 10-15mph on something really steep. The lack of trailer brakes could cause a nasty jack knife if you had to hard brake at speed with a trailer downhill.

That would be an example of wher I think you'd want a third brake,preferably a drum, because you'd be dragging to control speed even on straight portions.
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Old 02-28-14, 10:00 AM   #31
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High speed descending is not an issue(former Pro motorcycle racer), the graph and map do not do this justice and if you ask me are waaaaay out, in one section there is a sign saying 18% . Also, catching up to cars and trucks was a bit of issue, have to slow down and wait for a good spot to pass.

We also stick our knees and elbows out to help slow us down.

I do have a drum on my triple and that may be a better option to switch it over for big descents on the tandem pulling the trailer.

If I really want to get creative a trailer brake may be an idea.
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Old 02-28-14, 10:28 AM   #32
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The thing to do is to consider what you'd want if you were poised atop long, steep and twisty Mix Canyon Rd. I'd want front and rear discs. I think Bill McCready would want dual discs too.

Mix is about 5 miles from my house. We've done it on road bikes but never the whole thing on a tandem. There are sections like the switchback near the top which is near 26%. I prefer to do it on my MTB so I can ride along Blue Ridge and come down Gates which has several steep and unpaved sections. In 2003 - when we had the Solano Bicycle Classic - there was a 7.7 mile time trial which ended at the top of Mix Canyon. Here's the top two finishers and their time.

1. Jonathan Vaughters, Prime Alliance, at 0:33:27

2. Chris Horner, Saturn, s.t.
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Old 02-28-14, 11:51 AM   #33
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How do you figure that swept area increases with radius squared? If the disc was a plate, sure the area of that plate increases with radius squared, but it's not. The size of the pad remains the same, so the swept area is:

pi*r^2 - pi(r-discwidth)^2 = 2pi*r*discwidth - pi * discwidth^2

r=max dimension of rotor
r-discwidth = inner dimension of rotor, most material (except spindly arms) inside this is missing on a bike disc.

(discwidth = probably the wrong term, but the bit that gets swept by the pads - since the pads don't change for larger brake sizes, this is essentially constant)

Or, it's roughly the circumference of the disc times the width of the disc

The thickness is constant so mass, which is essentially the swept area times the thickness, also increases linearly with radius.

For a car, where the discs are solid plates, the area of the disc does increase with radius^2, but on a large bike disc, with the middle of the plate cut out that's not the case.
When we say "surface area" I key into area formulas which are non-linear.

So rather than get pie-faced (again) I plugged numbers and formulas into Excel presuming 20mm for swept area width and calculating 160/180/200mm discs. What I found is that yes indeed the area of the circle was non linear but the area of the ring was indeed linear. So rahill is correct and the swept area on bike disc brakes does indeed increase linearly with increased diameter.
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Old 02-28-14, 12:21 PM   #34
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If you have a tandem with only rim brakes, the cheapest and simplest upgrade is to go with deeper aluminum rims, like Deep-V or Kinlin 279, if you're not already running these. Just as with discs, rim brake cooling is all about surface area. Makes a huge difference. I wish there were even deeper alu rims.

We have a drum wheel that we use for touring. We've considered getting a front disc and fork, but find that we can get down anything we need to in sport trim with rims. So we keep the drum for touring.
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Old 03-03-14, 12:18 AM   #35
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If you have a tandem with only rim brakes, the cheapest and simplest upgrade is to go with deeper aluminum rims, like Deep-V or Kinlin 279, if you're not already running these. Just as with discs, rim brake cooling is all about surface area. Makes a huge difference. I wish there were even deeper alu rims.

We have a drum wheel that we use for touring. We've considered getting a front disc and fork, but find that we can get down anything we need to in sport trim with rims. So we keep the drum for touring.
There are deeper aluminium rims around, but they come with a weight penalty. H Plus Son make a 42mm rim (SL42) http://www.hplusson.com/products which they say weighs in at 615g, I have some 45mm cheap Chinese rims which weigh 880g each! They are a far cry from the sub 300g rims that I used to race on (single bike).

Cheers,

Cameron
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Old 03-04-14, 11:44 AM   #36
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Disc brakes have amazing stopping power...until they fade and have none. We have a Santana w/ the big WinZip rear disk and several years ago while touring in the Adirondack's I experienced a complete loss of rear braking power twice on long descents. We are a relatively light team (sub 300lbs) but we were pulling a loaded BOB trailer (approximately 50lbs) so it was a significant mass I was trying to stop. Fortunately, I was able to stop using just the front brake but it was not a fun experience. I'll admit there was probably some operator error in my braking technique (it was my first bike w/ disk brakes) but the fact that disk brakes can quickly fade to nothing is reason enough for me to not use two disks in the mountains. For safety reasons I added a rim brake for the rear wheel that is controlled with a CX brake lever on the tops of the handlebar. I also added a CX brake lever for the front brake. If I'm on the hoods or drops I have control of the front rim and rear disk brake and if I'm on the tops I can control both rim brakes. The rear rim brake certainly doesn't have the stopping power of the disk but it adds piece of mind to have it there as a back-up.

We also have a Cannondale road tandem that has dual disks; I love the braking power on that bike and have never had a problem with the brakes. However, for loaded touring in the mountains I would not feel comfortable using it due to the risk of failure.
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Old 03-04-14, 11:51 AM   #37
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Originally Posted by waynesulak View Post
I take Bill's idea of holding a brake in reserve is a real world perspective on how to use a tandem with one disk and one rim brake. None of use want to risk having no brakes while descending on our tandem. Like a front fork failure at speed, it really is disturbing to consider.

It occurs to me that two brakes is not the best design for a tandem that is going on big descents. On a one or a two disk tandem an extra rim brake lever mounted on the drop of the captain's bars and working on a disk brake wheel could serve the same purpose. This is not a drag brake or a brake you plan to use but an emergency brake. If one or both disks fade then the captain moves the to the drops and stops the bike with the cool rim brake. Rims brakes don't weigh much and are easy to add just before and after that big trip to Maui as long as you have the canti or V-Brake studs on the frame or fork.

This is similar to what I did but I added the extra levers on the top of the bars using levers like this: http://www.jensonusa.com/Brake-Lever...1-Cross-Levers
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Old 03-07-14, 04:56 PM   #38
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We have pulled the trailer at 23 / 24 on flat roads during training rides. It is a parachute without the windscreen installed. Ironically, Sofia prefered the wind in her hair.

I have told my stoker that the concept of loading the travel and dragging it along could be a nice way to make an event easier.

PK
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