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  1. #1
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    A few Tandem Specific Questions

    Hello-

    I recently acquired my first tandem, a 2001 or so Burley Duet, and have a few questions about parts. Note that this is a road oriented tandem, and we will be using it on the road.

    1. We had to flip the eccentric to the high position to reduce the saddle-to-pedal distance enough for my girlfriend to be able to captain comfortably. Are there any unforseen consequences of doing this? The bb is the type with set screws on the top. I did read somewhere that the eccentric is ususally assembled in the low position to lower the center of gravity of the rider, but it is not clear to me that this would change the geometry meaningfully.

    2. The captain seatpost has a super-beefy double-bolt seatpost clamp that I think may actually be a re-purposed unicycle seatpost clamp. I like the idea, and it has not come loose even once in our first week of riding. However, swaping it out for a shorter clamp might remove the need to flip the eccentric. Any ideas on which compromise to make?

    3. The bike has drop bars with shimano 105 brifters (I'm assuming short pull), and direct pull levers (I'm assuming long pull, but not sure). I really like the braking action, but I'm curious if Burley has been known to deliberately use long pull brakes with short pull brifters to increase the braking leverage on their tandems. The arms of the direct pull brakes look like they might be shorter than typical.

    4. Is there any reason I shouldn't use cyclocross style in-line brake levers on a tandem? The intent is to help my girlfriend brake more comfortably when she captains. She can currently brake very effectively, but she is more stretched out than she or I would want to be when she is in the drops. I'm new to this type of lever, and the stakes are more than twice the usual, so I thought it prudent to ask around.

    5. Anyone know what the modes of failure of the Thudbuster suspension seatposts are? I weight more than she does, and we switch off too often to change the elastomers each time. The manual warns users to never use softer elastomers for those recommended for their weight. Should we always ride with the elastomers for my weight, or should we disregard the manual and find a comfortable ballance? i.e. Are we just risking the discomfort of the stem bottoming out if we use too soft elastomers, or would our hubris be rewarded with an asploding post? This is a new LT version.

    Thanks!
    Drew and Molly

  2. #2
    Ride it like you stole it WheresWaldo's Avatar
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    Drew and Molly, try posting this in the Tandem specific forum, you will likely receive many responses in short order there.
    "Never use your face as a brake pad" - Jake Watson
    The Incidental Cyclist - Cycling in and around Union County

  3. #3
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    Thanks for the suggestion, Waldo. I wasn't sure which forum to post in; decided I should post here since all of my questions were mechanical in nature.

  4. #4
    Senior Member Retro Grouch's Avatar
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    1. The purpose of the eccentric is to take up the slack as the timing chain wears and elongates. My guess is that you're going to have trouble down the road with your current adaptation.

    2. The captain's seatpost clamp serves double duty because in addition to holding the captain's seatpost up it also has to resist rotation when the stoker pulls on the bars. If your stoker isn't a super aggressive rider a single bolt seat clamp will probably serve the purpose. If it was my bike I'd probably swap with the stoker's seatpost clamp and see how it works.

    3. I can't tell from your post what you are really asking. Does your bike have Tektro mini V brakes that are advertised as compatable with road brake levers? If so, I hate them because they make removing a wheel a PITA. I much prefer using regular length, linear pull, Avid or Shimano brakes with Travel Agent cable pull doublers.

    4. I don't know very much about cyclocross brake levers. My guess is they'd work if everything else was set up right, but I've never used them personally. I'd wonder if your partner will be able to get the brakeing power that's necessary on a tandem using cyclocross levers.

    5. My guess is that a too heavy rider would shorten the lifespan of the soft elastomer. A too hard elastomer isn't going to give very much "cush". Changing elastomers everytime that you switch places is going to be a PITA.

  5. #5
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    Quote Originally Posted by Retro Grouch
    1. The purpose of the eccentric is to take up the slack as the timing chain wears and elongates. My guess is that you're going to have trouble down the road with your current adaptation.

    2. The captain's seatpost clamp serves double duty because in addition to holding the captain's seatpost up it also has to resist rotation when the stoker pulls on the bars. If your stoker isn't a super aggressive rider a single bolt seat clamp will probably serve the purpose. If it was my bike I'd probably swap with the stoker's seatpost clamp and see how it works.

    3. I can't tell from your post what you are really asking. Does your bike have Tektro mini V brakes that are advertised as compatable with road brake levers? If so, I hate them because they make removing a wheel a PITA. I much prefer using regular length, linear pull, Avid or Shimano brakes with Travel Agent cable pull doublers.

    4. I don't know very much about cyclocross brake levers. My guess is they'd work if everything else was set up right, but I've never used them personally. I'd wonder if your partner will be able to get the brakeing power that's necessary on a tandem using cyclocross levers.

    5. My guess is that a too heavy rider would shorten the lifespan of the soft elastomer. A too hard elastomer isn't going to give very much "cush". Changing elastomers everytime that you switch places is going to be a PITA.
    1. I am aware of the purpose of the eccentric, and the need for proper timing chain tension. In general, for a given timing chain, proper tension will be achieved in one of two positions. What longevity problems do you forsee? The only thing I can think of is that it could be bad to have indentations from the set screws on both sides of the eccentric rather than just one.

    2. Swapping the seatpost collar sounds like a good idea. I'll try it out if the seatpost OD's are the same.

    3. I'm not by the bike at the moment, but now I'm certain they are Tektro Mini-V's. I found a posting from Bill McCready:
    http://www.sudibe.de/articles/billonrimbrakes.html

    Chris Timm, along with Vince and Sue, wonder about mini-Vs. I agree with Rich Shapiro's assessment that these brakes are not the best answer. Most other Burley dealers I've talked to about this have reached the same conclusion. While it is true that you could ditch Travel Agents if a V-brake's arms were 50% shorter, the resulting brake would be too short to clear tires. A mini-V's arms wlll clear 700c tires (but not 26-inch tires) because they are only 20% shorter. Since mini-Vs will cause your brake levers to bottom out unless the pads are adjusted close enough to the rim to prevent quick wheel removal, many Burley dealers installed Travel Agents on mini-Vs in order to keep their customers happy. Put simply, mini-V's (originally designed for BMX) are a poor match for integrated road bar levers. The manufacturer, Tektro, who now combines them with a longer stroke lever and markets them for "comfort" singles, does not recommend them for tandems.
    I have experienced the annoying wheel removal you guys referred to with the Tektro Mini-V's. I can still get the wheels off without tools, but I have to bottom out the micro-adjusts and apply fairly significant force to get the cable free. I haven't seen these levers attacked as unsafe yet; just inconvenient.

  6. #6
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    Quote Originally Posted by awagner
    I recently acquired my first tandem, a 2001 or so Burley Duet, and have a few questions about parts. Note that this is a road oriented tandem, and we will be using it on the road.

    1. We had to flip the eccentric to the high position to reduce the saddle-to-pedal distance enough for my girlfriend to be able to captain comfortably. Are there any unforseen consequences of doing this? The bb is the type with set screws on the top. I did read somewhere that the eccentric is ususally assembled in the low position to lower the center of gravity of the rider, but it is not clear to me that this would change the geometry meaningfully.
    You know the role that plays the eccentric. Basically, there is no difference between using the upper part or the lower part of the eccentric, so as long as her legs are long enough to allow enough adjustment, you're OK. The only drawback is that pedals are a bit higher, so reaching the ground will be a wee bit harder when stopping. No big deal.

    2. The captain seatpost has a super-beefy double-bolt seatpost clamp that I think may actually be a re-purposed unicycle seatpost clamp. I like the idea, and it has not come loose even once in our first week of riding. However, swaping it out for a shorter clamp might remove the need to flip the eccentric. Any ideas on which compromise to make?
    I think it's a standard 2-bolt seatpost. Just that it's a 29.8 mm seatpost instead of the typical 27.2 or 27.4 mm seapost used on a single bike. If I understand correctly, she uses a standard seatpost and you have a suspension one. If indeed she has a rigid one, there probably is little you can do to lower the captain's saddle. Still two options might help you to save 3-5 mm:
    – Some seatposts have a nice curve at the top whereas others have the post entering directly into the bracket. For example, with a Zoom seatpost, I was able to lower the stoker seatpost by 8 mm compared to the seatpost that originally came with my Co-Motion.
    – Some saddles have a lower profile than others.


    4. Is there any reason I shouldn't use cyclocross style in-line brake levers on a tandem? The intent is to help my girlfriend brake more comfortably when she captains. She can currently brake very effectively, but she is more stretched out than she or I would want to be when she is in the drops. I'm new to this type of lever, and the stakes are more than twice the usual, so I thought it prudent to ask around.
    No problem. Basically, these short mini-V levers have a pull compatible with caliper brakes and cantilevers. So you could install cyclocross levers. From what you describe, it might also be worthwile to replace the stem by a shorter one.
    Michel Gagnon
    Montréal (Québec, Canada)

  7. #7
    Senior Member Brian's Avatar
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    Moving to Tandems.

  8. #8
    Elite Rider Hermes's Avatar
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    I have an observation that leads to a question that the manufacturer may have to answer. How far back on the tandem can the center of mass be moved without changing the handling and braking characteristics of the tandem? I ask this question since you mentioned the readjustment of the shock absorbing stoker seat post to accommodate the heavier rider. It is my understanding that tandems are engineered to assume that the heavier rider will be the captain. This sets the center of mass more forward and I suspect sets design criteria for the frame, fork, wheel and component selection. If one moves the center of mass back toward the rear wheel, the handling and braking of the bike may be different. The reason I point this out is that you may want to experiment a bit to see how the bike handles and brakes under different conditions before you descend a steep hill at high speed come to a sharp turn and crash the bike. I suspect the normal operating conditions will not be a problem. The same situation applies to rear engine cars. One has to drive them differently e.g. applying power through corners.

    As a second point, the rear tire pressure will have to be increased when the heavier rider is the stoker.

    Good luck

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    Quote Originally Posted by lordoftherings
    I have an observation that leads to a question that the manufacturer may have to answer. How far back on the tandem can the center of mass be moved without changing the handling and braking characteristics of the tandem? I ask this question since you mentioned the readjustment of the shock absorbing stoker seat post to accommodate the heavier rider. It is my understanding that tandems are engineered to assume that the heavier rider will be the captain. This sets the center of mass more forward and I suspect sets design criteria for the frame, fork, wheel and component selection. If one moves the center of mass back toward the rear wheel, the handling and braking of the bike may be different. The reason I point this out is that you may want to experiment a bit to see how the bike handles and brakes under different conditions before you descend a steep hill at high speed come to a sharp turn and crash the bike. I suspect the normal operating conditions will not be a problem. The same situation applies to rear engine cars. One has to drive them differently e.g. applying power through corners.

    As a second point, the rear tire pressure will have to be increased when the heavier rider is the stoker.

    Good luck
    +1

    You did not say who is taller, you or your girlfriend, but all non-custom tandem frames that we have seen are designed with the larger compartment for the captain. Also, when one or both riders stand to climb, accelarate, or sprint, it takes a little bit of upper body strength to maintain control. We know that we are guilty of gender profiling ..... but, even if you are taller, heavier and stronger than your girlfriend, we can also think of a few reasons, all valid, why a team would want to split duties the way you present.
    Last edited by cornucopia72; 12-03-06 at 07:06 AM.

  10. #10
    Time for a change. stapfam's Avatar
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    Quote Originally Posted by lordoftherings
    I have an observation that leads to a question that the manufacturer may have to answer. How far back on the tandem can the center of mass be moved without changing the handling and braking characteristics of the tandem? I ask this question since you mentioned the readjustment of the shock absorbing stoker seat post to accommodate the heavier rider. It is my understanding that tandems are engineered to assume that the heavier rider will be the captain. This sets the center of mass more forward and I suspect sets design criteria for the frame, fork, wheel and component selection. If one moves the center of mass back toward the rear wheel, the handling and braking of the bike may be different. The reason I point this out is that you may want to experiment a bit to see how the bike handles and brakes under different conditions before you descend a steep hill at high speed come to a sharp turn and crash the bike. I suspect the normal operating conditions will not be a problem. The same situation applies to rear engine cars. One has to drive them differently e.g. applying power through corners.

    As a second point, the rear tire pressure will have to be increased when the heavier rider is the stoker.

    Good luck
    On the Handling side- I weigh 150lbs and my regular pilot weighs 180. 2 schools of thought that I have heard on the weight distribution. The more powerfull rider to go on the back-- This would generaly be the heavier rider. And then the way That I reckon- The better pilot goes on the front. I started on the front but It takes a lot of upper body strength to control a Tandem. As the speed goes up it takes more of that upper strength to control, and on our offroad riding- Stuart can control the Tandem better. Then I do occasionally take other riders out with me- and I still put the one that can control the bike better on the front. Sometimes it is the "Novice Tandem" rider and sometimes they go on the back.
    Tyre pressures I always keep the same but this is higher than the pressure Recommended for that Tyre in any case. If I had a real heavyweight on the back then I would go to a Wider tyre and still over inflate- This would cause more drag but still be acceptable with a lighter rider on the rear.

    I have a Thudbuster and it is the 3" travel form. I set it up with 2 blue Elastomers. This is just a bit firm for my weight but just in the limits- And it is just a bit soft for 180lbs-but just within the limits. On ocasions- Me and my regular pilot have swopped positions and the Thudbuster has still not bottomed out.

    Main thing is to get that Tandem to handle. This takes a lot of sorting out initially- but the biggest aid to setting it up is to sort the riders into their relevant positions. The one that can handle the steering and brakes and gearchanges is going to be the Pilot- But it is still the Stoker that controls the ride.
    How long was I in the army? Five foot seven.


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  11. #11
    Elite Rider Hermes's Avatar
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    Quote Originally Posted by stapfam
    Tyre pressures I always keep the same but this is higher than the pressure Recommended for that Tyre in any case. If I had a real heavyweight on the back then I would go to a Wider tyre and still over inflate- This would cause more drag but still be acceptable with a lighter rider on the rear.
    Here is a link from Precision Tandems web site http://www.precisiontandems.com/arttiresbymark.htm about tires and there is a chart for calculating tire pressure and formulas for tire pressure as a function of disproportionate tandem team weight.

  12. #12
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    Quote Originally Posted by lordoftherings
    I have an observation that leads to a question that the manufacturer may have to answer. How far back on the tandem can the center of mass be moved without changing the handling and braking characteristics of the tandem?

    On any bike, handling changes as soon as you start shifting weights around. As someone who tours regularly, I had already experienced first hand the different characteristics of a single bike with and without load in rear panniers only and with a full load in 4 panniers (a.k.a. loaded touring). The same issues exist with a tandem, except that part of the load pedals and wiggles around. I have yet to try my tandem with an adult stoker, but I have used it with and without my oldest child (50-60 lb soaking wet), with and without trailercycle, and with and without 6 panniers.

    Generally speaking, if you put the lighter person in front as the original poster plans, the frame will be more rigid than if you place the heavier person in front. But the rear wheel will be more sollicited. And in extreme cases (i.e. 100 lb female captain and 300 lb male stoker), front wheel traction would be critical.

    Definitely, as with any new vehicle, one must get used to it gradually. And unless they – and especially she, the captain – have previous tandem experience, I would suggest that the captain does a few solo rides at first, then short tandem rides in places where space is not critical. I know that my first tandem rides were 2-3 km long (in heavy traffic, I might add) and that was more than enough for me. Then came the 50 and 100 km rides.
    Michel Gagnon
    Montréal (Québec, Canada)

  13. #13
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    Quote Originally Posted by Retro Grouch
    1. The purpose of the eccentric is to take up the slack as the timing chain wears and elongates. My guess is that you're going to have trouble down the road with your current adaptation.
    Thankfully, this is just a guess, and is not correct.

    Put that eccentric wherever it works for you, so long as you tension properly. Also, depending on the specific geometry of your bike, by adding or removing a link (or perhaps half-link!) from your timing chain, you may get additional eccentric position choices.

    -Greg

  14. #14
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    Quote Originally Posted by gregm
    Thankfully, this is just a guess, and is not correct.

    Put that eccentric wherever it works for you, so long as you tension properly. Also, depending on the specific geometry of your bike, by adding or removing a link (or perhaps half-link!) from your timing chain, you may get additional eccentric position choices.

    -Greg
    How do you remove half a link?

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