PMK

I'm pretty certain the F150 with Andretti driving would cut across the grass, pretty fast I might add, take out the Porsche, and drive on for the win.

The driver of the Porsche would be stunned yet amazed.

Where I come from, fast guys are fast, regardless.

PK

DoubleDiamonDog

Well I guess that you are just wrong, unless someone slipped me some Kool Aid when I wasn't looking. Cannondale works for you and the way you ride. It doesn't work for me and others. I have ridden Cannondale tandems and for me the ride was too harsh and unpleasant. Could be the aluminum, could be frame geometry or a little of both. But we're a smallish team and did not require such a stiff frame. Although we could have afforded any material, we chose a custom built steel frame with a carbon fork. Works for us - not for you. During a century ride last summer, as we chatted with another couple the conversation as it often does came around to bikes. The couple we were chatting with had owned their Cannondale for a couple of years but were planning to get rid of it and purchase a bike with a different frame material. They were leaning toward steel because, as he put it, they just felt "beat up" at the end of a longish ride.

Enjoy your Cannondale, but believe it or not, it ain't the bike for everybody.

I am curious though, on your Cannondale, do you prefer an aluminum fork? Have you tried carbon fiber as a frame material?

Ritterview

Cannondale's are nearly as famous for being harsh/buzzy as they are for being stiff and a good value.

What I do not know is whether the Cannondales in this regard are representative of aluminum tandem frames, or whether they are less smooth than other aluminum tandem frames (e.g. Co-Motion, Santana).

Carbonfiberboy 

Our racing limo is steel frame, carbon fork. With 25c tires at 120 lbs., it's the smoothest bike on chipseal I've ever been on. I've had fellow riders watch us from behind when climbing in and out of the saddle. As far as they can see, when we're synced the frame doesn't flex. When we're out of sync it's obvious. We're IP, so I mean that our pedal loading is timed the same throughout the stroke when we're synced. I've watched tandems climbing on RAMROD and it can be almost hilarious, while the experienced teams are just beautiful. So I'd say that's a very important thing, maybe the most important thing.

waynesulak

I have hesitated to make that point about team sync but now that it is out there I agree. I believe it also applies to singles as well. A flexible bike does require more coordination and a smoother stroke than a stiff bike to efficiently transmit power.

The real problem with trying to analyze the frame stiffness issue is that there are so many factors involved. For most people it is not practical to isolate a change of frame from a change in components and add to that differences in rider size, strengths and even riding style. Most of us don't have a power meter on the crank and the rear wheel to see if there is any power lost. The result is we all have to live with our person subjective observations.

We ride a steel tandem because I could have one customized to the stiffness I desired. Local builders don't do a lot of work on Aluminum frames and carbon is beyond my limited ability to calculate stiffness. I can calculate an estimate of the difference in stiffness of steel tubes which allowed me to try tandem frames with known stiffness differences. After four different test frame configurations we settled on a frame that we like. No kool-Aide was involved just a lot of work obtaining used frames, modifying them and switching out the same components so that only variable was the frame.

Yeah I know I spent way too much time doing this but it I look at it as a separate hobby from actually riding the bike. I also think we ended up with the perfect about of stiffness in our tandem. The bottom line is that it is just more fun for us to ride. If someone could build me a carbon tandem that rode like our steel one and weighed a few pound less I would love it. I am not married to steel but it works and a few pounds is not that big a deal since we don't ride in the mountains.

rdtompki

Well, this thread has certainly taken a turn, but interesting one at that. We bought our one and only tandem with (obviously) no tandem experience. It happens to be steel. We also test road Co-Motion (steel) and Santana (material unknown). We selected a steel daVinci and have been happy with the durability, running gear, ride, etc. We're an older team, ride in sync and I wouldn't notice a loss of efficiency it it bit me you know where. I do accept that the daVinci drive train is certainly less efficient than a conventional drive train.

We may buy a new tandem when I retire. The two things I would look for: ride and cornering. I wouldn't settle for something less comfortable than the steel tandem we already have. I like the security with which we can corner at reasonable downhill speed and would insist on a long test ride before considering any new ride, much more than we did when we bought our first tandem since we were at that point just trying to keep from falling over.

If I were many years younger and racing I'd be darn interested in the efficiency aspects of frame material and design, but unless someone can show me some data that I can relate to our situation evidencing more than very low single digits of difference (wrt frame material) in terms of efficiency, I'll stick with what I perceive when riding the bike. I can easily see where a large, strong team would have significantly different issues than my wife and I encounter.

Kjkc

Changing out the adjustable stoker bar for us looks like a reasonable change, what manufacturers have folks had experience with and chosen? I also saw an adjustable carbon stoker bar as well?

bikefor2

Why do you think this is the case? I know some non-da Vinci teams seem to think so, but I haven't been convinced by anyone yet that it's true. Just curious...

rdtompki

Chains are not 100% efficient and small gears, I believe, tend to have greater losses than large gears. The daVinci has an additional chain drive, two additional bearings and some small intermediate cogs. HOWEVER, the word "certainly" was used in an engineering sense as in I believe you could measure a difference. Do I think it's significant, absolutely not, but I don't know whether the difference between convention and ICS is .1% or .01%; doesn't matter one bit to me. If I were racing I'd be looking at .1% as important plus a possible weight penalty. We love our daVinci and for us the ICS is perfect; I wouldn't ride anything else.

waynesulak

Chain drives have been around a long time and there is a lot of research out there if you want to research the energy losses.

I have spoken with Todd at daVinci about this and if I recall correctly he feels that some loss in drive efficiency is offset by the benefit to team comfort resulting in more power on the second half a a long ride. The people I know with daVinci bikes appear to love them. For us being tied together on the bike is part of the appeal as well as a the challenge. Some people like fixed gears. Choice is good.

conspiratemus1

So why don't you do just that, then come back here and tell us what you found? Otherwise you're just B-S'ing. Which is fine, no problem with that. But other posters (including me) have cited actual measurements of surrogates for power (time on climbs, time over courses) on this and other threads and the evidence is that you are just plain wrong about steel being inherently slower.

wheelspeed

In fairness to Mtnbke, maybe the difference in opinions here are because he's such a tall, big guy that his impressions are a little different than most of us who are 5-11" and weak and spindly (me).

I suppose a non-custom frame would feel completely different between a 17" model and a 24" model since tubes span larger distances, and I'd doubt a non-custom builder would use much different butting or tube diameters between frame sizes.

DoubleDiamonDog

Exactly - yet mtnbike was saying that aluminum was best for everyone and that "all other things being equal, no one put those drinking the Kool-Aid would ever "want" a steel tandem if they could alternatively have an aluminum one". The way he talks my concern is that noobies may take him seriously and follow his advice. He seemed very closed minded to the concept that other frame materials could be a better choice for some people. Then while criticizing others for not providing info to support their opinions, he provided none himself. Maybe the reason we haven't heard from him is because he is out doing some testing and will report back -what do you think?

I hope he comes back because I am curious about his thoughts on his aluminum fork and the short comings of carbon fiber. I would think that carbon fiber could be a great choice for him - maybe it is a matter of $, but on the other hand he says cannondale is fastest, bar none.

Brad Bedell

In my order of preference and experience. (note I said preference)

Carbon: I feel this is the ultimate building material. It can be exceptionally stiff or customized in ways that is simply not feasible for a steel bike. Sure, you can mix/match steel tubes, but to get something as precise, one would have to make custom mill runs of tubing. With Carbon, one can simply wrap a tube thicker or reinforce a joint better by adding layers. Cost to build: Carbon really is cheap compared to say, titanium. The money comes in from the experience of wrapping and materials handling.

Steel: Nothing rides like it. It's forgiving, you can dent the heck out of it and it will keep ticking. My next MTB will be steel. (current is aluminum) I'd love to have a Carbon MTB, but I've taken a few spills that would have destroyed the bike. My 36er frame is silly stiff and it's made of steel.

Titanium: It's sexy, expensive and springy. It comes in a close third behind steel due to cost. I'd likely buy steel over TI for this reason; unless I needed better environmental controls. (wet environment/etc)

Aluminum: Super stiff. If you can't afford Carbon and need a stiff/light weight bike; this would be what I'd get. I liked the Trek 1000 tandem we had once I had all the parts built up. It was under #28lbs ready to ride and the frame was actually lighter than my Cyfac Carbon frame by a few grams. Equally as stiff, but the road buzz from the aluminum killed it.

TandemGeek

Let us not lose sight of the fact that not every frame made from the same material will have the same ride qualities. There are some signficant differences between different steel, aluminum, titanium and composite frames that are designed by the various different builders.

For example, Santana's steel frames have a completely different feel from Co-Motion, as do the Bilenky, Ericksons, Burley and other steel frames. The same is true of Aluminum frames from Cannondale, Santana, Co-Motion, daVinci, and various different custom builders. A Titanium Litespeed Taliani has a different ride quality vs. a Seven, Santana or I suspect a tiCycles frame, and I suspect Kent Eriksen's ti frames have some unique qualities. Composites vary quite a bit from builder to builder: our Calfee is very different from a Santana Beyond, and I suspect the Cyfac have a signature feel that's different from a Calfee or Santana. Of course, embedded in these subjective ride quality differences are the influences that builder decisions regarding steering geometry, tubing design specs, and fabrication methods have... never mind the influence that different fork, wheel, tire and tire-pressue choices.

I'm still waiting to get our hands on a magnesium Paketa V2 or V2r and a Bamboo Calfee road tandem to see how they compare to the exotic composites and titanium frames.

wheelspeed

I note that you said "preference", but they still seem like generalizations. I've read reviews of recent aluminum frames on half-bikes that stated aluminum design has come a long way since the early 90s, and the latest decent aluminum frames are not harsh.

I'd suppose tube diameter has a big impact on stiffness, regardless of material. I'd think that Ti or steel frames using the tube-sizes of aluminum bikes would also be very stiff; similar to how modern aluminum bikes have seat stays almost as thin as steel bikes to remove harshness. It's a shame steel tubing didn't get the development during the past 8 years that aluminum tubing got. (Aluminum bikes now have ovalized ends using different orientations, conical tubes that are bigger diameter at the head and smaller at the seat post, etc.)

waynesulak

I believe that tubing diameter and wall thickness for a given material are what primarily determines stiffness. For example in steel tandems, Co-motions are stiffer than Santanas because they use a larger diameter main tubes while both companies for the most part use 8/5/8 butted tubing. The exception here is Santana's 7/4/7 tubed bike which is more flexible still than Santana's 8/5/8 steel tandem.

The nice thing about metal tubes is that the stiffness of metals is a known quality and can be found on the internet. From this the stiffness of the tube can be calculated using its diameter and wall thickness. This allows aluminum and steel bikes to be designed with the same stiffness or flex by using just the right size tubing in each material.

Carbon allows for a lot of customization with the layup however it appears to a casual observer like myself that Calfee uses the same manufactured tubes on all of its tandems and then stiffens as needed by adding material to the tube. Perhaps TandemGeek or others can shed more light on that subject. If this is the case however then all Calfee tandems frame's that did not have material added would have the same stiffness resulting from the same tubing set.

TandemGeek

Calfee uses a variety of different diameter tubing and both high modulus carbon with boron & the somewhat thicker intermediate modulus carbon tubing to produce their framesets. For the tandems, and in addition to being able to use the different materials, note that Calfee binds it's mitered, roll-wrapped carbon tubesets together using hand-laid, wet-wrapped epoxy-soaked carbon fabric, which gives the tandems their distintive "fat" joints. These joints can use more or less material to fine-tune the frame's stiffness by either extending the application area and/or using more material around the joint. This is also why Calfee can rework a frame if the customer finds their tandem isn't stiff enough and/or needs to make other changes, to include replacing rear stays or even the main frame tubes.

Case in point: When Craig was designing our tandem around a 32" stoker compartment he found that we'd need to go to a 2" diameter top tube (same as the boom tube) to get the needed stiffness for the very long stoker compartment even with our sub-300lb team weight. That wasn't desireable for a number of reasons so I asked him to modify the design and re-run the number with a 31" and 30.5" top tube. The 30.5" top tube allowed for the use of the 1.75" diameter top tube and I threw out another 1/2" of stoker compartment length just for some added margin. So, there are a number of different ways to go about "tuning" Calfee's tandem frames, even when they are built around stock composite tubing.

DoubleDiamonDog

Interesting info TandemGeek and it is a good example of an iterative design process where priorities may be adjusted a bit as one learns more about the implications.

The matter of an expansive stoker compartment is more important to some than others and then there is the question of how much is enough. I know that you prefer a longer stoker compartment but in this case you were willing to accept a shorter one (still generous I suspect) "for a number of reasons". Although I have some suspicions, would you mind sharing what those reasons were?

waynesulak

TandemGeek's story is also a great example of how the design process is usually shaped by series of compromises that balance conflicting priorities.

TandemGeek

Having lived with our Erickson tandems -- a '98 Signature and an '02 Custom Travel Tandem -- which both sported 32" stoker compartments, the questions I had for Debbie related to just how long the Calfee should be were:
Question 1. Would you miss having an extra inch of clearance between your bars and my saddle or your nose and my back? Answer: Probably not.
Question 2. Do you ever see us doing anything like serious racing or time trials where you might want to have a more stretched-out riding position? Answer: Probably not, but if we did, we can always use the Erickson.

Now, to be honest, I should have left well-enough alone at 30.5". I wasn't thinking when I dropped the other .5" as added margin in terms of how a 30" boom tube would influence the front bottom bracket's positioning in the eccentric. Regardless, while Debbie's Garmin 305 sometimes disappears under my rear-end, her bars still sit behind and below my saddle while she is still able to enjoy the same riding position on the tandem that she has on her single road bikes, noting she's only 5'2".

This was and remains a pretty important design feature for us, something we've reaffirmed on tandem test rides where shorter stoker compartments are the norm. This past weekend's ride on the Triplet was truly a pain in the a**, as Debbie's hands and my butt were in contact far too often for my liking. This will be a problem on just about any Triplet, with a few exceptions. In fact, there is a Precision Tripet for sale in middle Georgia that would be a perfect fit for us with it's 29.5" stoker compartments and lower than normal stand-over height except for one thing: the captain's top tube is just too darn long for me @ 58mm. I use a 53mm and have a couple 54's. I wish there was some way to make it work, but using a 50mm stem is really pushing the limits of proper frame fit and steering dynamics.

DoubleDiamonDog

Sounds like shortening the stoker compartment from 32" to 30" has been good for you and a good tradeoff it seems.

Staying with the 32" would have meant using 2" dia top tube instead of 1.75" to get the stiffness you needed - any downside to using the 2" instead of the 1.75" to get the 32" you had originally spec'd?

We have a shorter stoker compartment - only 27" - and my 5'-2" stoker rides in her most comfortable position and we never have the stoker hands / handlebar / captain's legs issue but maybe we get away with it because of the handlebar she uses. Instead of drop bars with dummies or bullhorns she has a variation on a flat bar designed by Jitensha Studio, made by Nitto, I believe. The bar is positioned at about the same height as her saddle. Her frame of reference is her commuter bike (she doesn't have a conventional road bike with drops) which has a flat handlebar but her stoker bar gives her more options on hand positioning, but not like drops of bullhorns would, nonetheless it seems to work well for her. No complaints on centuries anyway - we'll see when we move up to double centuries this summer.

It is fascinating the way different setups are preferred by different teams and the process by which they arrive at their chosen configurations. Also interesting to note that you designed the bike the way you would use it the vast majority of the time which I think makes great sense. Sometimes it seems that teams design to cover every contingency, which may seem prudent, but perhaps the main objective may be compromised a bit.

The thread has wandered far from the original question (as oftern happens) but is still interesting!

TandemGeek

Downside would have been knee clearance for me, as I tend to pedal with my knees-in. Even with the 1.75" tubes I find that I brush the sides of the top tube now and again, so the 2" would have been problematic as I'm too old to start modifying my pedal stroke. There was also an aesthetics issue associated with going to a 2" top tube and an even more expensive set of couplers, noting the pair of 2" and pair of 1.75" Ti S&S couplers were about $2875.

tredlodz

I went with the 2" top tube and couplers (Al couplers are a bit cheaper I think) on the basis of keeping the frame as stiff as possible. Before the bike arrived, I had some concerns about knees touching the top tube, but it's never been a problem. They do brush occasionally, but no more than on bikes with much narrower top tubes. One thing to note is that a standard water bottle cage is much wider and doesn't seem to give most people problems. Also the pump mount sticks out beyond the Stoker top tube, but doesn't cause any issues.

DoubleDiamonDog

Thanks TandemGeek and tredlodz. You each went a different direction and got what you wanted. As one who is a design professional (not bikes!) I am always intrigued by the decisions that are made as a design is refined, compromised and optimized.