Tandem crank-phasing is a frequent subject of hot debates on various tandem discussion forums and what-not that is best addressed one tandem team at a time. Really… I can’t even begin to count the number of threads I’ve seen over the years, although one of the better ones included a poll (somewhat skewed by the nature of the Internet community vs. what you typically see in the real world) and about 4 of 5 pages of postings that tried to wrestle with the whys and wherefores of crank phasing.
What is crank phasing? Well, believe it not, tandems can be configured to have the cranks set in more ways than one. The image below is something I threw together a few years ago to help illustrate what some of the more typical arrangements are and what they do.
While most tandems are depicted in marketing literature and put on the sales floor In-Phase most likely for aesthetics and simplicity’s sake, there are many strong proponents of riding 90° out-of-phase, and even many more who opt to put their cranks out-of-phase by just a few chain wheel teeth. As is often the case, riders who find themselves in the minority tend to spend a lot more time explaining and advocating the benefits of out-of-phase if only because the very obvious ‘Taffy Puller’ look you see when a tandem teams legs and pedals aren’t moving in a synchronized manner which is far more common.
I would venture a guess that 80% of the folks who ride tandems on a regular basis ride with their cranks synchronized or, “In-Phase”, another 15% or so vary the phasing by one or two teeth to bias the initial pedal resistance to either compensate for differences in fitness or personal preference, and 5% or so who ride 90 degrees out of phase.
I would also venture a guess that as suggested above most teams ride IP because that’s the way dealers set up tandems, that’s the way they are depicted in most marketing materials, and as already mentioned that’s what new tandem teams will see most other tandem teams doing. However, some teams that have taken enough time to give OOP a fair shake find that they prefer the “smoothing” effect OOP has on their pedal stoke and when climbing — which also translates to somewhat easier handling — and, yes, it does reduce wear and tear on the drive train. Other teams who have given it a go find that they cannot sprint or climb out of the saddle together when their cranks are 90 degrees out of phase. Also high on the list of “why not OOP” are the sometimes hard to quantify “feeling” and “aesthetics” associated with riding out of sync.
To the best of my knowledge, no one has actually ever been able to quantify the performance advantage or disadvantages of different crank phasing, although one tandem enthusiast conducting Parkinson’s research using tandems as a form of therapy had one time suggested he might be able to collect some data with the stationary tandems used in their studies since both the captain and stoker’s power is captured during their research. I’ll have to follow-up with him to see if they ever did that and what it may have revealed.
Ultimately, I have always suggested, there is only one way to know which suits a given team best: try a few variations for a month at a time and see which you really prefer. As for us, because of a number of reasons — to include riding off-road tandems which MUST either be in-sync or use an independent coasting system (ICS) like the one developed and sold by daVinci tandems due to potential risks to the stoker’s feet from trail hazards — we have found that In-Phase suits us. In fact, the late cycling guru Sheldon Brown would often times attach the following quote to the bottom of his postings regarding tandems and, to be frank, this has always summed up the true source of our crank phase preference:
There are essentially three entities riding a Tandem:
The captain, the stoker, and the spirit.
It is the spirit who likes in-phase cranks.