PDub62

Relative to your captain’s fear of losing power with shorter cranks, he may find just the opposite happens and he can ride at a higher power because the shorter arm will make it easier for him to spin a higher cadence.

I think that everyone’s assessment that this is a crank length issue is spot on. Based on the fact that you prefer a higher cadence than your captain, it may be best to not only increase your crank length but also decrease his. A shorter crank arm allows a higher cadence for a given foot speed (tangential velocity). If you change both sets of cranks I suspect you’ll find your team’s cadence will naturally increase thereby allowing you to be at a more comfortable cadence and be able to put down more power while also getting your captain to a more efficient cadence.

As a side note, my 9 year old daughter can comfortably spin 90-100 rpm with me on the tandem because she has 135 crank arms. When she was 6 she could spin that cadence with 115 crank arms.

headasunder

As a reasonably new tandem team (8500km over a couple of years mainly road with some good length mixed terrain bike touring etc) I have been following this thread with interest . Cadence has been a talking point with my stoker initially she was unhappy at my higher (than her) cadence it took a while for each of us to adapt the end result being a compromise of sorts and she is now happier at the higher cadence end of things or though I prefer to spin and she likes to push harder at a lower rpm. I knew a crankset change would improve things but didn't want to spend money on shorter cranks as our tandem is at the entry level price point and we plan on upgrading. I had never heard of running the cranks just a little out of phase but with nothing to lose today I moved the captains cranks back 2 teeth. The change for both captain and stoker was monumental from the captains point of view its is like getting a run into the power side of the pedal stroke (a running start versus a standing start) and my stoker commented on how it felt like her every pedal stroke counted, judging by the panting that was coming from behind me she was working very hard. We ending up riding in a heavier gear than usual and laying into the pedals, we live on the side of a hill so all roads lead to a climb and I felt like we shared the effort more evenly which was also my stokers perception. Its a total game changer for us so you should give it a try before forking out for new cranks.,

Darth Lefty 

This is a fascinating thread and I’m glad I read it.

LV2TNDM

[QUOTE=Carbonfiberboy;21515077]No, I can pedal fine on the 175s, hitting 115 if I want to. My single has 170s and I don't really notice the difference. It's only like 1/8" per crank, nothing really,..."

Interesting take. My experience with this difference in length was completely opposite. When racing in my 20's, I was out with a friend mountain biking. Crank lengths came up and I mentioned I was on 170's. He was on 175's. We happen to have the exact same saddle height and both rode SPDs, so we quickly swapped bikes. I assumed like you above that 5 little millimeters probably wouldn't even be noticed. I couldn't have been more wrong! It felt like the cranks were SIGNIFICANTLY longer than a 5mm increase. It was remarkable how much longer they felt; practically twice as long (not really, but the difference was truly astounding). It was eye-opening to say the least. Everyone is different, but I think you'd feel it if you could do swap onto different cranks mid-ride, all other things being equal. Difference in circumference is a 31mm increase from 1067mm (just under 3% increase). So even though the circumference increase is still small, it's VERY noticeable. To me at least.

Also, when I go between 175 on the tandem or mountain bike to the 172.5 on the road bike, I cannot feel the difference. Too hard to compare, given the apples to oranges comparison and time interval between rides.

Carbonfiberboy 

Perhaps the difference in our experiences is that I've been swapping back and forth between crank lengths regularly for ~15 years and have grown accustomed to both lengths. I don't remember if I noticed a difference on our first tandem ride.

Leisesturm

Hmm. Also late to the thread, but I've read every post. Count me in with the poster who wonders how accurate a powermeter can be under the conditions described in the o.p. Is it not possible that the Captain's display is showing an additional amount of power input by the Stokers cranks while the Stokers display is showing a corresponding loss? In any case, I think it is more likely the fact that the Stoker cannot select her own gears, rather than the fact that her cranks are of a different length that add to her frustration. In the recumbent world there are beasts called "back-to-back recumbent tandems" and these are mainly two wheel drive HPV's with the Captains cranks driving the front wheel and the Stokers cranks driving the rear wheel. Independently geared of necessity. It's where I would look if serious performance was an issue.

When I call for 'Power' to sprint through a stale green I don't always know if I got it all but if my Stoker does not hear a call of 'Stopping' (crank rotation) I know instantly that she did not hear it and I have to call again and/or fight the pedals if there must not be any acceleration at that time. Tandems were called an 'equalizer' by the o.p. and this is a common ... misconception, for want of a better word. Actually, in practice it is very hard to synchronize independent power sources. A single large engine has proven to be superior to two smaller engines every time, and automotive designers no longer experiment with them. Tandems allow couples to ride twogether. There is a trade-off of ultimate efficiency made for the greater good of ... twogetherness. If you read that as an indictment of heartrate monitors or powermeters onboard tandems ... well that's my take. The aero advantage of the excellent draft afforded the Stoker ultimately benefits both, and tandems are indisputably faster than singles, everything else being equal. But when is that ever the case?

I didn't give tandems much thought until 2005 when I met a blind woman who had ridden one a few times and was a member of a club that had tandems that could be rented. Our second date was in NYC's Central Park on a sunny Saturday in May and I was able to Captain the loaded tandem immediately. The brakes were ghastly. We never rented one of their bikes again and bought our own that very week. We have joined tandem clubs and met over two dozen teams in the last decade and more, none of which ride their tandems anymore. None have ever had a blind stoker. I think more teams expect the Stoker to be a laggard and this gives many Stokers a complex about how much or how much not they are working.

We don't worry about it. What would be the point? I know my Stoker is plenty strong. But if she wasn't ... we'd just have to deal with that and have fun anyway. We are slower than some, faster than some, but Team2024 always arrives wherever we are going at the same time. Finally, IMO crank length is an abstraction. It has only an oblique relationship to a riders height, inseam, femur length, etc. Simply put, cranks are limited by the cornering clearance available on road racing bicycles. Tandem bottom brackets are usually higher than road racer's and in theory Captains and Stokers alike could run 200mm cranks with no pedal strike problems through turns. In theory. Try to find 200mm cranks for sale. We have three tandems currently. On two of them the cranks are the same length for me and mine:170mm. I am 5'10". She is 5'6". On the exception, my cranks are 175mm and hers are 170. We have female friends that used to ride tandems at 4'11" and 5'2" and they too used 170mm on their tandems and now on their singles. FWIW.

diabloridr

I think it depends on the individual.

Like you I move between 170's (fixed gear) to 172.5 (regular single) to 175's (tandem) without noticing a difference.

OTOH, stoker *must* have 165's on her bikes. When we did a test ride on a tandem with 170's she experienced knee discomfort after 10 miles of flat riding.

TigerMom

Although my husband and I like to tandem 45degrees out of phase, I think your stoker’s power output problem on the “tandem vs her solo bike” is a cadence issue.

Following the “stoker is always right “ motto, if you cannot adjust your riding style to her cadence, you should consider changing your drive train to a Da Vinci “Independent Coasting System” which allows the Captain and Stoker to pedal independently.

Joint Venture

The da Vinci ICS does not allow for different cadence between captain and stoker. It allows for independent coasting. Also, it’s not easily retrofittable ... it requires some special design features with the frame (front derailleur stub, shell for the jackshaft/double freewheel/front cogs assembly).

merlinextraligh

As to the accuracy of power meters on a tandem, I can say that Garmin Vectors appear pretty accurate used on a tandem both Captain and Stoker. I’ started train with power 15 years ago, and used a power tap, quarqs, and vector, so hub crank and pedal power meters.

my stoker has a power tap on her single bike, and used vectors on the tandem until recently.

based on years of data for us, our tandem numbers are what you’d expect from our single bike results.

More importantly, for training purposes, the tandem power numbers are consistent over time. And for a power meter to be useful, it doesn’t need to be 100% accurate, it just needs to give consistent results.

Carbonfiberboy 

Agree. My stoker rode with 170s for 12 years, including loaded touring, though her perfect length is 150, which she has now. She likes it better, but we're not faster - though of course we're older every year. There's a short steep sprint hill on which our tandem has 3rd AG place and now we can't sprint up it at all.

TrotterDK

The problem you are addressing here is probably very common among tandem couples. It is not often that both riders have the same powers. My wife rode very restless when on tandem, but not when she was on her own bike. We have tried everything in the world to make our tandem ride more steady but not with much succes, including 90 degrees OOP. But one day I put the cranks in a 180 degrees OOP position. All of a sudden we were able to ride a stable and calm bike. More than that, we cycled much faster. With the changed crank position we had better balance as if our movements and force now are equalized. She can now use her strength better because there is more "room" for her. We do not find any significant disadvantages of running 180 degrees OOP. We have revised a little on our driving techniques. Uphill we no longer get up at the same time. Instead, we switch to do it, or stay seated and just use the gears. Hope that our story can be of some help.

conspiratemus1

My suggestion would be to apply a small piece of black electrical tape to the read-out screen so as to obscure the power number being reported. Then, once you have gotten used to not seeing the number, remove the gadget entirely and toss it in a drawer. I did that for all my computers and other bike gadgets many years ago and life has never been better.

I have no idea why the number that comes out of your gadget is less than you think it ought to be. It claims to measure some rather abstract physical quantity called "power" but does it really? Were you having more "re-creation" riding with your husband before you got the power meters? Are you paying less attention to your body now and trusting less what it's telling you? (or to the change in the flowers in the gardens you pass as spring grows into summer?)

"Numbers that come out of a toy" can dampen one's enjoyment of life à deux, just as knowing one's cholesterol level or blood pressure or coronavirus test result can lead to a sense, often erroneous, that one is not as healthy as one thought. I already know our average speed is slowly deteriorating as we age.

Now, if you are seriously training for some athletic event, you will already have your own regimen that may be telling you that the tandem, for unknown reasons, is not providing a big enough training demand to make you competitive. Fair enough. But if you're like all the rest of us, numbers that are "nice to know" are nice only if they make us feel, well, nice. Ride as hard as you can.... but count monarch butterflies instead of watts.