powers2b

Repairing a used tandem for a friend.
What is the optimal clock position differential for the cranks?
(currently I have the front crank at 3:00 and the rear at 2:00)
Is the clocking critical because of frame stress or just because the riders should be moving in sync?

godspiral

Assuming a slightly weaker rider in back,
I would guess 1:00 in rear would be optimal. The idea is to avoid both riders being very close to vertical simultaneously. Your initial position would produce 11:30 and 12:30 from the 2 riders which I assume is pretty weak.

I'd imagine pro teams use 12:00-3:00.

powers2b

Good point.
I completely missed that.
Thank you.

Xanti Andia

OK, I am e Newbie, but aren't tandems rigged with parallel cranks?, can anybody point me to a good explenation to this phase question?.

TandemGeek

It varies from team to team...

For reference purposes, what you're referring to is crank phasing or "phase". If you search the archives for "in out phase cranks" you'll find a plethora of threads dedicated to the pros and cons of riding either "In-Phase" (IP / in-sync), "Out-of-Phase" (OOP / out of sync), and all of the points that fall somewhere in-between Zero degees of difference to the effective max at 90 degrees. Running with cranks beyond 90 degrees up and to 180 degrees is not recommended because the likelihood of the captain driving the stoker's cranks into the ground while cornering is unacceptably high.

In short, 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. Rudy V. (zonatandem) will weigh in here shortly on why he and his stoker have been riding out of phase for many, many years and there are some other converts on the list who will also weigh in.

I would also venture a guess that most teams ride IP because that's the way most dealers set up tandems, that's the way they are depicted in most marketing materials, and as already mentioned that's how most teams ride. 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.

TandemGeek

Again, it varies from team to team and you'd be hard pressed to make your argument that for most tandem teams "The idea is to avoid both riders being very close to vertical simultaneously" (aka, synchronized or in-phase). See my previous post.

To the best of my recollection I've never seen a tandem team competing in a US Cycling sanctioned race (track, road, crit, time trials or off-road) riding more than a a few teeth out of phase... noting that I've never seen a daVinci with independent coasting / variable phase in a race. No, teams that race tend to ride with their pedals in-phase. Despite some of the benefits, most teams cannot sprint or stand and hammer out of the saddle together at maximum effort when they are out-of-phase.

Here are some photos from this year's Co-Motion Classic... check out the pedal positions:
https://www.co-motion.com/cctrvideo.html

And from 2005:
https://www.pbase.com/turnert/comotion

TandemGeek

Simple and to the point...
https://www.sheldonbrown.com/tandem2.html

More essential stuff from Sheldon regarding tandems and sync or timing chains:
https://www.sheldonbrown.com/synchain.html

cornucopia72

We ride 90 degrees OOP, the captain leading the stoker. We can climb and sprint while standing. For us, the only potential problem is stoker's pedals hitting the pavement while cornering and going over speed bumps. We have touched the pavement 3 times with no consequences always due to my lack of attention.

zonatandem

Mark is right on the money with in/out-of-phase. OOP is not recommended for off-road/singletrack riding.
Seeing that you are fixing up this tandem for someone, it would be good to ask them what their preference is.
Yes, most tandems shown in ads will have cranks 100% in-phase, as will most tandems for sale in bike shops.
But there are choices/preferences.
We like the idea of 90 degrees OOP and have been proponents of that for over 30 years.
Advantages of OOP: always a power stroke going over the top; easier take-off from standstills and at traffic signals; less wear on drivetrain; less flexing of frame; easier climbing while seated.
Disadvantages of OOP: If laying a hard/fast racing corner or crossing hi-speedbumps, there is a possibility of bashing a pedal (pay attention!); difficult standing for both riders while climbing, however, easy for one team member at the time standing. Claims of 'it doesn't look nice' or 'is she pedaling faster than you' are not uncommon.
Solution: if the tandem team is willing/interested, try 90 degrees OOP for a few weeks. If you see no advantage/benefit, go back to in-phase or whatever ever degree of OOP works best for you.

Pedal on TWOgether!
Rudy and Kay/zonatandem

zonatandem

In our 'younger days', we've done quite a few competitive events, including time trials, riding OOP.
Only once have we bashed a pedal on one of the first 'speedbumps' we ever encountered . . . crossing the border from AZ into Mexico, umpteen ago. Yup, banged up a Phil Wood pedal . . .
Pedal on TWOgether!
Rudy and Kay/zonatandem

powers2b

I forgot to check with the Master first.
Please disregard this thread.

TandemGeek

In retrospect, I now wish I had...

Here's a tip: Some things are better left unsaid.