TandemGeek

Let me twist your words a bit and see if this sheds some light on the matter: "I've always been a bit astounded at the prevalence of doubles and low-range / race gearing on bicycles marketed to the average consumer". In other words, tandems tend to come with gearing that is geared to the "average" users needs, noting that the sport riders and racers who make up a small segment of the overall tandem market can readily change the rear cluster to suit their needs. If you'd like to get some insight into tandem teams I'd invite you to visit my survey archive where you'll find several years worth of tandem enthusiast feedback on riding styles, combined age, annual mileage, etc: https://www.thetandemlink.com/surveys/surveycentral.html

Again, you're painting with a very broad brush across a wide range of cyclists, where only a very small number of the teams classify themselves as hammerheads or racers. Interestingly enough, you might find the results from Part I of my 2008 Annual Tandem Owners Survey to be of interest in this regard (Question #9 & others): https://www.opinionpower.com/results.cgi?id=316051829

As narrow as you like and constrained only by rear spacing / chainstay clearance, noting that two pair of any cranks can be used for a single-side drive configuration.

IMHO, much ado about nothing is made regarding boom tube deflection. Given that the majority of better tandems sold today use sound designs, materials, and methods I personally consider issues like boom tube deflection as primarily a marketing ploy where only a very small number of very large and powerful sprinters who team up on a tandem would really ever need to spend much time trying to address it via frame construction or drivetrain choices on contemporary, well-designed and built tandems. Dubious observations about timing chain slack being an indicator of frame flex seem to conveniently ignore the inherent elasticity of an 80" long chain that manifests itself when the chain goes from slack to full tension during power strokes to something less as captain and stoker's cranks that are in-phase (as most are) move through the top and bottom of the pedal stroke. Interestingly enough, what's not often mentioned is the much larger amount of overall side-to-side frame deflection that takes place at the captain's bottom bracket. The latter can easily be observed by placing a tandem into a wind trainer with the front wheel blocked: it is what it is and it's normal too but nothing that is overly detrimental to the safety or performance of a tandem. Thus, when I hear that someone has "thrown" a timing chain I can usually assume that it's because, a) the timing chain was not properly tensioned and, b) the tandem was likely being thrown side-to-side or hit a bump that set the slack and swinging bottom run of the chain off line enough to be caught by the stoker's crank and/or to derail itself at the rear timing ring instead of excess chain slack created by boom tube deflection.

As for single side drive reducing stress on the boom tube, yes and no. While it eliminates twisting effect on the rear bottom bracket, you still end up with the captain's power going into the sync chain and putting asymetric loads into the boom tube. However, if you really want to mess with your mind, now consider the fact that with single side drive you have now put all of the asymetrical drive train loads on the right side of the tandem: both those between the captain to stoker sync chain axles and those that exist between the rear crank and rear axle on all chain drive bikes. Is that better or worse than having them split up using a crossover crankset? (Rhetorical question here: no reply required)

As for the size of the timing rings, see all of the foregoing. Sync chains and timing rings comprise a simple 1:1, direct drive system. If you want to save wear and tear on the chain and rings, use a higher tooth count but remember, so long as you use odd numbered timing rings or keep your sync chain indexed on even numbered chain rings you can ignore normal wear / replacement indicators and run the same chain and rings until the rings look like saw blades. However, be mindful that the larger the timing ring and the wider the rear spacing is, the wider you're rear crank spindle will need to be. Conversely, a smaller timing ring can be used with a more narrow rear crank spindle can be. You could probably run the numbers on which of the two alternatives -- narrow Q & small rings vs. wider axle & larger rings -- reduces bending forces the most but, again, I really don't think it matters to 99% of the teams who ride contemporary tandems.

In closing, I don't want to come off as a contrarian. However, I hope that my feedback gives you pause to consider the larger tandem market's demographics and how they influence the component specifications used for most production and even many custom frame builds. And, with regard to the drivetrain issues you raised, everything on a tandem involves some sort of a trade off or compromise. There are really no right or wrong ways to configure a tandem -- within reason, that is -- and each team simply needs to figure out what works best for them.

SDS

My recollection is that the difference in width between a double and a triple, measured at the pedal holes, is 9mm. Not sure about that, but it isn't a large fraction of the normal 150mm (again, fuzzy recollection) double width. With kids I would get a triple.

I have chased narrow Q in a number of installations over the years, and on drive-side cranksets, the effort is pretty much wasted. The front derailleurs required to get the integrated brake/shift levers to work properly, prefer wide chainring spacing (wider than T.A Cyclotourist cranksets, for example) and a wide gap between the outside ring and the inside of the crankarm. And the chainstays may be wide to match, meaning that it is impossible to use a narrower bottom bracket spindle because that puts the chainrings into the chainstays. The wider dropout spacing of tandems can also cause problems.

The good news is that the front crankset on a tandem, usually does not have a front derailleur or chainstays to contend with, so it is possible to narrow it substantially with appropriate crankset and bottom bracket spindle choices. Again, it seems like a lot of effort to little gain, but if all BB spindle choices cost the same, it doesn't hurt to think about it.

aeroboy

TG, even after just a quick glance, the surveys were eye-opening. The people I would likely pair up with in races (my wife and training buddy) are or have been licensed racers, putting them into the elite category, and I am a current Worlds medalist (track). Our own experiences shape our perceptions.

I was under the impression that other than square taper designs, cranks now have a set q-factor - that you can't swap for shorter or longer BB spindles because they are all the same length. This is true on my Cervelo P3 anyway. It has an FSA track crank with an ISIS BB. The track crank has a narrower Q than FSA's ISIS road cranks and they all use 108mm spindles, although it may be possible to get different spindle lengths somewhere else? Is square taper still common with modern tandem cranks? I see that Santana uses Octalink. Do Octalink spindles come in varying widths?

There is so much to learn; there are so many questions. If tandems were more common it would be different because they could be observed on the road and at local bike shops. On single bikes, there are ways to deal with some "issues" that crop up, like chainring-to-chainstay clearance, for example. The chainstays can be longer, or they can be curved so that they exit the BB shell parallel, then curve outward when they are past the chainrings, or even past the crankarms. Longer chainstays would provide more stoker comfort as well. For all I know, long chainstays are common, or it is not commonly done on tandems because detrimental effects on frame stiffness are hard to overcome or unacceptable, or the wheelbase gets too long or some other reason.

Interestingly (or perhaps not) my friend and I never threw a timing chain on his old Freschi. However, we only rode it a handful of times. But we are powerful riders who love to hammer. So I would tend to believe that it is a set-up issue. I have also seen comments about out-of-round timing rings. This could possibly be improved by using track chainrings for the timing, but they tend to use oddball bolt circle diameters. Track chainrings are rounder than road rings, and they are cut deep to hold the chain. They are so good at doing this that I get away without a front derailleur on the road just fine and the chain rarely falls off, chain angle and all. Are timing rings "special" - are they cut this way as well, or are they just road chainrings? I remember a couple of years ago, in the Tour I think, a rider lost the TT because his chain dropped off the single front ring. He was chastised for not using a front derailleur. I've tried this with road cranks/chainrings and yes, the chain falls off at least once per ride, with a single ring up front and no front derailleur.

What it might come down to, is that if using a double crankset allows for a single-side drive and using a triple does not, the double would be hard to resist. I would prefer to run the timing chain on the outside of the drive crank rather than the inside, if it can be done. Is it important that the timing rings be aligned?

So why are odd numbered timing rings preferred? And then even numbered rings? Am I missing something? Are there two types of chainrings in this conversation or one? Sorry, I don't mean to offend but I didn't understand any of it.

TandemGeek

Square taper remains the key to fine-tuning Q-factor to suit preferences (e.g., Phil Wood) and, yes, there are still a few cranks being made for tandems: daVinci are my personal fav's, Middleburn and Specialites TA are the ones that come immediately to mind in regard to tandem crossover cranksets. You can still find some NOS Ultegra tandem cranks as well, but they don't have as many crank arm length options as the daVinci, Middleburn, and Specialites models. The MegaExo (FSA), UltraTorque (Campy), and other overly integrated cranksets do tend to lock you in, but I believe there are a few spindle length options in both ISIS and Octalink. Santana uses a proprietary 70x129mm spindle for their 160mm rear-spaced frames: the 70mm shell allows them to use oversized, round chainstays and the 160mm rear spacing drives the need for a very wide crank axle and special front derailleur mount to move the chainline outboard. Calfee has been able to source the same cranks used by Santana and spec's a 68x118mm Octalink BB for use on their 145 rear spaced tandems and I believe that 68x113mm models may also be available that would work on a triple, noting that I've used both 109mm and 113mm square tapers on Ericksons with the daVinci cranks... but no guarantee here.


17.0 - 17.5" stays are common on tandems, although we recently spec'd a new tandem with 16.5" stays. Although there are three competing issues on tandem stays: 145mm or 160mm drop-out width, heel clearance, and more recently clearance for 203mm disc rotors. Co-Motion handles this with some very stylish 17" S-shaped stays.

I can't think of a good reason to run the sync chain outboard on a same side drive tandem for a number of reasons, not the least of which is rear chain line. The sync chain's rings don't need to be precisely aligned, but I wouldn't recommend having them too far off-center, i.e., a few mm difference in centerline offset.

Odd aren't preferred, it's just that they wear differently than even number timing rings if the chain remains indexed whenever its removed and replaced. Rather than rambling on, let me offer a link to Sheldon Brown's site where he has an excellent page on tandem sync chains and timing rings that talks to this: https://www.sheldonbrown.com/synchain.html#chainring

aeroboy

Reasons I was thinking of:

1) An inboard timing chain would probably be limited in size.
2) Addressing the following scenario mentioned earlier in this thread: dropping your drive chain off the middle chain ring and into the timing ring.
3) When breaking a coupled tandem down, or converting a triple to double, I assume the timing chain(s) are removed. This would be much less pleasant an operation (on a single side drive) when the timing chain is running off an inboard ring on the final drive crank.

But then I realized later that an outboard timing ring is going to get more leverage on the BB spindle and bearings, which increases the chance of problems.

It is becoming apparent that a crossover drivetrain may be the best configuration for what I have in mind.

mrfish

Following your comments on gearing I was glad to hear you're winning races! You are certainly not the average tandemist.

Do post a picture of the rig you end up with. For your interest and given a picture is worth 1000 words, have a look here. These people in Berlin built themselves a nice single sided rig which uses 135mm spacing and basically mid range road components. Unfortunately only in German, but I can translate if you're interested in any short section. Click on the links where they describe all parts and the first non-working version of the frame etc...

https://www.sudibe.de/renntandem.html

aeroboy

Those pictures ... with the rear chainrings it is exactly as I have envisioned! What next? Since my last post, I have still not been able to find 165mm captain's cranks that are also low q factor. Standard road q these days is about 147mm which I could live with. The da Vinci ones are advertised at 158mm which is high for a road double and even a little high for a triple. And they are designed to use a short axle, which minimizes the possibility of the user puttiong a shorter axle in there to reduce q a meanigful amount. The single side config would bypass all of this; I'd love to know where they got the extra long chainring bolts needed to do that. Yes, that's all I need to make it work! Thank you!

aeroboy

Don't you worry. If the rig ever gets built - that is, if the builder puts up with my silly little requests, then I will proudly post pictures here. Actually, there is only one feature the frame would need, and I'm not sure if this one has it. At least I can't tell from the pictures. Are the chainstays bent?

Have they described how they got the extra long chainring bolts required to do that, and also what kind of cranks those are? The big timing rings look about right, too.

TandemGeek

Use this link to see component photos of the cranks and the chain ring specs:
https://www.sudibe.de/renntandem_teile.html

Per the site, cranks are Ultegra with 53/39 drive rings and 48t timing rings.

Hermes

Aeroboy, I think you are focusing on interesting but less important things with respect to tandems. Like road and track racing, tandem racing and performance riding are about team power, aero and power to weight ratio. Q-factor is an interesting discussion but IMHO, not where the action is.

Racing to Win

In our racing club, we have several racing tandem teams, ad hoc teams designed to win tandem races and tandems designed specifically to win a race e.g. the US National Championships. Parties and teams competing are P/1/2s and are US National and district champions.

One objective is to port over to the tandem as much single bike equipment i.e. racing wheelsets as possible and select as appropriate for the race, wind and terrain conditions.

Specially designed tandems to allow the captain and the stoker to have aero bars.

Team selection to fit into age groups and gender pairing i.e. YY, XX and XY teams where a particular team has a competitive advantage.

I am sure that the Canadian racing teams do similar things for your District and National events.

Gearing selection is done for the course and the race.

Performance Riding and Local TT Events

Teams riding the tandem in group rides or events ride the regular offering of Santana, CoMo, Cannondale, Trek and etc. I generally see triples but we have a lot of long steep climbs and on the tandem it is nice to be able to cruise up mountains.

Couples who are strong individual racers are great on the tandem.

Recreational Riding

We see a lot of tandem couples riding for recreation and who appear to have disproportionate abilities and the enthusiasts within this group seem to focus on equipment. We see a lot of very schwaggy tandems. To climb the hills in the bay area, they need very low gearing just to get around and we do not see them on the major climbs.

As always, YMMV.

Good luck with your purchase.

aeroboy

I tend to be obsessive about certain details and q factor is one of them. Actually it has nothing to do with racing the tandem because that is not the primary purpose of the machine. Exotic? Think again. This will be a family machine and by today's standards will be heavy. It will have 48 spokes front and rear. What it comes down to is that I happen to be dialled in with respect to things like q factor and crank length, as well as my position on the bike, and strive for consistency between the bikes that I ride. I ride better and with no knee pain using 165 cranks than with any longer length, and with less foot pain using the narrower q, plus I would prefer not to feel like I am riding a MTB/touring bike when riding the captain's position. I figure that if I'm going to spend car $ on a custom bike, that it might as well have as many things as possible the way I like them.

Hermes

FIne...get whatever you want or need, I was responding to this..."I would love to get into the tandem racing scene, especially TT events." and this 'The people I would likely pair up with in races (my wife and training buddy) are or have been licensed racers, putting them into the elite category, and I am a current Worlds medalist (track). Our own experiences shape our perceptions."

bikeriderdave

Yes, you SHOULD strive to match your single position on the tandem. But you will drive yourself crazy trying to "optimize" things for young stokers or a variety of stokers. Most people -- and, I dare say ALL kids -- will be much less sensitive to position variables than you are. You should also consider that a Periscope may not even shift well with a "low Q" stoker crank, because the rear seat tube OD (1.5 inches) limits inward front derailleur movement.
Because this is your first tandem (and because it seems that you are not quite sure how you will use it), why not buy a "stock" configuration and modify it to suit as you go? In a few years, you will know what works for you and will actually have a basis for custom tandem decisions...

Cavalão

Sorry to dig up an old thread, but I'm researching a single sided setup myself... looking at the photos in this link, it appears to me the stoker stem is not an Ultegra and rather some cheapie crank... I am guessing there wasn't room to put the chainring outboard on the Ultegra? Which means no can do for Dura Ace as well.