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Do any of you own a vintage (1970ís) tandem?

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Do any of you own a vintage (1970ís) tandem?

Old 05-21-23, 01:35 PM
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This one is from the late 70s but it has an updated drivetrain. I originally got this to ride with my then girlfriend who was about 100 lbs. It was very well behaved ( the tandemÖnot necessarily her) and we would stand to climb, etc. These days, I occasionally take it out with an ex(racing) teammate who fits on the back. With the two of us it flexes a bit more, but it doesnít stop us from making enemies on a club ride. It is really quite sturdily built and has decent geometry.

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Old 05-21-23, 02:01 PM
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Originally Posted by Robvolz
I have searched google images for "timing on the right side." Not finding any, and I'm having trouble picturing it. Are you suggesting a triple in the back and the inner ring be use for the timing chain?

Please send images if you can.
The timing chain can be either inboard or outboard of the rear-drive ring(s), pros and cons of both.
My preference is for timing chain inboard, but the problem is the chainstays are spreading out wider as you move back from the BB, so the bigger the timing ring, the less chainstay clearance you will have, unless the frame has an especially-deep indent for it. You can use small timing rings, any size really as long as they're the same F+R, but as the ring size goes down, the chain tension (and associated frame flex, and wear) goes up. Chain tension is inversely proportional to ring size.

The other way to use bigger timing rings inboard (besides a deep indent in the chainstay for clearance) is to use a longer BB spindle, which adds to the stoker's Q-factor or "tread" width, and may mess up your chain-line with the rear cluster.

Here's a pic of same-side drive, with adequately-large timing rings. I don't know whether they used an indent or longer spindle to get the clearance. Probably the latter, a triple spindle with only two rings for the rear drive. That works best with a wider rear hub like 140 mm or more, common on modern tandems. (I think Santana uses something silly like 160?)

In the pic they're using a Gates belt rather than a chain, but the concept is the same.

Here's an old Claud Butler ('40s maybe?), showing how important they thought it was to use a large timing ring while keeping the tread width as narrow as possible. The "indent" is extreme but it probably rode very well indeed. Builders used to pay more attention to narrow tread back then; nowadays people have pretty much given up on that, other than Grant Peterson who coined the term Q-factor for the same concept. I still like a narrow Q but I'm not sure I would go to such extremes as this Butler.

Track tandems traditionally had the timing chain on the right and inboard, though there were exceptions. Here's a nice Paramount track tandem done that way, pic courtesy of Classic Cycle of Bainbridge Island WA, used without permission. (fantastic shop and website, check them out!)

The other way, timing outside, is favored by John Allen who runs the sheldonbrown.com site. He has an article on how to have a triple for rear drive, plus same-side drive, so there are four rings on the stoker's right crank. Not that you need four necessarily, his method works with 1x or 2x rear drivetrains too.

The downside is the timing chain is further out from the bike center-plane, and this lateral offset of the chain causes a fair amount of frame flex. It bows the bottom tube (keel tube) the way the archer's string bends the bow. The taut upper run of the chain is actually pulling the two BB spindles closer to each other. This is felt as sponginess in the captain's pedal, and it causes a lot of slack to appear in the lower run of the chain. Enough slack to allow the chain to derail in certain circumstances, which can even cause a crash if it happens at the wrong time, like when you're standing on the pedals. Max chain force (and thus max frame flex, and max slack created) happens when you're sprinting, a very bad time to have the chain come off. I once saw a tandem team veer all the way across the road and almost go into the ditch on the other side of the road — good thing there was no oncoming traffic at the time. That captain was very experienced and also very strong, a multiple National champion, and we were sprinting when it happened. He could have taken us all down. I had noticed his chain was a bit loose at the beginning of the ride, so it's partly my fault for not saying anything! Moral of the story, keep your timing chain tight. Adjust it now and then, because chain wear causes the chain to get longer and looser. I've heard some people say that timing chain too tight is a problem, that is causes extra wear or some such, but I don't think they have thought it through. The chain only get looser in use, never tighter. Slack appears in the lower run every time you pedal. So start with it pretty snug. With one caveat: chainrings, spindles etc. have some degree of "runout" or eccentricity, so there can be tight and loose spots as you rotate the cranks. Make sure there isn't some tight spot that makes the chain overly tight at one spot. Better quality cranks and rings have less eccentricity and so tend not to have tight and loose spots, but it's worth checking.

The other things to do to minimize the slack in the bottom of the timing chain are (1) larger timing rings, (2) narrower chain-line and (3) large stiff bottom tube, preferably ovalized to minimize the bending of the frame that causes the excess slack. Unfortunately your new Colnago has a small, flexible bottom tube, round not ovalized, so you will get a lot of the "bow" and chain slack under hard pedaling. That frame might be best with timing chain inboard.

Anyway, the John Allen type with the timing chain outboard can be just fine if you pedal gently and never sprint, which is a lot of people. All these factors I'm talking about are incrmental and not deal-breakers, just be aware of all the factors and try to optimize as many of them as you can.

Mark B
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